Article
Engineering, Mechanical
Yuyang Chen, Dongying Liu, Ying Wu, Peng Yu, Yijie Liu
Summary: We present a reconfigurable electro-elastic topological insulator that possesses a large Chern number, providing a new valley phase. By utilizing piezoelectric metamaterials and band structure calculations, we successfully demonstrate nontrivial topological band gaps and edge states in this system.
INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES
(2023)
Article
Materials Science, Multidisciplinary
Kai Yang, Shaoyi Xu, Longwen Zhou, Zhiyuan Zhao, Tianyu Xie, Zhe Ding, Wenchao Ma, Jiangbin Gong, Fazhan Shi, Jiangfeng Du
Summary: Floquet engineering provides a powerful method to generate nonequilibrium topological phases with large topological invariants. This study demonstrates how Floquet Chern insulator phases can be detected through imaging the static and dynamic spin textures in momentum space using the nitrogen-vacancy center in diamond and its synthetic dimensions. The work confirms the versatility of Floquet driving in generating phases with large Chern numbers and establishes an experimental method to detect Floquet topological phases in two and higher spatial dimensions.
Article
Physics, Multidisciplinary
Axel Fuenfhaus, Thilo Kopp, Elias Lettl
Summary: This paper investigates how to calculate Chern numbers within the framework of vortex fields and addresses the problem of the winding number in the presence of topological defects.
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
(2022)
Article
Physics, Multidisciplinary
Ankur Das, Eyal Cornfeld, Sumiran Pujari
Summary: Topological insulator-based methods are used to classify gapped bands and semimetallic nodal defects. However, multiple bands with gap-closing points can also have nontrivial topology. A wave-function-based punctured-Chern invariant is constructed to capture this topology. It is shown to be applicable to systems with different gapless topologies.
PHYSICAL REVIEW LETTERS
(2023)
Article
Chemistry, Multidisciplinary
ShengNan Zhang, Bo Xie, QuanSheng Wu, Jianpeng Liu, Oleg V. Yazyev
Summary: We propose chiral decomposition rules for twisted N + M multilayer graphene configurations, which include arbitrary stacking order and mutual twist. In the chiral limit at the magic angle, the low-energy bands of these systems consist of chiral pseudospin doublets energetically entangled with two flat bands per valley induced by the moire superlattice potential. Numerical calculations based on realistic parametrization support the analytic construction. We also demonstrate that vertical displacement fields can open energy gaps between the pseudospin doublets and the two flat bands, allowing the flat bands to carry nonzero valley Chern numbers. These findings provide guidelines for the rational design of topological and correlated states in generic twisted graphene multilayers.
Article
Chemistry, Physical
Shuang Wu, Zhenyuan Zhang, K. Watanabe, T. Taniguchi, Eva Y. Andrei
Summary: In magic-angle twisted bilayer graphene, doping-induced Lifshitz transitions and van Hove singularities lead to the emergence of correlation-induced gaps and topologically non-trivial subbands. With the presence of a magnetic field, quantized Hall plateaus reveal the subband topology and signal the emergence of Chern insulators with Chern numbers. Additionally, a van Hove singularity at a filling of 3.5 suggests the possibility of a fractional Chern insulator, accompanied by a crossover from low-temperature metallic to high-temperature insulating behavior.
Article
Materials Science, Multidisciplinary
Yuanchuan Biao, Rui Yu
Summary: We provide a unified scheme for realizing a pair of Weyl points using long-range spin-orbit coupling, allowing the realization of Weyl points with arbitrary topological charges. This offers a scheme for realizing ideal unconventional Weyl states and using long-range spin-orbit coupling for exotic states.
Article
Materials Science, Multidisciplinary
Zhaochen Liu, Huan Wang, Jing Wang
Summary: This study proposes the use of magnetic moiré surface states of topological insulators as a platform for time-reversal symmetry breaking flat Chern bands. By constructing a generic continuum model, the study shows that the Zeeman-type moiré potentials can gap out the moiré surface Dirac cones and generate isolated flat Chern minibands. Importantly, the bandwidth of these minibands is not affected by the twisting angle, providing a promising platform for realizing time-reversal breaking correlated topological phases.
Article
Chemistry, Multidisciplinary
Dmitry Ovchinnikov, Xiong Huang, Zhong Lin, Zaiyao Fei, Jiaqi Cai, Tiancheng Song, Minhao He, Qianni Jiang, Chong Wang, Hao Li, Yayu Wang, Yang Wu, Di Xiao, Jiun-Haw Chu, Jiaqiang Yan, Cui-Zu Chang, Yong-Tao Cui, Xiaodong Xu
Summary: MnBi2Te4 is a van der Waals magnet that can form a Chern insulator when all spins are aligned by an applied magnetic field. Through in-depth investigation, it is found that the bulk electronic structure evolves as the magnetic state is tuned, with a one-to-one correspondence with layer thickness, topological order, and magnetic state. Additionally, band topology and magnetic order in this newly discovered topological magnet exhibit an interplay during the continuous tuning of the magnetic state.
Article
Chemistry, Multidisciplinary
Hongrun Zhang, Zhijian Shi, Zhicheng Jiang, Ming Yang, Jingwei Zhang, Ziyuan Meng, Tonghua Hu, Fucai Liu, Long Cheng, Yong Xie, Jincheng Zhuang, Haifeng Feng, Weichang Hao, Dawei Shen, Yi Du
Summary: This study reports the appearance of flat bands (FBs) in 2D geometrically frustrated systems caused by quantum destructive interference (QDI), providing experimental evidence of the complete electronic QDI induced FB contributed by the 2D breathing-kagome layers of Nb atoms in Nb3TeCl7 (NTC). It also establishes the tunable roles of the on-site energy over Nb sites on bandwidth, energy position, and topology of FBs in NTC, demonstrating the potential to manipulate FB characteristics in 4d transition-metal-based breathing-kagome materials.
ADVANCED MATERIALS
(2023)
Article
Physics, Applied
Tianchong Wu, Xu Jiang, Xin Wu, Qiang Han
Summary: This paper explores the acoustic transport through topological edge states in phononic crystals, introducing different valley phases to create one, two, and three topological edge states. By introducing various defects, the system shows resistance to bending defects, indicating significant potential for applications in noise control, acoustic communication, and acoustic-electrical integration.
JOURNAL OF APPLIED PHYSICS
(2021)
Article
Physics, Multidisciplinary
Yan-Qing Zhu, Zhen Zheng, Giandomenico Palumbo, Z. D. Wang
Summary: In this work, a four-dimensional topological insulator model is proposed, which exhibits different topological phases on its three-dimensional boundary by introducing perturbations. By introducing electromagnetic and pseudo-electromagnetic fields, exotic topological responses of this four-dimensional system are revealed, and these effects can be experimentally probed.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Condensed Matter
Rakesh Kumar Malakar, Asim Kumar Ghosh
Summary: A simple route to engineer topological phases with any desired winding and Chern numbers is achieved by adding a further neighbor hopping term in the Su-Schrieffer-Heeger (SSH) model. It is shown that topological phases with various winding numbers can be generated by introducing a single further neighbor term that maintains inversion, particle-hole, and chiral symmetries. The modulation of nearest neighbor and next-nearest-neighbor hopping parameters in another version of the SSH model also leads to multiple crossings within the edge states energy lines in both trivial and topological phases. Topological phase diagrams are plotted for different parametrizations.
JOURNAL OF PHYSICS-CONDENSED MATTER
(2023)
Article
Materials Science, Multidisciplinary
Kai Wang, Jia-Xiao Dai, L. B. Shao, Shengyuan A. Yang, Y. X. Zhao
Summary: Recent advances in topological artificial systems have allowed for the realization of topological states in higher dimensions. A tensor product theory is presented as a method for constructing Chern insulators with arbitrary dimensions and Chern numbers. This theory leads to novel higher-dimensional topological physics, with boundary states featuring nontrivial Chern charges.
Article
Materials Science, Multidisciplinary
Zhen-Yu Lan, Ai -Lei He, Yi-Fei Wang
Summary: Topological flat bands (TFBs) with higher Chern numbers are constructed in the monolayer star lattice by adding distant-neighbor hopping terms with staggered magnetic fluxes. TFBs with |C|=2 and |C|=3 are achieved by considering the third and fourth nearest-neighbor hopping terms, and TFBs with |C|=4 and |C|=5 are obtained by adding the fifth and sixth nearest-neighbor hopping terms. Multiple flat bands with various Chern numbers can be observed by tuning the distant-neighbor hopping amplitudes and the staggered-flux parameters. Fractional Chern insulator (FCI) states with different fractional fillings are also observed when hard-core bosons are filled into these TFB models.
Article
Physics, Multidisciplinary
Sankar Das Sarma
Summary: Majorana particles, which are the same as their antiparticles, show promise for quantum computing in condensed matter systems. This article discusses the search for Majorana modes in semiconductor heterostructures and the limitations imposed by disorder. Majorana zero modes are emergent phenomena in topological superconductors, and this Perspective provides an overview of their physics, recent experimental progress, and future outlook for success.
Article
Physics, Multidisciplinary
DinhDuy Vu, Sankar Das Sarma
Summary: An ergodic system subjected to an external periodic drive will be heated to infinite temperature, but this heating can be stopped during a prethermal period if the applied frequency is larger than the typical energy scale of the local Hamiltonian. This prethermal period exhibits an emergent symmetry that, if broken, leads to subharmonic oscillation of the discrete time crystal (DTC). The presence of dissipation affects the survival time of the prethermal DTC, with a bath coupling prolonging the prethermal period and interaction with the environment destabilizing spontaneous symmetry breaking, resulting in a nonmonotonic variation of the survival time.
PHYSICAL REVIEW LETTERS
(2023)
Article
Materials Science, Multidisciplinary
Jiabin Yu, Ming Xie, Fengcheng Wu, Sankar Das Sarma
Summary: Signatures of nematic nodal superconductivity have been observed in magic angle twisted bilayer graphene. Researchers propose a general topological mechanism explaining how nematic pairing leads to nodal superconductivity in this material.
Article
Materials Science, Multidisciplinary
Prathyush P. Poduval, Sankar Das Sarma
Summary: We theoretically investigate the issue of doping induced insulator to metal transition in bulk semiconductors by analyzing the density-dependent mean free path and the Anderson localization transition controlled by the Ioffe-Regel-Mott (IRM) criterion. We calculate the mean free path on the highly doped metallic side considering carrier scattering by ionized dopants. The Coulomb disorder of the charged dopants is screened by the carriers themselves, leading to an integral equation for localization. By solving this equation analytically and numerically, we provide detailed results for the critical density of the doping induced metal-insulator transition.
Article
Materials Science, Multidisciplinary
Nathan L. Foulk, Sankar Das Sarma
Summary: We demonstrate the potential realization of quantum Floquet matter, particularly the discrete time crystal (DTC), using modern silicon spin qubits based in quantum dots. This is significant as silicon spin qubits have advantages in dealing with charge noise. We show the differences between prethermal phenomena and true time-crystalline spatiotemporal order, and illustrate rich regime structures in a spin chain of four qubits that are distinct from the thermal regime.
Article
Materials Science, Multidisciplinary
Seth M. Davis, Yang-Zhi Chou, Fengcheng Wu, Sankar Das Sarma
Summary: We calculate the theoretical contribution of scattering by acoustic phonons to the doping and temperature dependence of electrical resistivity in Bernal bilayer graphene (BBG) and rhombohedral trilayer graphene (RTG). The nontrivial geometric features of the band structures of these systems strongly influence the resistivity's temperature and doping dependencies. Our focus on BBG and RTG is motivated by recent experiments in these systems that have discovered exotic low-temperature superconductivity. The understanding of the influence of band geometry on transport is crucial in these systems.
Article
Materials Science, Multidisciplinary
Haining Pan, Sankar Das Sarma
Summary: Motivated by the presence of Majorana zero modes in both the Kitaev chain model and the experimental semiconductor-superconductor Majorana nanowire, this theoretical study investigates the equivalence or similarity between the two models from the perspective of their corresponding dual spin models. By using the Jordan-Wigner transformation, the duality between the Kitaev chain and the transverse-field XY spin model is established, aiming to connect the Kitaev chain and the nanowire. The application of the Jordan-Wigner transformation to the nanowire reveals that the corresponding bosonic spin model is a generalized spin cluster model with staggered couplings. By projecting out the higher energy band of the spinful nanowire system, an effective low-energy spinless system is obtained, leading to the connection between the Kitaev chain and Majorana nanowire.
Article
Materials Science, Multidisciplinary
Yi-Ting Tu, Sankar Das Sarma
Summary: We analyze an experimental work which shows the failure of the Wiedemann-Franz law in graphene at low temperatures, attributing this failure to the non-Fermi liquid nature of the Dirac fluid. Despite theoretical efforts, the observations remain unexplained. Our analysis suggests that the opening of a gap at the Dirac point induced by the substrate may explain the results. Further experiments are needed to resolve the issue and determine the role of electron and hole transport in the presence of disorder and phonons.
Article
Materials Science, Multidisciplinary
Yi-Ting Tu, DinhDuy Vu, S. Das Sarma
Summary: Coupling a one-dimensional quasiperiodic interacting system to a Markovian bath, this study investigates the avalanche instability of the many-body localized phase numerically. The results show that many-body localization (MBL) is more stable in pseudorandom quasiperiodic systems than in randomly disordered systems for a disorder strength W > 8, potentially up to arbitrarily large system sizes. Real-space RG arguments support this conclusion and a detailed comparison between quasiperiodic and random MBL from the avalanche instability perspective reveals that they belong to different universality classes.
Article
Materials Science, Multidisciplinary
Donovan Buterakos, Sankar Das Sarma
Summary: We discuss interesting phenomena in the Hubbard model related to flat-band ferromagnetism. The first is a mathematical theorem that describes the conditions for degeneracy between a flat-band ferromagnetic and a nonferromagnetic state. This theorem is generally applicable and independent of geometry, but only holds for a small number of holes in a filled band. The second phenomenon challenges intuition by showing an example where particles do not prefer to doubly occupy low-energy states before filling higher-energy states. Lastly, we present a pattern of ferromagnetism in small pentagonal and hexagonal plaquettes at specific filling factors. These examples can be observed in quantum dot arrays available in laboratories.
Article
Materials Science, Multidisciplinary
DinhDuy Vu, Sankar Das Sarma
Summary: This paper investigates the temperature-induced melting of a Wigner solid in one-dimensional and two-dimensional electron lattices in the presence of strong disorder. The study finds that the melting temperature can be significantly enhanced by disorder, which helps explain why experiments often observe insulating disorder-pinned Wigner solids even at high temperatures.
Article
Materials Science, Multidisciplinary
Seongjin Ahn, Sankar Das Sarma
Summary: Based on theoretical analysis, this study demonstrates that electrons in high-mobility 2D GaAs are the best system for directly observing collective hydrodynamic effects. These effects can be observed even in narrow constrictions and small systems, independent of complicated transport features.
Article
Materials Science, Multidisciplinary
Yang-Zhi Chou, Fengcheng Wu, Jay D. Sau, Sankar Das Sarma
Summary: We investigate the competition between acoustic phonon mediated superconductivity and the long-range Coulomb interaction in moireless graphene multilayers. Our theory explains recent experimental findings in Bernal bilayer graphene and rhombohedral trilayer graphene, and predicts the existence of superconductivity in ABCA tetralayer graphene. The inclusion of realistic band structures with Van Hove singularities and Coulomb repulsion effects in our theory is crucial. Our work provides detailed predictions for graphene superconductivity induced by electron-acoustic phonon interaction, which should be investigated in future experiments.
Article
Materials Science, Multidisciplinary
Robert E. Throckmorton, S. Das Sarma
Summary: This study determines the decoherence time in a system of exchange-coupled electronic spin qubits by calculating the return probability. The multiqubit geometry is found to play a crucial role in the decoherence time.
Article
Materials Science, Multidisciplinary
Seongjin Ahn, Sankar Das Sarma
Summary: This theoretical study validates the experimentally observed sudden change in 2D resistivity with a spontaneous valley polarization transition from 2 to 1 at the critical density, showing quantitative consistency between the two.