arXiv subjects

Alestin Mawrie

Publications and source records attributed to Alestin Mawrie.

18 recordsLinked to original sources

arXiv2026

Lorentz-Covariant Landau Levels of Tilted Dirac Fermions in Nonuniform Fields

We develop an analytical theory of Landau quantization for tilted anisotropic Dirac fermions in an exponentially decaying magnetic field. Using anisotropy scaling and a Lorentz transformation, we recast the laboratory-frame problem into the isotropic Dirac equation in the boosted frame, where the exponentially decaying magnetic-field problem admits an exact solution. Transforming the boosted-frame spectrum back to the laboratory frame yields an implicit quantization condition with an intrinsically energy-dependent guiding-center parameter. We identify the conditions for physically admissible states. We further show that the formalism recovers the known uniform-field spectrum of tilted anisotropic Dirac fermions in the appropriate limit. Our results extend the Lorentz-covariant treatment of tilted anisotropic Dirac fermions to an exponentially decaying magnetic field and reveal the energy-dependent guiding-center structure generated by the inverse transformation to the laboratory frame.

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arXiv2026

Topological Scaling of Nonlinear Injection current and the Quantized Circular Photogalvanic Effect (CPGE)in tilted multi Weyl semimetals(mWSMs)

We develop a microscopic theory of nonlinear magneto-optical injection currents in multi-Weyl semimetals subjected to a uniform magnetic field. Using the Landau-level spectrum of a tilted multi-Weyl Hamiltonian with arbitrary monopole charge $ν$ as a starting point, we formulate a Kubo-type nonlinear response theory in the Landau-level basis and derive the second-order conductivity tensor. We identify distinct contributions originating from chiral-chiral, chiral-bulk, and bulk-bulk optical transitions, revealing characteristic monopole-charge scaling and sharp resonant structures governed by Landau-level selection rules and tilt-induced asymmetry. In the untilted limit, closed-form analytical expressions emerge that expose universal frequency thresholds and provide clear experimental signatures of higher-order Weyl topology. Our results establish nonlinear magneto-optical injection currents as a direct transport probe of chiral Landau levels and multi-Weyl topological charge.

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arXiv2025

A Quantum Framework for Negative Magnetoresistance in Multi-Weyl Semimetals

We develop a fully quantum-mechanical theory of negative magnetoresistance in multi-Weyl semimetals in the ${\bf E}\parallel{\bf B}$ configuration, where the chiral anomaly is activated. The magnetotransport response is governed by Landau quantization and the emergence of multiple chiral Landau levels associated with higher-order Weyl nodes. These anomaly-active modes have unidirectional dispersion fixed by the node's monopole charge and dominate charge transport. As the magnetic field increases, individual chiral branches successively cross the Fermi energy, producing discrete slope changes in the longitudinal conductivity and a step-like negative magnetoresistance. This quantized evolution provides a direct experimental signature of multi-Weyl topology. Bulk Landau levels contribute only at very low fields due to strong disorder scattering and do not affect the anomaly-driven regime. Our results establish a unified, fully quantum-mechanical framework in which negative magnetoresistance arises from the discrete Landau-quantized spectrum and microscopic impurity scattering, beyond semiclassical anomaly descriptions.

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arXiv2025

Enhanced Gilbert Damping via Cubic Spin-Orbit Coupling at 2DHG/Ferromagnetic Insulator Interface

We investigate the enhancement of Gilbert damping at 2DHG/ferromagnetic insulator (FI) interfaces, where spin pumping from the FI layer injects spins into the 2DHG, and cubic Rashba spin-orbit coupling (RSOC) significantly boosts spin relaxation and spin-pumping efficiency compared to 2DEG systems. The dominant contribution to spin damping arises from interband transitions which does exhibits conductivity-like behavior as the temperature, $ T \to 0 $. Our results reveal that damping remains stronger than in 2DEG due to the persistent influence of cubic RSOC. The interplay between RSOC and magnon absorption broadens the spectral response, with the damping peak shifting more notably at higher temperatures. Stronger RSOC expands the magnon interaction phase space, thus widening the damping spectrum. A key observation emerges with the Fermi level ($E_f$): a finite $E_f$ sustains spin imbalance and enhances damping, whereas $E_f = 0$ suppresses it, unlike in 2DEG. The electric field tunability of RSOC enables real-time control over spin relaxation and angular momentum transfer, offering a pathway toward voltage-controlled spintronic devices. These findings highlight the superior potential of 2DHG for tailoring spin dynamics via electric and thermal effects.

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arXiv2024

Unveiling the Chiral States in Multi-Weyl Semimetals through Magneto-Optical Spectroscopy

This study investigates the transport parameters in multi-Weyl semimetals, focusing on their magneto-optical properties and the role of chiral states. The tilting parameter is identified as a key factor in higher-order Weyl nodes, significantly influencing the magneto-optical response. We obtain a generic Landau-level expression for multi-Weyl semimetals, establishing a robust framework for analyzing their quantum transport properties. A comprehensive expression for the conductivity tensor components is presented, uncovering distinctive low-frequency peaks and other features shaped by the tilting parameter. Our findings reveal that the signatures of chiral states in the conductivity tensors become increasingly pronounced with the Weyl node order. Particularly, the tilting parameter is shown to impact Faraday rotation, at energies near the tilted Dirac cone energies. These results provide critical insights into the magneto-optical behavior of multi-Weyl semimetals and their potential for exploring topological phenomena.

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arXiv2024

Floquet-Engineered Valley-Topotronics in Kekulé-Y Bond Textured Graphene Superlattice

The exquisite distortion in a Kekulé-Y (Kek-Y) superlattice merges the two inequivalent Dirac cones (from the $K$- and the $K^\prime$- points) into the highest symmetric $Γ$-point in the hexagonal Brillouin zone. Here we report that a circularly polarised light not only opens up a topological gap at the $Γ$-point but also lifts the valley degeneracy at that point. Endowed with Floquet dynamics and by devising a scheme of high-frequency approximation, we have proposed that the handedness (left/right) in polarised light offers the possibility to realise the valley-selective circular dichroism in Kek-Y shaped graphene superlattice. Also, the non-vanishing Berry curvature and enumeration of valley resolved Chern number $\mathcal{C}_{K}/\mathcal{C}_{K^\prime}=+1/-1$ enable us to assign two pseudo-spin flavors (up/down) with the two valleys. Thereby, the above observations confirm the topological transition suggesting the ease of realising the valley quantum anomalous Hall (VQAH) state within the photon-dressed Kek-Y. These findings further manifest a non-zero optical valley polarisation which is maximum at the $Γ$-point. Our paper thus proposes an optically switchable topological valley filter which is desirous in the evolving landscape of valleytronics.

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arXiv2023

Magnetoresistive RAM with n-doped AlGaAs/GaAs writing/reading channels

We show that the tunable gate voltage in n-doped AlGaAs/GaAs QW (quantum well) is a key in designing an efficient and ultrafast MRAM (magnetoresistive random access memory). The Rashba spin-orbit coupling in such QWs can be tuned appropriately by the gate voltage to create an intense spin-Hall field which in turns interacts with the ferromagnetic layer of the MRAM through the mechanism of spin orbit torque. The strong spin-Hall field leads to an infinitesimally small switching time of the MRAM. Our proposed MRAM is thus a better alternative to the conventional ferromagnetic/spin-Hall effect bi-layers MRAM for the reason that the switching time can be varied with ease, which is unfeasible in the later. Concisely, not only that this work signals a possibility to design an ultra-fast MRAM, but it also suggests a model to fabricate a tunable switching time MRAM.

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arXiv2022

Quantum anomalous Hall phase and effective in-plane Lande-g factor in an inverted InAs/GaSb quantum well

The inverted band structure discovered in InAs/GaSb quantum well (QW) is found to host the topological quantum spin Hall (QSH) states. A QSH insulator hosts counterpropagating spin-polarized edge states that are protected by the time-reversal symmetry. The latest experiment reported a robust quantized Hall conductance arising from these QSH states that persists in an in-plane magnetic field as strong as $12$ Tesla. Based on the result of this experiment, we present here a precise calculation of the effective in-plane Lande-\textit{g} factor. We based our calculations on the tight-binding Hamiltonian projected on a square lattice that reproduces a slightly modified Bernevig-Hughes-Zhang (BHZ) Hamiltonian. We also study the topological phase transitions \textit{w.r.t.} a magnetic doping. At suitable doping, one type of spin states penetrate to the bulk of the QW and the system also enters the Quantum Anomalous Hall (QAH) state. We further confirm this through the calculations of quantum Hall conductance which shows a plateau at $e^2/h$ rather than $2e^2/h$ at such a doping state. The paper predicts a certain range of controllable parameters in an inverted QW for enabling a dissipationless charge transport needed for spintronics application.

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arXiv2022

Magnetotransport properties of the Quantum Spin Hall and Quantum Hall states in an inverted HgTe/CdTe and InAs/GaSb quantum wells

The quantum spin Hall (QSH) states discovered in an inverted band of InAs/GaSb and HgTe/CdTe quantum wells categorize them among the very superior candidates for topological insulators. In the presence of a magnetic field, these QSH states persist up to a magnetic field equal to the critical field, beyond which the edge states would consist of normal quantum Hall (QH) states. We provide the expression of this critical field which is found consistent with some previous literature. The critical field partitioned the spectrum into two types of quantum states, \textit{viz}. , the Quantum spin Hall (QSH) and Quantum Hall (QH) states. We present a theoretical study of the magnetotransport properties based on the Bernevig-Hughes-Zhang Hamiltonian that describes these QSH states. Our results of the Hall conductivity show the different responses at these two different topological regions. Around the low Fermi energy level, the system has a high Hall conductivity in the QH region, while the same is less dominant in the QSH region. Our results of the Hall conductivity thus help differentiate the type topological phase of the given quantum well.

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arXiv2021

Evolution of Majorona zero-energy edge states in a $T^2 = -1$ symmetry protected 1D topological superconductor with dominant spin-orbit coupling

We consider a 1D topological superconductor (TSC) constructed by coupling a pair of Kitaev's Majorana chains with opposite spin configurations. Such a 1D lattice model is known to be protected by a $T^2 = -1$ time-reversal symmetry. Furthermore, we consider a modeled Rashba spin-orbit coupling on such a system of $T^2=-1$ time-reversal symmetric TSC. The Rashba spin-orbit coupling together with the chemical potential engineered the phase transitions of the edge states in the system and consequently the number of Majorona's zero-energy edge modes (MZM's) emerging at the edge of the coupled chains. Correspondingly, the topological nature of the system is described by a phase diagram consisting of three different phases. The three phases are characterized by a topological winding number, $\mathcal{W}=1$, $2$ (with one and two MZM's: topological phases) and $\mathcal{W}=0$ (devoid of any MZM: trivial insulating phase).

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arXiv2019

Quantum thermoelectrics based on 2-D Semi-Dirac materials

We show that a gap parameter can fully describe the merging of Dirac cones in semi-Dirac materials from $K$- and $K^\prime$-points into the common $M$-point in the Brillouin zone. We predict that the gap parameter manifests itself by enhancing the thermoelectric figure of merit $zT$ as the chemical potential crosses the gap followed by a sign change in the Seebeck coefficient around the same point. Subsequently, we show that there is also a trade-off feature between the maximum power delivered and the efficiency when the chemical potential crosses the gap parameter. An optimal operating point that minimizes the power-efficiency trade-off is consequently singled out for the best thermoelectric performance. Our work paves the way for the use of 2D semi-Dirac materials for thermoelectric applications.

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arXiv2019

Direction dependent giant optical conductivity in 2D \textit{semi}-Dirac materials

We show that the gap parameter in \textit{semi}-Dirac material induces a large degree of sensitivity for inter-band optical conductivity with respect to the polarization direction. The optical conductivity reveals an abruptly large value at a certain frequency for light along a particular polarization direction while it is significantly suppressed along the direction orthogonal to the former. The direction-dependent optical conductivity may, in turn, be used to uniquely predict the dispersive nature of the 2D \textit{semi}-Dirac materials, in addition to other possible applications in the field of transparent conductors.

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arXiv2017

Electrical and thermoelectric transport properties of two-dimensional fermionic systems with $k$-cubic spin-orbit coupling

We investigate the effect of $k$-cubic spin-orbit interaction on electrical and thermoelectric transport properties of two-dimensional fermionic systems. We obtain exact analytical expressions of the inverse relaxation time (IRT) and the Drude conductivity for long-range Coulomb and short-range delta scattering potentials. The IRT reveals that the scattering is completely suppressed along the three directions $θ^\prime = (2n+1)π/3 $ with $ n=1,2,3$. We also obtain analytical results of the thermopower and thermal conductivity at low temperature. The thermoelectric transport coefficients obey the Wiedemann-Franz law, even in the presence of $k$-cubic Rashba spin-orbit coupling (RSOC) at low temperature. In the presence of quantizing magnetic field, the signature of the RSOC is revealed through the appearance of the beating pattern in the Shubnikov-de Haas (SdH) oscillations of thermopower and thermal conductivity in low magnetic field regime. The empirical formulae for the SdH oscillation frequencies accurately describe the locations of the beating nodes. The beating pattern in magnetothermoelectric measurement can be used to extract the spin-orbit coupling constant.

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arXiv2017

Effect of electron-hole asymmetry on optical conductivity in 8-Pmmn borophene

We present a detail theoretical study of the Drude weight and optical conductivity of 8-$Pmmn$ borophene having tilted anisotropic Dirac cones. We provide exact analytical expressions of $xx$ and $yy$ components of the Drude weight as well as maximum optical conductivity. We also obtain exact analytical expressions of the minimum energy ($ε_1$) required to trigger the optical transitions and energy ($ε_2$) needed to attain maximum optical conductivity. We find that the Drude weight and optical conductivity are highly anisotropic as a consequence of the anisotropic Dirac cone. The optical conductivities have a nonmonotonic behavior with photon energy in the regime between $ε_1$ and $ε_2$, as a result of the tilted parameter $v_t$. The tilted parameter can be extracted by knowing $ε_1$ and $ε_2$ from optical measurements. The maximum values of the components of the optical conductivity do not depend on the carrier density and the tilted parameter. The product of the maximum values of the anisotropic conductivities has the universal value $(e^2/4\hbar)^2$. The tilted anisotropic Dirac cones in 8-$Pmmn$ borophene can be realized by the optical conductivity measurement.

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arXiv2016

Electrical and optical conductivities of hole gas in $p$-doped bulk III-V semiconductors

We study electrical and optical conductivities of hole gas in $p$-doped bulk III-V semiconductors described by the Luttinger Hamiltonian. We provide exact analytical expressions of the Drude conductivity, inverse relaxation time for various impurity potentials, Drude weight and optical conductivity in terms of the Luttinger parameters $γ_1 $ and $γ_2$. The back scattering is completely suppressed as a result of the helicity conservation of the heavy and light hole states. We find that the inverse relaxation time of heavy holes is much less than that of the light holes for Coulomb-type and Gaussian-type impurity potentials and vice-versa for short-range impurity potentials. The Drude conductivity increases non-linearly with the increase of the hole density. The exponent of the density dependence of the conductivity is obtained in Thomas-Fermi limit. The Drude weight varies linearly with the density even in presence of the spin-orbit coupling. The finite-frequency optical conductivity goes as $\sqrtω$ and its amplitude strongly depends on the Luttinger parameters. The Luttinger parameters can be extracted from the optical conductivity measurement.

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arXiv2016

Optical conductivity of a 2DEG with anisotropic Rashba interaction at the interface of LaAlO$_3$/SrTiO$_3$

We study optical conductivity of a two-dimensional electron gas with anisotropic $k$-cubic Rashba spin-orbit interaction formed at the LaAlO$_3$/SrTiO$_3$ interface. The anisotropic spin splitting energy gives rise to different features of the optical conductivity in comparison to the isotropic $k$-cubic Rashba spin-orbit interaction. For large carrier density and strong spin-orbit couplings, the density dependence of Drude weight deviates from the linear behavior. The charge and optical conductivities remain isotropic despite anisotropic nature of the Fermi contours. An infinitesimally small photon energy would suffice to initiate inter-band optical transitions due to degeneracy along certain directions in momentum space. The optical conductivity shows a single peak at a given photon energy depending on the system parameters and then falls off to zero at higher photon energy. These features are lacking for systems with isotropic $k$-cubic Rashba spin-orbit coupling. These striking features can be used to extract the information about nature of the spin-orbit interaction experimentally and illuminate some light on the orbital origin of the two-dimensional electron gas.

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arXiv2016

Drude weight and optical conductivity of a two-dimensional heavy-hole gas with $k$-cubic spin-orbit interactions

We present detailed theoretical study on zero-frequency Drude weight and optical conductivity of a two-dimensional heavy-hole gas(2DHG) with $k$-cubic Rashba and Dresselhaus spin-orbit interactions. The presence of $k$-cubic spin-orbit couplings strongly modifies the Drude weight in comparison to the electron gas with $k$-linear spin-orbit couplings. For large hole density and strong $k$-cubic spin-orbit couplings, the density dependence of Drude weight deviates from the linear behavior. We establish a relation between optical conductivity and the Berry connection. Unlike two-dimensional electron gas with $k$-linear spin-orbit couplings, we explicitly show that the optical conductivity does not vanish even for equal strength of the two spin-orbit couplings. We attribute this fact to the non-zero Berry phase for equal strength of $k$-cubic spin-orbit couplings. The least photon energy needed to set in the optical transition in hole gas is one order of magnitude smaller than that of electron gas. Types of two van Hove singularities appear in the optical spectrum are also discussed.

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arXiv2014

Magnetotransport properties of two-dimensional fermions with $k$-cubic Rashba spin-orbit interaction

The spin-orbit interaction in heavy hole gas formed at $p$-doped semiconductor heterojunctions and electron gas at {\mbox SrTiO}${}_3$ surfaces is cubic in momentum. Here we report magnetotransport properties of k-cubic Rashba spin-orbit coupled two-dimensional fermionic systems. We study longitudinal (Shubnikov-de Haas (SdH) oscillations) and Hall component of the resistivity tensor analytically as well as numerically. The longitudinal resistivity shows beating pattern due to different SdH oscillation frequencies $ f_{\pm} $ for spin-up and spin-down fermions. We propose empirical forms of $ f_{\pm} $ as exact expressions are not available, which are being used to find location of the beating nodes. The beating nodes and the number of oscillations between any two successive nodes obtained from exact numerical results are in excellent agreement with those calculated from the proposed empirical form. In the Hall resistivity, an additional Hall plateau appears in between two conventional ones as spin-orbit coupling constant increases. The width of this additional plateau increases with spin-orbit coupling constant.

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