Showing 1–5 of 5 results for author: K, G V

Strain-induced Ettingshausen effect in spin-orbit coupled noncentrosymmetric metals

Authors: Gautham Varma K, Azaz Ahmad, Gargee Sharma

Abstract: Elastic deformations couple with electronic degrees of freedom in materials to generate gauge fields that lead to interesting transport properties. Recently, it has been well studied that strain-induced chiral magnetic fields in Weyl semimetals lead to interesting magnetotransport induced by the chiral anomaly (CA). Recent studies have revealed that CA is not necessarily only a Weyl-node property,… ▽ More Elastic deformations couple with electronic degrees of freedom in materials to generate gauge fields that lead to interesting transport properties. Recently, it has been well studied that strain-induced chiral magnetic fields in Weyl semimetals lead to interesting magnetotransport induced by the chiral anomaly (CA). Recent studies have revealed that CA is not necessarily only a Weyl-node property, but is rather a Fermi surface property, and is also present in a more general class of materials, for example, in spin orbit-coupled noncentrosymmetric metals (SOC-NCMs). The interplay of strain, CA, and charge and thermomagnetic transport in SOC-NCMs, however, remains unexplored. Here we resolve this gap. Using a tight-binding model for SOC-NCMs, we first demonstrate that strain in SOC-NCMs induces anisotropy in the spin-orbit coupling and generates an axial electric field. Then, using the quasi-classical Boltzmann transport formalism with momentum-dependent intraband and interband scattering processes, we show that strain in the presence of external magnetic field can generate temperature gradients via the Nernst-Ettingshausen effect, whose direction and behavior depends the on interplay of multiple factors: the angle between the applied strain and magnetic field, the presence of the chiral anomaly, the Lorentz force, and the strength of interband scattering. We further reveal that time-reversal symmetry breaking in the presence of an external magnetic field generates the Berry-curvature-driven anomalous Ettingshausen effect, which is qualitatively distinct from the conventional Lorentz-force-driven counterpart. In light of recent and forthcoming theoretical and experimental advances in the field of SOC-NCMs, we find our study to be particularly timely and relevant. △ Less

Submitted 29 August, 2025; v1 submitted 18 August, 2025; originally announced August 2025.

Comments: 13 pages, 8 figures. Figure 2 slightly modified in this version

Chiral anomaly-induced nonlinear Hall effect in spin-orbit coupled noncentrosymmetric metals

Authors: Gautham Varma K, Mohd. Hashim Raza, Azaz Ahmad

Abstract: Recent studies have shown that chiral anomaly is not limited to Weyl semimetals (WSMs), but are also shown by a larger class of materials called spin orbit coupled noncentrosymmetric metals (SOC-NCMs),which has shed more insight into the origin of chiral anomaly as a Fermi surface property rather than a nodal property. In this study, we explore nonlinear transport responses in SOC-NCMswithin the f… ▽ More Recent studies have shown that chiral anomaly is not limited to Weyl semimetals (WSMs), but are also shown by a larger class of materials called spin orbit coupled noncentrosymmetric metals (SOC-NCMs),which has shed more insight into the origin of chiral anomaly as a Fermi surface property rather than a nodal property. In this study, we explore nonlinear transport responses in SOC-NCMswithin the framework of semiclassical dynamics, employing the Maxwell-Boltzmann transport theory augmented by charge conservation and momentum-dependent scattering processes. We take into account both non-magnetic and magnetic impurity scattering mechanisms. We demonstrate that the chiral-anomaly-induced nonlinear Hall (CNLH) response exhibits a characteristic quadratic dependence on the applied magnetic field and remains negative for both types of impurities. We find that magnetic scatterers leading to enhanced/suppressed interband scattering modifies the magnitude of the signal, but does not affect its qualitative behavior. In contrast, the presence of tilt in the band dispersion induces a pronounced anisotropic response, including a magnetic-field-direction dependent sign reversal that can be categorized into weak and strong regimes. Furthermore, the CNLH response shows substantial directional anisotropy governed by the relative orientation of the external magnetic field and the tilt vector. Our findings will be helpful in designing the experimental setup to get direction-dependent conductivity, which can be tuned externally with the help of magnetic impurity sites. △ Less

Submitted 6 January, 2026; v1 submitted 1 August, 2025; originally announced August 2025.

Comments: Updated version

Journal ref: Phys. Rev. B 113, 035112(2026)

Nonlinear anomalous Hall effect in three-dimensional chiral fermions

Authors: Azaz Ahmad, Gautham Varma K., Gargee Sharma

Abstract: Chiral fermionic quasiparticles emerge in certain quantum condensed matter systems such as Weyl semimetals, topological insulators, and spin-orbit coupled noncentrosymmetric metals. Here, a comprehensive theory of the chiral anomaly-induced nonlinear anomalous Hall effect (CNLAHE) is developed for three-dimensional chiral quasiparticles, advancing previous models by rigorously including momentum-d… ▽ More Chiral fermionic quasiparticles emerge in certain quantum condensed matter systems such as Weyl semimetals, topological insulators, and spin-orbit coupled noncentrosymmetric metals. Here, a comprehensive theory of the chiral anomaly-induced nonlinear anomalous Hall effect (CNLAHE) is developed for three-dimensional chiral quasiparticles, advancing previous models by rigorously including momentum-dependent chirality-preserving and chirality-breaking scattering processes and global charge conservation. Focusing on two specific systems-Weyl semimetals (WSMs) and spinorbit coupled non-centrosymmetric metals (SOC-NCMs), we uncover that the nonlinear anomalous Hall conductivity in WSMs shows nonmonotonic behavior with the Weyl cone tilt and experiences a "strong-sign-reversal" with increasing internode scattering, diverging from earlier predictions. For SOC-NCMs, where nonlinear anomalous Hall conductivity has been less explored, we reveal that unlike WSM, the orbital magnetic moment alone can drive a large CNLAHE with distinctive features: the CNLAH conductivity remains consistently negative regardless of interband scattering intensity and exhibits a quadratic dependence on the magnetic field, contrasting the linear dependence in WSMs. Furthermore, we discover that in SOC-NCMs the Zeeman coupling of the magnetic field acts like an effective tilt term which can further enhance the CNLAH current. These findings offer fresh insights into the nonlinear transport dynamics of chiral quasiparticles and can be verified in upcoming experiments on such materials. △ Less

Submitted 4 September, 2024; originally announced September 2024.

Geometry, anomaly, topology, and transport in Weyl fermions

Authors: Azaz Ahmad, Gautham Varma K., Gargee Sharma

Abstract: Weyl fermions are one of the simplest objects that link ideas in geometry and topology to highenergy physics and condensed matter physics. Although the existence of Weyl fermions as elementary particles remains dubious, there is mounting evidence of their existence as quasiparticles in certain condensed matter systems. Such systems are termed Weyl semimetals (WSMs). Needless to say, WSMs have emer… ▽ More Weyl fermions are one of the simplest objects that link ideas in geometry and topology to highenergy physics and condensed matter physics. Although the existence of Weyl fermions as elementary particles remains dubious, there is mounting evidence of their existence as quasiparticles in certain condensed matter systems. Such systems are termed Weyl semimetals (WSMs). Needless to say, WSMs have emerged as a fascinating class of materials with unique electronic properties, offering a rich playground for both fundamental research and potential technological applications. This review examines recent advancements in understanding electron transport in Weyl semimetals (WSMs). We begin with a pedagogical introduction to the geometric and topological concepts critical to understanding quantum transport in Weyl fermions. We then explore chiral anomaly (CA), a defining feature of WSMs, and its impact on transport phenomena such as longitudinal magnetoconductance (LMC) and the planar Hall effect (PHE). The Maxwell-Boltzmann transport theory extended beyond the standard relaxation-time approximation is then discussed in the context of Weyl fermions, which is used to evaluate various transport properties. Attention is also given to the effects of strain-induced gauge fields and external magnetic fields in both time-reversal broken and inversion asymmetric inhomogeneous WSMs. The review synthesizes theoretical insights, experimental observations, and numerical simulations to provide a comprehensive understanding of the complex transport behaviors in WSMs, aiming to bridge the gap between theoretical predictions and experimental verification. △ Less

Submitted 3 June, 2024; originally announced June 2024.

Comments: Invited review. Comments welcome

Magnetotransport in spin-orbit coupled noncentrosymmetric and Weyl metals

Authors: Gautham Varma K, Azaz Ahmad, Sumanta Tewari, G. Sharma

Abstract: Recently, chiral anomaly (CA) has been proposed to occur in spin-orbit coupled noncentrosymmetric metals (SOC-NCMs), motivating CA to be a Fermi surface property rather than a Weyl node property. Although the nature of the anomaly is similar in both SOC-NCMs and Weyl systems, here we point out significant fundamental differences between the two. We show that the different nature of the orbital mag… ▽ More Recently, chiral anomaly (CA) has been proposed to occur in spin-orbit coupled noncentrosymmetric metals (SOC-NCMs), motivating CA to be a Fermi surface property rather than a Weyl node property. Although the nature of the anomaly is similar in both SOC-NCMs and Weyl systems, here we point out significant fundamental differences between the two. We show that the different nature of the orbital magnetic moment (OMM) in the two systems leads to non-trivial consequences -- particularly the sign of the longitudinal magnetoconductance always remains positive in a SOC non-centrosymmetric metal, unlike a Weyl metal that displays either sign. Furthermore,we investigate the planar Hall effect and the geometrical contribution to the Hall effect in the two systems and point out significant differences in the two systems. We conduct our analysis for magnetic and non-magnetic impurities, making our study important in light of current and upcoming experiments in both SOC-NCMs and Weyl metals. △ Less

Submitted 30 October, 2023; originally announced October 2023.