arXiv subjects

Ipsita Mandal

Publications and source records attributed to Ipsita Mandal.

At least 37 records · Page 2Linked to original sources

arXiv2025

Effects of time-periodic drive in the linear response for planar-Hall set-ups with Weyl and multi-Weyl semimetals

We investigate the influence of a time-periodic drive on three-dimensional Weyl and multi-Weyl semimetals in planar-Hall/planar-thermal-Hall set-ups. The drive is modelled here by circularly-polarized electromagnetic fields, whose effects are incorporated by a combination of the Floquet theorem and the van Vleck perturbation theory, applicable in the high-frequency limit. We evaluate the longitudinal and in-plane transverse components of the linear-response coefficients using the semiclassical Boltzmann formalism, thereby demonstrating the explicit analytical expressions of the conductivity for large frequencies. Our results corroborate the fact that the topological charges of the corresponding semimetals etch their trademark signatures in these transport properties, which can be detected in appropriate experiments.

cond-mat.mes-hall↗

arXiv2025

Stable non-Fermi liquid fixed point at the onset of incommensurate $2k_F$ charge density wave order

We consider the emergence of a non-Fermi liquid fixed point in a two-dimensional metal, at the onset of a quantum phase transition from a Fermi liquid state to an incommensurate charge density wave (CDW) ordered phase. The momentum of the CDW boson is centred at the wavevector $ \boldsymbol{ \mathcal Q} $, which connects a single pair of antipodal points on the Fermi surface with antiparallel tangent vectors. We employ the dimensional regularization technique in which the co-dimension of the Fermi surface is extended to a generic value, while keeping the dimension of the Fermi surface itself fixed at one. Although the system is strongly coupled at dimension $d=2$, the interactions become marginal at the upper critical dimension $d=d_c$, whose value is found to be $ 5/2$. Using a controlled perturbative expansion in the parameter $ε= d_c - d $, we compute the critical exponents of the stable infrared fixed point characterizing the quantum critical point. The scalings of the original theory are determined by setting $ε=1/2$, where the fermion self-energy is seen to scale with the frequency with a fractional power law of $2/3$, which is the telltale signature of a typical non-Fermi liquid phase.

cond-mat.str-el↗

arXiv2025

Hong-Ou-Mandel interferometry for fractional excitations: Unified framework and dip width scaling

Extending Hong--Ou--Mandel (HOM) interferometry to the fractional quantum Hall effect (FQHE) promises direct access to anyonic statistics, yet remains challenging: on-demand anyon injection is hindered by integer-charged minimal excitations, and recent HOM experiments in the FQHE lack a fully consistent theoretical framework. Here we provide a general theory of time-resolved HOM interferometry in quantum Hall systems. Combining the nonequilibrium bosonized edge theory (NEBET) with the unifying non-equilibrium perturbative theory (UNEPT), we derive exact and perturbative relations obeyed by the relevant cross-correlations of chiral currents valid for spatially extended tunneling operators and generic quadratic edge dynamics. Then, within the Tomonaga--Luttinger liquid (TLL) framework, we analyze the width of the HOM dip for injected pulses carrying integer and fractional charges. We show that it is governed by the width of the pulses and, for the fractional charge, by a non-trivial power-law behavior of the scaling dimension. Our results establish a robust theoretical foundation for interpreting recent experiments on anyonic statistics and electronic interferometry in the quantum Hall regime.

cond-mat.mes-hall↗

arXiv2025

Anisotropic conductivity for the type-I and type-II phases of Weyl/multi-Weyl semimetals in planar Hall set-ups

We compute the non-Drude part of the conductivity tensor in planar Hall set-ups, for tilted Weyl and multi-Weyl semimetals, considering both the type-I and type-II phases. We do so in three distinct set-ups, taking into account the possible relative orientations of the plane spanned by the electric and magnetic fields ($\mathbf E $ and $\mathbf B $) and the direction of the tilt-axis. We derive the analytical expressions for the response tensor, including the effects of the Berry curvature (BC) and the orbital magnetic moment (OMM), both of which arise due to a nontrivial topology of the three-dimensional manifold defined by the Brillouin zone. We exhibit the interplay of the BC-only and the OMM-dependent parts in the nonzero components of the magnetoelectric conductivity, and outline whether the contributions from the former or the latter dominate the overall response. Our results also show that, depending on the configuration of the planar Hall set-up, one may or may not get terms which have a linear-in-$ B$ dependence.

cond-mat.mes-hall↗

arXiv2025

Chiral anomaly and internode scatterings in multifold semimetals

In our quest to unravel the topological properties of nodal points in three-dimensional semimetals, one hallmark property which warrants our attention is the \textit{chiral anomaly}. In the Brillouin zone (BZ), the sign of the Berry-curvature field's monopole charge is referred to as the chirality ($χ$) of the node, leading to the notion of chiral quasiparticles sourcing chiral currents, induced by internode scatterings proportional to the chiral anomaly. Here, we derive the generic form of the chiral conductivity when we have multifold nodes. Since the sum of all the monopole charges in the BZ is constrained to vanish, the nodes appear in pairs of $χ=\pm 1$. Hence, the presence of band-crossing degeneracies of order higher than two make it possible to have two distinct scenarios: the pair of conjugate nodes in question comprise bands of (1) the same pseudospin variety and exhibiting Berry-curvature profiles differing by an overall factor of $χ$, or (2) two distinct pseudospin representations. Covering these two possibilities, we apply our derived formula to semimetals harbouring triple-point (threefold-degenerate) and Rarita-Schwinger-Weyl (fourfold-degenerate) nodes, and show the resulting expressions for the conductivity featuring the chiral anomaly.

cond-mat.mes-hall↗

arXiv2025

Electric and thermoelectric response for Weyl and multi-Weyl semimetals in planar Hall configurations including the effects of strain

We investigate the response tensors in planar Hall (or planar thermal Hall) configurations such that a three-dimensional Weyl or multi-Weyl semimetal is subjected to the influence of an electric field $\mathbf E $ (or temperature gradient $\nabla_{\mathbf r } T$) and an effective magnetic field $\mathbf B^{\rm tot}$, which are oriented at a generic angle with respect to each other. The effective magnetic field consists of two parts: (a) an actual/physical magnetic field $\mathbf B $, and (b) an emergent magnetic field $\mathbf B_5 $ which quantifies the elastic deformations of the sample. $\mathbf B_5 $ is an axial pseudomagnetic field because it couples to conjugate nodal points with opposite chiralities with opposite signs. We study the interplay of the orientations of these two components of $\mathbf B^{\rm tot}$ with respect to the direction of the electric field (or temperature gradient) and elucidate how it affects the characteristics involving the chirality of the node. Additionally, we show that the magnitude and sharpness of the conductivity tensor profiles strongly depend on the value of the topological charge at the node in question.

cond-mat.mes-hall↗

arXiv2025

Delta-function-potential junctions with quasiparticles occupying tilted bands with quadratic-in-momentum dispersion

We continue our explorations of the transport characteristics in junction-configurations comprising semimetals with quadratic band-crossings, observed in the bandstructures of both two- and three-dimensional materials. Here, we consider short potential barriers/wells modelled by delta-function potentials. We also generalize our analysis by incorporating tilts in the dispersion. Due to the parabolic nature of the spectra, caused by quadratic-in-momentum dependence, there exist evanescent waves, which decay exponenWe continue our explorations of the transport characteristics in junction-configurations comprising semimetals with quadratic band-crossings, observed in the bandstructures of both two- and three-dimensional materials. Here, we consider short potential barriers/wells modelled by delta-functions. We also generalize our analysis by incorporating tilts in the dispersion. Due to the parabolic nature of the spectra, caused by quadratic-in-momentum dependence, there exist evanescent waves, which decay exponentially as we move away from the junction represented by the location of the delta-function potential. Investigating the possibility of the appearance of bound states, we find that their energies appear as pairs of $\pm |E_b |$, reflecting the presence of the imaginary-valued wavevectors at both positive and negative values of energies of the propagating quasiparticles.

cond-mat.mes-hall↗

arXiv2025

Linear response of tilted anisotropic two-dimensional Dirac cones

We investigate the behaviour of the linear-response coefficients, when in-plane electric field ($\mathbf E$) or/and temperature gradient ($\nabla_{\mathbf r} T$) is/are applied on a two-dimensional semimetal harbouring anisotropic Dirac cones. The anisotropy is caused by (1) differing Fermi velocities along the two mutually perpendicular momentum axes, and (2) tilting parameters. Using the semiclassical Boltzmann formalism, we derive the forms of the response coefficients, in the absence and presence of a nonquantizing magnetic field $\mathbf B$. The magnetic field affects the response only when it is oriented perpendicular to the plane of the material, with the resulting expressions computed with the help of the so-called Lorentz-force operator, appearing in the linearized Boltzmann equation. The solution has to be found in a recursive manner, which produces terms in powers of $|\mathbf B|$. We discuss the validity of the Mott relation and the Wiedemann-Franz law for the Lorentz-operator-induced parts.

cond-mat.mes-hall↗

arXiv2025

Transmission through rectangular potentials in semimetals featuring quadratic dispersion

We revisit the problem of transmission of quasiparticles through a rectangular potential barrier, for semimetals featuring quadratic-in-momentum band-crossings at a nodal point. Although this was considered in Annals of Physics 419 (2020) 168235, the solutions corresponding to evanescent waves were missed, leading to a partial fulfillment of the boundary conditions required to determine the piecewise-continuous wavefunctions. In this paper, our aim is to correct those shortcomings, recompute the transmission coefficients, and show the resulting behaviour of the conductivity and the Fano factor for some representative parameter values.

cond-mat.mes-hall↗

arXiv2025

Direction-dependent conductivity in planar Hall set-ups with tilted Weyl/multi-Weyl semimetals

We compute the magnetoelectric conductivity tensors in planar Hall set-ups, which are built with tilted Weyl semimetals (WSMs) and multi-Weyl semimetals (mWSMs), considering all possible relative orientations of the electromagnetic fields ($\mathbf E $ and $\mathbf B $) and the direction of the tilt. The non-Drude part of the response arises from a nonzero Berry curvature in the vicinity of the WSM/mWSM node under consideration. Only in the presence of a nonzero tilt do we find linear-in-$ | \mathbf B| $ terms in set-ups where the tilt-axis is not perpendicular to the plane spanned by $\mathbf E $ and $ \mathbf B $. The advantage of the emergence of the linear-in-$ | \mathbf B| $ terms is that, unlike the various $| \mathbf B|^2 $-dependent terms that can contribute to experimental observations, they have purely a topological origin, and they dominate the overall response-characteristics in the realistic parameter regimes. The important signatures of these terms are that they (1) change the periodicity of the response from $π$ to $2π$, when we consider their dependence on the angle $θ$ between $\mathbf E $ and $\mathbf B $; and (2) lead to an overall change in sign of the conductivity depending on $θ$, when measured with respect to the $\mathbf B =0$ case.

cond-mat.mes-hall↗

arXiv2025

Reflections of topological properties in the planar-Hall response for semimetals carrying pseudospin-1 quantum numbers

We continue our investigations of the nature of the linear-response tensors in planar-Hall and planar-thermal Hall configurations, involving three-dimensional nodal-point semimetals, by considering here nodes hosting pseudospin-1 quasiparticles. Such systems exemplify multifold semimetals, as they have three bands crossing at a nodal point. We derive the explicit expressions of the electric, thermoelectric, and thermal coefficients, when the nodes are subjected to the combined influence of an electric field (and/or temperature gradient) and a weak (i.e., nonquantizing) magnetic field. In order to have a complete description, we consider the effects of the Berry curvature and the orbital magnetic moment on an equal footing, both of which originate from the underlying topological features of the bandstructure. Going beyond our previous works, we determine the out-of-plane response comprising the intrinsic anomalous-Hall and the Lorentz-force-contributed currents, and chalk out the effects of internode scatterings as well. Our theoretical explorations shed light on the mechanisms of transport in multifold semimetals, which are being investigated in contemporary experiments.

cond-mat.mes-hall↗

arXiv2025

Nature of Andreev bound states in Josephson junctions of triple-point semimetals

We study superconductor-barrier-superconductor (S-B-S) Josephson junctions constructed out of two-dimensional and three-dimensional triple-point semimetals, which feature a threefold degeneracy at a single nodal point. We assume a weak and homogeneous s-wave pairing in each superconducting region, and a potential difference is applied across a piece of normal-state semimetal to create the barrier region. We compute the wavefunctions of the Andreev bound states (ABSs), considering the thin-barrier limit. The appropriate boundary conditions at the S-B and B-S junctions allow us to compute the discrete energy eigenvalues $\pm |\varepsilon| $ of the ABSs. We get two distinct solutions for $|\varepsilon| $. This result differs from that in graphene and Weyl semimetals, where one obtains only one solution for $|\varepsilon| $. The multifold nature of the triple-point fermions is responsible for this difference. We also illustrate the behaviour of the Josephson current flowing across the S-B-S junction.

cond-mat.supr-con↗

arXiv2025

Characterizing topological pumping of charges in exactly solvable Rice-Mele chains of the non-Hermitian variety

We address the nature of the Thouless charge-pumping for a non-Hermitian (NH) generalization of the one-dimensional (1d) Rice-Mele model, considering a variety which allows closed-form analytical solutions for the eigensystems. The two-band system is subjected to an ``adiabatic'' time-periodic drive, which effectively gives us a closed two-dimensional (2d) manifold in the momentum-frequency space, mimicking a 2d Brillouin zone (BZ) for periodic boundary conditions. For open boundary conditions, we formulate the non-Bloch generalized Brillouin zone (GBZ). All these allow us to compute the Chern numbers of the 2d manifolds emerging for various parameter values, using the BZ or GBZ, which are well-defined integers in the gapped regions of the spectra. If Thouless pumping still holds for NH situations, the expectation values of the net displacement for the particles occupying a given band within a cycle, calculated using the right and left eigenvectors of a biorthogonal basis for the complex Hamiltonians, would coincide with the Chern numbers. However, we find that there are deviations from the expected quantized values whenever the spectra exhibit strongly-fluctuating magnitudes of the imaginary parts of the (generically) complex eigenvalues. This implies that we need to address the question of how to meaningfully define time-evolution, as well as adiabaticity, in the context of NH systems.

quant-ph↗

arXiv2025

Induction of non-Fermi liquids by critical cavity photons at the onset of superradiance

We investigate the emergence of a non-Fermi liquid (NFL) at a putative quantum critical point signalling the onset of superradiance, in a set-up involving cavity quantum electrodynamics. Although the finiteness of the cavity, being bounded by reflecting mirrors, endows the cavity photons with an effective mass, they become massless at the continuous phase-transition point. We consider the matter part coming from the fermions hopping on a honeycomb lattice near half-filling, featuring doped Dirac cones at two sets of inequivalent valleys. This choice is dictated by the presence of a fermion-boson interaction vertex, which can give rise to Landau damping of the critical bosons, eventually leading to an NFL phase for the fermions. To set up the quantum effective action, we identify the hot-spots of the generically anisotropic (trigonally-warped) Fermi surfaces, which give the sets of points having parallel/antiparallel tangent vectors. The cavity photons act as charge density wave (CDW) order parameters, connecting pairs of hot-spots belonging to the Fermi surface of a single valley. With these ingredients, we set upon identifying NFL phases, using the tools of dimensional regularization and renormalization-group-flow equations. Our final results indicate that stable NFL phases exist in the low-energy limit, for the projections of the flows along the CDW coupling constant.

cond-mat.str-el↗

arXiv2024

Signatures of topology in generic transport measurements for Rarita-Schwinger-Weyl semimetals

We investigate how the signatures of the topological properties of the bandstructures for nodal-point semimetals are embedded in the response coefficients, arising in two distinct experimental set-ups, by taking the Rarita-Schwinger-Weyl (RSW) semimetal as an example. The first scenario involves the computation of third-rank tensors representing second-order response coefficients, relating the charge/thermal current densities to the combined effects of the gradient of the chemical potential and an external electric field/temperature gradient. On the premises that internode scatterings can be ignored, the relaxation-time approximation leads to a quantized value for the nonvanishing components of each of these nonlinear response tensors, characterizing a single untilted RSW node. Furthermore, the final expressions turn out to be insensitive to the specific values of the chemical potential and the temperature. The second scenario involves computing the magnetoelectric conductivity under the action of collinear electric ($\mathbf E$) and magnetic ($\mathbf B$) fields, representing a planar Hall set-up. In particular, our focus is in bringing out the dependence of the linear-in-$|\mathbf B|$ parts of the conductivity tensor on the intrinsic topological properties of the bandstructure, which are nonvanishing only in the presence of a nonzero tilt in the energy spectrum.

cond-mat.mes-hall↗

arXiv2024

Thermoelectric response in nodal-point semimetals

In this review, the thermoelectric properties in nodal-point semimetals with two bands are discussed. For the two-dimensional (2D) cases, it is shown that the expressions of the thermoelectric coefficients take different values depending on the nature of the scattering mechanism responsible for transport, by considering examples of short-ranged disorder potential and screened charged impurities. An anisotropy in the energy dispersion spectrum invariably affects the thermopower quite significantly, as illustrated by the results for a node of semi-Dirac semimetal and a single valley of graphene. The scenario when a magnetic field of magnitude $B$ is applied perpendicular to the plane of the 2D semimetal is also considered. The computations for three-dimensional (3D) cases necessarily involve the inclusion of nontrivial Berry phase effects. In addition to demonstrating the expressions for the response tensors, the exotic behaviour observed in planar Hall and planar thermal Hall set-ups is also discussed.

cond-mat.mes-hall↗

arXiv2024

Transmission and conductance across junctions of isotropic and anisotropic three-dimensional semimetals

We compute the transmission coefficients and zero-temperature conductance for chiral quasiparticles propagating through various geometries, which consist of junctions of three-dimensional nodal-point semimetals. In the first scenario, we consider a potential step with two Rarita-Schwinger-Weyl or two birefringent semimetals, which are tilted with respect to the other on the two sides of the junction. The second set-up consists of a junction between a doped Dirac semimetal and a ferromagnetic Weyl semimetal, where an intrinsic magnetization present in the latter splits the doubly-degenerate Dirac node into a pair of Weyl nodes. A scalar potential is also applied in the region where the Weyl semimetal phase exists. Finally, we study sandwiches of Weyl/multi-Weyl semimetals, with the middle region being subjected to both scalar and vector potentials. Our results show that a nonzero transmission spectrum exists where the areas, enclosed by the Fermi surface projections (in the plane perpendicular to the propagation axis) of the incidence and transmission regions, overlap. Such features can help engineer unidirectional carrier propagation, topologically protected against impurity backscattering, because of the chiral nature of the charge carriers.

cond-mat.mes-hall↗

arXiv2024

Linear response in planar Hall and thermal Hall setups for Rarita-Schwinger-Weyl semimetals

We investigate the nature of the linear-response tensors in planar Hall and planar thermal Hall setups, where we subject a Rarita-Schwinger-Weyl (RSW) semimetal to the combined influence of an electric field $\mathbf E $ (and/or temperature gradient $\nabla_{\mathbf r } T$) and a weak (i.e., nonquantizing) magnetic field $\mathbf B $. For computing the in-plane transport components, we have added an elastic deformation which gives rise to a chirality-dependent effective magnetic field $ \mathbf B^{\text{tot}} = \mathbf B + χ\, \mathbf B_5 $, where $χ$ is the chirality of an RSW node. We have included the effects of orbital magnetic moment (OMM), in conjunction with the Berry curvature (BC), both of which appear as a consequence of nontrivial topology of the bandstructure. Due to the presence of four bands, RSW semimetals provide a richer structure for obtaining the linear-response coefficients, compared to the Weyl semimetals. In particular, we have found that the OMM-contributed terms may oppose or add up to the BC-only parts, depending on which band we are considering. Last, but not the least, we have determined the out-of-plane response comprising the intrinsic anomalous-Hall and the Lorentz-force-contributed currents, whose nature corroborates the findings of some recent experimental results.

cond-mat.mes-hall↗