arXiv subjects

Pankaj Bhalla

Publications and source records attributed to Pankaj Bhalla.

At least 19 recordsLinked to original sources

arXiv2026

Skew scattering induced contribution to orbital Hall response

Our study provides the disorder-induced contribution to the orbital Hall conductivity in three-dimensional Weyl semimetals with broken time-reversal symmetry. Using the quantum kinetic approach, we analyse the impact of side-jump and skew scattering contributions to the system. The dependence of the orbital Hall conductivity on both disorder potential and the Fermi energy is explicitly demonstrated. Furthermore, we demonstrate that the higher-order disorder contribution, especially from the third power of disorder potential, dominates the orbital Hall conductivity under an oscillating electric field in a time-reversal symmetry broken Weyl semimetal, suppressing other scattering mechanisms, including the side jump contributions. We can enhance the extrinsic orbital Hall conductivity by tuning the strength of the disorder potential, applied energy, and choosing the system with appropriate Weyl node separation. Finally, our results are supported by numerical estimations and highlight potential experimental relevance for advancing orbitronics device technologies.

cond-mat.mes-hall↗

arXiv2026

Semiclassical theory of frequency dependent linear magneto-optical transport in Weyl semimetals

We develop a semiclassical Boltzmann theory for frequency-dependent magneto-optical transport in Weyl semimetals (WSMs), incorporating momentum-dependent relaxation via a scattering matrix approach. The interplay of orbital magnetic moment, Weyl cone tilt, intervalley scattering, and electromagnetic driving is analyzed to obtain the full conductivity tensor in the presence of a static magnetic field. For untilted WSMs with orbital magnetic moment, strong intervalley scattering in the weak ac regime induces a sign reversal of the longitudinal magneto-optical conductivity (LMOC), thereby suppressing the chiral anomaly. In contrast, in the strong ac regime, intervalley scattering fails to neutralize the chiral imbalance within a driving cycle, and no sign reversal is observed. Orbital magnetic moment induces linear magnetic-field contributions, while chiral anomaly yields quadratic response accompanied by expected angular profiles. Tilt direction and orientation strongly affect LMOC such as, transverse tilt gives symmetric non-monotonic behavior, whereas parallel tilt leads to asymmetric, nearly monotonic response. Notably, negative LMOC arises intrinsically for parallel tilt, but requires orbital magnetic moment for transverse tilt. These results highlight frequency-dependent conductivity as a sensitive probe of chiral relaxation in MHz-THz magneto-optical experiments.

cond-mat.mes-hall↗

arXiv2026

Interband response in spin-orbit coupled nodal line semimetals

This study investigates the interband conductivity for nodal line semimetals (NLSMs) in the presence of spin-orbit coupling (SOC), where the disorder reshapes the transport properties. The SOC breaks spin degeneracy, thus fundamentally altering the band dispersion and enabling multiple interband transport channels. Using a quantum kinetic framework, we analyze the interband conductivity originating from disorder-driven (extrinsic) and field-driven (intrinsic) mechanisms. We find that the interband response shows an anisotropic nature due to disorder driven counterparts. Additionally, our predictions show a tunable prominent transition peak arising from non-Pauli-blocked states that can be controlled via band parameters as well as external stimuli. To have an experimental relevance, we provide a numerical estimation for the interband response of TaAs using density functional theory estimated parameters. These results suggest the investigation of disorder-enabled signatures in spin systems.

cond-mat.mes-hall↗

arXiv2025

Unveiling Novel Resonant Interband Contribution to Polarizability in three-dimensional systems

Polarizability plays an essential role in characterizing key phenomena, such as the screening effects, collective excitations, and dielectric functions present in the system. In three-dimensional materials, it typically comprises an intraband contribution, dependent on the chemical potential, and an interband contribution, largely independent of it. In this study, within the random phase approximation framework, we uncover a novel interband contribution that, unlike the conventional case, exhibits an explicit dependence on the chemical potential, which has no counterpart in two dimensions. In the long-wavelength limit, this term introduces a resonance feature with cubic wave-vector dependence when the chemical potential approaches the band edge, in contrast to the quadratic behavior characteristic of standard intraband and interband processes. Focusing on three-dimensional Dirac nodal line semimetals, we show that the polarizability is intraband-dominated at low frequencies, while interband processes prevail at intermediate and high frequencies, with the overall response being tunable via the chemical potential. Material-specific estimates for Ca$_3$P$_2$ and ZrSiS reveal a strong tunability of both contributions. These findings open new directions for probing frequency-dependent dielectric properties and hold promise for applications in tunable plasmonic and optoelectronic devices.

cond-mat.mes-hall↗

arXiv2025

Disorder induced dynamical interband response in Dirac nodal line semimetals

To obtain the total response of the system, the effect of disorder cannot be neglected, as it introduces a new contribution (i.e. extrinsic) in the total response of the system. In the study of dynamical (AC) effects, the interband response exhibits an exotic resonance peak due to interband transitions. Here, the dynamical interband response of Dirac nodal line semimetal is investigated by using the quantum kinetic approach. The scattering driven effect is analyzed under the first-order Born approximation (i.e., in the weak disorder limit) and reveals a resonance peak at $2\tilde{\mu}$. In contrast, the field driven intrinsic response peak depends on both the mass ($\tilde{M}$) and chemical potential ($\tilde{\mu}$). The results indicate that the total interband response of the 3D nodal line semimetals, is mainly dominated by the disorder induced contributions.

cond-mat.mes-hall↗

arXiv2025

Reshaping the anomalous Hall response in tilted 3D system with disorder correction

The anomalous Hall conductivity in the nodal line semimetals (NLSMs) due to the presence of a symmetry-protected nodal ring adds complexity in the investigation of their transport properties. By employing quantum kinetic theory and considering the weak disorder limit, we analyze the intraband and interband parts of anomalous Hall conductivity in the tilted 3D Dirac NLSMs. Our findings reveal that the net anomalous response is mainly contributed by the interband part. Further, the latter part gives non zero results by breaking inversion symmetry via tilt. We observe that the competition between the tilt and the chemical potential emerges kinks at distinct characteristic frequencies in the intrinsic interband part of the anomalous conductivity. On the other hand, the disorder driven interband component of the conductivity exhibits a prominent peak at low chemical potential, followed by a sign change. Notably, the disorder or extrinsic contribution to the response dominates over the intrinsic interband contribution, making it a crucial factor for the study of the overall response of a three-dimensional system.

cond-mat.mes-hall↗

arXiv2025

Tunable optical bistability of two-dimensional tilted Dirac system

We study the phenomenon of controlling the light by light known as the optical bistability for the two-dimensional tilted Dirac system. Using the Boltzmann approach under relaxation time approximation, we find that the optical bistability can be controlled by the nonlinear response of the system. For the prototype, we consider an inversion symmetry broken system. We find that the optical bistability associated with the nonlinear response is tunable with the strength of the tilt, gap and chemical potential. This suggests the inputs for the development of future-generation optical devices.

physics.optics↗

arXiv2024

Longitudinal DC Conductivity in Dirac Nodal Line Semimetals: Intrinsic and Extrinsic Contributions

Nodal line semimetals, a class of topological quantum materials, exhibit a variety of novel phenomena due to their properties, such as bands touching on a one-dimensional line or a ring in the Brillouin zone and drumhead-like surface states. In addition, these semimetals are protected by the combined space-inversion and time-reversal ($\mathcal{PT}$) symmetry. In this study, we investigate the longitudinal DC conductivity of the Dirac nodal line semimetals for the broken $\mathcal{PT}$-symmetric system by the mass term. Here, using the quantum kinetic technique, we find the intrinsic (field-driven) and extrinsic (scattering-driven) contributions to the total DC conductivity due to interband effects. Interestingly, the resulting intrinsic conductivity is the Fermi sea contribution, while the extrinsic stems from the Fermi surface contribution. We show that at low chemical potential, the extrinsic part contributes more and dominates over the traditional Drude intraband term, while at the high chemical potential, the intrinsic conductivity contributes. Furthermore, the total DC response due to interband effects saturates at high chemical potential and its strength decreases with increasing mass value. Our findings suggest that the extrinsic contributions are rich enough to understand the overall feature of the response for the three-dimensional system.

cond-mat.str-el↗

arXiv2023

Light-induced Nonlinear Spin Hall Current in Single-layer WTe$_2$

In this theoretical investigation, we analyze light-induced nonlinear spin Hall currents in a gated single-layer 1T$'$-WTe$_2$, flowing transversely to the incident laser polarization direction. Our study encompasses the exploration of the second and third-order rectified spin Hall currents using an effective low-energy Hamiltonian and employing Kubo's formalism. We extend our analysis to a wide frequency range spanning both transparent and absorbing regimes, investigating the influence of light frequency below and above the optical band gap. Additionally, we investigate the influence of an out-of-plane gate potential on the system, disrupting inversion symmetry and effectively manipulating both the strength and sign of nonlinear spin Hall responses. We predict a pronounced third-order spin Hall current relative to its second-order counterpart. The predicted nonlinear spin currents show strong anisotropic dependence on the laser polarization angle. The outcomes of our study contribute to a generalized framework for nonlinear response theory within the spin channel will impact the development of the emerging field of opto-spintronic.

cond-mat.mes-hall↗

arXiv2022

Quantum Kinetic Theory of Nonlinear Optical Currents: Finite Fermi surface and Fermi sea contributions

The quantum kinetic framework provides a versatile method for investigating the dynamical optical and transport currents of crystalline solids. In this paper, starting from the density-matrix equations of motion, we present a general theoretical path to obtain nonlinear optical responses elegantly and transparently. We devise a kinetic theory applicable to materials with arbitrary band structures and captures intraband and interband coherence effects, finite Fermi surfaces, and disorder effects. We present a classification of nonlinear optical currents arising from the interference of interband and intraband components of the density matrix with distinct symmetry and quantum geometrical origin for each contribution. In this context, we report four findings. (i) The Fermi Golden Rule approach is insufficient to derive the correct expression for the injection current, a shortcoming that we remedy in our theory while associating the injection current with the intraband-interband contribution to the second-order density matrix. (ii) The interband-intraband contribution yields a resonant current that survives irrespective of any symmetry constraint in addition to the well-known anomalous nonlinear current (non-resonant), which requires time-reversal symmetry. (iii) Quite generally, the nonlinear current is significantly enhanced by contributions from the finite Fermi surface. (iv) The finite Fermi surface and Fermi sea additionally lead to sizable novel nonlinear effects via contributions we term double resonant and higher-order pole. As an illustration, we compute the nonlinear response of topological antiferromagnet CuMnAs and thin film tilted Weyl semimetals dominated by interband coherence effects. We find that the nonlinear response of CuMnAs is responsive to the direction of finite magnetization field and choice of the polarization angle of the beam, while Weyl semimetal only to tilt.

cond-mat.mes-hall↗

arXiv2022

Quantum kinetic theory of nonlinear thermal current

We investigate the second-order nonlinear electronic thermal transport induced by temperature gradient. We develop the quantum kinetic theory framework to describe thermal transport in presence of a temperature gradient. Using this, we predict an intrinsic scattering time independent nonlinear thermal current in addition to the known extrinsic nonlinear Drude and Berry curvature dipole contributions. We show that the intrinsic thermal current is determined by the band geometric quantities and is non-zero only in systems where both the space inversion and time-reversal symmetries are broken. We employ the developed theory to study the thermal response in tilted massive Dirac systems. We show that besides the different scattering time dependence, the various current contributions have distinct temperature dependence in the low temperature limit. Our systematic and comprehensive theory for nonlinear thermal transport paves the way for future theoretical and experimental studies on intrinsic thermal responses.

cond-mat.mes-hall↗

arXiv2022

Second Harmonic Helicity and Faraday Rotation in Gated Single-Layer 1T$'$-WTe$_2$

Single-layer of 1T$'$ phase of WTe$_2$ provides a rich platform for exotic physical properties such as nonlinear Hall effect and high-temperature quantum spin hall transport. Utilizing a continuum model and diagrammatic method, we calculate the second harmonic conductivity of monolayer 1T$'$-WTe$_2$ modulated by an external vertical electric field and electron doping. We obtain a finite helicity and Faraday rotation for the second harmonic signal in response to linearly polarized incident light in the presence of time-reversal symmetry. The second harmonic signal's helicity is highly controllable by altering the bias potential and serves as an optical indicator of the nonlinear Hall current. Our study motivates future experimental investigation for the helicity spectroscopy of two dimensional materials.

cond-mat.mes-hall↗

arXiv2021

Pseudogauge field driven acoustoelectric current in two-dimensional hexagonal Dirac materials

Using a diagrammatic scheme, we study the acoustoelectric effects in two-dimensional (2D) hexagonal Dirac materials due to the sound-induced pseudo-gauge field. We analyze both uniform and {\em spatially dispersive} currents in response to copropagating and counterpropagating sound waves, respectively. In addition to the longitudinal acoustoelectric current, we obtain an exotic {\em transverse} charge current flowing perpendicular to the sound propagation direction owing to the interplay of transverse and longitudinal gauge field components $j_T\propto A_L A^\ast_T$. In contrast to the almost isotropic directional profile of the longitudinal uniform current, a highly anisotropic transverse component $j_T\sim\sin(6\theta)$ is achieved that stems from the inherited three-fold symmetry of the hexagonal lattice. However, both longitudinal and transverse parts of the dispersive current are predicted to be strongly anisotropic $\sim\sin^2(3\theta)$ or $\cos^2(3\theta)$. We quantitatively estimate the pseudogauge field contribution to the acoustoelectric current that can be probed in future experiments in graphene and other 2D hexagonal Dirac materials.

cond-mat.mes-hall↗

arXiv2021

Unidirectional magneto-transport of linearly dispersing topological edge states

Quantum spin-Hall edges are envisaged as next-generation transistors, yet they exhibit dissipationless transport only over short distances. Here we show that in a diffusive sample, where charge puddles with odd spin cause back-scattering, a magnetic field drastically increases the mean free path and drives the system into the ballistic regime with a Landauer-Buttiker conductance. A strong non-linear non-reciprocal current emerges in the diffusive regime with opposite signs on each edge, and vanishes in the ballistic limit. We discuss its detection in state-of-the-art experiments.

cond-mat.mes-hall↗

arXiv2021

Quantum geometry induced second harmonic generation

Quantum geometry of the electron wave function plays a significant role in the linear and non-linear responses of crystalline materials. Here, we study quantum geometry induced second harmonic generation. We identify non-linear responses stemming from the quantum geometric tensor and the quantum geometric connection in systems with finite Fermi surfaces and disorder. In addition to the injection, shift, and anomalous currents we find two new contributions, which we term double resonant and higher-order pole contributions. Our findings can be tested in state-of-the-art devices in WTe2 (time-reversal symmetric system) and in CuMnAs (parity-time reversal symmetric systems).

cond-mat.mes-hall↗

arXiv2021

Non-linear ballistic response of quantum spin-Hall edge states

Topological edge states exhibit dissipationless transport and electrically-driven topological phase transitions, making them ideal for next-generation transistors that are not constrained by Moore's law. Nevertheless, their dispersion has never been probed and is often assumed to be simply linear, without any rigorous justification. Here we determine the non-linear electrical response of topological edge states in the ballistic regime and demonstrate the way this response ascertains the presence of symmetry breaking terms in the edge dispersion, such as deviations from non-linearity and tilted spin quantization axes. The non-linear response stems from discontinuities in the band occupation on either side of a Zeeman gap, and its direction is set by the spin orientation with respect to the Zeeman field. We determine the edge dispersion for several classes of topological materials and discuss experimental measurement.

cond-mat.mes-hall↗

arXiv2021

Optical phonon contribution to the thermal conductivity of a quantum paraelectric

Motivated by recent experimental findings, we study the contribution of a quantum critical optical phonon branch to the thermal conductivity of a paraelectric system. We consider the proximity of the optical phonon branch to transverse acoustic phonon branch and calculate its contribution to the thermal conductivity within the Kubo formalism. We find a low temperature power law dependence of the thermal conductivity as $T^{\alpha}$, with $1 < \alpha < 2$, (lower than $T^3$ behavior) due to optical phonons near the quantum critical point. This result is in accord with the experimental findings and indicates the importance of quantum fluctuations in the thermal conduction in these materials.

cond-mat.mtrl-sci↗

arXiv2020

Intrinsic Contribution to Non-linear Thermoelectric Effect

Irradiation of the strong light on the material leads to numerous non-linear effects that are essential to understand the physics of excited states of the system and for optoelectronics. Here, we study the non-linear thermoelectric effect due to the electric and thermal fields applied on a non-centrosymmetric system. The phenomenon arises on the Fermi surface with the transitions of electrons from valence to conduction bands. We derive the formlism to investigate these effects and find that the non-linearity in these effects namely non-linear Seebeck and non-linear Peltier effects depends on the ratio of the non-linear to the linear conductivities. The theory is tested for a hexagonally warped and gapped topological insulator. Results show enhancement in the longitudinal and Hall effects on increasing the warping strength while show opposite behavior with the surface gap.

cond-mat.mes-hall↗