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Register a new userNonlinear magnetotransport shaped by Fermi surface topology and convexity in WTe2
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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.
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While recent advances in band theory and sample growth have expanded the series of extremely large magnetoresistance (XMR) semimetals in transition metal dipnictides $TmPn_2$ ($Tm$ = Ta, Nb; $Pn$ = P, As, Sb), the experimental study on their electronic structure and the origin of XMR is still absent. Here, using angle-resolved photoemission spectroscopy combined with first-principles calculations and magnetotransport measurements, we performed a comprehensive investigation on MoAs$_2$, which is isostructural to the $TmPn_2$ family and also exhibits quadratic XMR. We resolve a clear band structure well agreeing with the predictions. Intriguingly, the unambiguously observed Fermi surfaces (FSs) are dominated by an open-orbit topology extending along both the [100] and [001] directions in the three-dimensional Brillouin zone. We further reveal the trivial topological nature of MoAs$_2$ by bulk parity analysis. Based on these results, we examine the proposed XMR mechanisms in other semimetals, and conclusively ascribe the origin of quadratic XMR in MoAs$_2$ to the carriers motion on the FSs with dominant open-orbit topology, innovating in the understanding of quadratic XMR in semimetals.
For many materials, a precise knowledge of their dispersion spectra is insufficient to predict their ordered phases and physical responses. Instead, these materials are classified by the geometrical and topological properties of their wavefunctions. A key challenge is to identify and implement experiments that probe or control these quantum properties. In this review, we describe recent progress in this direction, focusing on nonlinear electromagnetic responses that arise directly from quantum geometry and topology. We give an overview of the field by discussing new theoretical ideas, groundbreaking experiments, and the novel materials that drive them. We conclude by discussing how these techniques can be combined with new device architectures to uncover, probe, and ultimately control novel quantum phases with emergent topological and correlated properties.
We report on a systematic study of Hall effect using high quality single crystals of type-II Weyl semimetal WTe2 with the applied magnetic field B//c. The residual resistivity ratio of 1330 and the large magnetoresistance of 1.5times10^6 % in 9 T at 2 K, being in the highest class in the literature, attest to their high quality. Based on a simple two-band model, the densities (n_e and n_h) and mobilities (mu_e and mu_h) for electron and hole carriers have been uniquely determined combining both Hall- and electrical-resistivity data. The difference between ne and nh is ~1% at 2 K, indicating that the system is in an almost compensated condition. The negative Hall resistivity growing rapidly below ~20 K is due to a rapidly increasing mu_h/mu_e approaching one. Below 3 K in a low field region, we found the Hall resistivity becomes positive, reflecting that mu_h/mu_e finally exceeds one in this region. These anomalous behaviors of the carrier densities and mobilities might be associated with the existence of a Lifshitz transition and/or the spin texture on the Fermi surface.
Andreev reflection (AR) refers to the electron-hole conversion at the normal metal-superconductor interface. In a three-dimensional metal with spherical Fermi surface, retro (specular) AR can occur with the sign reversal of all three (a single) components of particle velocity. Here, we predict a novel type of AR with the inversion of two velocity components, dubbed anomalous-trajectory Andreev reflection (AAR), which can be realized in a class of materials with torus-shaped Fermi surface, such as doped nodal line semimetals. For its toroidal circle perpendicular to the interface, the Fermi torus doubles the AR channels and generates multiple AR processes. In particular, the AAR and retro AR are found to dominate electron transport in the light and heavy doping regimes, respectively. We show that the AAR visibly manifests as a ridge structure in the spatially resolved nonlocal conductance, in contrast to the peak structure for the retro AR. Our work opens a new avenue for the AR spectroscopy and offers a clear transport signature of torus-shaped Fermi surface.
We report a quantum magnetotransport signature of a change in Fermi surface topology in the Rashba semiconductor BiTeI with systematic tuning of the Fermi level $E_F$. Beyond the quantum limit, we observe a marked increase/decrease in electrical resistivity when $E_F$ is above/below the Dirac node that we show originates from the Fermi surface topology. This effect represents a measurement of the electron distribution on the low-index ($n=0,-1$) Landau levels and is uniquely enabled by the finite bulk $k_z$ dispersion along the $c$-axis and strong Rashba spin-orbit coupling strength of the system. The Dirac node is independently identified by Shubnikov-de Haas oscillations as a vanishing Fermi surface cross section at $k_z=0$. Additionally we find that the violation of Kohlers rule allows a distinct insight into the temperature evolution of the observed quantum magnetoresistance effects.
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