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Artykuły w czasopismach na temat "Graphene moiré superlattice"
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Peña, Tara, Aditya Dey, Shoieb A. Chowdhury, Ahmad Azizimanesh, Wenhui Hou, Arfan Sewaket, Carla Watson, Hesam Askari i Stephen M. Wu. "Moiré engineering in 2D heterostructures with process-induced strain". Applied Physics Letters 122, nr 14 (3.04.2023): 143101. http://dx.doi.org/10.1063/5.0142406.
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We report deterministic control over a moiré superlattice interference pattern in twisted bilayer graphene by implementing designable device-level heterostrain with process-induced strain engineering, a widely used technique in industrial silicon nanofabrication processes. By depositing stressed thin films onto our twisted bilayer graphene samples, heterostrain magnitude and strain directionality can be controlled by stressor film force (film stress × film thickness) and patterned stressor geometry, respectively. We examine strain and moiré interference with Raman spectroscopy through in-plane and moiré-activated phonon mode shifts. Results support systematic C3 rotational symmetry breaking and tunable periodicity in moiré superlattices under the application of uniaxial or biaxial heterostrain. Experimental results are validated by molecular statics simulations and density functional theory based first principles calculations. This provides a method not only to tune moiré interference without additional twisting but also to allow for a systematic pathway to explore different van der Waals based moiré superlattice symmetries by deterministic design.
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Jadaun, Priyamvada, i Bart Soreé. "Review of Orbital Magnetism in Graphene-Based Moiré Materials". Magnetism 3, nr 3 (28.08.2023): 245–58. http://dx.doi.org/10.3390/magnetism3030019.
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Recent years have seen the emergence of moiré materials as an attractive platform for observing a host of novel correlated and topological phenomena. Moiré heterostructures are generated when layers of van der Waals materials are stacked such that consecutive layers are slightly mismatched in their lattice orientation or unit cell size. This slight lattice mismatch gives rise to a long-wavelength moiré pattern that modulates the electronic structure and leads to novel physics. The moiré superlattice results in flat superlattice bands, electron–electron interactions and non-trivial topology that have led to the observation of superconductivity, the quantum anomalous Hall effect and orbital magnetization, among other interesting properties. This review focuses on the experimental observation and theoretical analysis of orbital magnetism in moiré materials. These systems are novel in their ability to host magnetism that is dominated by the orbital magnetic moment of Bloch electrons. This orbital magnetic moment is easily tunable using external electric fields and carrier concentration since it originates in the quantum anomalous Hall effect. As a result, the orbital magnetism found in moiré superlattices can be highly attractive for a wide array of applications including spintronics, ultra-low-power magnetic memories, spin-based neuromorphic computing and quantum information technology.
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Lin, Miao-Ling, Min Feng, Jiang-Bin Wu, Fei-Rong Ran, Tao Chen, Wei-Xia Luo, Heng Wu i in. "Intralayer Phonons in Multilayer Graphene Moiré Superlattices". Research 2022 (30.05.2022): 1–11. http://dx.doi.org/10.34133/2022/9819373.
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Moiré pattern in twisted multilayers (tMLs) induces many emergent phenomena by subtle variation of atomic registry to modulate quasiparticles and their interactions, such as superconductivity, moiré excitons, and moiré phonons. The periodic superlattice potential introduced by moiré pattern also underlies patterned interlayer coupling at the interface of tMLs. Although this arising patterned interfacial coupling is much weaker than in-plane atomic interactions, it is crucial in moiré systems, as captured by the renormalized interlayer phonons in twisted bilayer transitional metal dichalcogenides. Here, we determine the quantitative relationship between the lattice dynamics of intralayer out-of-plane optical (ZO) phonons and patterned interfacial coupling in multilayer graphene moiré superlattices (MLG-MS) by the proposed perturbation model, which is previously challenging for MLGs due to their out-of-phase displacements of adjacent atoms in one atomic plane. We unveil that patterned interfacial coupling introduces profound modulations on Davydov components of nonfolded ZO phonon that are localized within the AB-stacked constituents, while the coupling results in layer-extended vibrations with symmetry of moiré pattern for moiré ZO phonons. Our work brings further degrees of freedom to engineer moiré physics according to the modulations imprinted on the phonon frequency and wavefunction.
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Miao, Wenjing, Hao Sheng i Jingang Wang. "Vertical Stress Induced Anomalous Spectral Shift of 13.17° Moiré Superlattice in Twist Bilayer Graphene". Molecules 28, nr 7 (28.03.2023): 3015. http://dx.doi.org/10.3390/molecules28073015.
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The electronic states of the twist bilayer graphene (TBG) moiré superlattice are usually regulated by the rotation angle, applied electric field, applied magnetic field, carrier concentration and applied stress, and thus exhibit novel physical properties. Squeezing, that is, applying vertical compressive stress to the graphene layers, has profound significance in regulating the photoelectric properties of the moiré superlattice and constructing optical nanodevices. This paper presents the photoelectric properties of a TBG moiré superlattice with a twist angle of 13.17° and tunability under vertical stress. Interlayer distance decreases nonlinearly with compressive stress from 0 to 10 GPa, giving rise to weakened interlayer coupling compared to a Bernal-stacked graphene bilayer and an enhanced repulsive effect between the layers. The calculated Bloch wave functions show a strong dependence on stress. With the increase in stress, the band gaps of the system present a nonlinear increase, which induces and enhances the interlayer charge transfer and leads to the redshift of the absorption spectrum of the moiré superlattice system. By analyzing the differences in the Bloch wave function and charge density differences, we explain the nature of the physical mechanism of photoelectric property change in a stress-regulated twist superlattice system. This study provides a theoretical basis for the identification of piezoelectric properties and the stress regulation of photoelectric devices based on TBG, and also provides a feasible method for regulating the performance of TBG.
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Dai, Guoqiang, Xiangtao Chen, Ying Jing i Jingang Wang. "Anti-Symmetric Electromagnetic Interactions’ Response in Electron Circular Dichroism and Chiral Origin of Periodic, Complementary Twisted Angle in Twisted Bilayer Graphene". Molecules 27, nr 19 (2.10.2022): 6525. http://dx.doi.org/10.3390/molecules27196525.
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Many novel physical properties of twisted bilayer graphene have been discovered and studied successively, but the physical mechanism of the chiral modulation of BLG by a twisted angle lacks theoretical research. In this work, the density functional theory, the wavefunction analysis of the excited state, and the quantum theory of atoms in molecules are used to calculate and analyze the anti-symmetric chiral characteristics of zigzag-edge twisted bilayer graphene quantum dots based on periodic complementary twisted angles. The analysis of the partial density of states shows that Moiré superlattices can effectively adjust the contribution of the atomic basis function of the fragment to the transition dipole moment. The topological analysis of electron density indicates that the Moiré superlattices structure can enhance the localization of the system, increasing the electron density of the Moiré central ring, reducing the electron surge capacity in general and inducing the reversed helical properties of the top and underlying graphene, which can be used as the origin of the chiral discrimination; it also reveals the mole in the superlattice chiral physical mechanism. On this basis, we will also study the nonlinear optical properties of twisted bilayer graphene based on a twisted angle.
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Gao, Lei, Xinchun Chen, Yuan Ma, Yu Yan, Tianbao Ma, Yanjing Su i Lijie Qiao. "Origin of the moiré superlattice scale lateral force modulation of graphene on a transition metal substrate". Nanoscale 10, nr 22 (2018): 10576–83. http://dx.doi.org/10.1039/c8nr01558a.
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The moiré superlattice scale lateral force modulation of graphene on a transition metal substrate originates from the joint effects of the graphene–substrate interfacial interaction and the tip–graphene interaction.
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Li, Hu, Raffaello Papadakis, Tanveer Hussain, Amir Karton i Jiangwei Liu. "Moiré patterns arising from bilayer graphone/graphene superlattice". Nano Research 13, nr 4 (kwiecień 2020): 1060–64. http://dx.doi.org/10.1007/s12274-020-2744-6.
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Li, Zhenyao, Jia-Min Lai i Jun Zhang. "Review of phonons in moiré superlattices". Journal of Semiconductors 44, nr 1 (1.01.2023): 011902. http://dx.doi.org/10.1088/1674-4926/44/1/011902.
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Abstract Moiré patterns in physics are interference fringes produced when a periodic template is stacked on another similar one with different displacement and twist angles. The phonon in two-dimensional (2D) material affected by moiré patterns in the lattice shows various novel physical phenomena, such as frequency shift, different linewidth, and mediation to the superconductivity. This review gives a brief overview of phonons in 2D moiré superlattice. First, we introduce the theory of the moiré phonon modes based on a continuum approach using the elastic theory and discuss the effect of the moiré pattern on phonons in 2D materials such as graphene and MoS2. Then, we discuss the electron–phonon coupling (EPC) modulated by moiré patterns, which can be detected by the spectroscopy methods. Furthermore, the phonon-mediated unconventional superconductivity in 2D moiré superlattice is introduced. The theory of phonon-mediated superconductivity in moiré superlattice sets up a general framework, which promises to predict the response of superconductivity to various perturbations, such as disorder, magnetic field, and electric displacement field.
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Moutinho, Marcus V. O., Pedro Venezuela i Marcos A. Pimenta. "Raman Spectroscopy of Twisted Bilayer Graphene". C 7, nr 1 (26.01.2021): 10. http://dx.doi.org/10.3390/c7010010.
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When two periodic two-dimensional structures are superposed, any mismatch rotation angle between the layers generates a Moiré pattern superlattice, whose size depends on the twisting angle θ. If the layers are composed by different materials, this effect is also dependent on the lattice parameters of each layer. Moiré superlattices are commonly observed in bilayer graphene, where the mismatch angle between layers can be produced by growing twisted bilayer graphene (TBG) samples by CVD or folding the monolayer back upon itself. In TBG, it was shown that the coupling between the Dirac cones of the two layers gives rise to van Hove singularities (vHs) in the density of electronic states, whose energies vary with θ. The understanding of the behavior of electrons and their interactions with phonons in atomically thin heterostructures is crucial for the engineering of novel 2D devices. Raman spectroscopy has been often used to characterize twisted bilayer graphene and graphene heterostructures. Here, we review the main important effects in the Raman spectra of TBG discussing firstly the appearance of new peaks in the spectra associated with phonons with wavevectors within the interior of the Brillouin zone of graphene corresponding to the reciprocal unit vectors of the Moiré superlattice, and that are folded to the center of the reduced Brillouin Zone (BZ) becoming Raman active. Another important effect is the giant enhancement of G band intensity of TBG that occurs only in a narrow range of laser excitation energies and for a given twisting angle. Results show that the vHs in the density of states is not only related to the folding of the commensurate BZ, but mainly associated with the Moiré pattern that does not necessarily have a translational symmetry. Finally, we show that there are two different resonance mechanisms that activate the appearance of the extra peaks: the intralayer and interlayer electron–phonon processes, involving electrons of the same layer or from different layers, respectively. Both effects are observed for twisted bilayer graphene, but Raman spectroscopy can also be used to probe the intralayer process in any kind of graphene-based heterostructure, like in the graphene/h-BN junctions.
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Thomas, Loji K., i Michael Reichling. "Capillary force-induced superlattice variation atop a nanometer-wide graphene flake and its moiré origin studied by STM". Beilstein Journal of Nanotechnology 10 (1.04.2019): 804–10. http://dx.doi.org/10.3762/bjnano.10.80.
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We present strong experimental evidence for the moiré origin of superlattices on graphite by imaging a live transition from one superlattice to another with concurrent and direct measurement of the orientation angle before and after rotation using scanning tunneling microscopy (STM). This has been possible due to a fortuitous observation of a superlattice on a nanometer-sized graphene flake wherein we have induced a further rotation of the flake utilizing the capillary forces at play at a solid–liquid interface using STM tip motion. We propose a more “realistic” tip–surface meniscus relevant to STM at solid–liquid interfaces and show that the capillary force is sufficient to account for the total expenditure of energy involved in the process.
Rozprawy doktorskie na temat "Graphene moiré superlattice"
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Woods, Colin. "Investigations into the interfacial interaction of graphene with hexagonal boron nitride". Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/investigations-into-the-interfacial-interaction-of-graphene-with-hexagonal-boron-nitride(de99f43b-790f-4a32-b696-060ed700a5bd).html.
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This thesis, submitted to the University of Manchester, covers a range of topics related to current research in two-dimensional materials under the title: 'Investigations into the interfacial interaction of graphene with hexagonal boron nitride.'In the last decade, two-dimensional materials have become a rich source of original research and potential applications. The main advantage lies in the ability to produce novel composite structures, so-called 'layered heterostructures', which are only a few atomic layers thick. One can utilise the unique properties of several species of crystal separately, or how they interact to realise a diverse range of uses. Two such crystals are graphene and hexagonal boron nitride. Hexagonal boron nitride has, so far, been used primarily as a substrate for graphene, allowing researchers to get the most out of graphene's impressive individual properties. However, in this thesis, the non-trivial van der Waals interaction between graphene and hexagonal boron nitride is examined. The interface potential reveals itself as a relatively large-scale, orientation-dependant superlattice, which is described in chapters 1 and 2.I In Chapter 4, the effect of this superlattice is examined by measurement of its effect upon the electrons in graphene, where its modulation leads to the creation of second and third generation Dirac points, revealing Hofstadter's Butterfly. As well as an excellent example of the physics possible with graphene, it also presents a new tool with which to create novel devices possessing tailored electronic properties. II In chapter 5, the consequential effect of the superlattice potential on the structure of graphene is studied. Results are discussed within the framework of the Frenkel-Kontorova model for a chain of atoms on a static background potential. Results are consistent with relaxation of the graphene structure leading to the formation of a commensurate ground state. This has exciting consequences for the production of heterostructures by demonstrating that alignment angle can have large effects upon the physical properties of the crystals. III In chapter 6, the van der Waals potential is shown to be responsible for the self-alignment of the two crystals. This effect is important for the fabrication of perfectly aligned devices and may lead to new applications based on nanoscale motion.
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Kumar, Chandan. "Quantum transport in Graphene Moire Superlattice and p-n junction". Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5428.
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The discovery of graphene has revolutionized the field of mesoscopic condensed matter physics. It has started a new field of van-der Waals heterostructure in which different two-dimensional materials including graphene can be stacked on top of each other. In the last few years graphene based van-der Walls heterostructure has lead to many interesting physics like Hofstadter’s butterfly, Valley Hall effect, Mott insulator and superconductivity. In this thesis, two different kinds of graphene heterostructures, namely, graphene moiré superlattice (GMSL) and graphene p-n junction (GPNJ) have been studied extensively. The GMSL is realized by aligning and stacking graphene and hexagonal boron nitride with an accuracy of . This leads to additional set of Dirac cones known as cloned Dirac cones (CDC) which are placed symmetrically around the primary Dirac cone (PDC). As a part of the thesis, we have studied the magneto-conductance on GMSL devices as a function of carrier concentration and temperature, which reveals a transition from weak anti-localization (WAL) near the PDC to weak localization (WL) near the CDC. The transition is explained due to the shift of Berry phase, which is measured experimentally by probing the Shubnikov-de Haas oscillations. Furthermore, we study the low frequency 1/f noise at multiple Dirac cones in GMSL devices. Our results reveal that the low-frequency noise in GMSL devices can be tuned by more than two-orders of magnitude by changing carrier concentration as well as by modifying the band structure. We find that the noise is suppressed at the CDC compared to the PDC and understood in terms of screening. In the second part of the thesis, we study the equilibration of quantum Hall edges in GPNJ devices, which are realized in dual gated geometry. The equilibration of electron-like and hole-like edges in graphene p-n junction have been studied in single and bilayer graphene in both unipolar and bipolar regime, when the different symmetries likes valley, spin and orbital degrees of freedoms are broken. Our studies reveal the partial equilibration based on the spin polarization of the quantum Hall edges. Furthermore, we have carried out shot noise measurements to understand the dynamics and mixing of quantum Hall edges at the p-n junction, which could be used as an electronic beam splitter
Streszczenia konferencji na temat "Graphene moiré superlattice"
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Leifer, Klaus. "Fabrication of new-generation of Moiré superlattice on bilayer graphene by electron beam induced fluorination". W European Microscopy Congress 2020. Royal Microscopical Society, 2021. http://dx.doi.org/10.22443/rms.emc2020.1155.
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Ohlberg, Douglas A. A., Andreij C. Gadelha, Diego Tamia, Eliel G. S. Neto, Daniel A. Miranda, Jessica S. Lemos, Fabiano C. Santana i in. "Observation of moiré superlattices on twisted bilayer graphene by scanning microwave impedance microscopy". W Low-Dimensional Materials and Devices 2020, redaktorzy Nobuhiko P. Kobayashi, A. Alec Talin, Albert V. Davydov i M. Saif Islam. SPIE, 2020. http://dx.doi.org/10.1117/12.2570651.
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