In magnetic topological insulators, quantized electronic transport is interwined with spontaneous magnetic ordering, as magnetization controls band gaps, hence band topology, through the exchange interaction. We show that considering the exchange gaps at the mean-field level is inadequate to predict phase transitions between electronic states of distinct topology. Thermal spin fluctuations disturbing the magnetization can act as frozen disorders that strongly scatter electrons, reducing the onset temperature of quantized transport appreciably even in the absence of structural impurities. This effect, which has hitherto been overlooked, provides an alternative explanation of recent experiments on intrinsic magnetic topological insulators.
Intrinsic magnetic topological insulator ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ is believed to be an axion insulator in its antiferromagnetic ground state. However, direct identification of axion insulators remains experimentally elusive because the observed vanishing Hall resistance, while indicating the onset of the axion field, is inadequate to distinguish the system from a trivial normal insulator. Using numerical Green's functions, we theoretically demonstrate the quantized magnetoelectric current in a tunnel junction of atomically thin ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ sandwiched be…
Quantized Anomalous Hall Effect in Magnetic Topological Insulators
霍尔效应、反常霍尔效应和自旋霍尔效应分别是由洛伦兹力和自旋轨道耦合引起的固体中的基本输运过程。近年来,人们发现了量子形式的霍尔效应和自旋霍尔效应。然而,量子化反常霍尔(QAH)效应尚未在实验上实现。在QAH绝缘体中,自发磁矩和自旋-轨道耦合结合产生拓扑非平凡的电子结构,导致量子化的霍尔效应而无需任何外部磁场。在这项工作中,基于最先进的第一性原理计算,我们预测的辉碲铋矿半导体Bi $_2$ Te $_3$,Bi $_2$ Se $_3$,和Sb $_2$ Te $_3$形成磁有序的绝缘体时,掺杂过渡金属元素(Cr或Fe),在鲜明对比,传统的稀磁半导体中,自由载流子是必要的调解磁耦合。二维薄膜中的磁序产生了以有限的陈数为特征的拓扑电子结构,具有量子化的霍尔电导$e^{2}/h$。长期追求的QAH绝缘体状态的实验实现可以在室温下实现稳健的无耗散电荷传输。
One-dimensional (1D) topologically protected states are usually formed at the interface between two-dimensional (2D) materials with different topological invariants. Therefore, 1D chiral interface channels (CICs) can be created at the boundary of two quantum anomalous Hall (QAH) insulators with different Chern numbers. Such a QAH junction can function as a chiral edge current distributer at zero magnetic field, but its realization remains challenging. Here, by employing an in-situ mechanical mask, we use molecular beam epitaxy (MBE) to synthesize QAH insulator junctions, in which two QAH insul…
The quantized conductance plateaus and zero conductance fluctuation are the general consequence of electron transport in chiral edge states of Hermitian Chern insulators. Here we show that the physics of electron transport through chiral or helical edge channels becomes much richer when the non-Hermicity is allowed. In the presence of an unbalanced non-Hermicity where the chiral edge states have finite-lifetime, the conductance of the edge channels is not quantized, but its conductance fluctuation is zero. For the balanced non-Hermicity, however, the chiral edge states have infinite-lifetime, …
Recently,a half-quantized Hall conductance (HQHC) plateau is experimentally observed in a semi-magnetic topological insulator heterostructure. However,the heterostructure is metallic with a nonzero longitudinal conductance, which contradicts the common belief that quantized Hall conductance is usually observed in insulators.In this work,we systematically study the surface transport of the semi-magnetic topological insulator with both gapped and gapless Dirac surfaces in the presence of dephasing process.In particular, we reveal that the HQHC is directly related to the half-quantized chiral cur…
We identify topological aspects of the subextensive magnetic moment contributed by the surfaces of a three-dimensional crystallite -- assumed to be insulating in the bulk as well as on all surface facets, with trivial Chern invariants in the bulk. The geometric component of this subextensive moment is given by its derivative with respect to the chemical potential, at zero temperature and zero field, per unit surface area, and hence corresponds to the surface magnetic compressibility. The sum of the surface compressibilities contributed by two opposite facets of a cube-shaped crystallite is qua…
We uncover a new family of few-body topological phases in periodically driven fermionic systems in two dimensions. These phases, which we term correlation-induced anomalous Floquet insulators (CIAFIs), are characterized by quantized contributions to the bulk magnetization from multi-particle correlations, and are classified by a family of integer-valued topological invariants. The CIAFI phases do not require many-body localization, but arise in the generic situation of k-particle localization, where the system is localized (due to disorder) for any finite number of particles up to a maximum nu…
In this Letter, we study an Anderson-localization-induced quantized transport in disordered Chern insulators (CIs). By investigating the disordered CIs with a step potential, we find that the chiral interface states emerge along the interfaces of the step potential, and the energy range for such quantized transport can be manipulated through the potential strength. Furthermore, numerical simulations on cases with a multi-step potential demonstrate that such chiral state can be spatially shifted by varying the Fermi energy, and the energy window for quantized transport is greatly enlarged. Expe…
We study the quantized charge pumping of higher-order topological insulators (HOTIs) with edge-corner correspondences based on the combination of the rotation of in-plane magnetic field and the quantum spin Hall effect. A picture of a specific charge pumping process is uncovered with the help of the non-equilibrium Green's function method. Significantly, we demonstrate that the quantized charge pumping current is achieved without the participation of bulk states, and the charges move along the boundary of the sample. Furthermore, the effects of external parameters on the pumping current is als…
Quantized Hall drift in a frequency-encoded photonic Chern insulator
Université de Montréal(蒙特利尔大学);INO-CNR(意大利国家研究委员会光学研究所);Università di Trento(特伦托大学);Ecole Polytechnique(巴黎综合理工学院);Institut Polytechnique de Paris(巴黎理工学院);Advanced Institute for Materials Research (WPI-AIMR), Tohoku University(东北大学材料科学研究高等研究院);Institut Courtois(库尔瓦研究所)
Topological axion states in magnetic insulator MnBi$_2$Te$_4$ with the quantized magnetoelectric effect
量子物质的拓扑态在凝聚态物理和材料科学中引起了极大的关注。量子材料中的时间反演不变(TRI)拓扑态的研究在理论和实验上都取得了巨大的进展。作为一个巨大的成功,成千上万的TRI拓扑材料预测通过扫描搜索。由于磁性拓扑材料的磁结构多样,人们期望在其中出现更丰富的奇异现象,但由于磁性拓扑材料的磁结构和相变复杂,这方面的研究相对滞后。在这里,我们预测的tetradymite型化合物MnBi $_2$ Te $_4$和它的相关材料主机有趣的磁性拓扑状态。MnBi $_2$ Te $_4$的磁基态是一个反铁磁相,它导致一个具有大的拓扑非平凡能隙($\sim$ 0.2~eV)的反铁磁拓扑绝缘体态.它是轴子态的母态,具有带隙的体态和表面态,以及量子化的拓扑磁电效应。MnBi $_2$ Te $_4$的铁磁相导致在费米能级上具有两个Weyl点以及一个空穴型和一个电子型费米口袋的理想的最小II型Weyl半金属,这在其他地方从未发现过。我们进一步提出了一个简单而统一的连续介质模型来描述这类材料的显著拓扑特征。
We study the generalization of the three-dimensional two-band Hopf insulator to the case of many bands, where all the bands are separated from each other by band gaps. The obtained $\mathbb{Z}$ classification of such a $N$-band Hopf insulator is related to the quantized isotropic magnetoelectric coefficient of its bulk. The boundary of a $N$-band Hopf insulator can be fully gapped, and we find that there is no unique way of dividing a finite system into bulk and boundary. Despite this non-uniqueness, we find that the magnetoelectric coefficient of the bulk and the anomalous Hall conductivity o…
Dynamical Superfluid and Bose-Insulator Phases in Quantized Polariton Lattices
School of Science and Engineering, The Chinese University of Hong Kong (Shenzhen)(香港中文大学(深圳)理学院);Beijing Academy of Quantum Information Sciences(北京量子信息科学研究院)