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Journal articles on the topic 'Semimetals'

Author: Grafiati
Published: 4 June 2021
Last updated: 26 July 2024

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1

Hu, Jin, Su-Yang Xu, Ni Ni, and Zhiqiang Mao. "Transport of Topological Semimetals." Annual Review of Materials Research 49, no. 1 (July 2019): 207–52. http://dx.doi.org/10.1146/annurev-matsci-070218-010023.

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Three-dimensional (3D) topological semimetals represent a new class of topological matters. The study of this family of materials has been at the frontiers of condensed matter physics, and many breakthroughs have been made. Several topological semimetal phases, including Dirac semimetals (DSMs), Weyl semimetals (WSMs), nodal-line semimetals (NLSMs), and triple-point semimetals, have been theoretically predicted and experimentally demonstrated. The low-energy excitation around the Dirac/Weyl nodal points, nodal line, or triply degenerated nodal point can be viewed as emergent relativistic fermions. Experimental studies have shown that relativistic fermions can result in a rich variety of exotic transport properties, e.g., extremely large magnetoresistance, the chiral anomaly, and the intrinsic anomalous Hall effect. In this review, we first briefly introduce band structural characteristics of each topological semimetal phase, then review the current studies on quantum oscillations and exotic transport properties of various topological semimetals, and finally provide a perspective of this area.
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2

Nie, Simin, Gang Xu, Fritz B. Prinz, and Shou-cheng Zhang. "Topological semimetal in honeycomb lattice LnSI." Proceedings of the National Academy of Sciences 114, no. 40 (September 19, 2017): 10596–600. http://dx.doi.org/10.1073/pnas.1713261114.

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Recognized as elementary particles in the standard model, Weyl fermions in condensed matter have received growing attention. However, most of the previously reported Weyl semimetals exhibit rather complicated electronic structures that, in turn, may have raised questions regarding the underlying physics. Here, we report promising topological phases that can be realized in specific honeycomb lattices, including ideal Weyl semimetal structures, 3D strong topological insulators, and nodal-line semimetal configurations. In particular, we highlight a semimetal featuring both Weyl nodes and nodal lines. Guided by this model, we showed that GdSI, the long-perceived ideal Weyl semimetal, has two pairs of Weyl nodes residing at the Fermi level and that LuSI (YSI) is a 3D strong topological insulator with the right-handed helical surface states. Our work provides a mechanism to study topological semimetals and proposes a platform for exploring the physics of Weyl semimetals as well as related device designs.
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3

Ominato, Yuya, Ai Yamakage, and Kentaro Nomura. "Electric Polarization in Magnetic Topological Nodal Semimetal Thin Films." Condensed Matter 3, no. 4 (November 30, 2018): 43. http://dx.doi.org/10.3390/condmat3040043.

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We theoretically study the electric polarization in magnetic topological nodal semimetal thin films. In magnetically doped topological insulators, topological nodal semimetal phases emerge once the exchange coupling overcomes the band gap. Changing the magnetization direction, nodal structure is modulated and the system becomes topological nodal point or line semimetals. We find that nodal line semimetals are characterized by non-linear electric polarization, which is not observed in nodal point semimetals. The non-linear response originates from the existence of the surface states. Screening effect is self consistently included within a mean field approximation and the non-linear electric polarization is observed even in the presence of screening effect.
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4

Gao, Heng, Jörn W. F. Venderbos, Youngkuk Kim, and Andrew M. Rappe. "Topological Semimetals from First Principles." Annual Review of Materials Research 49, no. 1 (July 2019): 153–83. http://dx.doi.org/10.1146/annurev-matsci-070218-010049.

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We review recent theoretical progress in the understanding and prediction of novel topological semimetals. Topological semimetals define a class of gapless electronic phases exhibiting topologically stable crossings of energy bands. Different types of topological semimetals can be distinguished on the basis of the degeneracy of the band crossings, their codimension (e.g., point or line nodes), and the crystal space group symmetries on which the protection of stable band crossings relies. The dispersion near the band crossing is a further discriminating characteristic. These properties give rise to a wide range of distinct semimetal phases such as Dirac or Weyl semimetals, point or line node semimetals, and type I or type II semimetals. In this review we give a general description of various families of topological semimetals, with an emphasis on proposed material realizations from first-principles calculations. The conceptual framework for studying topological gapless electronic phases is reviewed, with a particular focus on the symmetry requirements of energy band crossings, and the relation between the different families of topological semimetals is elucidated. In addition to the paradigmatic Dirac and Weyl semimetals, we pay particular attention to more recent examples of topological semimetals, which include nodal line semimetals, multifold fermion semimetals, and triple-point semimetals. Less emphasis is placed on their surface state properties, their responses to external probes, and recent experimental developments.
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5

Chang, Guoqing, Su-Yang Xu, Daniel S. Sanchez, Shin-Ming Huang, Chi-Cheng Lee, Tay-Rong Chang, Guang Bian, et al. "A strongly robust type II Weyl fermion semimetal state in Ta3S2." Science Advances 2, no. 6 (June 2016): e1600295. http://dx.doi.org/10.1126/sciadv.1600295.

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Weyl semimetals are of great interest because they provide the first realization of the Weyl fermion, exhibit exotic quantum anomalies, and host Fermi arc surface states. The separation between Weyl nodes of opposite chirality gives a measure of the robustness of the Weyl semimetal state. To exploit the novel phenomena that arise from Weyl fermions in applications, it is crucially important to find robust separated Weyl nodes. We propose a methodology to design robust Weyl semimetals with well-separated Weyl nodes. Using this methodology as a guideline, we search among the material parameter space and identify by far the most robust and ideal Weyl semimetal candidate in the single-crystalline compound tantalum sulfide (Ta3S2) with new and novel properties beyond TaAs. Crucially, our results show that Ta3S2has the largestk-space separation between Weyl nodes among known Weyl semimetal candidates, which is about twice larger than the measured value in TaAs and 20 times larger than the predicted value in WTe2. Moreover, all Weyl nodes in Ta3S2are of type II. Therefore, Ta3S2is a type II Weyl semimetal. Furthermore, we predict that increasing the lattice by <4% can annihilate all Weyl nodes, driving a novel topological metal-to-insulator transition from a Weyl semimetal state to a topological insulator state. The robust type II Weyl semimetal state and the topological metal-to-insulator transition in Ta3S2are potentially useful in device applications. Our methodology can be generally applied to search for new Weyl semimetals.
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6

Zou, Yuxiao, Ying Liu, and Guofeng Song. "Mid-Infrared Sensor Based on Dirac Semimetal Coupling Structure." Sensors 22, no. 6 (March 9, 2022): 2116. http://dx.doi.org/10.3390/s22062116.

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A multilayer structure based on Dirac semimetals is investigated, where long-range surface plasmon resonance (LRSPR) of a dielectric layer/Dirac semimetal/dielectric layer are coupled with surface plasmon polaritons (SPPs) on graphene to substantially improve the Goos–Hänchen (GH) shift of Dirac semimetals in the mid-infrared band. This has important implications for the study of mid-infrared sensors. We studied the reflection coefficient and phase of this multilayer structure using a generalized transport matrix. We established that subtle changes in the refractive index of the sensing medium and the Fermi energy of the Dirac semimetal significantly affected the GH shift. Our numerical simulations show that the sensitivity of the coupling structure is more than 2.7×107 λ/RIU, which can be used as a potential new sensor application. The novelty of this work is the design of a tunable, highly sensitive, and simple structured mid-infrared sensor that takes advantage of the excellent properties of Dirac semimetals.
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7

Galeeva, Alexandra V., Ivan V. Krylov, Konstantin A. Drozdov, Anatoly F. Knjazev, Alexey V. Kochura, Alexander P. Kuzmenko, Vasily S. Zakhvalinskii, Sergey N. Danilov, Ludmila I. Ryabova, and Dmitry R. Khokhlov. "Electron energy relaxation under terahertz excitation in (Cd1− x Zn x )3As2 Dirac semimetals." Beilstein Journal of Nanotechnology 8 (January 17, 2017): 167–71. http://dx.doi.org/10.3762/bjnano.8.17.

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We demonstrate that measurements of the photo-electromagnetic effect using terahertz laser radiation provide an argument for the existence of highly conductive surface electron states with a spin texture in Dirac semimetals (Cd1− x Zn x )3As2. We performed a study on a range of (Cd1− x Zn x )3As2 mixed crystals undergoing a transition from the Dirac semimetal phase with an inverse electron energy spectrum to trivial a semiconductor with a direct spectrum in the crystal bulk by varying the composition x. We show that for the Dirac semimetal phase, the photo-electromagnetic effect amplitude is defined by the number of incident radiation quanta, whereas for the trivial semiconductor phase, it depends on the laser pulse power, irrespective of wavelength. We assume that such behavior is attributed to a strong damping of the interelectron interaction in the Dirac semimetal phase compared to the trivial semiconductor, which may be due to the formation of surface electron states with a spin texture in Dirac semimetals.
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8

Ang, L. K., Yee Sin Ang, and Ching Hua Lee. "Universal model for electron thermal-field emission from two-dimensional semimetals." Physics of Plasmas 30, no. 3 (March 2023): 033103. http://dx.doi.org/10.1063/5.0137400.

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We present the theory of out-of-plane (or vertical) electron thermal-field emission from two-dimensional (2D) semimetals. We show that the current–voltage–temperature characteristic is well captured by a universal scaling relation applicable for broad classes of 2D semimetals, including graphene and its few-layer, nodal point semimetal, Dirac semimetal at the verge of topological phase transition, and nodal line semimetal. Here, an important consequence of the universal emission behavior is revealed: In contrast to the common expectation that band topology shall manifest differently in the physical observables, band topologies in two spatial dimension are indistinguishable from each other and bear no special signature in electron emission characteristics. Our findings represent the quantum extension of the universal semiclassical thermionic emission scaling law in 2D materials and provide theoretical foundations for the understanding of electron emission from cathode and charge interface transport for the design of 2D-material-based vacuum nanoelectronics.
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9

Liu, D. F., A. J. Liang, E. K. Liu, Q. N. Xu, Y. W. Li, C. Chen, D. Pei, et al. "Magnetic Weyl semimetal phase in a Kagomé crystal." Science 365, no. 6459 (September 19, 2019): 1282–85. http://dx.doi.org/10.1126/science.aav2873.

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Weyl semimetals are crystalline solids that host emergent relativistic Weyl fermions and have characteristic surface Fermi-arcs in their electronic structure. Weyl semimetals with broken time reversal symmetry are difficult to identify unambiguously. In this work, using angle-resolved photoemission spectroscopy, we visualized the electronic structure of the ferromagnetic crystal Co3Sn2S2 and discovered its characteristic surface Fermi-arcs and linear bulk band dispersions across the Weyl points. These results establish Co3Sn2S2 as a magnetic Weyl semimetal that may serve as a platform for realizing phenomena such as chiral magnetic effects, unusually large anomalous Hall effect and quantum anomalous Hall effect.
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10

Rong, Jia-Nan, Liang Chen, and Kai Chang. "Chiral Anomaly-Enhanced Casimir Interaction between Weyl Semimetals." Chinese Physics Letters 38, no. 8 (September 1, 2021): 084501. http://dx.doi.org/10.1088/0256-307x/38/8/084501.

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We theoretically study the Casimir interaction between Weyl semimetals. When the distance a between semi-infinite Weyl semimetals is in the micrometer regime, the Casimir attraction can be enhanced by the chiral anomaly. The Casimir attraction depends sensitively on the relative orientations between the separations ( b 1, b 2) of Weyl nodes in the Brillouin zone and show anisotropic behavior for the relative orientation of these separations ( b 1, b 2) when they orient parallel to the interface. This anisotropy is quite larger than that in conventional birefringent materials. The Casimir force can be repulsive in the micrometer regime if the Weyl semimetal slabs are sufficiently thin and the direction of Weyl nodes separations ( b 1, b 2) is perpendicular to the interface. The Casimir attraction between Weyl semimetal slabs decays slower than 1/a 4 when the Weyl nodes separations b 1 and b 2 are both parallel to the interface.
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11

Xu, Su-Yang, Ilya Belopolski, Daniel S. Sanchez, Chenglong Zhang, Guoqing Chang, Cheng Guo, Guang Bian, et al. "Experimental discovery of a topological Weyl semimetal state in TaP." Science Advances 1, no. 10 (November 2015): e1501092. http://dx.doi.org/10.1126/sciadv.1501092.

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Weyl semimetals are expected to open up new horizons in physics and materials science because they provide the first realization of Weyl fermions and exhibit protected Fermi arc surface states. However, they had been found to be extremely rare in nature. Recently, a family of compounds, consisting of tantalum arsenide, tantalum phosphide (TaP), niobium arsenide, and niobium phosphide, was predicted as a Weyl semimetal candidates. We experimentally realize a Weyl semimetal state in TaP. Using photoemission spectroscopy, we directly observe the Weyl fermion cones and nodes in the bulk, and the Fermi arcs on the surface. Moreover, we find that the surface states show an unexpectedly rich structure, including both topological Fermi arcs and several topologically trivial closed contours in the vicinity of the Weyl points, which provides a promising platform to study the interplay between topological and trivial surface states on a Weyl semimetal’s surface. We directly demonstrate the bulk-boundary correspondence and establish the topologically nontrivial nature of the Weyl semimetal state in TaP, by resolving the net number of chiral edge modes on a closed path that encloses the Weyl node. This also provides, for the first time, an experimentally practical approach to demonstrating a bulk Weyl fermion from a surface state dispersion measured in photoemission.
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12

Chen, Guifeng, Bolin Long, Lei Jin, Hui Zhang, Zishuang Cheng, Xiaoming Zhang, and Guodong Liu. "Synthesis of Weyl Semi-Metal Co3Sn2S2 by Hydrothermal Method and Its Physical Properties." Metals 12, no. 5 (May 11, 2022): 830. http://dx.doi.org/10.3390/met12050830.

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In the field of condensed matter physics, as new quantum materials, topological semimetals have a special topological energy band structure and nontrivial band crossings in the energy band, which will have many excellent topological properties, such as internal insulation of topological insulators and the presence of conduction electrons on the surface; this makes topological semimetals exhibit wider application prospects in electronic devices. So far, the experimental synthesis of topological semimetals was performed using physical methods to synthesize bulk single crystals, which is not conducive to the commercial application of micro and small devices. Weyl semimetal Co3Sn2S2 with shandite structure was successfully synthesized experimentally by a green and environmentally friendly hydrothermal method. Adjusting its reaction temperature, molar atomic ratio of elements and annealing temperature, and other experimental conditions, we analyze the crystal structure and physical properties of Co3Sn2S2, with the nanocrystal size being about 200 nm. We found that the Co3Sn2S2 synthesized by the hydrothermal method has a Curie temperature at 100 K to undergo ferromagnetic transition.
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13

Fu, Chenguang, Satya N. Guin, Thomas Scaffidi, Yan Sun, Rana Saha, Sarah J. Watzman, Abhay K. Srivastava, et al. "Largely Suppressed Magneto-Thermal Conductivity and Enhanced Magneto-Thermoelectric Properties in PtSn4." Research 2020 (April 7, 2020): 1–8. http://dx.doi.org/10.34133/2020/4643507.

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Highly conductive topological semimetals with exotic electronic structures offer fertile ground for the investigation of the electrical and thermal transport behavior of quasiparticles. Here, we find that the layer-structured Dirac semimetal PtSn4 exhibits a largely suppressed thermal conductivity under a magnetic field. At low temperatures, a dramatic decrease in the thermal conductivity of PtSn4 by more than two orders of magnitude is obtained at 9 T. Moreover, PtSn4 shows both strong longitudinal and transverse thermoelectric responses under a magnetic field. Large power factor and Nernst power factor of approximately 80–100 μW·cm-1·K-2 are obtained around 15 K in various magnetic fields. As a result, the thermoelectric figure of merit zT is strongly enhanced by more than 30 times, compared to that without a magnetic field. This work provides a paradigm for the decoupling of the electron and hole transport behavior of highly conductive topological semimetals and is helpful for developing topological semimetals for thermoelectric energy conversion.
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14

Wang, Xiao, Xiaoxing Wei, and Caixia Song. "Growth of Semimetals Bismuth and Antimony Films on Reactive Substrate." Journal of Nanomaterials 2015 (2015): 1–5. http://dx.doi.org/10.1155/2015/581486.

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Semimetal Bi and Sb thin films with novel hierarchical structures were synthesized on zinc substrate via a hydrothermal method. X-ray diffraction (XRD) analysis confirmed the formation of pure semimetals Bi and Sb. Scanning electron microscopy images showed that Bi films constructed with microtube arrays and hierarchical microspheres can be obtained selectively by altering the concentration of Bi3+ions. The synthesized Sb films were constructed with bowl-shaped particles. The growth process of these semimetal architectures was briefly discussed.
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15

Chu, Chun-Guang, An-Qi Wang, and Zhi-Min Liao. "Josephson effect in topological semimetal-superconductor heterojunctions." Acta Physica Sinica 72, no. 8 (2023): 087401. http://dx.doi.org/10.7498/aps.72.20230397.

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Topological semimetals are exotic phases of quantum matter with gapless electronic excitation protected by symmetry. Benefitting from its unique relativistic band dispersion, topological semimetals host abundant quantum states and quantum effects, esuch as Fermi-arc surface states and chiral anomaly. In recent years, due to the potential application in topological quantum computing, the hybrid system of topology and superconductivity has aroused wide interest in the community. Recent experimental progress of topological semimetal-superconductor heterojunctions is reviewed in two aspects: 1) Josephson current as a mode filter of different topological quantum states; 2) detection and manipulation of topological superconductivity and Majorana zero modes. For the former, utilizing Josephson interference, ballistic transport of Fermi-arc surface states is revealed, higher-order topological phases are discovered, and finite-momentum Cooper pairing and superconducting diode effect are realized. For the latter, by detecting a.c. Josephson effect in Dirac semimetal, the 4π-periodic supercurrent is discovered. By all-electric gate control, the topological transition of superconductivity is obtained. Outlooks of future research on topological semimetal-superconductor heterojunctions and their application in Majorana braiding and topological quantum computing are discussed.
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16

Rice, Anthony, and Kirstin Alberi. "Epitaxial Integration of Dirac Semimetals with Si(001)." Crystals 13, no. 4 (March 28, 2023): 578. http://dx.doi.org/10.3390/cryst13040578.

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Topological semimetals contain novel combinations of properties that make them useful in a variety of applications, including optoelectronics, spintronics and low energy computing, and catalysis. Although they have been grown with high quality as bulk single crystals, incorporation with semiconductor substrates will ultimately be required to maximize their technological reach. Here, epitaxial growth of the Dirac semimetal Cd3As2 on Si(001) is demonstrated through two routes. First, Cd3As2(112) epilayers are grown on Si(001) via an intermediate CdTe(111) buffer layer. Second, Cd3As2(112) is grown directly on Si(001). This work sets the foundation for integration of novel semimetal materials with existing CMOS technology.
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17

Huang, Shin-Ming, Su-Yang Xu, Ilya Belopolski, Chi-Cheng Lee, Guoqing Chang, Tay-Rong Chang, BaoKai Wang, et al. "New type of Weyl semimetal with quadratic double Weyl fermions." Proceedings of the National Academy of Sciences 113, no. 5 (January 19, 2016): 1180–85. http://dx.doi.org/10.1073/pnas.1514581113.

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Weyl semimetals have attracted worldwide attention due to their wide range of exotic properties predicted in theories. The experimental realization had remained elusive for a long time despite much effort. Very recently, the first Weyl semimetal has been discovered in an inversion-breaking, stoichiometric solid TaAs. So far, the TaAs class remains the only Weyl semimetal available in real materials. To facilitate the transition of Weyl semimetals from the realm of purely theoretical interest to the realm of experimental studies and device applications, it is of crucial importance to identify other robust candidates that are experimentally feasible to be realized. In this paper, we propose such a Weyl semimetal candidate in an inversion-breaking, stoichiometric compound strontium silicide, SrSi2, with many new and novel properties that are distinct from TaAs. We show that SrSi2 is a Weyl semimetal even without spin–orbit coupling and that, after the inclusion of spin–orbit coupling, two Weyl fermions stick together forming an exotic double Weyl fermion with quadratic dispersions and a higher chiral charge of ±2. Moreover, we find that the Weyl nodes with opposite charges are located at different energies due to the absence of mirror symmetry in SrSi2, paving the way for the realization of the chiral magnetic effect. Our systematic results not only identify a much-needed robust Weyl semimetal candidate but also open the door to new topological Weyl physics that is not possible in TaAs.
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18

Chen, M. N., W. C. Chen, and Yu Zhou. "Topological hybrid semimetal phases and anomalous Hall effects in a three dimensional magnetic topological insulator." Journal of Physics: Condensed Matter 34, no. 2 (October 28, 2021): 025502. http://dx.doi.org/10.1088/1361-648x/ac2ed7.

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Abstract In this work, we propose a ferromagnetic Bi2Se3 as a candidate to hold the coexistence of Weyl- and nodal-line semimetal phases, which breaks the time reversal symmetry. We demonstrate that the type-I Weyl semimetal phase, type-I-, type-II- and their hybrid nodal-line semimetal phases can arise by tuning the Zeeman exchange field strength and the Fermi velocity. Their topological responses under U(1) gauge field are also discussed. Our results raise a new way for realizing Weyl and nodal-line semimetals and will be helpful in understanding the topological transport phenomena in three-dimensional material systems.
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19

Nakashima, S., M. Hase, K. Mizoguchi, H. Harima, K. Sakai, S. Cho, A. DiVenere, and J. B. Ketterson. "Coherent phonons in mixed semimetals and semimetal superlattices." Physica B: Condensed Matter 263-264 (March 1999): 67–69. http://dx.doi.org/10.1016/s0921-4526(98)01301-5.

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20

Yadav, Suman, Atul Gour, Madhu Sarwan, and Sadhna Singh. "Mechanical and Optical Properties of Topological Semimetal Compound YPtBi." Journal of Physics: Conference Series 2603, no. 1 (October 1, 2023): 012016. http://dx.doi.org/10.1088/1742-6596/2603/1/012016.

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Abstract We have reported the mechanical properties of topological semimetals half-Heusler compound YPtBi with LDA and GGA approximation which is implemented in density functional theory. We have calculated elastic parameters which ensure good machinability, covalent bonding, brittleness, low value of Kleinman parameter and high Vickers hardness. Our results reveal the hardness or large resistance of these topological semimetals. Moreover, Born mechanical stability conditions are well fulfilled by the topological semimetal YPtBi. Present study reveals that the low value of bulk modulus and shear modulus wheras high value of Youngs modulus of this topological semimetals which deforms easily with applied external force. We have also calculated optical properties of topological semi-metal YPtBi with both LDA and GGA. Optical properties are calculated in terms of dielectric function and we have calculated dielectric constant, optical reflectivity, absorption co-efficient, optical conductivity, refractive index and electron energy loss in the energy range 0 – 14 eV. We have found higher dielectric constants with GGA in comparison to LDA that imply YPtBi is excellent materials in solar cell applications. Also, YPtBi possess high refractive index in the visible range and it is optically isotropic.
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21

Wang, Jing, Biao Lian, and Shou-Cheng Zhang. "Generation of Spin Currents by Magnetic Field in 𝒯- and 𝒫-Broken Materials." SPIN 09, no. 04 (December 2019): 1940013. http://dx.doi.org/10.1142/s2010324719400137.

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Pure spin currents carry information in quantum spintronics and could play an essential role in the next generation low-energy-consumption electronics. Here, we theoretically predict that the magnetic field can induce a quantum spin current without a concomitant charge current in metals without time reversal symmetry [Formula: see text] and inversion symmetry [Formula: see text] but respect the combined [Formula: see text] symmetry. It is governed by the magnetic moment of the Bloch states on the Fermi surface, and can be regarded as a spinful generalization of the gyrotropic magnetic effect in [Formula: see text]-broken metals. The effect is explicitly studied for a minimal model of an antiferromagnetic Dirac semimetal, where the experimental signature is proposed. We further propose candidate materials, including topological antiferromagnetic Dirac semimetals, Weyl semimetals and tenary Heusler compounds.
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22

Le, Congcong, Xianxin Wu, Shengshan Qin, Yinxiang Li, Ronny Thomale, Fu-Chun Zhang, and Jiangping Hu. "Dirac semimetal in β-CuI without surface Fermi arcs." Proceedings of the National Academy of Sciences 115, no. 33 (July 30, 2018): 8311–15. http://dx.doi.org/10.1073/pnas.1803599115.

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Anomalous surface states with Fermi arcs are commonly considered to be a fingerprint of Dirac semimetals (DSMs). In contrast to Weyl semimetals, however, Fermi arcs of DSMs are not topologically protected. Using first-principles calculations, we predict that β-cuprous iodide (β-CuI) is a peculiar DSM whose surface states form closed Fermi pockets instead of Fermi arcs. In such a fermiological Dirac semimetal, the deformation mechanism from Fermi arcs to Fermi pockets stems from a large cubic term preserving all crystal symmetries and from the small energy difference between the surface and bulk Dirac points. The cubic term in β-CuI, usually negligible in prototypical DSMs, becomes relevant because of the particular crystal structure. As such, we establish a concrete material example manifesting the lack of topological protection for surface Fermi arcs in DSMs.
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23

Morali, Noam, Rajib Batabyal, Pranab Kumar Nag, Enke Liu, Qiunan Xu, Yan Sun, Binghai Yan, Claudia Felser, Nurit Avraham, and Haim Beidenkopf. "Fermi-arc diversity on surface terminations of the magnetic Weyl semimetal Co3Sn2S2." Science 365, no. 6459 (September 19, 2019): 1286–91. http://dx.doi.org/10.1126/science.aav2334.

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Bulk–surface correspondence in Weyl semimetals ensures the formation of topological “Fermi arc” surface bands whose existence is guaranteed by bulk Weyl nodes. By investigating three distinct surface terminations of the ferromagnetic semimetal Co3Sn2S2, we verify spectroscopically its classification as a time-reversal symmetry-broken Weyl semimetal. We show that the distinct surface potentials imposed by three different terminations modify the Fermi-arc contour and Weyl node connectivity. On the tin (Sn) surface, we identify intra–Brillouin zone Weyl node connectivity of Fermi arcs, whereas on cobalt (Co) termination, the connectivity is across adjacent Brillouin zones. On the sulfur (S) surface, Fermi arcs overlap with nontopological bulk and surface states. We thus resolve both topologically protected and nonprotected electronic properties of a Weyl semimetal.
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Fereidouni, A., M. H. Doha, K. Pandey, R. Basnet, J. Hu, and H. O. H. Churchill. "Enhancement of 2D topological semimetal transport properties by current annealing." Applied Physics Letters 121, no. 11 (September 12, 2022): 113101. http://dx.doi.org/10.1063/5.0102933.

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Observation of intrinsic quantum transport properties of two-dimensional (2D) topological semimetals can be challenging due to suppression of high mobility caused by extrinsic factors introduced during fabrication. We demonstrate current annealing as a method to substantially improve electronic transport properties of 2D topological semimetal flakes. Contact resistance and resistivity were improved by factors up to [Formula: see text] and [Formula: see text], respectively, in devices based on exfoliated flakes of two topological semimetals, ZrSiSe and BaMnSb2. Using this method, carrier mobility in ZrSiSe was improved by a factor of 3800, resulting in observation of record-high mobility for exfoliated ZrSiSe. Quantum oscillations in annealed ZrSiSe appeared at magnetic fields as low as 5 T, and magnetoresistance increased by a factor of 104. We argue that a thermal process underlies this improvement. Finally, Raman spectroscopy and analysis of quantum oscillations in ZrSiSe indicate that the phonon modes and Fermi surface area are unchanged by current annealing.
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Liu, Yiyuan, Yu-Fei Liu, Xin Gui, Cheng Xiang, Hui-Bin Zhou, Chuang-Han Hsu, Hsin Lin, Tay-Rong Chang, Weiwei Xie, and Shuang Jia. "Bond-breaking induced Lifshitz transition in robust Dirac semimetal VAI3." Proceedings of the National Academy of Sciences 117, no. 27 (June 18, 2020): 15517–23. http://dx.doi.org/10.1073/pnas.1917697117.

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Topological electrons in semimetals are usually vulnerable to chemical doping and environment change, which restricts their potential application in future electronic devices. In this paper, we report that the type-II Dirac semimetalVAl3hosts exceptional, robust topological electrons which can tolerate extreme change of chemical composition. The Dirac electrons remain intact, even after a substantial part of V atoms have been replaced in theV1−xTixAl3solid solutions. This Dirac semimetal state ends atx=0.35, where a Lifshitz transition to p-type trivial metal occurs. The V–Al bond is completely broken in this transition as long as the bonding orbitals are fully depopulated by the holes donated from Ti substitution. In other words, the Dirac electrons inVAl3are protected by the V–Al bond, whose molecular orbital is their bonding gravity center. Our understanding on the interrelations among electron count, chemical bond, and electronic properties in topological semimetals suggests a rational approach to search robust, chemical-bond-protected topological materials.
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Wang, Zong-Yao, Xiang-Can Cheng, Bao-Zong Wang, Jin-Yi Zhang, Yue-Hui Lu, Chang-Rui Yi, Sen Niu, et al. "Realization of an ideal Weyl semimetal band in a quantum gas with 3D spin-orbit coupling." Science 372, no. 6539 (April 15, 2021): 271–76. http://dx.doi.org/10.1126/science.abc0105.

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Weyl semimetals are three-dimensional (3D) gapless topological phases with Weyl cones in the bulk band. According to lattice theory, Weyl cones must come in pairs, with the minimum number of cones being two. A semimetal with only two Weyl cones is an ideal Weyl semimetal (IWSM). Here we report the experimental realization of an IWSM band by engineering 3D spin-orbit coupling for ultracold atoms. The topological Weyl points are clearly measured via the virtual slicing imaging technique in equilibrium and are further resolved in the quench dynamics. The realization of an IWSM band opens an avenue to investigate various exotic phenomena that are difficult to access in solids.
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Cheskis, Dima. "Magneto-Optical Tools to Study Effects in Dirac and Weyl Semimetals." Symmetry 12, no. 9 (August 25, 2020): 1412. http://dx.doi.org/10.3390/sym12091412.

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Research regarding topological Dirac and Weyl semimetals contributes to our understanding not only of the field of solid-state physics, but also the field of high-energy physics as the physics of Dirac and Weyl semimetals resembles the physics of Dirac and Weyl massless fermions. In condensed matter physics, the Weyl nodes are detached in momentum space and may be realized as emergent quasiparticles with a distinct chirality, left-handed or right-handed. These states lead to phenomena like the chiral anomaly and the anomalous Hall effect (AHE). Furthermore, the combination of quantum effects and magnetic effects in magnetic Weyl semimetals is very intriguing. Magneto-optical tools, which are usually used to study magnetic phenomena, also contribute to magnetic Weyl semimetals. Moreover, with the magneto-optical technique, it is possible to follow the dynamics of the processes and to study the lifetime of the Weyl states. In this work, we review and discuss the effects of using magneto-optical tools for studying quantum effects like the chiral anomaly or magnetic effects in magnetic Weyl and Dirac systems using the magneto-optical Kerr effect (MOKE) or Faraday systems including a single detection and imaging. Examples of using magneto-optical systems in the research of ultrafast magnetic dynamics of thin polycrystalline nickel and permaloy are reviewed as are the magnetic spatial dynamics by employing magneto-optical Kerr or Faraday microscopy tools with ferromagnetic thin films. Interestingly, the excitation of a circularly polarized femtosecond laser pulse could lead to the breakage of time-reversal symmetry and to the transformation of the Dirac state to the Floquet–Weyl semimetal state. The development of a suitable ultrafast magneto-optical system for Weyl systems is discussed, and the practical difficulties for the realization of such a system are considered.
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Lee, Sang-Eon, Myeong-jun Oh, Sanghyun Ji, Jinsu Kim, Jin-Hyeon Jun, Woun Kang, Younjung Jo, and Myung-Hwa Jung. "Orbit topology analyzed from π phase shift of magnetic quantum oscillations in three-dimensional Dirac semimetal." Proceedings of the National Academy of Sciences 118, no. 29 (July 15, 2021): e2023027118. http://dx.doi.org/10.1073/pnas.2023027118.

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With the emergence of Dirac fermion physics in the field of condensed matter, magnetic quantum oscillations (MQOs) have been used to discern the topology of orbits in Dirac materials. However, many previous researchers have relied on the single-orbit Lifshitz–Kosevich (LK) formula, which overlooks the significant effect of degenerate orbits on MQOs. Since the single-orbit LK formula is valid for massless Dirac semimetals with small cyclotron masses, it is imperative to generalize the method applicable to a wide range of Dirac semimetals, whether massless or massive. This report demonstrates how spin-degenerate orbits affect the phases in MQOs of three-dimensional massive Dirac semimetal, NbSb2. With varying the direction of the magnetic field, an abrupt π phase shift is observed due to the interference between the spin-degenerate orbits. We investigate the effect of cyclotron mass on the π phase shift and verify its close relation to the phase from the Zeeman coupling. We find that the π phase shift occurs when the cyclotron mass is half of the electron mass, indicating the effective spin gyromagnetic ratio as gs = 2. Our approach is not only useful for analyzing MQOs of massless Dirac semimetals with a small cyclotron mass but also can be used for MQOs in massive Dirac materials with degenerate orbits, especially in topological materials with a sufficiently large cyclotron mass. Furthermore, this method provides a useful way to estimate the precise gs value of the material.
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Chen, Cheng, Huaiqiang Wang, Dinghui Wang, and Haijun Zhang. "Strain-Engineered Nonlinear Hall Effect in HgTe." SPIN 09, no. 04 (December 2019): 1940017. http://dx.doi.org/10.1142/s2010324719400174.

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As paradigmatic phenomena, Hall effects have inspired tremendous studies of symmetry and topology in condensed matter physics. Intriguingly, a second-order nonlinear Hall effect was recently proposed in noncentrosymmetric materials even in the presence of time-reversal symmetry. This effect originates from the Berry curvature dipole of electronic band structures and was predicted in Dirac and Weyl materials such as transition metal dichalcogenides and Weyl semimetals. Although it has been experimentally verified in some transition metal dichalcogenides, no obvious observation of such effects has been reported in Weyl semimetals. Taking advantage of the ideal Weyl phase with no coexisting trivial bands at the Fermi level, we use strained HgTe as a concrete example to show that the ideal Weyl semimetal is a promising platform for demonstrating the nonlinear Hall effect. Based on numerical calculations of the Berry curvature dipole, it was found that the magnitude of nonlinear Hall effect can be simply engineered by in-plane strain. Our work provides a versatile platform with high tunability, which could greatly facilitate the study of nonlinear Hall effect in three-dimensional topological materials.
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Shekhar, Chandra, Nitesh Kumar, V. Grinenko, Sanjay Singh, R. Sarkar, H. Luetkens, Shu-Chun Wu, et al. "Anomalous Hall effect in Weyl semimetal half-Heusler compounds RPtBi (R = Gd and Nd)." Proceedings of the National Academy of Sciences 115, no. 37 (August 28, 2018): 9140–44. http://dx.doi.org/10.1073/pnas.1810842115.

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Topological materials ranging from topological insulators to Weyl and Dirac semimetals form one of the most exciting current fields in condensed-matter research. Many half-Heusler compounds, RPtBi (R = rare earth), have been theoretically predicted to be topological semimetals. Among various topological attributes envisaged in RPtBi, topological surface states, chiral anomaly, and planar Hall effect have been observed experimentally. Here, we report an unusual intrinsic anomalous Hall effect (AHE) in the antiferromagnetic Heusler Weyl semimetal compounds GdPtBi and NdPtBi that is observed over a wide temperature range. In particular, GdPtBi exhibits an anomalous Hall conductivity of up to 60 Ω−1⋅cm−1 and an anomalous Hall angle as large as 23%. Muon spin-resonance (μSR) studies of GdPtBi indicate a sharp antiferromagnetic transition (TN) at 9 K without any noticeable magnetic correlations above TN. Our studies indicate that Weyl points in these half-Heuslers are induced by a magnetic field via exchange splitting of the electronic bands at or near the Fermi energy, which is the source of the chiral anomaly and the AHE.
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31

Burkov, A. A. "Topological semimetals." Nature Materials 15, no. 11 (October 25, 2016): 1145–48. http://dx.doi.org/10.1038/nmat4788.

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32

Ghosh, Suvendu, Snehasish Nandy, and A. Taraphder. "Revisiting quantum transport across junctions of single and double-Weyl semimetals." Journal of Physics: Conference Series 2518, no. 1 (June 1, 2023): 012005. http://dx.doi.org/10.1088/1742-6596/2518/1/012005.

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Abstract Different types of transport in topological semimetals probe the signatures of their band topology directly. Using Landuer-Buttiker formalism, we study transport through a rectangular potential barrier created across a junction between two topological multi-Weyl semimetals (MSMs). In contrast to a regular Weyl semimetal with topological charge J = 1, MSMs are allowed to have monopole charges J > 1. Consequently, the band structures show highly anisotropic dispersions, being linear exclusively in one momentum direction, and exhibiting a power law dependence, governed by the topological charge J, in other two directions. In this work, we restrict ourselves to MSMs with J = 1 and 2, i.e. single- and double-Weyl semimetals, and our study reveals several unconventional features, which are unique to our systems of study and are useful as diagnostic tools for such topological systems and help to understand the role of anisotropies in these systems. Most strikingly, our study uncovers that the barrier becomes completely transparent to the particles obliquely incident on the barrier only when the incident energy (E) exactly equals to the half of the barrier-height (U) with a certain condition. On the other hand, we show that the Klein tunneling, i.e. the perfect transmission of the particles incident normally on the barrier, exists not only in E < U limit but also in E > U limit. Our study also identifies a new limit (E < U) of occurrence of classical Ramsauer-Townsend effect like condition. The results presented in this work could be tested in simple experiments.
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Boyda, D. L., V. V. Braguta, M. I. Katsnelson, and A. Yu Kotov. "Phase diagram and Chiral Magnetic Effect in Dirac Semimetals from Lattice Simulation." EPJ Web of Conferences 175 (2018): 03001. http://dx.doi.org/10.1051/epjconf/201817503001.

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Dirac Semimetals Na3Bi and Cd3As2 are recently discovered materials, which low energy electronic spectrum is described by two flavours of massless 3+1D fermions. In order to study electronic properties of these materials we formulated lattice field theory with rooted staggered fermions on anisotropic lattice. It is shown that in the limit of zero temporal lattice spacing this theory reproduces effective theory of Dirac semimetals. Using the lattice field theory we study the phase diagram of Dirac semimetals in the plane effective coupling constant - Fermi velocity anisotropy. We also measure conductivity of Dirac Semimetals within lattice field theory in external magnetic field. Our results confirm the existence of Chiral Magnetic Effect in Dirac Semimetals.
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Teng, Yu Jia. "Heusler Compounds and their Topological Semimetal States." Materials Science Forum 1027 (April 2021): 33–41. http://dx.doi.org/10.4028/www.scientific.net/msf.1027.33.

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Heusler compounds are a family of materials with high tunability due to their structure and lots of states or properties have been discovered in it. Topological semimetals (TSM) are a new phase of quantum matter that many materials have been reported to have this phase, including Heusler compounds. In this review, basic concepts of Heusler compounds and main properties of three TSMs are first reviewed, followed by analysis of topological semimetal states in Heusler compounds. In the end, the most suitable TSM state in Heusler compound is given.
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35

Huang, Silu, Jisun Kim, W. A. Shelton, E. W. Plummer, and Rongying Jin. "Nontrivial Berry phase in magnetic BaMnSb2 semimetal." Proceedings of the National Academy of Sciences 114, no. 24 (May 24, 2017): 6256–61. http://dx.doi.org/10.1073/pnas.1706657114.

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The subject of topological materials has attracted immense attention in condensed-matter physics because they host new quantum states of matter containing Dirac, Majorana, or Weyl fermions. Although Majorana fermions can only exist on the surface of topological superconductors, Dirac and Weyl fermions can be realized in both 2D and 3D materials. The latter are semimetals with Dirac/Weyl cones either not tilted (type I) or tilted (type II). Although both Dirac and Weyl fermions have massless nature with the nontrivial Berry phase, the formation of Weyl fermions in 3D semimetals require either time-reversal or inversion symmetry breaking to lift degeneracy at Dirac points. Here we demonstrate experimentally that canted antiferromagnetic BaMnSb2 is a 3D Weyl semimetal with a 2D electronic structure. The Shubnikov–de Hass oscillations of the magnetoresistance give nearly zero effective mass with high mobility and the nontrivial Berry phase. The ordered magnetic arrangement (ferromagnetic ordering in the ab plane and antiferromagnetic ordering along the c axis below 286 K) breaks the time-reversal symmetry, thus offering us an ideal platform to study magnetic Weyl fermions in a centrosymmetric material.
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36

Liao, Xin, Chang Xu, Zi-Pu Fan, Ying-Ying Lan, Na Li, Chun-Guang Chu, An-Qi Wang, Dong Sun, and Zhi-Min Liao. "Gate-enhanced broadband photodetection based on Cd3As2/graphene Dirac heterojunctions." Applied Physics Letters 122, no. 3 (January 16, 2023): 031105. http://dx.doi.org/10.1063/5.0139561.

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Dirac semimetals are promising materials for broadband and fast photodetection due to their gapless nature. Dirac heterostructures consisting of 2D Dirac semimetal graphene and its 3D analogue Cd3As2 should take the ascendency of high carrier mobility in both materials, while overcome the limitation of weak optical absorption in graphene-based devices and suppress the dark current occurring in pure Cd3As2 photodetectors. Herein, we report high-performance photodetectors based on a 3D Dirac semimetal Cd3As2/monolayer graphene heterostructure, which show broadband photoresponse from visible (488 nm) to mid-infrared (10 μm) wavelength region at room temperature without an external bias. The photodetectors are with a maximum responsivity of 0.34 mA/W at 488 nm and a fast response speed of ∼13 μs. In addition, the photoresponse can be enhanced by a gate voltage even in a long wavelength region. Our work suggests that the combination of the graphene and 3D Dirac semimetal is promising for high-performance photodetectors with broadband detection, high sensitivity, and rapid response.
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Boyko, Yu I., V. V. Bogdanov, Z. F. Nazyrov, R. V. Vovk, and B. V. Grinyov. "“Metallization” of semimetals by an external electric field." Low Temperature Physics 49, no. 11 (November 1, 2023): 1268–70. http://dx.doi.org/10.1063/10.0021372.

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The paper considers the possibility of changing the energy spectrum of the electronic subsystem of semimetals from a non-degenerate to a degenerate state under the action of an external electric field. This “metallization” of semimetals is achieved by increasing the concentration of free electrons in the external field. The work also considers the possible transition of “metallized” semimetals to the superconducting state. The evaluations made show that for the size of the sample R ≤ 100 nm and for the magnitude of the field source voltage U ≈ 10 V, “metallized” semimetals and their solid solutions can undergo transition to a superconducting state at temperatures Tc ≥ 100 K, which is an order of magnitude higher than the characteristic temperature value Tc for classic metals.
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Xu, Xin-Xin, Zi-Ming Wang, Dong-Hui Xu, and Chui-Zhen Chen. "Photoinduced Floquet higher-order Weyl semimetal in C 6 symmetric Dirac semimetals." Chinese Physics B, May 2, 2024. http://dx.doi.org/10.1088/1674-1056/ad4634.

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Abstract Topological Dirac semimetals are a parent state from which other exotic topological phases of matter, such as Weyl semimetals and topological insulators, can emerge. In this study, we investigate a Dirac semimetal possessing sixfold rotational symmetry and hosting higher-order topological hinge Fermi arc states, which is irradiated by circularly polarized light. Our findings reveal that circularly polarized light splits each Dirac node into a pair of Weyl nodes due to the breaking of time-reversal symmetry, resulting in the realization of the Weyl semimetal phase. This Weyl semimetal phase exhibits rich boundary states, including two-dimensional surface Fermi arc states and hinge Fermi arc states confined to six hinges. Furthermore, by adjusting the incident direction of the circularly polarized light, we can control the degree of tilt of the resulting Weyl cones, enabling the realization of different types of Weyl semimetals.
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39

Gao, Ling-Long, Yan Liu, and Hong-Da Lyu. "Black hole interiors in holographic topological semimetals." Journal of High Energy Physics 2023, no. 3 (March 6, 2023). http://dx.doi.org/10.1007/jhep03(2023)034.

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Abstract We study the black hole interiors in holographic Weyl semimetals and holographic nodal line semimetals. We find that the black hole singularities are of Kasner form. In the topologically nontrivial phase at low temperature, both the Kasner exponents of the metric fields and the proper time from the horizon to the singularity are almost constant, likely reflecting the topological nature of the topological semimetals. We also find some specific behaviors inside the horizon in each holographic semimetal model.
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He, Wen-Yu, Xiao Yan Xu, and K. T. Law. "Kramers Weyl semimetals as quantum solenoids and their applications in spin-orbit torque devices." Communications Physics 4, no. 1 (March 31, 2021). http://dx.doi.org/10.1038/s42005-021-00564-w.

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AbstractKramers Weyl semimetals are Weyl semimetals that have Weyl points pinned at the time reversal invariant momenta. Recently it has been discovered that all chiral crystals host Weyl points at time reversal invariant momenta, so metals with chiral lattice symmetry all belong to the category of Kramers Weyl semimetals. In this work, we show that due to the chiral lattice symmetry, Kramers Weyl semimetals have the unique longitudinal magnetoelectric effect in which the charge current induced spin and orbital magnetization is parallel to the direction of the current. This feature allows Kramers Weyl semimetals to act as nanoscale quantum solenoids with both orbital and spin magnetization. As the moving electrons of Kramers Weyl semimetal can generate longitudinal magnetization, Kramers Weyl semimetals can be used for new designs of spin-orbit torque devices with all electric control of magnetization switching for magnets with perpendicular magnetic anisotropy.
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jia, kaixiang, Xinyu Liu, Rong Ma, Hao Geng, L. Sheng, and Dingyu Xing. "Phase Diagram of Three DimensionalDisordered Nodal-Line Semimetals: Weak Localization To Anderson Localization." New Journal of Physics, November 2, 2023. http://dx.doi.org/10.1088/1367-2630/ad08f4.

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Abstract Nodal-line semimetals are new members of the topological materials family whose experimental&#xD;characterization has seen recent progress using both ARPES and quantum oscillation measurements.&#xD;Here, we theoretically study the presence of a disorder-induced phase transition in a cubic lattice&#xD;nodal-line semimetal using numerical diagonalization and spectral calculations. In contrast to the&#xD;3D nodal-point semimetals, we found that nodal-line semimetals do not display a stable disordered&#xD;semimetal phase, as an infinitely weak disorder can lead to a diffusive metal phase. The absence of&#xD;a semimetal phase is also reflected in the quadratic relationship of the electronic specific heat at low&#xD;temperatures. Furthermore, we illustrate that a localization transition occurs under the influence of&#xD;strong disorder, shifting the material from a weakly localized diffusive metal state to an Anderson&#xD;insulator. This transition is substantiated by calculating the adjacent gap ratio and the typical&#xD;density of states.
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Lanzillo, Nicholas A., Utkarsh Bajpai, and Ching-Tzu Chen. "Topological semimetal interface resistivity scaling for vertical interconnect applications." Applied Physics Letters 124, no. 18 (April 29, 2024). http://dx.doi.org/10.1063/5.0200403.

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In this work, we explore the electron scattering characteristics at interfaces between normal metals and topological semimetals in bulk as well as in thin film structures. We consider Cu/Ta and CoSi/Ta as representative metal/metal and topological semimetal/metal interface structures, respectively. For bulk interface structures, we find that metal/topological semimetal interfaces have roughly 20× higher interfacial resistivity than normal metal/metal interfaces primarily due to the low electronic density of states, the Fermi level in bulk topological semimetals. For thin films, we find that normal metal/metal interfacial resistivity shows a weak dependence on film thickness and is generally close to the corresponding bulk value. Interfaces between surface-conduction dominated topological semimetals, such as CoSi and normal metals in thin films, however, show decreasing interfacial resistivity with decreasing film thickness. This apparent reduction in interface resistivity originates from the surface-dominated transport, where the total transmission across the interface varies little with reduced film thickness, yielding an effective increase in interface conductivity at smaller dimensions. These results suggest that topological semimetals may be attractive candidates for next-generation interconnect materials with critically small dimensions where interfaces with other metals are ubiquitous.
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Lotfi, Jafar, and Babak Abdollahipour. "Thermoelectric effects in ballistic junctions of 2D-Weyl semimetals." Physica Scripta, May 15, 2024. http://dx.doi.org/10.1088/1402-4896/ad4c17.

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Abstract Two-dimensional Weyl semimetals are a variant of topological materials in two dimensions, which are realized in three atomic layer materials. These materials possess isotropic or anisotropic dispersions around Weyl nodes and present some common physical properties with their 3D counterparts. We study the thermoelectric effects in a ballistic junction of 2D-Weyl semimetal with isotropic or anisotropic dispersions around the Weyl points. We demonstrate that these two types of 2D-Weyl semimetals exhibit different thermoelectric responses at low chemical potentials of the leads. The Weyl semimetal layer's physical characteristics can significantly affect these junctions' thermoelectric properties. Moreover, significant Seebeck coefficient and thermoelectric figure of merit of these junctions are only observed at the low chemical potential of the leads. In particular, we unveil that thermoelectric effects in the ballistic junction of 2D-Weyl semimetals are not as efficient as their 3D counterparts.
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Zhang, Cheng-Long, Tian Liang, M. S. Bahramy, Naoki Ogawa, Vilmos Kocsis, Kentaro Ueda, Yoshio Kaneko, Markus Kriener, and Yoshinori Tokura. "Berry curvature generation detected by Nernst responses in ferroelectric Weyl semimetal." Proceedings of the National Academy of Sciences 118, no. 44 (October 27, 2021). http://dx.doi.org/10.1073/pnas.2111855118.

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Significance An ideal Weyl semimetal with high tunability is an undoubtedly important platform for realizing and manipulating exotic quantum properties of topological semimetals. Currently, all the existing nonmagnetic Weyl semimetals are not ideal and out of external control, namely, no couplings to an order parameter. In this work, we report with a topological phase transition diagram the successful realization of a Weyl semimetal phase by chemically engineering the PbTe-SnTe alloy. Furthermore, we demonstrate that the Weyl semimetal phase is strongly coupled with the underlying ferroelectric order, which exhibits turn on/off properties when the ferroelectric order appears/disappears. The Weyl phase is detected experimentally by a Berry curvature–sensitive thermoelectric probe called in-plane Nernst effect, which excludes the Drude response.
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45

Cichorek, T., Ł. Bochenek, J. Juraszek, Yu V. Sharlai, and G. P. Mikitik. "Detection of relativistic fermions in Weyl semimetal TaAs by magnetostriction measurements." Nature Communications 13, no. 1 (July 5, 2022). http://dx.doi.org/10.1038/s41467-022-31321-4.

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AbstractThus far, a detection of the Dirac or Weyl fermions in topological semimetals remains often elusive, since in these materials conventional charge carriers exist as well. Here, measuring a field-induced length change of the prototype Weyl semimetal TaAs at low temperatures, we find that its c-axis magnetostriction amounts to relatively large values whereas the a-axis magnetostriction exhibits strong variations with changing the orientation of the applied magnetic field. It is discovered that at magnetic fields above the ultra-quantum limit, the magnetostriction of TaAs contains a linear-in-field term, which, as we show, is a hallmark of the Weyl fermions in a material. Developing a theory for the magnetostriction of noncentrosymmetric topological semimetals and applying it to TaAs, we additionally find several parameters characterizing the interaction between the relativistic fermions and elastic degrees of freedom in this semimetal. Our study shows how dilatometry can be used to unveil Weyl fermions in candidate topological semimetals.
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Feng, Xuewei, Zhi Gen Yu, Haoyue Guo, Yida Li, Yong‐Wei Zhang, and Kah‐Wee Ang. "Direct Observation of Semimetal Contact Induced Charge Doping and Strain Effect in CVD‐Grown Monolayer MoS2 Transistors." Advanced Electronic Materials, March 5, 2024. http://dx.doi.org/10.1002/aelm.202300820.

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AbstractTwo‐dimensional Materials (2DMs) offer significant promise for advancing device miniaturization and extending Moore's law. Despite the challenges posed by high contact resistance in transistors, recent discoveries highlight semimetals as an effective approach for achieving ohmic contact with near‐quantum‐limit contact resistance. The energy band hybridization between semimetal and MoS2 is found to create degenerate states and heavily doped contact, which is proposed as the underlying mechanism responsible for reducing contact resistance. However, a quantitative and comprehensive characterization of the semimetal‐MoS2 interface is lacking, leaving the physical interactions elusive. This study reveals that semimetals induce n‐type doping and tensile strain in monolayer MoS2 grown using CVD, which serve as the contact resistance and mobility boosters. Among the semimetals investigated, including Bismuth (Bi), Antimony (Sb), and their alloy, Bi results in the highest electron doping of 2 × 1013 cm−2 and a 0.5% tensile strain, leading to reduced contact resistance and enhanced mobility. First‐principles calculations and spectroscopy measurements unveil the impact of electron doping and strain in MoS2, and the thermal effects are subsequently explored. This research underscores the potential of semimetals in boosting device performance and lays the foundation for reducing contact resistance in transistors made from 2D materials.
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47

Biswal, Bubunu, Ramesh Rajarapu, Saroj Poudyal, Renu Yadav, Prahalad Kanti Barman, Manasi Mandal, Ravi Prakash Singh, B. R. K. Nanda, and Abhishek Misra. "Layered semimetal electrodes for future heterogeneous electronics." Applied Physics Letters 123, no. 11 (September 11, 2023). http://dx.doi.org/10.1063/5.0164063.

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Integration of the emerging layered materials with the existing CMOS platform is a promising solution to enhance the performance and functionalities of the future CMOS based integrated circuits. In this direction, we have experimentally studied the suitability of the layered semimetals, namely, Td-WTe2, 1T′-MoTe2, 1T-PtTe2, and 1T-PtSe2, as an electrode with two most commonly used semiconductors, i.e., silicon (Si) and germanium (Ge) used in the CMOS technology. Two kinds of devices, i.e., metal–oxide–semiconductor (MOS) capacitors and metal-semiconductor (MS) diodes, are investigated with these semimetals as a conducting electrode. Through detailed electrical and physical characterizations, it is established that these semimetals form excellent interface with the underneath dielectric (SiO2) in the MOS structure and with the semiconductor (Ge) in the MS diode. Near ideal CV curves of MOS devices and large ON-current in the MS diodes signify that these semimetals act perfectly well as a contact electrode. Reduction in the Schottky barrier height of the MS diodes with decreasing values of the semimetal WF suggests the excellent interface of these semimetals with the Ge substrate. Most importantly, these semimetals do not add any unwanted series resistance across the current conduction path in the diode. Guided by these experimental observations, we propose that these semimetals can indeed be integrated with conventional CMOS platform, thus paving a way for an era of CMOS based heterogeneous electronics.
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48

Shoriki, Kentaro, Keigo Moriishi, Yoshihiro Okamura, Kohei Yokoi, Hidetomo Usui, Hiroshi Murakawa, Hideaki Sakai, Noriaki Hanasaki, Yoshinori Tokura, and Youtarou Takahashi. "Large nonlinear optical magnetoelectric response in a noncentrosymmetric magnetic Weyl semimetal." Proceedings of the National Academy of Sciences 121, no. 12 (March 14, 2024). http://dx.doi.org/10.1073/pnas.2316910121.

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Weyl semimetals resulting from either inversion ( P ) or time-reversal ( T ) symmetry breaking have been revealed to show the record-breaking large optical response due to intense Berry curvature of Weyl-node pairs. Different classes of Weyl semimetals with both P and T symmetry breaking potentially exhibit optical magnetoelectric (ME) responses, which are essentially distinct from the previously observed optical responses in conventional Weyl semimetals, leading to the versatile functions such as directional dependence for light propagation and gyrotropic effects. However, such optical ME phenomena of (semi)metallic systems have remained elusive so far. Here, we show the large nonlinear optical ME response in noncentrosymmetric magnetic Weyl semimetal PrAlGe, in which the polar structural asymmetry and ferromagnetic ordering break P and T symmetry. We observe the giant second harmonic generation (SHG) arising from the P symmetry breaking in the paramagnetic phase, being comparable to the largest SHG response reported in Weyl semimetal TaAs. In the ferromagnetically ordered phase, it is found that interference between this nonmagnetic SHG and the magnetically induced SHG emerging due to both P and T symmetry breaking results in the magnetic field switching of SHG intensity. Furthermore, such an interference effect critically depends on the light-propagating direction. The corresponding magnetically induced nonlinear susceptibility is significantly larger than the prototypical ME material, manifesting the existence of the strong nonlinear dynamical ME coupling. The present findings establish the unique optical functionality of P - and T -symmetry broken ME topological semimetals.
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Wu, Fang Jia, Shasha Ke, Yong Guo, Huaiwu Zhang, and HF Lu. "Non-centrosymmetric Weyl Semimetal State and Strain Effect in the Twisted-brick Phase Transition Metal Monochalcogenides." Nanoscale, 2023. http://dx.doi.org/10.1039/d2nr04946e.

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Weyl semimetals are a class of gapless electronic excitation topological quantum materials upon breaking time-reversal or inversion symmetry. Here, we demonstrate the existence of the Weyl semimetal state in the...
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Abdol, Somayeh Oskoui, and Babak Abdollahipour. "Asymmetrical plasmonic absorber and reflector based on tilted Weyl semimetals." Scientific Reports 11, no. 1 (July 29, 2021). http://dx.doi.org/10.1038/s41598-021-94808-y.

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Abstract:
AbstractWe investigate the surface plasmon polariton dispersion and optical spectra of a thin film of tilted Weyl semimetal. Tilted Weyl semimetals possess tilted Weyl cones at the Weyl nodes and are categorized to type-I with closed Fermi surfaces and type-II with overtilted Weyl cones and open Fermi surfaces. We find that the surface plasmon polariton dispersion of this system is nonreciprocal even in the absence of the external magnetic field. Moreover, we demonstrate that the tilt parameter has a profound effect in controlling this nonreciprocity. We reveal that the thin film of type-II Weyl semimetal hosts the surface plasmon polariton modes with the negative group velocity. Furthermore, we show that the angular optical spectra of this structure are highly asymmetric and this angular asymmetry in the absorptivity and reflectivity depends profoundly on the tilt parameter of the tilted Weyl semimetal. These exciting features propose employing the tilted Weyl semimetals in optical sensing devices, optical data storage, and devices for quantum information processing.
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