scholarly journals Quantum anomalous Hall effect from intertwined moiré bands

2021 ◽  
Author(s):  
Kin Fai Mak ◽  
Tingxin Li ◽  
Shengwei Jiang ◽  
Bowen Shen ◽  
Yang Zhang ◽  
...  
Keyword(s):  
Electric Field ◽  
Electron Correlation ◽  
Anomalous Hall Effect ◽  
Mott Insulator ◽  
Zero Magnetic Field ◽  
Hall Resistance ◽  
High Symmetry ◽  
Topological Phase ◽  
Wigner Crystals ◽  
And Topology

Abstract Electron correlation and topology are two central threads of modern condensed matter physics. Semiconductor moiré materials provide a highly tunable platform for studies of electron correlation. Correlation-driven phenomena, including the Mott insulator, generalized Wigner crystals, stripe phases and continuous Mott transition, have been demonstrated. However, nontrivial band topology has remained elusive. Here we report the observation of a quantum anomalous Hall (QAH) effect in AB-stacked MoTe2/WSe2 moiré heterobilayers. Unlike in the AA-stacked structures, an out-of-plane electric field controls not only the bandwidth but also the band topology by intertwining moiré bands centered at different high-symmetry stacking sites. At half band filling, corresponding to one particle per moiré unit cell, we observe quantized Hall resistance, h/e^2 (with h and e denoting the Planck’s constant and electron charge, respectively), and vanishing longitudinal resistance at zero magnetic field. The electric-field-induced topological phase transition from a Mott insulator to a QAH insulator precedes an insulator-to-metal transition; contrary to most known topological phase transitions, it is not accompanied by a bulk charge gap closure. Our study paves the path for discovery of a wealth of emergent phenomena arising from the combined influence of strong correlation and topology in semiconductor moiré materials.

scholarly journals Large discrete jumps observed in the transition between Chern states in a ferromagnetic topological insulator

2016 ◽  
Vol 2 (7) ◽  
pp. e1600167 ◽  
Author(s):  
Minhao Liu ◽  
Wudi Wang ◽  
Anthony R. Richardella ◽  
Abhinav Kandala ◽  
Jian Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Metastable State ◽  
Large Fraction ◽  
Surface States ◽  
Anomalous Hall Effect ◽  
Escape Rate ◽  
Zero Magnetic Field ◽  
Hall Resistance ◽  
Edge States ◽  
Longitudinal Resistance

A striking prediction in topological insulators is the appearance of the quantized Hall resistance when the surface states are magnetized. The surface Dirac states become gapped everywhere on the surface, but chiral edge states remain on the edges. In an applied current, the edge states produce a quantized Hall resistance that equals the Chern numberC= ±1 (in natural units), even in zero magnetic field. This quantum anomalous Hall effect was observed by Changet al. With reversal of the magnetic field, the system is trapped in a metastable state because of magnetic anisotropy. We investigate how the system escapes the metastable state at low temperatures (10 to 200 mK). When the dissipation (measured by the longitudinal resistance) is ultralow, we find that the system escapes by making a few very rapid transitions, as detected by large jumps in the Hall and longitudinal resistances. Using the field at which the initial jump occurs to estimate the escape rate, we find that raising the temperature strongly suppresses the rate. From a detailed map of the resistance versus gate voltage and temperature, we show that dissipation strongly affects the escape rate. We compare the observations with dissipative quantum tunneling predictions. In the ultralow dissipation regime, two temperature scales (T1~ 70 mK andT2~ 145 mK) exist, between which jumps can be observed. The jumps display a spatial correlation that extends over a large fraction of the sample.

scholarly journals Intrinsic quantized anomalous Hall effect in a moiré heterostructure

Science ◽  
2019 ◽  
Vol 367 (6480) ◽  
pp. 900-903 ◽  
Author(s):  
M. Serlin ◽  
C. L. Tschirhart ◽  
H. Polshyn ◽  
Y. Zhang ◽  
J. Zhu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Energy Gap ◽  
Hexagonal Boron Nitride ◽  
Magnetic Ordering ◽  
Anomalous Hall Effect ◽  
Zero Magnetic Field ◽  
Strong Interactions ◽  
Hall Resistance ◽  
Magnetic Memory ◽  
Electrical Currents

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.

scholarly journals Electric-Field-Driven Topological Phase Switching and Skyrmion-Lattice Metastability in Magnetoelectric Cu2OSeO3

2018 ◽  
Vol 10 (1) ◽  
Author(s):  
J. S. White ◽  
I. Živković ◽  
A. J. Kruchkov ◽  
M. Bartkowiak ◽  
A. Magrez ◽  
...  
Keyword(s):  
Electric Field ◽  
Topological Phase ◽  
Phase Switching

scholarly journals Progress Review on Topological Properties of Heusler Materials

2020 ◽  
Vol 213 ◽  
pp. 02016
Author(s):  
Zhi Lin
Keyword(s):  
Hall Effect ◽  
Surface States ◽  
Anomalous Hall Effect ◽  
Edge State ◽  
Chiral Anomaly ◽  
Dirac Fermion ◽  
High Symmetry ◽  
Heusler Compounds ◽  
Topological Properties ◽  
Topological State

Starting from crystal, electronic and magnetic structures of Heusler compounds, this paper studies the new topological materials related to Heusler compounds and their topological properties, such as anomalous Hall effect, skyrmions, chiral anomaly, Dirac fermion, Weyl fermion, transverse Nernst thermoelectric effect, thermal spintronics and topological surface states. It can be discovered that the topological state of Heusler compound can be well protected due to its high symmetry, thus producing rich topological properties. Heusler materials belonged to Weyl semimetals usually have strong anomalous Hall effect, and the Heusler materials with doping or Anomalous Nernst Effect (ANE) usually have higher thermoelectric figure of merit. These anomalous effects are closely related to the strong spin–orbit interaction. In application, people can use the non-dissipative edge state of quantum anomalous Hall effect to develop a new generation of low-energy transistors and electronic devices. The conversion efficiency of thermoelectric materials can be improved by ANE, and topological superconductivity can be used to promote the progress of quantum computation.

scholarly journals Electric-field-tuned topological phase transition in ultrathin Na3Bi

Nature ◽  
2018 ◽  
Vol 564 (7736) ◽  
pp. 390-394 ◽  
Author(s):  
James L. Collins ◽  
Anton Tadich ◽  
Weikang Wu ◽  
Lidia C. Gomes ◽  
Joao N. B. Rodrigues ◽  
...  
Keyword(s):  
Phase Transition ◽  
Electric Field ◽  
Topological Phase ◽  
Topological Phase Transition

scholarly journals Electric-field-induced metal maintained by current of the Mott insulator Ca2RuO4

2013 ◽  
Vol 3 (1) ◽  
Author(s):  
Fumihiko Nakamura ◽  
Mariko Sakaki ◽  
Yuya Yamanaka ◽  
Sho Tamaru ◽  
Takashi Suzuki ◽  
...  
Keyword(s):  
Electric Field ◽  
Mott Insulator

scholarly journals Large nonlinear Hall effect in (FeCo)0.67Ge0.33/Ge heterojunctions

2019 ◽  
Vol 33 (13) ◽  
pp. 1950121 ◽  
Author(s):  
Juan Pei ◽  
Shu-Qin Xiao ◽  
Li-Min He ◽  
Kun Zhang ◽  
Huan-Huan Li ◽  
...  
Keyword(s):  
Hall Effect ◽  
Potential Barrier ◽  
Coupling Effect ◽  
Magnetic Semiconductor ◽  
Anomalous Hall Effect ◽  
Hall Resistance ◽  
Band Model ◽  
Semiconductor Films ◽  
Text Type ◽  
Interfacial Potential

The large nonlinear Hall effect was found in (FeCo)[Formula: see text]Ge[Formula: see text]/Ge heterojunctions formed by sputtering amorphous [Formula: see text]-type (FeCo)[Formula: see text]Ge[Formula: see text] magnetic semiconductor films on near intrinsic n-type Ge substrate. It is very interesting that the mechanisms of the large nonlinear Hall effect in (FeCo)[Formula: see text]Ge[Formula: see text]/Ge heterojunctions are different at different temperature ranges. Below 10 K, the Hall resistance of (FeCo)[Formula: see text]Ge[Formula: see text]/Ge heterojunctions is almost the same as the anomalous Hall effect of (FeCo)[Formula: see text]Ge[Formula: see text] ferromagnetic films. While the temperature increased from 10 to 60 K, the nonlinear Hall resistance, longitudinal conductance, and magnetoresistance all increased quickly and reached the maximum at T[Formula: see text]=[Formula: see text]60 K. In this case, thermally excited conducting carriers can tunnel through the interfacial potential barrier in (FeCo)[Formula: see text]Ge[Formula: see text]/Ge heterojunctions. Thus, in the range of 10–60 K, the enhanced nonlinear Hall resistance can be attributed to the anomalous Hall effect which was further enhanced by interfacial Rashba spin–orbit coupling effect. When the temperature further increased from 60 to 250 K, the interfacial potential barrier weakened gradually, and the Hall resistance and magnetoresistance decreased due to the shunting of the Ge substrate. In this case, the nonlinear Hall effect of (FeCo)[Formula: see text]Ge[Formula: see text]/Ge heterojunctions can be explained very well by the two-band model of nonlinear Hall effect.

The Impurity Spin-Dependent Scattering Effects in the Transport and Spin Resonance of Conduction Electrons in Bismuth Doped Silicon

2015 ◽  
Vol 242 ◽  
pp. 327-331 ◽  
Author(s):  
Andrey V. Soukhorukov ◽  
Davud V. Guseinov ◽  
Alexei V. Kudrin ◽  
Sergey A. Popkov ◽  
Alexandra P. Detochenko ◽  
...  
Keyword(s):  
Hall Effect ◽  
Spin Relaxation ◽  
Electron Spin ◽  
Anomalous Hall Effect ◽  
Hall Resistance ◽  
Resonance Spectroscopy ◽  
Electron Spin Relaxation ◽  
Conduction Electrons ◽  
Spin Resonance ◽  
Hall Effect Measurements

Transport and spin relaxation characteristics of the conduction electrons in silicon samples doped with bismuth in the 1.1·1013- 7.7·1015cm-3concentration range were studied by the Hall and electron spin resonance spectroscopy. Hall effect measurements in the temperature range 10-80 K showed a deviation from the linear dependence of the Hall resistance in the magnetic field, which is a manifestation of the anomalous Hall effect. The magnetoresistance investigation shows that with current increasing magnetoresistance may change its sign from positive to negative, which is most clearly seen when the bismuth concentration goes up to 7.7·1015cm-3. The conduction electron spin relaxation rate dramatically increases in silicon samples with sufficiently low concentration of bismuth ~ 2·1014cm-3. All these results can be explained in terms of the concept of spin-dependent and spin flip scattering induced by heavy bismuth impurity centers.

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