arXiv subjects

Sumanta Tewari

Publications and source records attributed to Sumanta Tewari.

At least 37 records · Page 2Linked to original sources

arXiv2023

Hydrogen induces chiral conduction channels in the topological magnet

Chirality, a characteristic handedness that distinguishes 'left' from 'right', cuts widely across all of nature$^1$, from the structure of DNA$^2$ to opposite chirality of particles and antiparticles$^3$. In condensed matter chiral fermions have been identified in Weyl semimetals$^4$ through their unconventional electrodynamics arising from 'axial' charge imbalance between chiral Weyl nodes of topologically nontrivial electronic bands. Up to now it has been challenging or impossible to create transport channels of Weyl fermions in a single material that could be easily configured for advancing chiral logic or spintronics$^{5,6}$. Here we generate chirality-directed conduction channels in inversion-symmetric Weyl ferromagnet (FM) $MnSb_2Te_4$, emergent from a deep connection between chirality in reciprocal and real space. We alter the bandstructure on-demand with an intake and a subsequent release of ionic hydrogen ($H^+$) $-$ a process we show to induce the tilt and rotation of Weyl bands. The transformed Weyl FM states feature a doubled Curie temperature $\geq50K$ and an enhanced angular transport chirality synchronous with a rare field-antisymmetric longitudinal resistance $-$ a low-field tunable 'chiral switch' that roots in the interplay of Berry curvature$^7$, chiral anomaly$^8$ and hydrogen-engendered mutation of Weyl nodes.

cond-mat.mtrl-sci↗

arXiv2023

Magnetochiral anisotropy-induced nonlinear planar Hall effect in Topological Insulator surface states

In an intriguing recent experiment, it has been found that the two-dimensional (2D) surface states of a three-dimensional (3D) strong topological insulator (TI) support a non-zero Hall voltage transverse to an applied electric field even when the external magnetic field is in the plane (i.e., the in-plane Lorentz force vanishes). This so-called planar Hall effect (PHE) of TI surface states is found to be non-linear, i.e., the Hall voltage scales quadratically with the applied electric field and linearly with the in-plane magnetic field. In this paper, we derive the non-linear PHE for strong topological insulator surface states and show that the derivations contained in the previous literature are incomplete, which can lead to quantitative or even in some cases qualitative errors in the estimates for the nonlinear planar Hall resistance. We derive the complete expressions for the non-linear planar Hall currents for TI surface states with broken particle-hole symmetry and provide results for different regimes of the surface state Hamiltonian which can be compared with future experiments.

cond-mat.mes-hall↗

arXiv2023

Anisotropic positive linear and sub-linear magnetoresistivity in the cubic type-II Dirac metal Pd$_3$In$_7$

We report a transport study on Pd$_3$In$_7$ which displays multiple Dirac type-II nodes in its electronic dispersion. Pd$_3$In$_7$ is characterized by low residual resistivities and high mobilities, which are consistent with Dirac-like quasiparticles. For an applied magnetic field $(μ_{\text{0}} H)$ having a non-zero component along the electrical current, we find a large, positive, and linear in $μ_{\text{0}} H$ longitudinal magnetoresistivity (LMR). The sign of the LMR and its linear dependence deviate from the behavior reported for the chiral-anomaly-driven LMR in Weyl semimetals. Interestingly, such anomalous LMR is consistent with predictions for the role of the anomaly in type-II Weyl semimetals. In contrast, the transverse or conventional magnetoresistivity (CMR for electric fields $\textbf{E} \bot μ_{\text{0}} \textbf{H}$) is large and positive, increasing by $10^3-10^4$ \% as a function of $μ_{\text{0}}H$ while following an anomalous, angle-dependent power law $ρ_{\text{xx}}\propto (μ_{\text{0}}H)^n$ with $n(θ) \leq 1$. The order of magnitude of the CMR, and its anomalous power-law, is explained in terms of uncompensated electron and hole-like Fermi surfaces characterized by anisotropic carrier scattering likely due to the lack of Lorentz invariance.

cond-mat.mes-hall↗

arXiv2023

Magnetotransport in spin-orbit coupled noncentrosymmetric and Weyl metals

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.

cond-mat.mes-hall↗

arXiv2023

Magnetochiral anisotropy-induced nonlinear Hall effect in spin-orbit coupled Rashba conductors

We theoretically predict the existence of a non-zero magnetochiral anisotropy-induced nonlinear Hall effect or a second harmonic Hall voltage transverse to an applied current in spin-orbit coupled Rashba conductors in the presence of an in-plane magnetic field B. This is distinct from the Berry curvature dipole (BCD)-induced nonlinear Hall effect in systems with non-trivial bandstructure because the former requires broken time-reversal symmetry while the BCD-induced effect is non-zero even in time-reversal symmetric systems. This result is independent of the existence of other types of interactions, such as hexagonal warping or cubic Dresselhaus interactions. We find that for E||B, the magnitude of the nonlinear Hall current flowing in a direction perpendicular to the applied electric field is exactly 1/3 of the magnitude of the non-linear rectification current responsible for magnetoresistance parallel to the applied electric field obtained in the E\perp B configuration.

cond-mat.mes-hall↗

arXiv2023

Symmetric, off-diagonal, resistance from rotational symmetry breaking in graphene-WSe$_2$ heterostructure: prediction for a large magic angle in a Moire system

We show that any two-dimensional system with a non-zero \textit{symmetric} off-diagonal component of the resistance matrix, $R_{xy}=R_{yx} \neq 0$, must have the in-plane rotational symmetry broken down to $C_2$. Such a resistance response is Ohmic, and is different from the Hall response which is the \textit{anti-symmetric} part of the resistance tensor, $R_{xy}=-R_{yx}$, is rotationally symmetric in the 2D plane, and requires broken time-reversal symmetry. We show how a minute amount of strain due to lattice mismatch - less than $1 \%$ - can produce a vastly exaggerated symmetric off-diagonal response - $\frac{R_{xy}}{R_{xx}} \sim 20\%$ - because of the momentum matching constraints in a Moire system. Our results help explain an important new transport experiment on graphene-WSe$_2$ heterostructures, as well as are relevant for other experimental systems with rotational symmetry breaking, such as nematic systems and Kagome charge density waves. Additionally, our work predicts an example of a `magic' angle, $θ\sim 27^0$, in a Moire system which is a significant fraction of $π$. Our prediction that the anomalous resistance anisotropy occurs at a large value of magic angle, in contrast to known examples of magic angle transport anomalies that are small fractions of $π$, can be experimentally tested in graphene-WSe$_2$ heterostructures.

cond-mat.mes-hall↗

arXiv2023

Quantum oscillations of the nonlinear planar effects signifying chiral anomaly in Weyl Semimetals

In view of searching the signature of the celebrated chiral anomaly (CA) in Weyl semimetals (WSMs) in ongoing experiments, quantum oscillation in linear response regime has been considered as an important signature in the magneto transports in WSMs, due to its unique relation to CA. Investigating the nonlinear planar effects (NPEs) starting from the semiclassical regime to the ultra-quantum limit within the framework of Boltzmann transport theory incorporating Landau quantization, we here propose the quantum oscillations in NPEs can serve as a robust signature of CA in WSMs. By obtaining analytical expressions, we show that the quantum oscillations of the nonlinear effects exhibit two different period scales in 1/B (B is the magnetic field) compared to the linear responses where only one period scale exists. We find that these quantum oscillations in NPEs are attributed to the deviation of chiral chemical potential (CCP), which is proportional to the finite band tilt as well as transverse electric field and therefore, directly linked to CA in WSMs. In addition, we also show that the CA-induced nonlinear magneto conductivity is linear and independent in the magnetic field in the semiclassical and ultraquantum regimes, respectively. We conclude that the proposed behaviors of NPEs in different regimes uniquely signify the existence of CA and therefore, can serve as a probe of identifying CA in WSMs in experiments.

cond-mat.mes-hall↗

arXiv2022

Longitudinal magnetoconductance and the planar Hall conductance in inhomogeneous Weyl semimetals

Elastic deformations (strain) couple to the electronic degrees of freedom in Weyl semimetals as an axial magnetic field (chiral gauge field), which in turn affects their impurity dominated diffusive transport. Here we study the longitudinal magnetoconductance (LMC) in the presence of strain, Weyl cone tilt, and finite intervalley scattering, taking into account the momentum dependence of the scattering processes (both internode and intranode), as well as charge conservation. We show that strain induced chiral gauge field results in `strong sign-reversal' of the LMC, which is characterized by the reversal of orientation of the magnetoconductance parabola with respect to the magnetic field. On the other hand, external magnetic field results in `strong sign-reversal', only for sufficiently strong intervalley scattering. When both external and chiral gauge fields are present, we observe both strong and weak sign-reversal, where in the case of weak sign-reversal, the rise and fall of magnetoconductivity depends on the direction of the magnetic field and/or the chiral gauge field, and is not correlated with the orientation of the LMC parabola. The combination of the two fields is shown to generate striking features in the LMC phase diagram as a function of various parameters such as tilt, strain, and intervalley scattering. We also study the effect of strain induced chiral gauge field on the planar Hall conductance and highlight its distinct features that can be probed experimentally.

cond-mat.mes-hall↗

arXiv2022

Partially-separated Majorana modes in a disordered medium

Focusing on the implications of recent experiments on Majorana zero modes in semiconductor-superconductor (SM-SC) heterostructures, we critically examine the quantization of the zero-bias differential conductance as a possible unambiguous signature of Majorana physics in the presence of disorder. By numerically calculating the zero-bias conductance (ZBC) maps as function of Zeeman splitting and chemical potential for different disorder realizations, we show that the presence of quantized "islands" characterized by a ZBC value (approximately) equal to $2e^2/h$ and having a finite area/volume in a multi-dimensional parameter space represents a unique signature of Majorana physics supporting Majorana zero modes (MZMs) or partially-separated Majorana modes (ps-MMs). We find that in the presence of strong disorder Majorana physics only emerges locally and gives rise to ps-MMs, which, in turn, generate small quantized islands when one of the Majorana modes is located at the end of the system. Observing these small islands may require sample selection and the systematic scanning of a large volume in the control parameter space. Upon decreasing disorder, the quantized islands increase in size and eventually coalesce into large topological regions. Since the presence of MZMs localized at the opposite ends of the system is typically associated with large quantized islands, looking for MZM-induced edge-to-edge correlations is premature in the absence of convincing experimental evidence for (even small) quantized islands. We conclude that the observation of quantized islands demonstrates unambiguously the presence of the key ingredients necessary for Majorana physics, provides an excellent diagnostic tool for evaluating the disorder strength, and, consequently, represents the next natural milestone in the Majorana search.

cond-mat.mes-hall↗

arXiv2022

Chiral anomaly induced nonlinear Nernst and thermal Hall effects in Weyl semimetals

Chiral anomaly or Adler-Bell-Jackiw anomaly in Weyl semimetals (WSMs) has a significant impact on the electron transport behaviors, leading to remarkable longitudinal or planar electrical and thermoelectric transport phenomena in the presence of electromagnetic gauge fields. These phenomena are consequences of the imbalanced chiral charge and energy induced by chiral anomaly in the presence of parallel electric ($\mathbf{E}$) and magnetic ($\mathbf{B}$) fields ($\mathbf{E \cdot B }\neq 0$) or $(\mathbf{B \cdot \nabla }T\neq 0)$ ($\mathbf{\nabla}T$ is the thermal gradient). We here propose another two fascinating transport properties, namely, the nonlinear planar Nernst effect and nonlinear planar thermal Hall effect induced by chiral anomaly in the presence of $\mathbf{B \cdot \nabla}T\neq 0$ in WSMs. Using the semiclassical Boltzmann transport theory, we derive the analytical expressions for the chiral anomaly induced nonlinear Nernst and thermal Hall transport coefficients and also evaluate the fundamental mathematical relations among them in the nonlinear regime. The formulas we find in this current work are consistent with that predicted for the nonlinear anomalous electrical and thermoelectric effects induced by Berry curvature dipole recently. Additionally, in contrast to the recent work, by utilizing the lattice Weyl Hamiltonian with intrinsic chiral chemical potential, we find that the chiral anomaly induced nonlinear planar effects can exist even for a pair of oppositely tilted or non-tilted Weyl cones in both time reversal and inversion broken WSMs. The chiral anomaly induced nonlinear planar effects predicted here along with the related parameter dependencies are hence possible to be realized in realistic WSMs in experiment.

cond-mat.mes-hall↗

arXiv2022

Revisiting magnetotransport in Weyl semimetals

A series of recent papers have claimed that intranode scattering, alone, can contribute to positive longitudinal magnetoconductance (LMC) due to chiral anomaly (CA) in Weyl semimetals (WSMs). We revisit the problem of CA induced LMC in WSMs, and show that intranode scattering, by itself, does not result in enhancement of LMC. In the limit of zero internode scattering, chiral charge must remain conserved, which is shown to actually decrease LMC. Only in the presence of a non-zero internode scattering (however weak), one obtains a positive LMC due to non-conservation of chiral charge. Even weak internode scattering suffices in generating positive LMC, since it redistributes charges across both the nodes, although on a time scale larger than that of the intranode scattering. Furthermore, our calculations reveal that, in contrast to recent works, in inhomogeneous WSMs strain induced axial magnetic field $B_5$, by itself, leads to negative longitudinal magnetoconductance and a negative planar Hall conductance.

cond-mat.mes-hall↗

arXiv2021

Topological properties of multilayer magnon insulators

Two-dimensional magnetic insulators can be promising hosts for topological magnons. In this study, we show that ABC-stacked honeycomb lattice multilayers with alternating Dzyaloshinskii-Moriya interaction (DMI) reveal a rich topological magnon phase diagram. Based on our bandstructure and Berry curvature calculations, we demonstrate jumps in the thermal Hall behavior that corroborate with topological phase transitions triggered by adjusting the DMI and interlayer coupling. We connect the phase diagram of generic multilayers to a bilayer and a trilayer system. We find an even-odd effect amongst the multilayers where the even layers show no jump in thermal Hall conductivity, but the odd layers do. We also observe the presence of topological proximity effect in our trilayer. Our results offer new schemes to manipulate Chern numbers and their measurable effects in topological magnonic systems.

cond-mat.mes-hall↗

arXiv2021

Nonlinear transport in Weyl semimetals induced by Berry curvature dipole

Topological Weyl semimetals (WSMs) have been predicted to be excellent candidates for detecting Berry curvature dipole (BCD) and the related non-linear effects in electronics and optics due to the large Berry curvature concentrated around the Weyl nodes. And yet, linearized models of isolated tilted Weyl cones only realize a diagonal non-zero BCD tensor which sum to zero in the model of WSM with multiple Weyl nodes in the presence of mirror symmetry. On the other hand, recent \textit{ab initio} work has found that realistic WSMs like TaAs-type or MoTe$_2$-type compounds, which have mirror symmetry, indeed show an off-diagonal BCD tensor with an enhanced magnitude for its non-zero components. So far, there is a lack of theoretical work addressing this contradiction for 3D WSMs. In this paper, we systematically study the BCD in 3D WSMs using lattice Weyl Hamiltonians, which go beyond the linearized models. We find that the non-zero BCD and its related important features for these WSMs do not rely on the contribution from the Weyl nodes. Instead, they are dependent on the part of the Fermi surface that lies \textit{between} the Weyl nodes, in the region of the reciprocal space where neighboring Weyl cones overlap. For large enough chemical potential such Fermi surfaces are present in the lattice Weyl Hamiltonians as well as in the realistic WSMs. We also show that, a lattice Weyl Hamitonian with a non-zero chiral chemical potential for the Weyl cones can also support dips or peaks in the off-diagonal components of the BCD tensor near the Weyl nodes themselves, consistent with recent \textit{ab initio} work.

cond-mat.mes-hall↗

arXiv2021

Anomalous transport in Kane fermions

Kane fermions are characterized by a linear Dirac cone intersecting with a flat band, resembling a pseudo-spin-1 Dirac semimetal. Similar to relativistic Dirac fermions, Kane fermions satisfy a linear energy-momentum relation and can be classified as being pseudo-relativistic. Though not protected by symmetry or by topology, Kane fermions can emerge by suitable band engineering, for example, in mercury-telluride compounds. Here we study the Berry curvature of Kane fermions that emerges in the presence of time-reversal symmetry breaking weak Zeeman fields. We discuss the related anomalous transport coefficients and discuss the anisotropy in these responses that can be probed in experiments.

cond-mat.mes-hall↗

arXiv2021

Stabilizing Topological Superfluidity of Lattice Fermions

Attractive interaction between spinless fermions in a two-dimensional lattice drives the formation of a topological superfluid. But the topological phase is dynamically unstable towards phase separation when the system has a high density of states and large interaction strength. This limits the critical temperature to an experimentally challenging regime where, for example, even ultracold atoms and molecules in optical lattices would struggle to realize the topological superfluid. We propose that the introduction of a weaker longer-range repulsion, in addition to the short-range attraction between lattice fermions, will suppress the phase separation instability. Taking the honeycomb lattice as an example, we show that our proposal significantly enlarges the stable portion of the topological superfluid phase and increases the critical temperature by an order of magnitude. Our work opens a route to enhance the stability of topological superfluids by engineering inter-particle interactions.

cond-mat.quant-gas↗

arXiv2021

From Majorana fermions to topological quantum computation in semiconductor/superconductor heterostructures

We present a pedagogical review of topological superconductivity and its consequences in spin-orbit coupled semiconductor/superconductor heterostructures. We start by reviewing the historical origins of the notions of Dirac and Majorana fermions in particle physics and discuss how lower dimensional versions of these emerge in one dimensional superconductors. Ultimately, we focus on Majorana zero-modes, which emerge at defects in the Majorana equation. We then review the definition of the topological invariant, and how it allows the prediction of such Majorana modes from the bulk bandstructure of realistic superconductors, which do not have Lorentz invariance. Finally, we end with a discussion of protocols for how to detect such Majorana modes and use them for topological quantum computation.

cond-mat.supr-con↗

arXiv2021

Chiral anomaly induced nonlinear Hall effect in multi-Weyl semimetals

After the experimental realization, the Berry curvature dipole (BCD) induced nonlinear Hall effect (NLHE) has attracted tremendous interest to the condensed matter community. Here, we investigate another family of Hall effect, namely, chiral anomaly induced nonlinear Hall effect (CNHE) in multi-Weyl semimetal (mWSM). In contrast to the BCD induced NLHE, CNHE appears because of the combination of both chiral anomaly and anomalous velocity due to non-trivial Berry curvature. Using the semiclassical Boltzmann theory within the relaxation time approximation, we show that, in contrast to the chiral anomaly induced linear Hall effect, the magnitude of CNHE decreases with the topological charge n. Interestingly, we find that unlike the case of n=1, the CNHE has different behaviors in different planes. Our prediction on the behavior of CNHE in mWSM can directly be checked in experiments.

cond-mat.mes-hall↗

arXiv2020

Fundamental relations for anomalous thermoelectric transport coefficients in the non-linear regime

In a series of recent papers anomalous Hall and Nernst effects have been theoretically discussed in the non-linear regime and have seen some early success in experiments. In this paper, by utilizing the role of Berry curvature dipole, we derive the fundamental mathematical relations between the anomalous electric and thermoelectric transport coefficients in the non-linear regime. The formulae we derive replace the celebrated Wiedemann-Franz law and Mott relation of anomalous thermoelectric transport coefficients defined in the linear response regime. In addition to fundamental and testable new formulae, an important byproduct of this work is the prediction of nonlinear anomalous thermal Hall effect which can be observed in experiments.

cond-mat.mes-hall↗