scholarly journals Giant spontaneous Hall effect in a nonmagnetic Weyl–Kondo semimetal

2021 ◽  
Vol 118 (8) ◽  
pp. e2013386118 ◽  
Author(s):  
Sami Dzsaber ◽  
Xinlin Yan ◽  
Mathieu Taupin ◽  
Gaku Eguchi ◽  
Andrey Prokofiev ◽  
...  
Keyword(s):  
Hall Effect ◽  
Time Reversal ◽  
Anomalous Hall Effect ◽  
Time Reversal Symmetry ◽  
Strong Electron ◽  
Band Theory ◽  
Fermion Systems ◽  
Topological Quantum ◽  
Interacting Systems ◽  
Nontrivial Topology

Nontrivial topology in condensed-matter systems enriches quantum states of matter to go beyond either the classification into metals and insulators in terms of conventional band theory or that of symmetry-broken phases by Landau’s order parameter framework. So far, focus has been on weakly interacting systems, and little is known about the limit of strong electron correlations. Heavy fermion systems are a highly versatile platform to explore this regime. Here we report the discovery of a giant spontaneous Hall effect in the Kondo semimetal Ce3Bi4Pd3 that is noncentrosymmetric but preserves time-reversal symmetry. We attribute this finding to Weyl nodes—singularities of the Berry curvature—that emerge in the immediate vicinity of the Fermi level due to the Kondo interaction. We stress that this phenomenon is distinct from the previously detected anomalous Hall effect in materials with broken time-reversal symmetry; instead, it manifests an extreme topological response that requires a beyond-perturbation-theory description of the previously proposed nonlinear Hall effect. The large magnitude of the effect in even tiny electric and zero magnetic fields as well as its robust bulk nature may aid the exploitation in topological quantum devices.

scholarly journals Loop Currents and Anomalous Hall Effect from Time-Reversal Symmetry-Breaking Superconductivity on the Honeycomb Lattice

2019 ◽  
Vol 9 (3) ◽  
Author(s):  
P. M. R. Brydon ◽  
D. S. L. Abergel ◽  
D. F. Agterberg ◽  
Victor M. Yakovenko
Keyword(s):  
Symmetry Breaking ◽  
Hall Effect ◽  
Time Reversal ◽  
Anomalous Hall Effect ◽  
Honeycomb Lattice ◽  
Time Reversal Symmetry ◽  
Loop Currents

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 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 Crystal time-reversal symmetry breaking and spontaneous Hall effect in collinear antiferromagnets

2020 ◽  
Vol 6 (23) ◽  
pp. eaaz8809 ◽  
Author(s):  
Libor Šmejkal ◽  
Rafael González-Hernández ◽  
T. Jungwirth ◽  
J. Sinova
Keyword(s):  
Symmetry Breaking ◽  
Hall Effect ◽  
Time Reversal ◽  
Spin Structure ◽  
Transverse Velocity ◽  
Time Reversal Symmetry ◽  
Large Magnitude ◽  
Low Dissipation ◽  
Magnetization Density ◽  
Symmetry Breaking Phenomena

Electrons, commonly moving along the applied electric field, acquire in certain magnets a dissipationless transverse velocity. This spontaneous Hall effect, found more than a century ago, has been understood in terms of the time-reversal symmetry breaking by the internal spin structure of a ferromagnetic, noncolinear antiferromagnetic, or skyrmionic form. Here, we identify previously overlooked robust Hall effect mechanism arising from collinear antiferromagnetism combined with nonmagnetic atoms at noncentrosymmetric positions. We predict a large magnitude of this crystal Hall effect in a room temperature collinear antiferromagnet RuO2 and catalog, based on symmetry rules, extensive families of material candidates. We show that the crystal Hall effect is accompanied by the possibility to control its sign by the crystal chirality. We illustrate that accounting for the full magnetization density distribution instead of the simplified spin structure sheds new light on symmetry breaking phenomena in magnets and opens an alternative avenue toward low-dissipation nanoelectronics.

scholarly journals Natural van der Waals heterostructural single crystals with both magnetic and topological properties

2019 ◽  
Vol 5 (11) ◽  
pp. eaax9989 ◽  
Author(s):  
Jiazhen Wu ◽  
Fucai Liu ◽  
Masato Sasase ◽  
Koichiro Ienaga ◽  
Yukiko Obata ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Hall Effect ◽  
Exchange Coupling ◽  
Van Der Waals ◽  
Surface States ◽  
Anomalous Hall Effect ◽  
Topological Quantum ◽  
Magnetic Layers ◽  
Topological Surface ◽  
Ferromagnetic Hysteresis

Heterostructures having both magnetism and topology are promising materials for the realization of exotic topological quantum states while challenging in synthesis and engineering. Here, we report natural magnetic van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n that exhibit controllable magnetic properties while maintaining their topological surface states. The interlayer antiferromagnetic exchange coupling is gradually weakened as the separation of magnetic layers increases, and an anomalous Hall effect that is well coupled with magnetization and shows ferromagnetic hysteresis was observed below 5 K. The obtained homogeneous heterostructure with atomically sharp interface and intrinsic magnetic properties will be an ideal platform for studying the quantum anomalous Hall effect, axion insulator states, and the topological magnetoelectric effect.

scholarly journals Disorder-induced nonlinear Hall effect with time-reversal symmetry

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Z. Z. Du ◽  
C. M. Wang ◽  
Shuai Li ◽  
Hai-Zhou Lu ◽  
X. C. Xie
Keyword(s):  
Hall Effect ◽  
Time Reversal ◽  
Time Reversal Symmetry

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.

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