850 research outputs found
Nonlinear magnetotransport shaped by Fermi surface topology and convexity in WTe2
The nature of Fermi surface defines the physical properties of conductors and
many physical phenomena can be traced to its shape. Although the recent
discovery of a current-dependent nonlinear magnetoresistance in spin-polarized
non-magnetic materials has attracted considerable attention in spintronics,
correlations between this phenomenon and the underlying fermiology remain
unexplored. Here, we report the observation of nonlinear magnetoresistance at
room temperature in a semimetal WTe2, with an interesting temperature-driven
inversion. Theoretical calculations reproduce the nonlinear transport
measurements and allow us to attribute the inversion to temperature-induced
changes in Fermi surface convexity. We also report a large anisotropy of
nonlinear magnetoresistance in WTe2, due to its low symmetry of Fermi surfaces.
The good agreement between experiments and theoretical modeling reveals the
critical role of Fermi surface topology and convexity on the nonlinear
magneto-response. These results lay a new path to explore ramifications of
distinct fermiology for nonlinear transport in condensed-matter
Quantum frequency doubling in the topological insulator Bi2Se3
The nonlinear Hall effect due to Berry curvature dipole (BCD) induces
frequency doubling, which was recently observed in time-reversal-invariant
materials. Here we report novel electric frequency doubling in the absence of
BCD on a surface of the topological insulator Bi2Se3 under zero magnetic field.
We observe that the frequency-doubling voltage transverse to the applied ac
current shows a threefold rotational symmetry, whereas it forbids BCD. One of
the mechanisms compatible with the symmetry is skew scattering, arising from
the inherent chirality of the topological surface state. We introduce the Berry
curvature triple, a high-order moment of the Berry curvature, to explain skew
scattering under the threefold rotational symmetry. Our work paves the way to
obtain a giant second-order nonlinear electric effect in high mobility quantum
materials, as the skew scattering surpasses other mechanisms in the clean
limit
Canted Spin Texture and Quantum Spin Hall Effect in WTe2
We report an unconventional quantum spin Hall phase in the monolayer
T-WTe, which exhibits hitherto unknown features in other
topological materials. The low-symmetry of the structure induces a canted spin
texture in the plane, which dictates the spin polarization of
topologically protected boundary states. Additionally, the spin Hall
conductivity gets quantized () with a spin quantization axis parallel
to the canting direction.
These findings are based on large-scale quantum simulations of the spin Hall
conductivity tensor and nonlocal resistances in multi-probe geometries using a
realistic tight-binding model elaborated from first-principle methods.
The observation of this canted quantum spin Hall effect, related to the
formation of topological edge states with nontrivial spin polarization, demands
for specific experimental design and suggests interesting alternatives for
manipulating spin information in topological materials.Comment: For comments please contact [email protected]
Charge-to-Spin Interconversion in Low-Symmetry Topological Materials
The spin polarization induced by the spin Hall effect (SHE) in thin films
typically points out of the plane. This is rooted not in a fundamental
constraint but on the specific symmetries of traditionally studied systems. We
theoretically show that the reduced symmetry of strong spin-orbit coupling
materials such as or enables new forms of
intrinsic SHE that produce large and robust in-plane spin polarizations.
Through quantum transport calculations on realistic device geometries with
disorder, we show that the charge-to-spin interconversion efficiency can reach
\% and is gate tunable. The numerically extracted spin
diffusion lengths () are long and yield large values of the figure
of merit nm, largely superior to
conventional SHE materials. These findings vividly emphasize how crystal
symmetry governs the intrinsic SHE, and how it can be exploited to broaden the
range and efficiency of spintronic functionalities.Comment: Any comments are appreciated. 6 pages + 4 figures. Supplemental
material available upon reques
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