scholarly journals Quantum anomalous Hall effect in intrinsic magnetic topological insulator MnBi2Te4

Science ◽  
2020 ◽  
Vol 367 (6480) ◽  
pp. 895-900 ◽  
Author(s):  
Yujun Deng ◽  
Yijun Yu ◽  
Meng Zhu Shi ◽  
Zhongxun Guo ◽  
Zihan Xu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Quantum Transport ◽  
Topological Insulator ◽  
Time Reversal ◽  
Magnetic Order ◽  
Anomalous Hall Effect ◽  
Time Reversal Symmetry ◽  
Zero Field ◽  
Exotic States ◽  
Ferromagnetic Layers

In a magnetic topological insulator, nontrivial band topology combines with magnetic order to produce exotic states of matter, such as quantum anomalous Hall (QAH) insulators and axion insulators. In this work, we probe quantum transport in MnBi2Te4 thin flakes—a topological insulator with intrinsic magnetic order. In this layered van der Waals crystal, the ferromagnetic layers couple antiparallel to each other; atomically thin MnBi2Te4, however, becomes ferromagnetic when the sample has an odd number of septuple layers. We observe a zero-field QAH effect in a five–septuple-layer specimen at 1.4 kelvin, and an external magnetic field further raises the quantization temperature to 6.5 kelvin by aligning all layers ferromagnetically. The results establish MnBi2Te4 as an ideal arena for further exploring various topological phenomena with a spontaneously broken time-reversal symmetry.

Spin Glass State in Iron-Doped Bi2Fe0.128Te2.844Se0.145 Topological Insulator

2014 ◽  
Vol 215 ◽  
pp. 127-130
Author(s):  
Liudmila I. Koroleva ◽  
Artiom S. Morozov ◽  
Sergey F. Marenkin ◽  
Irina V. Fedorchenko ◽  
Rhita A. Szymczak
Keyword(s):  
Magnetic Field ◽  
Single Crystal ◽  
Spin Glass ◽  
Topological Insulator ◽  
Time Reversal ◽  
Temperature Increase ◽  
Freezing Temperature ◽  
Time Reversal Symmetry ◽  
Electric Resistance ◽  
Small Temperature

The researching of dependence of magnetization from temperature T and magnetic field in the Bi2Fe0.128Te2.844Se0.145 single-crystal showed that it have spinglass-like state with freezing temperature Tf= 40 K. Its electric resistance up to 100 K is ~ 103 Ohm and decreases with the temperature increase. At T > 110 K electric resistance ~ 10-2 Ohm and magnetization is four times smaller than in spinglass-like state. It can be assumed from these results that this sample is topological insulator at T > 110 K and at small temperature, where it is spinglass-like, offers the breaking of the time reversal symmetry.

scholarly journals Giant c-axis nonlinear anomalous Hall effect in Td-MoTe2 and WTe2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Archana Tiwari ◽  
Fangchu Chen ◽  
Shazhou Zhong ◽  
Elizabeth Drueke ◽  
Jahyun Koo ◽  
...  
Keyword(s):  
Hall Effect ◽  
Time Reversal ◽  
Low Temperatures ◽  
Magnetic Order ◽  
Anomalous Hall Effect ◽  
Time Reversal Symmetry ◽  
Inversion Center ◽  
Scattering Process ◽  
Berry Curvature ◽  
Skew Scattering

AbstractWhile the anomalous Hall effect can manifest even without an external magnetic field, time reversal symmetry is nonetheless still broken by the internal magnetization of the sample. Recently, it has been shown that certain materials without an inversion center allow for a nonlinear type of anomalous Hall effect whilst retaining time reversal symmetry. The effect may arise from either Berry curvature or through various asymmetric scattering mechanisms. Here, we report the observation of an extremely large c-axis nonlinear anomalous Hall effect in the non-centrosymmetric Td phase of MoTe2 and WTe2 without intrinsic magnetic order. We find that the effect is dominated by skew-scattering at higher temperatures combined with another scattering process active at low temperatures. Application of higher bias yields an extremely large Hall ratio of E⊥/E|| = 2.47 and corresponding anomalous Hall conductivity of order 8 × 107 S/m.

scholarly journals Unsplit superconducting and time reversal symmetry breaking transitions in Sr2RuO4 under hydrostatic pressure and disorder

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Vadim Grinenko ◽  
Debarchan Das ◽  
Ritu Gupta ◽  
Bastian Zinkl ◽  
Naoki Kikugawa ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Symmetry Breaking ◽  
Time Reversal ◽  
Order Parameter ◽  
Muon Spin Rotation ◽  
Horizontal Line ◽  
Time Reversal Symmetry ◽  
Zero Field ◽  
Symmetry Protected ◽  
Line Node

AbstractThere is considerable evidence that the superconducting state of Sr2RuO4 breaks time reversal symmetry. In the experiments showing time reversal symmetry breaking, its onset temperature, TTRSB, is generally found to match the critical temperature, Tc, within resolution. In combination with evidence for even parity, this result has led to consideration of a dxz ± idyz order parameter. The degeneracy of the two components of this order parameter is protected by symmetry, yielding TTRSB = Tc, but it has a hard-to-explain horizontal line node at kz = 0. Therefore, s ± id and d ± ig order parameters are also under consideration. These avoid the horizontal line node, but require tuning to obtain TTRSB ≈ Tc. To obtain evidence distinguishing these two possible scenarios (of symmetry-protected versus accidental degeneracy), we employ zero-field muon spin rotation/relaxation to study pure Sr2RuO4 under hydrostatic pressure, and Sr1.98La0.02RuO4 at zero pressure. Both hydrostatic pressure and La substitution alter Tc without lifting the tetragonal lattice symmetry, so if the degeneracy is symmetry-protected, TTRSB should track changes in Tc, while if it is accidental, these transition temperatures should generally separate. We observe TTRSB to track Tc, supporting the hypothesis of dxz ± idyz order.

scholarly journals DMRG study of strongly interacting $\mathbb{Z}_2$ flatbands: a toy model inspired by twisted bilayer graphene

2020 ◽  
Vol 3 (2) ◽  
Author(s):  
Paul Eugenio ◽  
Ceren Dag
Keyword(s):  
Magnetic Field ◽  
Time Reversal ◽  
Ground States ◽  
Bilayer Graphene ◽  
Chern Number ◽  
Strong Interactions ◽  
Time Reversal Symmetry ◽  
Density Matrix Renormalization ◽  
Topological Quantum ◽  
Twisted Bilayer Graphene

Strong interactions between electrons occupying bands of opposite (or like) topological quantum numbers (Chern=\pm1=±1), and with flat dispersion, are studied by using lowest Landau level (LLL) wavefunctions. More precisely, we determine the ground states for two scenarios at half-filling: (i) LLL’s with opposite sign of magnetic field, and therefore opposite Chern number; and (ii) LLL’s with the same magnetic field. In the first scenario – which we argue to be a toy model inspired by the chirally symmetric continuum model for twisted bilayer graphene – the opposite Chern LLL’s are Kramer pairs, and thus there exists time-reversal symmetry (\mathbb{Z}_2ℤ2). Turning on repulsive interactions drives the system to spontaneously break time-reversal symmetry – a quantum anomalous Hall state described by one particle per LLL orbital, either all positive Chern |{++\cdots+}\rangle|++⋯+⟩ or all negative |{--\cdots-}\rangle|−−⋯−⟩. If instead, interactions are taken between electrons of like-Chern number, the ground state is an SU(2)SU(2) ferromagnet, with total spin pointing along an arbitrary direction, as with the \nu=1ν=1 spin-\frac{1}{2}12 quantum Hall ferromagnet. The ground states and some of their excitations for both of these scenarios are argued analytically, and further complimented by density matrix renormalization group (DMRG) and exact diagonalization.

scholarly journals Engineering the breaking of time-reversal symmetry in gate-tunable hybrid ferromagnet/topological insulator heterostructures

2018 ◽  
Vol 3 (1) ◽  
Author(s):  
Joon Sue Lee ◽  
Anthony Richardella ◽  
Robert D. Fraleigh ◽  
Chao-xing Liu ◽  
Weiwei Zhao ◽  
...  
Keyword(s):  
Topological Insulator ◽  
Time Reversal ◽  
Time Reversal Symmetry
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