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Journal articles on the topic 'Twisted Bilayer Graphene, Thermoelectric Effect'

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Author: Grafiati

Published: 6 September 2023

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1

Deng, Shuo, Xiang Cai, Yan Zhang, and Lijie Li. "Enhanced thermoelectric performance of twisted bilayer graphene nanoribbons junction." Carbon 145 (April 2019): 622–28. http://dx.doi.org/10.1016/j.carbon.2019.01.089.

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2

Saito, Yu, Fangyuan Yang, Jingyuan Ge, Xiaoxue Liu, Takashi Taniguchi, Kenji Watanabe, J. I. A. Li, Erez Berg, and Andrea F. Young. "Isospin Pomeranchuk effect in twisted bilayer graphene." Nature 592, no. 7853 (April 7, 2021): 220–24. http://dx.doi.org/10.1038/s41586-021-03409-2.

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3

Chen, Zefeng, Hongwei Yang, Yihong Xiao, Jintao Pan, Yu Xia, and Wenguo Zhu. "Photonic spin Hall effect in twisted bilayer graphene." Journal of the Optical Society of America A 38, no. 8 (July 28, 2021): 1232. http://dx.doi.org/10.1364/josaa.430598.

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4

Finocchiaro, F., F. Guinea, and P. San-Jose. "Quantum spin Hall effect in twisted bilayer graphene." 2D Materials 4, no. 2 (February 2, 2017): 025027. http://dx.doi.org/10.1088/2053-1583/aa5265.

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5

Moutinho, Marcus V. O., Pedro Venezuela, and Marcos A. Pimenta. "Raman Spectroscopy of Twisted Bilayer Graphene." C 7, no. 1 (January 26, 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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6

Kommini, Adithya, and Zlatan Aksamija. "Very high thermoelectric power factor near magic angle in twisted bilayer graphene." 2D Materials 8, no. 4 (August 20, 2021): 045022. http://dx.doi.org/10.1088/2053-1583/ac161d.

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7

Alisultanov, Z. Z. "Large and tunable thermoelectric effect in single layer graphene on bilayer graphene." Modern Physics Letters B 29, no. 03 (January 30, 2015): 1550003. http://dx.doi.org/10.1142/s0217984915500037.

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The conductivity and thermopower of a trilayer graphene based system have been studied within the framework of a simple model. It has been shown that kinks of the conductivity and peaks of the thermopower of the monolayer graphene formed on a tunable bilayer graphene appear near the edges of the band gap of the tunable bilayer graphene.

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8

Li, Zedong, and Z. F. Wang. "Quantum anomalous Hall effect in twisted bilayer graphene quasicrystal." Chinese Physics B 29, no. 10 (October 2020): 107101. http://dx.doi.org/10.1088/1674-1056/abab77.

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9

Liu, Wenxiang, Yongqiang Wu, Yang Hong, Bo Hou, Jingchao Zhang, and Yanan Yue. "Full-spectrum thermal analysis in twisted bilayer graphene." Physical Chemistry Chemical Physics 23, no. 35 (2021): 19166–72. http://dx.doi.org/10.1039/d1cp01715b.

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10

Mreńca-Kolasińska, Alina, Peter Rickhaus, Giulia Zheng, Klaus Richter, Thomas Ihn, Klaus Ensslin, and Ming-Hao Liu. "Quantum capacitive coupling between large-angle twisted graphene layers." 2D Materials 9, no. 2 (February 25, 2022): 025013. http://dx.doi.org/10.1088/2053-1583/ac5536.

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Abstract Large-angle twisted bilayer graphene (tBLG) is known to be electronically decoupled due to the spatial separation of the Dirac cones corresponding to individual graphene layers in the reciprocal space. The close spacing between the layers causes strong capacitive coupling, opening possibilities for applications in atomically thin devices. Here, we present a self-consistent quantum capacitance model for the electrostatics of decoupled graphene layers, and further generalize it to deal with decoupled tBLG at finite magnetic field and large-angle twisted double bilayer graphene at zero magnetic field. We probe the capacitive coupling through the conductance, showing good agreement between simulations and experiments for all the systems considered. We also propose a new experiment utilizing the decoupling effect to induce a huge and tunable bandgap in bilayer graphene by applying a moderately low bias. Our model can be extended to systems composed of decoupled graphene multilayers as well as non-graphene systems, opening a new realm of quantum-capacitively coupled materials.

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11

Veerpal and Ajay. "Exotic Electronic Properties of Twisted Bilayer Graphene-Emergence of Twistronics." Journal of Physics: Conference Series 2518, no. 1 (June 1, 2023): 012013. http://dx.doi.org/10.1088/1742-6596/2518/1/012013.

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Abstract In Twistronics we study the effect of relative twist between the layers of a material on the electronic properties of that layered materials. There are expected to be hundreds of layered materials which can give rise to thousands or even more layered materials with combination of layers and relative twist between the layers. There is a great possibility to encounter many exotic electronic properties in these rather less explored layered materials with relative twist between the layers. There is a lot to explore and understand, to unlock full potential of twistronics. A lot of theoretical and experimental studies have been done and are being done to explore the electronic properties of twisted bilayer graphene, making it a good material to start with to explore the hidden potential of twistronics. Here we present a simple theoretical model study for commensurate twisted bilayer graphene. Starting from understanding of moire pattern in twisted bilayer graphene our study goes through writing of tight binding Hamiltonian, computational codes to determine various model parameters, solution of Hamiltonian to obtain quasi particle energies and density of states near Fermi energy in twisted bilayer graphene. Our theoretical calculations have produced flat band near Dirac point and Van-Hove singularities near Fermi energy, which agree qualitatively with recent experimental studies.

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12

Cea, Tommaso, and Francisco Guinea. "Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene." Proceedings of the National Academy of Sciences 118, no. 32 (August 6, 2021): e2107874118. http://dx.doi.org/10.1073/pnas.2107874118.

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The polarizability of twisted bilayer graphene, due to the combined effect of electron–hole pairs, plasmons, and acoustic phonons, is analyzed. The screened Coulomb interaction allows for the formation of Cooper pairs and superconductivity in a significant range of twist angles and fillings. The tendency toward superconductivity is enhanced by the coupling between longitudinal phonons and electron–hole pairs. Scattering processes involving large momentum transfers, Umklapp processes, play a crucial role in the formation of Cooper pairs. The magnitude of the superconducting gap changes among the different pockets of the Fermi surface.

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13

Zhang, Lufeng, Tongyun Huang, Ying Liang, and Tianxing Ma. "Ground state superconducting pair correlations in twisted bilayer graphene." Modern Physics Letters B 34, no. 01 (December 18, 2019): 2050016. http://dx.doi.org/10.1142/s0217984920500165.

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Motivated by the recent novel electronic features extracted from the magic-angle graphene superlattices, we studied the ground state superconducting pairing correlations within the Hubbard model on a twisted bilayer honeycomb lattice. Using Constrained-Path Quantum Monte Carlo method, we found that the [Formula: see text] pairing correlation dominates over other pairing patterns among various electron fillings and interaction strengths, and the effective pairing interaction was enhanced as the on-site Coulomb interaction increased. We further examined the effect of the nearest neighbor interaction [Formula: see text], and the effective pairing interaction with [Formula: see text] pairing symmetry was also enhanced by either a repulsive or attractive interaction. Our intensive numerical results confirm the interaction driven superconductivity with a dominant [Formula: see text] pairing symmetry in twisted bilayer graphene.

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14

Yar, Abdullah. "Brownian dynamics of Dirac fermions in twisted bilayer graphene." Physica Scripta 98, no. 9 (August 25, 2023): 095949. http://dx.doi.org/10.1088/1402-4896/acf0f5.

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Abstract Brownian dynamics of Dirac fermions in twisted bilayer graphene is investigated within the framework of semiclassical relativistic Langevin equations. We find that under the influence of orthogonal, commensurate ac drives in the periodic ratchet potential of a substrate, the charge carriers in the system exhibit pronounced random dynamics, tuned by the twist angle, making twisted bilayer graphene distinct from monolayer graphene. It is shown that as threshold twist angle matches the optimal angle, deterministic running states appear in the limit of weak thermal noise where the diffusion rate is enhanced significantly compared to bare thermal diffusion. Analysis of the real space trajectories and diffusion coefficient illustrates the significant role of thermal noise in the random motion of Dirac fermions. In addition, we find that the Brownian particle shows remarkable ratchet effect as a net current.

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15

Chen, Guangze, Maryam Khosravian, Jose L. Lado, and Aline Ramires. "Designing spin-textured flat bands in twisted graphene multilayers via helimagnet encapsulation." 2D Materials 9, no. 2 (February 2, 2022): 024002. http://dx.doi.org/10.1088/2053-1583/ac4af8.

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Abstract Twisted graphene multilayers provide tunable platforms to engineer flat bands and exploit the associated strongly correlated physics. The two-dimensional nature of these systems makes them suitable for encapsulation by materials that break specific symmetries. In this context, recently discovered two-dimensional helimagnets, such as the multiferroic monolayer NiI2, are specially appealing for breaking time-reversal and inversion symmetries due to their nontrivial spin textures. Here we show that this spin texture can be imprinted on the electronic structure of twisted bilayer graphene by proximity effect. We discuss the dependence of the imprinted spin texture on the wave-vector of the helical structure, and on the strength of the effective local exchange field. Based on these results we discuss the nature of the superconducting instabilities that can take place in helimagnet encapsulated twisted bilayer graphene. Our results put forward helimagnetic encapsulation as a powerful way of designing spin-textured flat band systems, providing a starting point to engineer a new family of correlated moire states.

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16

Sharpe, Aaron L., Eli J. Fox, Arthur W. Barnard, Joe Finney, Kenji Watanabe, Takashi Taniguchi, M. A. Kastner, and David Goldhaber-Gordon. "Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene." Science 365, no. 6453 (July 25, 2019): 605–8. http://dx.doi.org/10.1126/science.aaw3780.

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When two sheets of graphene are stacked at a small twist angle, the resulting flat superlattice minibands are expected to strongly enhance electron-electron interactions. Here, we present evidence that near three-quarters (34) filling of the conduction miniband, these enhanced interactions drive the twisted bilayer graphene into a ferromagnetic state. In a narrow density range around an apparent insulating state at34, we observe emergent ferromagnetic hysteresis, with a giant anomalous Hall (AH) effect as large as 10.4 kilohms and indications of chiral edge states. Notably, the magnetization of the sample can be reversed by applying a small direct current. Although the AH resistance is not quantized, and dissipation is present, our measurements suggest that the system may be an incipient Chern insulator.

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17

Lin, Jiang-Xiazi, Ya-Hui Zhang, Erin Morissette, Zhi Wang, Song Liu, Daniel Rhodes, K. Watanabe, T. Taniguchi, James Hone, and J. I. A. Li. "Spin-orbit–driven ferromagnetism at half moiré filling in magic-angle twisted bilayer graphene." Science 375, no. 6579 (January 28, 2022): 437–41. http://dx.doi.org/10.1126/science.abh2889.

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Strong electron correlation and spin-orbit coupling (SOC) can have a profound influence on the electronic properties of materials. We examined their combined influence on a two-dimensional electronic system at the atomic interface between magic-angle twisted bilayer graphene and a tungsten diselenide crystal. We found that strong electron correlation within the moiré flatband stabilizes correlated insulating states at both quarter and half filling, and that SOC transforms these Mott-like insulators into ferromagnets, as evidenced by a robust anomalous Hall effect with hysteretic switching behavior. The coupling between spin and valley degrees of freedom could be demonstrated through control of the magnetic order with an in-plane magnetic field or a perpendicular electric field. Our findings establish an experimental knob to engineer topological properties of moiré bands in twisted bilayer graphene and related systems.

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18

Armghan, Ammar, Meshari Alsharari, Khaled Aliqab, Osamah Alsalman, Juveriya Parmar, and Shobhit K. Patel. "Graphene Twistronics: Tuning the Absorption Spectrum and Achieving Metamaterial Properties." Mathematics 11, no. 7 (March 24, 2023): 1579. http://dx.doi.org/10.3390/math11071579.

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Graphene twistronics using multilayer graphene is presented in such a way that it provides a metamaterial effect. This manuscript also analyzes the prediction of behavior using machine learning. The metamaterial effect is achieved by twisting the graphene layers. Graphene twistronics is a new concept for changing the electrical and optical properties of bilayer graphene by applying a small angle twist between the layers. The angle twists of 5°, 10°, and 15° are analyzed for the proposed graphene twistronics design. Tuning in the absorption spectrum is achieved by applying small twists to the angles of the bilayer graphene. Results in the form of absorption, conductivity, permeability, permittivity, and impedance are presented for different twist angles. The twisted graphene layers also demonstrate negative permittivity and negative permeability, similar to metamaterials. These negative refraction properties of graphene twistronics provide flexibility and transparency, which can be applied in photovoltaic applications. Machine-learning-based regression models are used to reduce the simulation time and resources. The results show that a regression model can reliably estimate intermediate wavelength absorption values with an R2 of 0.9999.

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19

Zhang, Shi-Hao, Bo Xie, Ran Peng, Xiao-Qian Liu, Xin Lu, and Jian-Peng Liu. "Novel electrical properties of moiré graphene systems." Acta Physica Sinica 72, no. 6 (2023): 1. http://dx.doi.org/10.7498/aps.72.20230120.

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In this review, we discuss the electronic structures, topological properties, correlated states, nonlinear optical responses, as well as phonon and electron-phonon coupling effects of moiré graphene superlattices. First, we illustrate that topologically non-trivial flat bands and moiré orbital magnetism are ubiquitous in various twisted graphene systems. In particular, the topological flat bands of magic-angle twisted bilayer graphene (TBG) can be explained from a zeroth pseudo-Landau-level picture, which can naturally explain the experimentally observed quantum anomalous Hall effect and some of the other correlated states. These topologically nontrivial flat bands may lead to nearly quantized piezoelectric response, which can be used to directly probe the valley Chern numbers in these moiré graphene systems. A simple and general chiral decomposition rule is reviewed and discussed, which can be used to predict the low-energy band dispersions of generic twisted mulilayer graphene system and alternating twisted multilayer graphene system. This review further discusses nontrivial interaction effects of magic-angle TBG such as the correlated insulator states, density wave states, cascade transitions, and nematic states, and proposes nonlinear optical measurement as an experimental probe to distinguish the different "featureless" correlated states.The phonon properties and electron-phonon coupling effects are also briefly reviewed. The novel physics emerging from band-aligned graphene-insulator heterostructres is also discussed in this review. In the end, we make a summary and an outlook about the novel physical properties of moiré superlattices, two-dimensional materials, moiré superlattices－ two dimensional materials.

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20

Serlin, M., C. L. Tschirhart, H. Polshyn, Y. Zhang, J. Zhu, K. Watanabe, T. Taniguchi, L. Balents, and A. F. Young. "Intrinsic quantized anomalous Hall effect in a moiré heterostructure." Science 367, no. 6480 (December 19, 2019): 900–903. http://dx.doi.org/10.1126/science.aay5533.

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The quantum anomalous Hall (QAH) effect combines topology and magnetism to produce precisely quantized Hall resistance at zero magnetic field. We report the observation of a QAH effect in twisted bilayer graphene aligned to hexagonal boron nitride. The effect is driven by intrinsic strong interactions, which polarize the electrons into a single spin- and valley-resolved moiré miniband with Chern number C = 1. In contrast to magnetically doped systems, the measured transport energy gap is larger than the Curie temperature for magnetic ordering, and quantization to within 0.1% of the von Klitzing constant persists to temperatures of several kelvin at zero magnetic field. Electrical currents as small as 1 nanoampere controllably switch the magnetic order between states of opposite polarization, forming an electrically rewritable magnetic memory.

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21

Tschirhart, C. L., M. Serlin, H. Polshyn, A. Shragai, Z. Xia, J. Zhu, Y. Zhang, et al. "Imaging orbital ferromagnetism in a moiré Chern insulator." Science 372, no. 6548 (May 27, 2021): 1323–27. http://dx.doi.org/10.1126/science.abd3190.

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Electrons in moiré flat band systems can spontaneously break time-reversal symmetry, giving rise to a quantized anomalous Hall effect. In this study, we use a superconducting quantum interference device to image stray magnetic fields in twisted bilayer graphene aligned to hexagonal boron nitride. We find a magnetization of several Bohr magnetons per charge carrier, demonstrating that the magnetism is primarily orbital in nature. Our measurements reveal a large change in the magnetization as the chemical potential is swept across the quantum anomalous Hall gap, consistent with the expected contribution of chiral edge states to the magnetization of an orbital Chern insulator. Mapping the spatial evolution of field-driven magnetic reversal, we find a series of reproducible micrometer-scale domains pinned to structural disorder.

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22

Sboychakov, Artem O., Kliment I. Kugel, and Antonio Bianconi. "Moiré-like Superlattice Generated van Hove Singularities in a Strained CuO2 Double Layer." Condensed Matter 7, no. 3 (August 23, 2022): 50. http://dx.doi.org/10.3390/condmat7030050.

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While it is known that the double-layer Bi2Sr2CaCu2O8+y (BSCCO) cuprate superconductor exhibits a one-dimensional (1D) incommensurate superlattice (IS), the effect of IS on the electronic structure remains elusive. Following the recent shift of interest from an underdoped phase to optimum and overdoped phases in BSCCO by increasing the hole doping x, controlled by the oxygen interstitials concentration y, here we focus on the multiple splitting of the density of states (DOS) peaks and emergence of higher order van Hove singularities (VHS) due to the 1D incommensurate superlattice. It is known that the 1D incommensurate wave vector q=ϵb (where b is the reciprocal lattice vector of the orthorhombic lattice) is controlled by the misfit strain between different atomic layers in the range 0.209–0.215 in BSCCO and in the range 0.209–0.25 in Bi2Sr2Ca1−xYxCu2O8+y (BSCYCO). This work reports the theoretical calculation of a complex pattern of VHS due to the 1D incommensurate superlattice with large 1D quasi-commensurate supercells with the wave vector ϵ=9/η in the range 36>η>43. The similarity of the complex VHS splitting and appearing of higher order VHS in a mismatched CuO2 bilayer with VHS due to the moiré lattice in strained twisted bilayer graphene is discussed. This makes a mismatched CuO2 bilayer quite promising for constructing quantum devices with tuned physical characteristics.

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23

Kumar, Naveen, Abhirup Chaudhuri, Vinay Arya, Chirodeep Bakli, and Chandan Bera. "Significantly reduced thermal conductivity and enhanced thermoelectric performance of twisted bilayer graphene." Journal of Applied Physics 134, no. 4 (July 24, 2023). http://dx.doi.org/10.1063/5.0153052.

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Twisted bilayer graphene (tBLG) is an intriguing low-dimensional material due to the possible modulation of electronic and thermal properties and a subject of intense research, both for its fundamental physics as well as for its potential in technological applications. Here, the thermoelectric properties of bilayer graphene are investigated for twist angles of 0° and 20°. The thermoelectric properties are calculated using density functional theory, molecular dynamics, and Boltzmann transport theory. An increase in the power factor is observed for 20° tBLG due to an increase in the Seebeck coefficient by 2.2 times at 700 K. The thermal conductivity for 20° tBLG is reduced by 20% and 22% for 325 and 700 K, respectively, as compared to BLG. Consequently, an overall ∼3 times enhancement of a thermoelectric figure of merit (ZT) for 20° tBLG compared to BLG at 700 K is obtained. A strong effect of boundary scattering on thermal transport is observed. However, for electron transport, it is negligible for 20° tBLG. Due to this combined effect, an increase of 194 times in ZT is obtained at a ribbon width of L=10 nm and T = 700 K for 20° tBLG. This indicates that 20° twisted bilayer graphene could be an efficient thermoelectric power generator and can be a suitable material for carbon-based technology and devices.

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24

Chakraborty, Atasi, Kamal Das, Subhajit Sinha, Pratap Chandra Adak, Mandar M. Deshmukh, and Amit Agarwal. "Nonlinear anomalous Hall eﬀects probe topological phase-transitions in twisted double bilayer graphene." 2D Materials, August 22, 2022. http://dx.doi.org/10.1088/2053-1583/ac8b93.

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Abstract Nonlinear anomalous Hall effect is the Berry curvature dipole induced second-order Hall voltage or temperature difference induced by a longitudinal electric field or temperature gradient. These are the prominent Hall responses in time-reversal symmetric systems. These band-geometry induced responses in recently realized twistronic platforms can probe their novel electronic band structure and topology. Here, we investigate the family (electrical, thermoelectric, and thermal) of second-order nonlinear anomalous Hall effects in the moiré system of twisted double bilayer graphene. We combine the semiclassical transport framework with the continuum model of twisted double bilayer graphene to demonstrate that the nonlinear anomalous Hall signals can probe topological phase transitions in moiré systems. We show that the whole family of nonlinear anomalous Hall responses undergo a sign reversal across a topological phase transition. Our study establishes a deeper connection between valley topology and nonlinear Hall effects in time-reversal symmetric systems.

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25

Ghawri, Bhaskar, Phanibhusan S. Mahapatra, Manjari Garg, Shinjan Mandal, Saisab Bhowmik, Aditya Jayaraman, Radhika Soni, et al. "Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene." Nature Communications 13, no. 1 (March 21, 2022). http://dx.doi.org/10.1038/s41467-022-29198-4.

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AbstractThe planar assembly of twisted bilayer graphene (tBLG) hosts multitude of interaction-driven phases when the relative rotation is close to the magic angle (θm = 1.1∘). This includes correlation-induced ground states that reveal spontaneous symmetry breaking at low temperature, as well as possibility of non-Fermi liquid (NFL) excitations. However, experimentally, manifestation of NFL effects in transport properties of twisted bilayer graphene remains ambiguous. Here we report simultaneous measurements of electrical resistivity (ρ) and thermoelectric power (S) in tBLG for several twist angles between θ ~ 1.0 − 1.7∘. We observe an emergent violation of the semiclassical Mott relation in the form of excess S close to half-filling for θ ~ 1.6∘ that vanishes for θ ≳ 2∘. The excess S (≈2 μV/K at low temperatures T ~ 10 K at θ ≈ 1.6∘) persists upto ≈40 K, and is accompanied by metallic T-linear ρ with transport scattering rate (τ−1) of near-Planckian magnitude τ−1 ~ kBT/ℏ. Closer to θm, the excess S was also observed for fractional band filling (ν ≈ 0.5). The combination of non-trivial electrical transport and violation of Mott relation provides compelling evidence of NFL physics intrinsic to tBLG.

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26

Hesp, Niels C. H., Iacopo Torre, David Barcons-Ruiz, Hanan Herzig Sheinfux, Kenji Watanabe, Takashi Taniguchi, Roshan Krishna Kumar, and Frank H. L. Koppens. "Nano-imaging photoresponse in a moiré unit cell of minimally twisted bilayer graphene." Nature Communications 12, no. 1 (March 12, 2021). http://dx.doi.org/10.1038/s41467-021-21862-5.

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AbstractGraphene-based moiré superlattices have recently emerged as a unique class of tuneable solid-state systems that exhibit significant optoelectronic activity. Local probing at length scales of the superlattice should provide deeper insight into the microscopic mechanisms of photoresponse and the exact role of the moiré lattice. Here, we employ a nanoscale probe to study photoresponse within a single moiré unit cell of minimally twisted bilayer graphene. Our measurements reveal a spatially rich photoresponse, whose sign and magnitude are governed by the fine structure of the moiré lattice and its orientation with respect to measurement contacts. This results in a strong directional effect and a striking spatial dependence of the gate-voltage response within the moiré domains. The spatial profile and carrier-density dependence of the measured photocurrent point towards a photo-thermoelectric induced response that is further corroborated by good agreement with numerical simulations. Our work shows sub-diffraction photocurrent spectroscopy is an exceptional tool for uncovering the optoelectronic properties of moiré superlattices.

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27

"Pomeranchuk effect in twisted bilayer graphene." Journal Club for Condensed Matter Physics, November 29, 2020. http://dx.doi.org/10.36471/jccm_november_2020_01.

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28

Shankar, A. S., D. O. Oriekhov, Andrew K. Mitchell, and L. Fritz. "Kondo effect in twisted bilayer graphene." Physical Review B 107, no. 24 (June 1, 2023). http://dx.doi.org/10.1103/physrevb.107.245102.

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29

Nakatsuji, Naoto, and Mikito Koshino. "Moiré disorder effect in twisted bilayer graphene." Physical Review B 105, no. 24 (June 14, 2022). http://dx.doi.org/10.1103/physrevb.105.245408.

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30

Lee, Dong Su, Christian Riedl, Thomas Beringer, A. H. Castro Neto, Klaus von Klitzing, Ulrich Starke, and Jurgen H. Smet. "Quantum Hall Effect in Twisted Bilayer Graphene." Physical Review Letters 107, no. 21 (November 16, 2011). http://dx.doi.org/10.1103/physrevlett.107.216602.

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31

Angeli, M., E. Tosatti, and M. Fabrizio. "Valley Jahn-Teller Effect in Twisted Bilayer Graphene." Physical Review X 9, no. 4 (October 14, 2019). http://dx.doi.org/10.1103/physrevx.9.041010.

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32

Zhen Zhan, Yalei Zhang, and Shengjun Yuan. "Lattice relaxation and substrate effects on the electronic properties of graphene superlattice." Acta Physica Sinica, 2022, 0. http://dx.doi.org/10.7498/aps.71.20220872.

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When two two-dimensional (2D) materials with different lattice constants or with different rotation angles are stacked on top of another, a moiré superlattice can be constructed. The electronic properties of the superlattice are strongly dependent on the stacking configurations, twist angles and substrates. For instance, theoretically, when the rotation angle of twisted bilayer graphene is reduced to a set of specific values, the so-called magic angles, flat bands appear near the charge neutrality, and the electron-electron interaction is significantly enhanced. The Mott insulator and unconventional superconductivity are detected in the twisted bilayer graphene with twist angle around 1.1°. For a moiré pattern with a large enough periodicity, lattice relaxation caused by an interplay between van der Waals forces and the in-plane elasticity forces happens. The atomic relaxation forces atoms to deviate from their equilibrium positions and make the system reconstructed. In this review, we mainly focus on the effect of the lattice relaxation and substrates on the electronic properties of the graphene superlattices. From both theoretical and experimental points of view, the lattice relaxation effect on the atomic structures and electronic properties of graphene-based superlattices, for example, the twisted bilayer graphene, twisted trilayer graphene, graphene-hexagonal boron nitride superlattice and twisted bilayer graphene-boron nitride superlattice are discussed. Finally, a summary and perspective of the investigation of the 2D materials superlattice are presented.

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33

Zhang, Cheng-Ping, Jiewen Xiao, Benjamin T. Zhou, Jin-Xin Hu, Ying-Ming Xie, Binghai Yan, and K. T. Law. "Giant nonlinear Hall effect in strained twisted bilayer graphene." Physical Review B 106, no. 4 (July 18, 2022). http://dx.doi.org/10.1103/physrevb.106.l041111.

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34

Liu, Meng-Qi, Yan-Li Li, and Zhi-Gang Sun. "The electronic structures and predominant thermoelectric performance of the twisted InSb/Graphene bilayer." Physica E: Low-dimensional Systems and Nanostructures, June 2022, 115358. http://dx.doi.org/10.1016/j.physe.2022.115358.

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35

Vahedi, Javad, Robert Peters, Ahmed Missaoui, Andreas Honecker, and Guy Trambly de Laissardière. "Magnetism of magic-angle twisted bilayer graphene." SciPost Physics 11, no. 4 (October 27, 2021). http://dx.doi.org/10.21468/scipostphys.11.4.083.

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We investigate magnetic instabilities in charge-neutral twisted bilayer graphene close to so-called ``magic angles’’ using a combination of real-space Hartree-Fock and dynamical mean-field theories. In view of the large size of the unit cell close to magic angles, we examine a previously proposed rescaling that permits to mimic the same underlying flat minibands at larger twist angles. We find that localized magnetic states emerge for values of the Coulomb interaction UU that are significantly smaller than what would be required to render an isolated layer antiferromagnetic. However, this effect is overestimated in the rescaled system, hinting at a complex interplay of flatness of the minibands close to the Fermi level and the spatial extent of the corresponding localized states. Our findings shed new light on perspectives for experimental realization of magnetic states in charge-neutral twisted bilayer graphene.

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36

Shayeganfar, Farzaneh, and Ali Ramazani. "Quantum Transport and Fractional Hall Effect in Moiré Correlated/Anticorrelated Interface Channels." Journal of Materials Chemistry C, 2023. http://dx.doi.org/10.1039/d3tc02222f.

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Twisted bilayer graphene (tBLG) including interlayer interaction and rotational disorder shows anomalous electronic transport as a function of twist-angles (tAs). Quantum criticality of metal-insulator transitions of twisted nanostructures has been...

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37

Aggarwal, Deepanshu, Rohit Narula, and Sankalpa Ghosh. "A primer on Twistronics: A massless Dirac Fermion's journey to Moir'e patterns and Flat bands in Twisted Bilayer Graphene." Journal of Physics: Condensed Matter, February 6, 2023. http://dx.doi.org/10.1088/1361-648x/acb984.

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Abstract The recent discovery of superconductivity in magic-angle twisted bilayer graphene has sparked a renewed interest in the strongly-correlated physics of $sp^2$ carbons, in stark contrast to preliminary investigations which were dominated by the one-body physics of the massless Dirac fermions. We thus provide a self-contained, theoretical perspective of the journey of graphene from its single-particle physics-dominated regime to the strongly-correlated physics of the flat bands. Beginning from the origin of the Dirac points in condensed matter systems, we discuss the effect of the superlattice on the Fermi velocity and Van Hove singularities in graphene and how it leads naturally to investigations of the moir'{e} pattern in van der Waals heterostructures exemplified by graphene-hexagonal boron-nitride and twisted bilayer graphene. Subsequently, we illuminate the origin of flat bands in twisted bilayer graphene at the magic angles by elaborating on a broad range of prominent theoretical works in a pedagogical way while linking them to available experimental support, where appropriate. We conclude by providing a list of topics in the study of the electronic properties of twisted bilayer graphene not covered by this review but may readily be approached with the help of this primer.

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38

Tseng, Chun-Chih, Xuetao Ma, Zhaoyu Liu, Kenji Watanabe, Takashi Taniguchi, Jiun-Haw Chu, and Matthew Yankowitz. "Anomalous Hall effect at half filling in twisted bilayer graphene." Nature Physics, August 11, 2022. http://dx.doi.org/10.1038/s41567-022-01697-7.

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39

Löfwander, Tomas, Pablo San-Jose, and Elsa Prada. "Quantum Hall effect in graphene with twisted bilayer stripe defects." Physical Review B 87, no. 20 (May 21, 2013). http://dx.doi.org/10.1103/physrevb.87.205429.

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40

Moon, Pilkyung, and Mikito Koshino. "Energy spectrum and quantum Hall effect in twisted bilayer graphene." Physical Review B 85, no. 19 (May 29, 2012). http://dx.doi.org/10.1103/physrevb.85.195458.

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41

Duan, Junxi, Yu Jian, Yang Gao, Huimin Peng, Jinrui Zhong, Qi Feng, Jinhai Mao, and Yugui Yao. "Giant Second-Order Nonlinear Hall Effect in Twisted Bilayer Graphene." Physical Review Letters 129, no. 18 (October 24, 2022). http://dx.doi.org/10.1103/physrevlett.129.186801.

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42

Niu, Ruirui, Xiangyan Han, Zhuangzhuang Qu, Zhiyu Wang, Zhuoxian Li, Qianling Liu, Chunrui Han, and Jianming Lu. "Correlated states in alternating twisted bilayer-monolayer-monolayer graphene." Chinese Physics B, October 27, 2022. http://dx.doi.org/10.1088/1674-1056/ac9de4.

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Abstract Highly controlled electronic correlation in twisted graphene heterostructures has gained enormous research interests recently, encouraging exploration in a wide range of moiré superlattices beyond the celebrated twisted bilayer graphene. Here we characterize correlated states in an alternating twisted Bernal bilayer-monolayer-monolayer graphene of ~1.74º, and find that both van Hove singularities and multiple correlated states are asymmetrically tuned by displacement fields. In particular, when one electron per moiré unit cell is occupied in the electron-side flat band, or the hole-side flat band (i.e., three holes per moiré unit cell), the correlated peaks are found to counterintuitively grow with heating and maximize around 20 K – a signature of Pomeranchuk effect. Our multilayer heterostructure opens more opportunities to engineer complicated systems for investigating correlated phenomena.

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43

Zhu, yujian, Yiwei Chen, Qingxin Li, Yongdao Chen, Yan Huang, Wang Zhu, Dongdong An, et al. "Tunable multi-bands in twisted double bilayer graphene." 2D Materials, April 24, 2022. http://dx.doi.org/10.1088/2053-1583/ac69bb.

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Abstract The bandstructure of a material, playing an important role in its electron transport property, is usually governed by the lattice configuration. Materials with a field-effect tunable band, such as bilayer and rhombohedral trilayer graphene, are more flexible for electronic applications. Here, on dual-gated twisted double bilayer graphene (TDBG) samples with small twist angle around 1°, we observe vertical electric-field-tunable bandstructures at multiple moiré fillings positions with bandgap values continuously varying from zero to tens of mili-electron volts. Moreover, within the first moiré filling on both electron and hole sides, the carrier transport deviates from Fermi liquid behaviour, with measured resistivity exhibiting linear temperature dependence between 1.5 K and 50 K. Furthermore, under a vertical magnetic field, the coupling between the two bilayer graphene layers can also be turned on and off by the displacement field. Our results suggest TDBG with small twist angle is a platform for studying the electrostatic field tunable multiple moiré bands evolution and the resulting emergent correlated electronic states.

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Wang, Xian, Yingqi Cui, Li Zhang, and Mingli Yang. "Enhanced second-order Stark effect in twisted bilayer graphene quantum dots." Nano Research, January 30, 2021. http://dx.doi.org/10.1007/s12274-021-3318-y.

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45

Hasegawa, Yasumasa, and Mahito Kohmoto. "Periodic Landau gauge and quantum Hall effect in twisted bilayer graphene." Physical Review B 88, no. 12 (September 20, 2013). http://dx.doi.org/10.1103/physrevb.88.125426.

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Sato, Kentaro, Riichiro Saito, Chunxiao Cong, Ting Yu, and Mildred S. Dresselhaus. "Zone folding effect in RamanG-band intensity of twisted bilayer graphene." Physical Review B 86, no. 12 (September 7, 2012). http://dx.doi.org/10.1103/physrevb.86.125414.

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47

Hu, Jin-Xin, Zi-Ting Sun, Ying-Ming Xie, and K. T. Law. "Josephson Diode Effect Induced by Valley Polarization in Twisted Bilayer Graphene." Physical Review Letters 130, no. 26 (June 30, 2023). http://dx.doi.org/10.1103/physrevlett.130.266003.

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48

"Twist in the Tale: Exploring the Dielectric Screening Effect in Twisted Bilayer Graphene." JPS Hot Topics 2 (2022). http://dx.doi.org/10.7566/jpsht.2.001.

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Although the screening of an external electric field, strongly influences the electronic states of two-dimensional material stack, it is not well understood. Magnetotransport measurements of twisted double bilayer graphene uncovered the screening of atomic layers.

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49

Liang, Xia, Zachary A. H. Goodwin, Valerio Vitale, Fabiano Corsetti, Arash A. Mostofi, and Johannes Lischner. "Effect of bilayer stacking on the atomic and electronic structure of twisted double bilayer graphene." Physical Review B 102, no. 15 (October 29, 2020). http://dx.doi.org/10.1103/physrevb.102.155146.

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50

Jimeno‐Pozo, Alejandro, Zachary A. H. Goodwin, Pierre A. Pantaleón, Valerio Vitale, Lennart Klebl, Dante M. Kennes, Arash A. Mostofi, Johannes Lischner, and Francisco Guinea. "Short Versus Long Range Exchange Interactions in Twisted Bilayer Graphene." Advanced Physics Research, August 13, 2023. http://dx.doi.org/10.1002/apxr.202300048.

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AbstractThis study discusses the effect of long‐range interactions within the self‐consistent Hartree‐Fock (HF) approximation in comparison to short‐range atomic Hubbard interactions on the band structure of twisted bilayer graphene (TBG) at charge neutrality for various twist angles. Starting from atomistic calculations, it determines the quasi‐particle band structure of TBG with Hubbard interactions for three magnetic orderings: modulated anti‐ferromagnetic (MAFM), (NAFM) and hexagonal anti‐ferromagnetic (HAFM). Then, it develops an approach to incorporate these magnetic orderings along with the HF potential in the continuum approximation. Away from the magic angle, it observes a drastic effect of the magnetic order on the band structure of TBG compared to the influence of the HF potential. Near the magic angle, the HF potential plays a major role in the band structure, with HAFM and MAFM being secondary effects, but NAFM appears to still significantly distort the electronic structure at the magic angle. These findings suggest that the spin‐valley degenerate broken symmetry state often found in HF calculations of charge neutral TBG near the magic angle should favor magnetic order, since the atomistic Hubbard interaction will break this symmetry in favor of spin polarization.

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