Journal articles: 'Topological semimetals'

1

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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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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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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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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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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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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7

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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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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9

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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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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11

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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12

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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Lai, Hsin-Hua, Sarah E. Grefe, Silke Paschen, and Qimiao Si. "Weyl–Kondo semimetal in heavy-fermion systems." Proceedings of the National Academy of Sciences 115, no. 1 (December 18, 2017): 93–97. http://dx.doi.org/10.1073/pnas.1715851115.

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Insulating states can be topologically nontrivial, a well-established notion that is exemplified by the quantum Hall effect and topological insulators. By contrast, topological metals have not been experimentally evidenced until recently. In systems with strong correlations, they have yet to be identified. Heavy-fermion semimetals are a prototype of strongly correlated systems and, given their strong spin-orbit coupling, present a natural setting to make progress. Here, we advance a Weyl–Kondo semimetal phase in a periodic Anderson model on a noncentrosymmetric lattice. The quasiparticles near the Weyl nodes develop out of the Kondo effect, as do the surface states that feature Fermi arcs. We determine the key signatures of this phase, which are realized in the heavy-fermion semimetal Ce3Bi4Pd3. Our findings provide the much-needed theoretical foundation for the experimental search of topological metals with strong correlations and open up an avenue for systematic studies of such quantum phases that naturally entangle multiple degrees of freedom.

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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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15

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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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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17

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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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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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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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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Yang, Xiaosen, Yang Cao, and Yunjia Zhai. "Non-Hermitian Weyl semimetals: Non-Hermitian skin effect and non-Bloch bulk–boundary correspondence." Chinese Physics B 31, no. 1 (January 1, 2022): 010308. http://dx.doi.org/10.1088/1674-1056/ac3738.

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Abstract We investigate novel features of three-dimensional non-Hermitian Weyl semimetals, paying special attention to the unconventional bulk–boundary correspondence. We use the non-Bloch Chern numbers as the tool to obtain the topological phase diagram, which is also confirmed by the energy spectra from our numerical results. It is shown that, in sharp contrast to Hermitian systems, the conventional (Bloch) bulk–boundary correspondence breaks down in non-Hermitian topological semimetals, which is caused by the non-Hermitian skin effect. We establish the non-Bloch bulk–boundary correspondence for non-Hermitian Weyl semimetals: the topological edge modes are determined by the non-Bloch Chern number of the bulk bands. Moreover, these topological edge modes can manifest as the unidirectional edge motion, and their signatures are consistent with the non-Bloch bulk–boundary correspondence. Our work establishes the non-Bloch bulk–boundary correspondence for non-Hermitian topological semimetals.

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Fang, Chen, Hongming Weng, Xi Dai, and Zhong Fang. "Topological nodal line semimetals." Chinese Physics B 25, no. 11 (November 2016): 117106. http://dx.doi.org/10.1088/1674-1056/25/11/117106.

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Yan, Binghai, and Claudia Felser. "Topological Materials: Weyl Semimetals." Annual Review of Condensed Matter Physics 8, no. 1 (March 31, 2017): 337–54. http://dx.doi.org/10.1146/annurev-conmatphys-031016-025458.

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Wang, Jian. "Superconductivity in topological semimetals." National Science Review 6, no. 2 (December 10, 2018): 199–202. http://dx.doi.org/10.1093/nsr/nwy155.

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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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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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Chen, Qin, Yuxing Zhou, Binjie Xu, Zhefeng Lou, Huancheng Chen, Shuijin Chen, Chunxiang Wu, et al. "Large Magnetoresistance and Nontrivial Berry Phase in Nb₃Sb Crystals with A15 Structure." Chinese Physics Letters 38, no. 8 (September 1, 2021): 087501. http://dx.doi.org/10.1088/0256-307x/38/8/087501.

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Compounds with the A15 structure have attracted extensive attention due to their superconductivity and nontrivial topological band structures. We have successfully grown Nb3Sb single crystals with the A15 structure and systematically measured the longitudinal resistivity, Hall resistivity and quantum oscillations in magnetization. Similar to other topological trivial/nontrivial semimetals, Nb3Sb exhibits large magnetoresistance (MR) at low temperatures (717%, 2 K and 9 T), unsaturating quadratic field dependence of MR and up-turn behavior in ρxx (T) curves under magnetic field, which is considered to result from a perfect hole-electron compensation, as evidenced by the Hall resistivity measurements. The nonzero Berry phase obtained from the de-Hass van Alphen (dHvA) oscillations demonstrates that Nb3Sb is topologically nontrivial. These results indicate that Nb3Sb superconductor is also a semimetal with large MR and nontrivial Berry phase. This indicates that Nb3Sb may be another platform to search for the Majorana zero-energy mode.

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Nguyen, Thanh, Yoichiro Tsurimaki, Ricardo Pablo-Pedro, Grigory Bednik, Tongtong Liu, Anuj Apte, Nina Andrejevic, and Mingda Li. "Topological signatures in nodal semimetals through neutron scattering." New Journal of Physics 24, no. 1 (January 1, 2022): 013016. http://dx.doi.org/10.1088/1367-2630/ac45cb.

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Abstract Topological nodal semimetals are known to host a variety of fascinating electronic properties due to the topological protection of the band-touching nodes. Neutron scattering, despite its power in probing elementary excitations, has not been routinely applied to topological semimetals, mainly due to the lack of an explicit connection between the neutron response and the signature of topology. In this work, we theoretically investigate the role that neutron scattering can play to unveil the topological nodal features: a large magnetic neutron response with spectral non-analyticity can be generated solely from the nodal bands. A new formula for the dynamical structure factor for generic topological nodal metals is derived. For Weyl semimetals, we show that the locations of Weyl nodes, the Fermi velocities and the signature of chiral anomaly can all leave hallmark neutron spectral responses. Our work offers a neutron-based avenue toward probing bulk topological materials.

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Wang, Huan, Chun-Juan He, Sheng Xu, Yi-Yan Wang, Xiang-Yu Zeng, Jun-Fa Lin, Xiao-Yan Wang, et al. "Single crystal growth of topological semimetals and magnetic topological materials." Acta Physica Sinica 72, no. 3 (2023): 038101. http://dx.doi.org/10.7498/aps.72.20211961.

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Topological materials have attracted much attention due to their novel physical properties. These materials can not only serve as a platform for studying the fundamental physics, but also demonstrate a significant potential application in electronics, and they are studied usually in two ways. One is to constantly explore new experimental phenomena and physical problems in existing topological materials, and the other is to predict and discover new topological material systems and carry out synthesis. In a word, high-quality crystals are very important for studying quantum oscillations, angle resolved photoemission spectra or scanning tunneling microscopy. In this work, the classifications and developments of topological materials, including topological insulators, topological semimetals, and magnetic topological materials, are introduced. As usually employed growth methods in growing topological materials, flux and vapour transport methods are introduced in detail. Other growth methods, such as Bridgman, float-zone, vapour deposition and molecular beam epitaxy methods, are also briefly mentioned. Then the details about the crystal growth of some typical topological materials, including topological insulators/semimetals, high Chern number chiral topological semimetals and magnetic topological materials, are elaborated. Meanwhile, the identification of crystal quality is also briefly introduced, including the analysis of crystal composition and structure, which are greatly important.

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31

Guo, Cheng, Yibin Hu, Gang Chen, Dacheng Wei, Libo Zhang, Zhiqingzi Chen, Wanlong Guo, et al. "Anisotropic ultrasensitive PdTe2-based phototransistor for room-temperature long-wavelength detection." Science Advances 6, no. 36 (September 2020): eabb6500. http://dx.doi.org/10.1126/sciadv.abb6500.

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Emergent topological Dirac semimetals afford fresh pathways for optoelectronics, although device implementation has been elusive to date. Specifically, palladium ditelluride (PdTe2) combines the capabilities provided by its peculiar band structure, with topologically protected electronic states, with advantages related to the occurrence of high-mobility charge carriers and ambient stability. Here, we demonstrate large photogalvanic effects with high anisotropy at terahertz frequency in PdTe2-based devices. A responsivity of 10 A/W and a noise-equivalent power lower than 2 pW/Hz0.5 are achieved at room temperature, validating the suitability of PdTe2-based devices for applications in photosensing, polarization-sensitive detection, and large-area fast imaging. Our findings open opportunities for exploring uncooled and sensitive photoelectronic devices based on topological semimetals, especially in the highly pursuit terahertz band.

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Xu, Bing, Zi-Yang Qiu, Run Yang, Yao-Min Dai, and Xiang-Gang Qiu. "Optical properties of topological semimetals." Acta Physica Sinica 68, no. 22 (2019): 227804. http://dx.doi.org/10.7498/aps.68.20191510.

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Schoop, Leslie M., Florian Pielnhofer, and Bettina V. Lotsch. "Chemical Principles of Topological Semimetals." Chemistry of Materials 30, no. 10 (April 10, 2018): 3155–76. http://dx.doi.org/10.1021/acs.chemmater.7b05133.

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Mikitik, G. P., and Yu V. Sharlai. "Magnetic Susceptibility of Topological Semimetals." Journal of Low Temperature Physics 197, no. 3-4 (August 13, 2019): 272–309. http://dx.doi.org/10.1007/s10909-019-02225-3.

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35

Akanda, Md Rakibul Karim. "Catalog of magnetic topological semimetals." AIP Advances 10, no. 9 (September 1, 2020): 095222. http://dx.doi.org/10.1063/5.0020096.

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36

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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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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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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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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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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Zhang, Delin, Wei Jiang, Hwanhui Yun, Onri Jay Benally, Thomas Peterson, Zach Cresswell, Yihong Fan, et al. "Robust negative longitudinal magnetoresistance and spin–orbit torque in sputtered Pt3Sn and Pt3SnxFe1-x topological semimetal." Nature Communications 14, no. 1 (July 12, 2023). http://dx.doi.org/10.1038/s41467-023-39408-2.

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AbstractContrary to topological insulators, topological semimetals possess a nontrivial chiral anomaly that leads to negative magnetoresistance and are hosts to both conductive bulk states and topological surface states with intriguing transport properties for spintronics. Here, we fabricate highly-ordered metallic Pt3Sn and Pt3SnxFe1-x thin films via sputtering technology. Systematic angular dependence (both in-plane and out-of-plane) study of magnetoresistance presents surprisingly robust quadratic and linear negative longitudinal magnetoresistance features for Pt3Sn and Pt3SnxFe1-x, respectively. We attribute the anomalous negative longitudinal magnetoresistance to the type-II Dirac semimetal phase (pristine Pt3Sn) and/or the formation of tunable Weyl semimetal phases through symmetry breaking processes, such as magnetic-atom doping, as confirmed by first-principles calculations. Furthermore, Pt3Sn and Pt3SnxFe1-x show the promising performance for facilitating the development of advanced spin-orbit torque devices. These results extend our understanding of chiral anomaly of topological semimetals and can pave the way for exploring novel topological materials for spintronic devices.

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Alomeare, Helda, Ferhat Nutku, and Mustafa Sarisaman. "Circular dichroism in nonlinear topological Weyl semimetals." Journal of Optics, April 10, 2024. http://dx.doi.org/10.1088/2040-8986/ad3cf3.

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Abstract In recent years, the field of topological photonics has emerged as a promising area of research due to its potential for developing new photonic devices with unique properties. Topological Weyl semimetals (TWS), which are characterized by the presence of Weyl points in their electronic band structure, are one such example of a material with interesting topological properties. In this study, Kerr and Faraday rotations were used to determine the nonlinear characteristics of TWS. We focused on surfaces where no Fermi arcs are involved, so that Maxwell's equations would contain some peculiar topological terms. In Weyl semimetals with a specific topology, the distance between Weyl nodes aligned along the z-direction functions as a magnet. This results in a significant polar Kerr/Faraday rotation effect that is proportional to the separation distance, when light is directed onto the surface of the topological Weyl semimetal that lacks Fermi arc states. Conversely, when the light is directed onto a surface with Fermi arc states, the Voigt effect is quadratically proportional to the separation distance. We considered electromagnetic wave propagation in a nonlinear Kerr-type medium. We have derived and solved the linear and nonlinear Helmholtz equations for topological Weyl semimetals by using tanh method. Our findings reveal that wave solutions could have some potentially significant implications for the design and optimization of photonic devices based on topological Weyl semimetals.

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Kirschbaum, Diana, Monika Lužnik, Gwenvredig Le Roy, and Silke Paschen. "How to identify and characterize strongly correlated topological semimetals." Journal of Physics: Materials, November 23, 2023. http://dx.doi.org/10.1088/2515-7639/ad0f30.

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Abstract How strong correlations and topology interplay is a topic of greatcurrent interest. In this perspective paper, we focus oncorrelation-driven gapless phases. We take the time-reversal symmetricWeyl semimetal as an example because it is expected to have clear (albeitnonquantized) topological signatures in the Hall response and because thefirst strongly correlated representative, the noncentrosymmetricWeyl-Kondo semimetal Ce3Bi4Pd3, has recently been discovered. Wesummarize its key characteristics and use them to construct a prototypeWeyl-Kondo semimetal temperature-magnetic field phase diagram. Thisallows for a substantiated assessment of other Weyl-Kondo semimetalcandidate materials. We also put forward a new scaling plot that comparesthe magnitude of the intrinsic Berry curvature-induced Hall response withthe inverse Weyl velocity, a measure of correlation strength. It suggeststhat the topological Hall response is drastically enhanced by strongcorrelations. We hope that our work will guide the search for newWeyl-Kondo semimetals and correlated topological semimetals in general,and also trigger new theoretical work.

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44

Lei, Shiming, Kevin Allen, Jianwei Huang, Jaime M. Moya, Tsz Chun Wu, Brian Casas, Yichen Zhang, et al. "Weyl nodal ring states and Landau quantization with very large magnetoresistance in square-net magnet EuGa4." Nature Communications 14, no. 1 (September 19, 2023). http://dx.doi.org/10.1038/s41467-023-40767-z.

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AbstractMagnetic topological semimetals allow for an effective control of the topological electronic states by tuning the spin configuration. Among them, Weyl nodal line semimetals are thought to have the greatest tunability, yet they are the least studied experimentally due to the scarcity of material candidates. Here, using a combination of angle-resolved photoemission spectroscopy and quantum oscillation measurements, together with density functional theory calculations, we identify the square-net compound EuGa4 as a magnetic Weyl nodal ring semimetal, in which the line nodes form closed rings near the Fermi level. The Weyl nodal ring states show distinct Landau quantization with clear spin splitting upon application of a magnetic field. At 2 K in a field of 14 T, the transverse magnetoresistance of EuGa4 exceeds 200,000%, which is more than two orders of magnitude larger than that of other known magnetic topological semimetals. Our theoretical model suggests that the non-saturating magnetoresistance up to 40 T arises as a consequence of the nodal ring state.

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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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46

Misawa, Takahiro, and Kentaro Nomura. "Semi-quantized Spin Pumping and Spin-Orbit Torques in Topological Dirac Semimetals." Scientific Reports 9, no. 1 (December 2019). http://dx.doi.org/10.1038/s41598-019-55802-7.

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AbstractWe study the time-development processes of spin and charge transport phenomena in a topological Dirac semimetal attached to a ferromagnetic insulator with a precessing magnetization. Compared to conventional normal metals, topological Dirac semimetals manifest a large inverse spin Hall effect when a spin current is pumped from the attached ferromagnetic insulator. It is shown that the induced charge current is semi-quantized, i.e., it depends only on the distance between the two Dirac points in momentum space and hardly depends on the disorder strength when the system remains in the topological Dirac semimetal phase. As an inverse effect, we show that the electric field applied to the topological Dirac semimetal exerts a spin torque on the local magnetization in the ferromagnetic insulator via the exchange interaction and the semi-quantized spin Hall effect. Our study demonstrates that the topological Dirac semimetal offers a less-dissipative platform for spin-charge conversion and spin switching.

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Ouyang, Wenkai, Alexander C. Lygo, Yubi Chen, Huiyuan Zheng, Dung Vu, Brandi L. Wooten, Xichen Liang, Joseph P. Heremans, Susanne Stemmer, and Bolin Liao. "Extraordinary Thermoelectric Properties of Topological Surface States in Quantum‐Confined Cd₃As₂ Thin Films." Advanced Materials, April 29, 2024. http://dx.doi.org/10.1002/adma.202311644.

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AbstractTopological insulators and semimetals have been shown to possess intriguing thermoelectric properties promising for energy harvesting and cooling applications. However, thermoelectric transport associated with the Fermi arc topological surface states on topological Dirac semimetals remains less explored. In this work, we systematically examine thermoelectric transport in a series of topological Dirac semimetal Cd3As2 thin films grown by molecular beam epitaxy. Surprisingly, we find significantly enhanced Seebeck effect and anomalous Nernst effect at cryogenic temperatures when the Cd3As2 layer is thin. In particular, we observe a peak Seebeck coefficient of nearly 500 µV K−1 and a corresponding thermoelectric power factor over 30 mW K−2 m−1 at 5 K in a 25‐nm‐thick sample. Combining angle‐dependent quantum oscillation analysis, magnetothermoelectric measurement, transport modeling and first‐principles simulation, we isolate the contributions from bulk and surface conducting channels and attribute the unusual thermoelectric properties to the topological surface states. Our analysis showcases the rich thermoelectric transport physics in quantum‐confined topological Dirac semimetal thin films and suggests new routes to achieving high thermoelectric performance at cryogenic temperatures.This article is protected by copyright. All rights reserved

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Fu, Bo, Jin-Yu Zou, Zi-Ang Hu, Huan-Wen Wang, and Shun-Qing Shen. "Quantum anomalous semimetals." npj Quantum Materials 7, no. 1 (September 20, 2022). http://dx.doi.org/10.1038/s41535-022-00503-0.

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AbstractThe topological states of matter and topological materials have been attracting extensive interests as one of the frontier topics in condensed matter physics and materials science since the discovery of quantum Hall effect in 1980s. So far all the topological phases such as integer quantum Hall effect and topological insulators are characterized by integer topological invariants. None is a half integer or fractional. Here we propose a type of semimetals which hosts a single cone of Wilson fermions. The Wilson fermions possess linear dispersion near the Dirac point, but break the chiral or parity symmetry such that an unpaired Dirac cone can be realized on a lattice. In order to avoid the fermion doubling problem, the chiral symmetry or parity symmetry must be broken explicitly if the hermiticity, locality and translational invariance all hold. We find that the system can be classified by the relative homotopy group, and a half-integer topological invariant. We term the nontrivial quantum phase as quantum anomalous semimetal. The work opens the door towards exploring novel states of matter with fractional topological charge.

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Zhang, Libo, Zhiqingzi Chen, Kaixuan Zhang, Lin Wang, Huang Xu, Li Han, Wanlong Guo, et al. "High-frequency rectifiers based on type-II Dirac fermions." Nature Communications 12, no. 1 (March 11, 2021). http://dx.doi.org/10.1038/s41467-021-21906-w.

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AbstractThe advent of topological semimetals enables the exploitation of symmetry-protected topological phenomena and quantized transport. Here, we present homogeneous rectifiers, converting high-frequency electromagnetic energy into direct current, based on low-energy Dirac fermions of topological semimetal-NiTe2, with state-of-the-art efficiency already in the first implementation. Explicitly, these devices display room-temperature photosensitivity as high as 251 mA W−1 at 0.3 THz in an unbiased mode, with a photocurrent anisotropy ratio of 22, originating from the interplay between the spin-polarized surface and bulk states. Device performances in terms of broadband operation, high dynamic range, as well as their high sensitivity, validate the immense potential and unique advantages associated to the control of nonequilibrium gapless topological states via built-in electric field, electromagnetic polarization and symmetry breaking in topological semimetals. These findings pave the way for the exploitation of topological phase of matter for high-frequency operations in polarization-sensitive sensing, communications and imaging.

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Fu, Jun-Jie, Shu-Tong Guan, Jiao Xie, and Jin An. "Quantum Transport on the Surfaces of Topological Nodal-line Semimetals." New Journal of Physics, January 2, 2024. http://dx.doi.org/10.1088/1367-2630/ad19fb.

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Abstract Topological nodal-line semimetals are always characterized by the drumhead surface states at the open boundaries. In this paper we first derive an analytical expression for the surface Green’s function of a nodal-line semimetal. By making use of this result, we explore the charge and spin transport properties of a metallic chain on the surface of a nodal line semimetal, as functions of the gate voltage applied on the top of the material. According to the size of the nodal loop, due to the coupling to the surface modes, the charge conductance in the chain is found to show a robust plateau at e2/h, or to exhibit multiple valleys at e2/h. Correspondingly, the spin polarization of the transmitted current is 100% at the plateau region, or exhibits multiple peaks at nearly 100%. This feature can be viewed as a transport signature of the topological nodal-line semimetals.

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Journal articles on the topic 'Topological semimetals'

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