scholarly journals Giant nonlinear Hall effect in twisted bilayer WTe2

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Zhihai He ◽  
Hongming Weng
Keyword(s):  
Fermi Level ◽  
Hall Effect ◽  
Time Reversal ◽  
Large Amplitude ◽  
Second Order ◽  
Time Reversal Symmetry ◽  
Inversion Symmetry ◽  
Berry Curvature ◽  
High Tunability

AbstractIn a system with broken inversion symmetry, a second-order nonlinear Hall effect can survive even in the presence of time-reversal symmetry. In this work, we show that a giant nonlinear Hall effect can exist in twisted bilayer WTe2 system. The Berry curvature dipole of twisted bilayer WTe2 (θ = 29.4°) can reach up to ~1400 Å, which is much larger than that in previously reported nonlinear Hall systems. In twisted bilayer WTe2 system, there exist abundant band anticrossings and band inversions around the Fermi level, which brings a complicated distribution of Berry curvature, and leads to the nonlinear Hall signals that exhibit dramatically oscillating behavior in this system. Its large amplitude and high tunability indicate that the twisted bilayer WTe2 can be an excellent platform for studying the nonlinear Hall effect.

scholarly journals Topological thermal Hall effect due to Weyl magnons

2018 ◽  
Vol 96 (11) ◽  
pp. 1216-1223 ◽  
Author(s):  
S.A. Owerre
Keyword(s):  
Hall Effect ◽  
Time Reversal ◽  
Low Temperatures ◽  
Three Dimensional ◽  
Zero Magnetic Field ◽  
Time Reversal Symmetry ◽  
Frustrated Magnets ◽  
Berry Curvature ◽  
Theoretical Evidence ◽  
Distribution Distance

We present the first theoretical evidence of zero magnetic field topological (anomalous) thermal Hall effect due to Weyl magnons in stacked noncoplanar frustrated kagomé antiferromagnets. The Weyl magnons in this system result from macroscopically broken time-reversal symmetry by the scalar spin chirality of noncoplanar chiral spin textures. Most importantly, they come from the lowest excitation, therefore they can be easily observed experimentally at low temperatures due to the population effect. Similar to electronic Weyl nodes close to the Fermi energy, Weyl magnon nodes at the lowest excitation are the most important. Indeed, we show that the topological (anomalous) thermal Hall effect in this system arises from nonvanishing Berry curvature due to Weyl magnon nodes at the lowest excitation, and it depends on their distribution (distance) in momentum space. The present result paves the way to directly probe low excitation Weyl magnons and macroscopically broken time-reversal symmetry in three-dimensional frustrated magnets with the anomalous thermal Hall effect.

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 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 Nonreciprocal thermal transport in a multiferroic helimagnet

2020 ◽  
Vol 6 (40) ◽  
pp. eabd3703
Author(s):  
Yuji Hirokane ◽  
Yoichi Nii ◽  
Hidetoshi Masuda ◽  
Yoshinori Onose
Keyword(s):  
Symmetry Breaking ◽  
Time Reversal ◽  
Thermal Transport ◽  
Condensed Matter ◽  
Electric Polarization ◽  
Time Reversal Symmetry ◽  
Inversion Symmetry ◽  
Vector Product ◽  
Thermal Rectification ◽  
Longitudinal Thermal Conductivity

Breaking of spatial inversion symmetry induces unique phenomena in condensed matter. In particular, by combining this symmetry with magnetic fields or another type of time-reversal symmetry breaking, noncentrosymmetric materials can be made to exhibit nonreciprocal responses, which are responses that differ for rightward and leftward stimuli. However, the effect of spatial inversion symmetry breaking on thermal transport in uniform media remains to be elucidated. Here, we show nonreciprocal thermal transport in the multiferroic helimagnet TbMnO3. The longitudinal thermal conductivity depends on whether the thermal current is parallel or antiparallel to the vector product of the electric polarization and magnetization. This phenomenon is thermal rectification that is controllable with external fields in a uniform crystal. This discovery may pave the way to thermal diodes with controllability and scalability.

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
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