arXiv subjects

Ojasvi Pal

Publications and source records attributed to Ojasvi Pal.

5 recordsLinked to original sources

arXiv2024

Polarization and third-order Hall effect in III-V semiconductor heterojunctions

We study Berry connection polarizability (BCP) induced electric polarization and third-order Hall (TOH) effect in a two-dimensional electron/hole gas (2DEG/2DHG) with Rashba-Dresselhaus (RD) spin-orbit couplings in III-V semiconductor heterostructures. The electric polarization decreases with the increase of the Fermi energy and is responsive to the electric field orientation in the presence of RD spin-orbit couplings for both systems. We determine the BCP-induced TOH conductivity ($χ_{\perp}^{\text{I}}$) along with the TOH conductivity associated with the band velocity ($χ_{\perp}^{\text{II}}$). We find that the presence of an infinitesimal amount of Dresselhaus coupling in addition to the dominant Rashba coupling results in finite TOH responses. These conductivities vanish when the field is aligned with and/or orthogonal to the symmetry lines $k_x\pm k_y=0$ in both systems. For typical system parameters in a 2DEG with $k$-linear RD interactions, the magnitude of $χ_{\perp}^{\text{I}}$ is smaller than that of $χ_{\perp}^{\text{II}}$. On the other hand, when both the SO couplings are comparable, $χ_{\perp}^{\text{I}}$ shows a notable increase in magnitude, owing to the distinctive characteristics of BCP. The TOH conductivity of 2DEG remains unchanged when Rashba and Dresselhaus spin-orbit couplings are exchanged. For 2DHG with $k$-cubic RD interactions, $χ_{\perp}^{\text{I},h}$ exhibits a larger magnitude compared to $χ_{\perp}^{\text{II},h}$. Unlike the electron case, the BCP induced $χ_{\perp}^{\text{I},h}$ alters under the exchange of spin-orbit coupling parameters, whereas $χ_{\perp}^{\text{II},h}$ remains the same.

cond-mat.mes-hall↗

arXiv2023

Nonlinear magnetotransport in a two-dimensional system with merging Dirac points

We study the linear, second-order nonlinear (NL) current and voltage responses of a two-dimensional gapped semi-Dirac system with merging Dirac nodes along the $x$ direction under the influence of a weak magnetic field ($B$), using the semiclassical Boltzmann formalism. We investigate the effect of band geometric quantities like Berry curvature and orbital magnetic moment in the responses up to linear order in $B$. We derive exact analytical expressions of the linear magnetoconductivities, second-harmonic NL anomalous Hall (NAH), and anomalous velocity and Lorentz force induced (NAL) conductivities, unveiling their dependence on Fermi energy and a gap parameter $δ_0$. For $δ_0 > 0$, the Fermi surface topology changes at a particular Fermi energy, which is reflected in the nature of conductivities through a kink. The ratio of NAL and NAH conductivities is found to be independent of $δ_0$ and inversely related to Fermi energy. The NL dc current exhibits distinct orientations depending on the Fermi energy, magnetic field, polarization of the electromagnetic wave. In the presence of magnetic field, the NL dc current vector can be rotated through large angles on variation of Fermi energy. For high Fermi energies, the NL dc current is directed nearly along the $y$-axis for $x$-polarized and low-frequency circularly polarized light, whereas it aligns close to $x$-axis for high-frequency circularly polarized light. These orientations of the NL dc current are predominantly governed by the mirror symmetry of the system along the $x$ direction. Additionally, we also study the NL voltage responses of the system by applying current along the $x$ and $y$ directions. The system exhibits asymmetry in the $B$-dependencies of the NL resistivities, which may serve as an experimentally relevant signature for band geometric quantities and merging Dirac nodes in such systems.

cond-mat.mes-hall↗

arXiv2022

Berry curvature induced anisotropic magnetotransport in a quadratic triple-component fermionic system

Triple-component fermions are pseudospin-1 quasiparticles hosted by certain three-band semimetals in the vicinity of their band-touching nodes [Phys. Rev. B {\bf 100}, 235201 (2019)]. The excitations comprise of a flat band and two dispersive bands. The energies of the dispersive bands are $E_{\pm}=\pm\sqrt{α^2_n k^{2n}_\perp+v^2_z k^2_z}$ with $k_\perp=\sqrt{k^2_x+k^2_y}$ and $n=1,2,3$. In this work, we obtain the exact expression of Berry curvature, approximate form of density of states and Fermi energy as a function of carrier density for any value of $n$. In particular, we study the Berry curvature induced electrical and thermal magnetotransport properties of quadratic $(n=2)$ triple-component fermions using semiclassical Boltzmann transport formalism. Since the energy spectrum is anisotropic, we consider two orientations of magnetic field (${\bf B}$): (i) ${\bf B}$ applied in the $x$-$y$ plane and (ii) ${\bf B}$ applied in the $x$-$z$ plane. For both the orientations, the longitudinal and planar magnetoelectric/magnetothermal conductivities show the usual quadratic-$B$ dependence and oscillatory behaviour with respect to the angle between the applied electric field/temperature gradient and magnetic field as observed in other topological semimetals. However, the out-of-plane magnetoconductivity has an oscillatory dependence on angle between the applied fields for the second orientation but is angle-independent for the first one. We observe large differences in the magnitudes of transport coefficients for the two orientations at a given Fermi energy. A noteworthy feature of quadratic triple-component fermions which is typically absent in conventional systems is that certain transport coefficients and their ratios are independent of Fermi energy within the low-energy model.

cond-mat.mes-hall↗

arXiv2021

Berry curvature induced magnetotransport in 3D noncentrosymmetric metals

We study the magnetoelectric and magnetothermal transport properties of noncentrosymmetric metals using semiclassical Boltzmann transport formalism by incorporating the effects of Berry curvature and orbital magnetic moment. These effects impart quadratic-B dependence to the magnetoelectric and magnetothermal conductivities, leading to intriguing phenomena such as planar Hall effect, negative magnetoresistance, planar Nernst effect and negative Seebeck effect. The transport coefficients associated with these effects show the usual oscillatory behavior with respect to the angle between the applied electric field and magnetic field. The bands of noncentrosymmetric metals are split by Rashba spin-orbit coupling except at a band touching point. For Fermi energy below (above) the band touching point, giant (diminished) negative magnetoresistance is observed. This difference in the nature of magnetoresistance is related to the magnitudes of the velocities, Berry curvature and orbital magnetic moment on the respective Fermi surfaces, where the orbital magnetic moment plays the dominant role. The absolute magnetoresistance and planar Hall conductivity show a decreasing (increasing) trend with Rashba coupling parameter for Fermi energy below (above) the band touching point.

cond-mat.mes-hall↗

arXiv2020

Unconventional phases in a Haldane model of dice lattice

We propose a Haldane-like model of dice lattice analogous to graphene and explore its topological properties within the tight-binding formalism. The topological phase boundary of the system is identical to that of Haldane model of graphene but the phase diagram is richer than the latter due to existence of a distorted flat band. The system supports phases which have a "gapped-out" valence (conduction) band and an indirect overlap between the conduction (valence) band and the distorted flat band. The overlap of bands imparts metallic character to the system. These phases may be further divided into topologically trivial and nontrivial ones depending on the Chern number of the "gapped-out" band. The semimetallic phases exist as distinct points that are well separated from each other in the phase diagram and exhibit spin-1 Dirac-Weyl dispersion at low energies. The Chern numbers of the bands in the Chern-insulating phases are $0$ and $\pm2$. This qualifies the system to be candidate for quantum anomalous Hall effect with two chiral channels per edge. Counterpropagating edge states emanate from the flat band in certain topologically trivial phases. The system displays beating pattern in Shubnikov de Haas oscillations for unequal magnitude of mass terms in the two valleys. We show that the chemical potential and ratio of topological parameters of the system viz. Semenoff mass and next-neighbor hopping amplitude may be experimentally determined from the number of oscillations between the beating nodes and the beat frequency, respectively.

cond-mat.mes-hall↗