arXiv subjects

Debabrata Sinha

Publications and source records attributed to Debabrata Sinha.

17 recordsLinked to original sources

arXiv2026

Electrical and Thermal conductance through a Nodal Surface Semimetal-Insulator-Superconductor junction

Motivated by the unique dispersions close to the two dimensional band crossing in a topologically charged nodal surface semimetal (NSSM) spectrum, we perform theoretical analysis of quantum tunnelling through a junction consisting of such NSSM, an insulator and a s-wave superconductor (acronymed NSSM-I-SC junction). In particular, for excitation energies both more and less than the superconducting gap potential $Δ$ we probe the normal and Andreev conductance for different incident orientations and thereby find the tunnelling electrical conductance through the heterostructure. The present work considers only the thin barrier limit which witness the conductance G to oscillate periodically with frequency $π$ as a function of the barrier strength, both in high and low doping limit. Such periodic behavior is also observed while calculating the thermal conductance $κ$ through the junction. Novelty of this problem is that the behavior of these G or $κ$ with insulator width are, in many respect, different compared to that from a normal metal - insulator - superconductor (NIS) junction on graphene or silicene. The findings can thus motivate experimentalists to culture renewed control over electric or thermal transport on topological materials.

cond-mat.mes-hall↗

arXiv2025

Light Induced Quantum Anomalous Hall Effect in Cubic Rashba Spin-Orbit Coupled Systems

We investigate topological phase transitions in a two-dimensional electron system with cubic Rashba spin-orbit coupling driven by circularly polarized light. Within the Floquet framework, we demonstrate that light-matter interaction induces nontrivial band topology characterized by a quantized anomalous Hall response, with Chern insulating phases of C = 0, 1, and 3. These transitions are governed by gap closings at high-symmetry points in the Brillouin zone, controlled by the intensity and energy of the incident light. Introducing a weak linear Rashba term displaces Dirac points in momentum space without modifying the topology, whereas a purely linear Rashba system remains topologically trivial (C = 0). When both linear and cubic Rashba couplings are finite, the linear term confines nonzero-Chern phases to narrow parameter windows. In contrast, incorporating a linear Dresselhaus term into the cubic Rashba system can trigger topological transitions even at small coupling strengths. These results clarify the interplay between distinct spin-orbit interactions in Floquet-engineered Chern insulators and offer experimentally relevant pathways for achieving light-controlled topological phases.

cond-mat.str-el↗

arXiv2021

Giant nonlinear response due to unconventional oscillation in Nodal-line semimetals

Quantum oscillations in magnetoconductance of a material at low temperatures and in presence of an intense magnetic field are described by the Shubnikov de Haas (SdH) effect. It is widely assumed to be the hallmark of the Fermi surface of a given metal. In contrast to the canonical situation, we identify an exotic oscillation in nonlinear responses of three-dimensional nodal line semimetals (NLSMs) which persist even at temperatures where the typical SdH-like oscillations vanish. This oscillation occurs due to the periodic gap-closing of a pair of Landau levels at zero Fermi energy with the variation of the magnetic field. The emergence of the oscillation is a remarkable fingerprint of ring dispersion and the corresponding frequency can be used to determine the radius of the ring. Using the Boltzmann equation, we calculate the second harmonic generation of nodal line semimetals under parallel DC electric and strong magnetic fields. The second harmonic conductivity diverges at the gap closing condition leading to the giant nonlinear response in NLSMs.

cond-mat.str-el↗

arXiv2021

Quantum anomaly and anomalous Josephson effect in inversion asymmetric Weyl semimetals

We study a Josephson junction involving an inversion-asymmetric Weyl semimetal in presence of time-reversal symmetric (TRS) or time-reversal symmetry broken tilt in the Weyl spectra. We reveal that both types of tilts in the Weyl nodes lead to a Josephson $0$-$π$ transition and a zero bias valley/chiral supercurrent. Strikingly, the TRS tilt gives rise to a pure valley Josephson current (VJC) and TRS broken tilt induces a pure chirality Josephson current (CJC) in this system. The VJC and CJC are the manifestation of valley symmetry broken and $\mathbb{Z}_2$ symmetry broken by the respective tilt. We obtain the reversal of a pure VJC and pure CJC even in the zero bias condition controllable by the junction length. Our analysis of controllability of valley and chirality dependent transport in an inversion asymmetric Weyl semimetal junction could allow applications in valleytronics and chiralitytronics, respectively. The tilt induced Josephson effect provides an alternative route for supercurrent $0$-$π$ transition, different from the conventional ferromagnetism Josephson junctions where the spin polarization is essential. In the long junction and zero temperature limit, VJC and CJC are associated with a quantum anomaly which is manifested through a discontinuous jump in the current in absence of TRS and TRS breaking tilts, respectively.

cond-mat.mes-hall↗

arXiv2020

Chirality-dependent planar Hall effect in inhomogeneous Weyl semimetals

The planar Hall effect (PHE), the appearance of an in-plane transverse voltage in the presence of co-planar electric ($\mathbf{E}$) and magnetic ($\mathbf{B}$) fields, occurs in regular Weyl semimetals (WSMs) as one of the fundamental manifestations of chiral anomaly. A major issue, therefore, is whether there are alternate route to PHE, without invoking chiral anomaly. We demonstrate that PHE exists in an inhomogeneous Weyl semimetal (IWSM) even in the absence of the aforesaid anomaly. Using semiclassical Boltzmann transport theory, we show that PHE appears in an IWSM due to the strain-induced chiral gauge potential, which couples to the Weyl fermions of opposite chirality with opposite sign. Our study shows a resultant phase shift in the current associated with opposite chirality Weyl nodes, which, remarkably, leads to a finite chirality-dependent planar Hall effect (CPHE) in the IWSMs. Interestingly, we show that a small tilt in the Weyl node can generate a pure CPHE even in the absence of an applied magnetic field. The CPHE has important implications in `chiralitytronics'. We also discuss the experimental feasibility of these novel effects of strain in type-I IWSMs.

cond-mat.str-el↗

arXiv2020

Josephson effect in type-I Weyl Semimetals

The emergent Weyl fermions in condensed matter generally break the Lorentz invariance resulting in a tilted (type-I) or over-tilted (type-II) energy dispersion. The tilting energy spectrums can lead to exotic quantum interference effects in a junction set up. Here, we theoretically investigate the Josephson current in a Weyl superconductor-Weyl (semi)metal-Weyl superconductor junction of a time-reversal (TR) broken type-I Weyl semimetal. We demonstrate that the Cooper pairs of BCS-like pairing acquire a finite momentum in case of inversion symmetric tilt. Consequently, the system exhibits tilt induced anomalous current phase relations which are manifested by supercurrent $0$-$π$ transition and Josephson $ϕ$ junction. On the contrary, these effects remain absent in case of inversion breaking tilt and for FFLO-like pairing in the Weyl superconductor. We further chart out qualitative differences between the two distinct types of pairings by studying the critical current dependency on junction length. Our study opens a new avenue to probe the unconventional superconducting pairings in TR-broken Weyl semimetals. It is also quite interesting that the tilting in Weyl nodes naturally leads to anomalous current phase relations in this model without any magnetic manipulation!

cond-mat.str-el↗

arXiv2019

Josephson junctions of Weyl and multi-Weyl semimetals

We study a Josephson junction involving a Weyl and a multi-Weyl semimetal separated by a barrier region of width $d$ created by putting a gate voltage $U_0$ over the Weyl semimetal. The topological winding number of such a junction changes across the barrier. We show that $I_c R_N$ for such junctions, where $I_c$ is the critical current and $R_N$ the normal state resistance, in the thin barrier limit, has a universal value independent of the barrier potential. We provide an analytical expression of the Andreev bound states and use it to demonstrate that the universal value of $I_c R_N$ is a consequence of change in topological winding number across the junction. We also study AC Josephson effect in such a junction in the presence of an external microwave radiation, chart out its current-voltage characteristics, and show that the change in the winding number across the junction shapes the properties of its Shapiro steps. We discuss the effect of increasing barrier thickness $d$ on the above-mentioned properties and chart out experiments which may test our theory.

cond-mat.str-el↗

arXiv2019

Transport across junctions of a Weyl and a multi-Weyl semimetal

We study transport across junctions of a Weyl and a multi-Weyl semimetal (WSM and a MSM) separated by a region of thickness $d$ which has a barrier potential $U_0$. We show that in the thin barrier limit ($U_0 \to \infty$ and $d \to 0$ with $χ=U_0 d/(\hbar v_F)$ kept finite, where $v_F$ is velocity of low-energy electrons and $\hbar$ is Planck's constant), the tunneling conductance $G$ across such a junction becomes independent of $χ$. We demonstrate that such a barrier independence is a consequence of the change in the topological winding number of the Weyl nodes across the junction and point out that it has no analogue in tunneling conductance of either junctions of two-dimensional topological materials (such as graphene or topological insulators) or those made out of WSMs or MSMs with same topological winding numbers. We study this phenomenon both for normal-barrier-normal (NBN) and normal-barrier-superconductor (NBS) junctions involving WSMs and MSMs with arbitrary winding numbers and discuss experiments which can test our theory.

cond-mat.str-el↗

arXiv2018

{\em Zitterbewegung} in Spin-Orbit Coupled Systems and Ehrenfest's Theorem

We use Ehrenfest's theorem to provide a particularly simple derivation of the {\em zitterbewegung} in the dynamics of initial Gaussian wave packets in a two-dimensional electron gas. For initial packets which are very wide in the $y$-direction, the {\em zitterbewegung} is only in the $y$-component of the velocity. We extend our Ehrenfest theorem based calculation to the spin-orbit coupled spinor Bose-Einstein condensate (BEC) to predict that there can be {\em zitterbewegung} in the $x$-component of the velocity in this situation driven by a combination of the nonlinear interaction in the condensate and the splitting due to the spin-orbit coupling.

cond-mat.str-el↗

arXiv2018

Andreev tunnelling and Josephson current in light irradiated graphene

We investigate the Andreev tunneling and Josephson current in graphene irradiated with high-frequency linearly polarized light. The corresponding stroboscopic dynamics can be solved using Floquet mechanism which results in an effective stationary theory to the problem. It exhibits anisotropy in the Dirac spectrum and modifies the so-called pseudospin-momentum locking in graphene. The Andreev reflection at a normal graphene - superconductor (NS) interface becomes an oscillatory function of the optical strength. Specifically we find that, by varying the polarization direction we can both suppress AR considerably or cause the Andreev transport to remain maximum at sub-gap excitation energies even in the presence of Fermi level mismatch. Furthermore, we study the optical effect on the Andreev bound states (ABS) within a short normal-graphene sheet, sandwiched between two s-wave superconductors. It shows redistribution of the low energy regime in the ABS spectrum, which in turn, has major effect in shaping the Josephson super-current. Subjected to efficient tuning, such current can be sufficiently altered even at the charge neutrality point. Our observations provide useful feedback in regulating the quantum transport in Dirac-like systems, achieved via controlled off-resonant optical irradiation on them.

cond-mat.str-el↗

arXiv2018

Spin Transport and Spin Pump in Graphene-like Materials: Effect of tilt in Dirac cones

We study the spin transport phenomena in two-dimensional graphene-like materials with arbitrary tilted Dirac cones. The tilt arises due to next-nearest hopping when the bottom of the conduction band and top of the valence band does not simultaneously coincide at Dirac point. We consider normal-ferromagnetic-normal (N-F-N) junction of the materials and using the generalized scattering approach calculate the spin current. Here, we show that tilting the Dirac cones can strongly change the transport properties by modifying the period of oscillation of the spin current. The spin conductance can be effectively tuned by the tilt with taking advantage of the modified interference condition. A pure spin current reversal also possible with a smooth variation of the tilting. We further study the spin current by the adiabatic precession of a doped ferromagnet on top of the material. It is shown that the spin-mixing conductance and hence the spin current can become zero by turning the tilt of the Dirac cone. Our findings provide an efficient way towards high controllability of spin transport by tuning the tilt of the ferromagnetic junction and can be very useful in the field of spintronics. The model also presents a simplified way to measure the tilt of Dirac cone of those materials.

cond-mat.str-el↗

arXiv2016

Spin texture of an irradiated warped topological insulator surface

Topological insulator is a new state of matter which exhibits exotic surface electronic properties. Determining the spin texture of this class of material is of paramount importance for understanding its topological order and can lead to potential applications in spintronics. Here, we have investigated the nature of the surface state of the topological insulator with hexagonal warping subjected to an off-resonant circularly polarized light. The resulting electronic ground state exhibits a novel feature of spin texture breaking the conventional spin-momentum locking present on a topological insulator surface. The observed spin texture is shown to be a consequence of the symmetry group of the underlying crystal. The generalisation of our method to the other 2D graphene-like systems are straightforward. Our calculation charts a simple experimental route for a realisation of the non-trivial spin-textures.

cond-mat.str-el↗

arXiv2015

Quantum oscillation and wave packet revival in conical graphene structure

We present analytical expressions for the eigenstates and eigenvalues of electrons confined in a graphene monolayer in the presence of a disclination. The calculations are performed in the continuum limit approximation in the vicinity of the Dirac points, solving Dirac equation by freezing out the carrier radial motion. We include the effect of an external magnetic field and show the appearence of Aharonov-Bohm oscillation and find out the conditions of gapped and gapless states in the spectrum. We show that the gauge field due to a disclination lifts the orbital degeneracy originating from the existence of two valleys. The broken valley degeneracy has a clear signature on quantum oscillations and wave packet dynamics.

cond-mat.mes-hall↗

arXiv2014

Bound state and persistent currents in the presence of torsion and Rashba spin-orbit coupling

We study a model of an electron on a cylindrical surface, which is coupled to the torsion field due to a dislocation along the axis of the cylinder. We discuss the effect of this torsion field on the energy spectrum of the electrons and analytically calculate persistent currents in the presence of Rashba spin-orbit coupling. We also analyze bound state energy spectra in presence of Rashba spin-orbit interaction. Our results show that the presence of the torsional field due to the dislocation significantly modifies the energy spectrum of the system. The dislocation induced persistent spin current in this system is calculated, and we find a correspondence between the dislocation mediated spin current and the azimuthal spin current.

cond-mat.str-el↗

arXiv2012

Annealing of supersolidity in plastically deformed solid $^4$He

We present a numerical study of a continuum plasticity field coupled to a Ginzburg-Landau model for superfluidity. The results suggest that a supersolid fraction may appear as a long-lived transient during the time evolution of the plasticity field at higher temperatures where both dislocation climb and glide are allowed. Supersolidity, however, vanishes with annealing. As the temperature is decreased, dislocation climb is arrested and any residual supersolidity due to incomplete annealing remains frozen. Our results provide a resolution of many perplexing issues concerning a variety of experiments on solid $^4$He.

cond-mat.mtrl-sci↗

arXiv2011

Non-commutative Quantum Mechanics in Three Dimensions and Rotational Symmetry

We generalize the formulation of non-commutative quantum mechanics to three dimensional non-commutative space. Particular attention is paid to the identification of the quantum Hilbert space in which the physical states of the system are to be represented, the construction of the representation of the rotation group on this space, the deformation of the Leibnitz rule accompanying this representation and the implied necessity of deforming the co-product to restore the rotation symmetry automorphism. This also implies the breaking of rotational invariance on the level of the Schroedinger action and equation as well as the Hamiltonian, even for rotational invariant potentials. For rotational invariant potentials the symmetry breaking results purely from the deformation in the sense that the commutator of the Hamiltonian and angular momentum is proportional to the deformation.

hep-th↗

arXiv2010

A Family of Non-commutative geometries

It is shown that the non-commutativity in quantum Hall system may get modified. The self-adjoint extension of the corresponding Hamiltonian leads to a family of non-commutative geometries labeled by the self-adjoint extension parameters. We explicitly perform an exact calculation using a singular interaction and show that, when projected to a certain Landau level, the emergent non-commutative geometries of the projected coordinates belong to a one parameter family. There is a possibility of obtaining the filling fraction of fractional quantum Hall effect by suitably choosing the value of the self-adjoint extension parameter.

hep-th↗