arXiv subjects

A. Taraphder

Publications and source records attributed to A. Taraphder.

At least 19 recordsLinked to original sources

arXiv2026

Symmetry-selective field-induced triplet superconductivity in Ising-superconductor monolayer NbSe$_2$

We investigate superconductivity in monolayer NbSe$_2$, an Ising superconductor, under an in-plane Zeeman field $h_x$, focusing on the emergence of symmetry selected equal-spin triplet pairing. Using a self-consistent Bogoliubov--de Gennes approach with realistic hopping parameters for monolayer NbSe$_2$ on a triangular lattice, we determine the energetically favored singlet pairing states in a range of chemical potentials $\mu$ for onsite, nearest-neighbor, and next-nearest-neighbor pairing channels, and map the resulting phase diagram in $(h_x,\mu)$ plane. A momentum-resolved analysis reveals distinct dominant contributions in order parameters arise from the surroundings of $\Gamma$, $K$, and $K'$ points of the Brillouin zone. We find that an in-plane magnetic field helps to induce a triplet pairing whose symmetry is determined by the parent singlet state, upon opening the triplet interaction channel. For the nonlocal pairing channels, chiral-$d$ pairing is energetically favored and it induces chiral-$p$ equal-spin triplet component with opposite chirality. We further find that Rashba spin-orbit coupling, relevant to substrate coupling and electrostatic gating, suppresses the superconducting orders and reduces the critical field. Our results establish a direct link between the symmetry of the parent singlet condensate and the emergent triplet superconductivity, highlighting monolayer NbSe$_2$ as a promising platform for field-tunable mixed-parity superconducting states.

cond-mat.supr-con↗

arXiv2026

Emergent Pair Density Wave and Incoherent Metallic State in a Strongly Correlated Doped System

We investigate the dynamical emergence of a state driven by the interplay between antiferromagnetism (AFM) and singlet $d$-wave superconductivity (SC) within a slave-rotor mean-field framework. By decomposing the electron into charge and spin degrees of freedom, the formalism captures strong-correlation effects beyond conventional mean-field approaches. A PDW order is found to emerge dynamically in the coexistence region of AFM and SC. The AFM-SC coexistence region is significantly modified with correlation, leading to a systematic shift of the tetra-critical point. The doping and temperature evolution of the AFM, SC, and PDW order parameters, together with the rotor condensate amplitude $\phi$, which characterizes charge coherence, shows a crossover from a coherent to an incoherent metal with the suppression of coherent quasi-particle spectral weight. Moreover, in the AFM + $(\phi \neq 0)$ region, coherent quasi-particle bands coexist with incoherent Hubbard-like excitations, whereas only incoherent spectral features survive in the AFM + $(\phi = 0)$ regime. The SC phase exhibits nodal quasi-particles consistent with $d$-wave pairing.

cond-mat.str-el↗

arXiv2026

Observation of intertwined charge density wave order and superconductivity in Janus monolayer

Low-dimensional transition-metal dichalcogenides (TMDCs) provide an ideal platform for studying the emergence of charge density wave (CDW) and superconductivity. The discovery of emergent CDW order in 1T $\mathrm{ZrTe_2}$ monolayer raises an important question: does this instability persist when one $\mathrm{Te}$ chalcogen layer is substituted by $\mathrm{Se}$? In the present work, we investigate the CDW (2$\times$2$\times$1) and superconducting instability in 1T $\mathrm{ZrSeTe}$ Janus monolayer using first-principles calculations. The phonon spectrum exhibits a pronounced anomaly at the $\mathrm{M}$ point of the irreducible Brillouin zone, arising from enhanced electron-phonon interaction together with electronic instabilities originating from both interband and intraband scattering. The resulting lattice distortion reconstructs the electronic structure, opening a small indirect band gap, driving the system from a semi-metallic to a semiconducting state. The energy gain associated with the distortion is significantly smaller than that of $\mathrm{ZrTe_2}$ monolayer, indicating that the replacement of one $\mathrm{Te}$ chalcogen layer with $\mathrm{Se}$ weakens the CDW instability. We have further investigated the effects of electronic correlation and biaxial strain, both acts as effective tuning parameters for the instabilities concerened. In the high temperature undistorted phase, $\mathrm{ZrSeTe}$ exhibits phonon mediated two-gap superconductivity. It originates primarily from the robust coupling between the soft phonon mode at $\mathrm{M}$ point and the electronic bands predominantly derived from $\mathrm{Zr}$ $\mathit{d}$ and $\mathrm{Te}$ $\mathit{p}$ orbitals crossing the Fermi level. Spin-orbit coupling (SOC) further modifies the electronic states and reduces the superconducting transition temperature.

cond-mat.supr-con↗

arXiv2025

Phonon dynamics and chiral modes in the two-dimensional square-octagon lattice

Chiral phonons, originally identified in two-dimensional hexagonal lattices and later extended to kagome, square, and other lattices, have been extensively studied as manifestations of broken inversion and time-reversal symmetries in vibrational dynamics. In this work, we investigate the vibrational dynamics of the two-dimensional square-octagon lattice using a spring-mass model with central-force interactions. The model incorporates mass contrast and variable coupling strengths among nearest, next-nearest, and third-nearest neighbors. From the dynamical matrix, we obtain the phonon dispersion relations and identify tunable phononic band gaps governed by both mass and spring-constant ratios. The angular dependence of phase and group velocities is analyzed to reveal the pronounced anisotropy inherent to this lattice geometry. We also examine the distinctive features of the square-octagon geometry, including flat-band anomalies in the density of states and anisotropic sound propagation induced by longer-range couplings. In addition, we explore the emergence of chiral phonons by introducing a time reversal symmetry-breaking term in the dynamical matrix, and to elucidate their optical signatures, we construct a minimal model to study infrared circular dichroism arising from chiral phonon modes.

cond-mat.stat-mech↗

arXiv2025

Mott Criticality as the Confinement Transition of a Pseudogap-Mott Metal

The phenomenon of Mott insulation involves the localization of itinerant electrons due to strong local repulsion. Upon doping, a pseudogap (PG) phase emerges - marked by selective gapping of the Fermi surface without conventional symmetry breaking in spin or charge channels. A key challenge is understanding how quasiparticle breakdown in the Fermi liquid gives rise to this enigmatic state, and how it connects to both the Mott insulating and superconducting phases. Here, we develop a renormalization-based construction of strongly correlated lattice models that captures the emergence of the pseudogap phase and its transition to a Mott insulator. Applying a many-body tiling scheme to the fixed-point impurity model uncovers a lattice model with electron interactions and Kondo physics. At half-filling, the interplay between Kondo screening and bath charge fluctuations in the impurity model leads to Fermi liquid breakdown. This reveals a pseudogap phase characterized by a non-Fermi liquid (the Mott metal) residing on nodal arcs, gapped antinodal regions of the Fermi surface, and an anomalous scaling of the electronic scattering rate with frequency. The eventual confinement of holon-doublon excitations of this exotic metal obtains a continuous transition into the Mott insulator. Our results identify the pseudogap as a distinct long-range entangled quantum phase, and offer a new route to Mott criticality beyond the paradigm of local quantum criticality.

cond-mat.str-el↗

arXiv2025

Pressure induced evolution of anisotropic superconductivity and Fermi surface nesting in a ternary boride

Using Migdal-Eliashberg theory implemented in Electron Phonon Wannier (EPW) code, we have investigated anisotropic superconductivity in a ternary boride $\mathrm{Ta(MoB)_2}$. It is a single-gap, anisotropic, phonon-mediated superconductor having a critical temperature $\mathrm{T_c}\sim \, 19.3$ K. A dominant contribution to superconductivity arises from the robust coupling between electronic states, primarily created by the $\mathrm{d_{xy}}$,$\mathrm{d_{x^2 - y^2}}$ orbitals of Mo atoms and the in-plane vibrations of Mo atoms. A weak Fermi surface nesting and a small electron-phonon coupling cannot induce charge density wave-like instabilities, as evidenced by the lack of a significant peak in the real part of the total Lindhard susceptibility and the absence of phonon softening. Furthermore, we have studied its electronic and superconducting properties under hydrostatic pressure up to 76.69 GPa, owing to its low bulk modulus and metastability. The persistent reduction in the density of states at the Fermi level, Fermi surface nesting and the stiffening of phonon modes lead to a diminution of superconductivity under pressure up to 59.71 GPa. At 76.69 GPa, a modification in the topology of the Fermi surface, namely a Lifshitz transition, occurs resulting in a sudden enhancement of nesting. This enhanced nesting, in turn, induces an abrupt stabilisation of superconductivity at 76.69 GPa, resulting in a V-shaped response to pressure.

cond-mat.supr-con↗

arXiv2025

Inhomogeneous phase stiffness in two-dimensional $s$-wave disordered superconductors

We investigate the effect of white-noise disorder on the local phase stiffness and thermodynamic properties of a two-dimensional $s$-wave superconductor. Starting from a local attractive model and using path-integral formalism, we derive an effective action by decoupling the superconducting order parameter into amplitude and phase components in a gauge-invariant manner. Perturbative techniques are applied to the phase fluctuation sector to derive an effective phase-only XY model for disordered superconducting systems. Solving the saddle-point Green's function using Bogoliubov-de Gennes theory, we calculate the distributions of nearest-neighbor couplings for various disorder strengths. A single-peak distribution is observed for low disorder strength, which becomes bimodal with one peak at negative couplings as the disorder strength increases. The local phase stiffness remains randomly distributed throughout the lattice and shows no correlation with pairing amplitudes. The temperature dependence of the superfluid stiffness ($J_s$) is studied using Monte Carlo simulations. At strong disorder and low temperatures, $J_s$ increases with increasing temperature, exhibiting anomalous behavior that may indicate the onset of a glassy transition. Additionally, calculations of the Edwards-Anderson order parameter in this disorder regime suggest the emergence of a $phase$-$glass$ state at very low temperatures.

cond-mat.supr-con↗

arXiv2024

Emergence of spin-phonon coupling in a Gd-doped Y$_2$CoMnO$_6$ double perovskite oxide: a combined experimental and ab-initio study

We present Raman spectroscopy results backed by first-principles calculations and investigate the nature of possible spin-phonon coupling (SPC) in a Gd-doped Y$_2$CoMnO$_6$ (YGCMO) double perovskite oxide. The influence of Gd substitution, A-site ordering, and anti-site disorder is also studied. YGCMO exhibits anti-site disorder leading to both ferromagnetic (between Co and Mn) and antiferromagnetic interactions (Co-Co, Mn-Mn, Gd-Co/Mn), making the SPC quite intriguing. An analysis of the temperature-dependent phonon frequencies for the stretching modes of YGCMO indicates that SPC here possibly emerges from the simultaneous presence of competing ferromagnetic and antiferromagnetic interactions. The SPC strength comes out to be 0.29 cm$^{-1}$. Our density functional theory (DFT) calculations show that Phonon modes shifted towards lower frequency with Gd doping. Similarly, A-site ordring and anti-site disorder significantly alter the Raman spectra. Experimental findings are also corroborated by first-principles DFT calculations, which indicate that anti-site disorder and Gd doping enhances SPC in YGCMO. This implies a strong influence of A-site cationic radii, and B-site (Co/Mn) ordering on SPC in the bulk double perovskite systems. The phonon dynamics of YGCMO are, therefore, correlated with magnetic ordering, indicating potential applications in spintronics devices.

cond-mat.mtrl-sci↗

arXiv2024

Extended Kohler's scaling, a low temperature anomaly and Isosbestic point in the charge density wave state of 1T-VSe$_2$

1T-VSe$_2$ is a narrow band transition metal chalcogenide that shows charge density wave (CDW) state below $T_{CDW}$ = 110 K. Here, we have explored the relevance of Kohler's rule and the thermal transport properties of VSe$_2$ across the CDW state. The magnetoresistance (MR) follows Kohler's rule above $T_{CDW}$, while an extended Kohler's rule is employed below $T_{CDW}$. Interestingly, we observed an anomaly in MR at T = 20 K, below which MR value decreases on lowering temperature. This anomaly is also reflected in the slope ($κ$) of Kohler's plots and the relative change in the thermal excitation induced carrier density ($n_T$) also. The $T_{CDW}$ remains largely unaffected in both electrical resistivity ($ρ(T)$) and longitudinal Seebeck coefficient ($\it{S_{xx}}$) even under a strong magnetic field of 14 Tesla. However, the application of magnetic field enhances the peak intensity of $\it{S_{xx}}$ at T $\sim$ 60 K. Additionally, $\it{S_{xx}(T)}$ curves measured at different fields exhibit a crossover at T = 20 K, which suggest the existence of unique feature in the CDW state of VSe$_2$ \textit{i.e.} a locally exact isosbestic point.

cond-mat.str-el↗

arXiv2024

Topological Optical Pseudospin Injection Beyond Weyl Semimetals

Photoinduced effects are now reckoned to be important tools to reveal a rich gamut of entrancing physics in topological materials, which are normally inaccessible to conventional probes. Here we investigate one of these intriguing effects, namely, optical pseudospin injection (OPI) beyond ordinary Weyl semimetals (WSMs), specifically in multi-WSMs (mWSMs) and higher-order WSMs. Remarkably, we demonstrate that OPI in mWSMs is independent of the frequency of the light and linearly proportional to the quantized topological charge as a consequence of the inherent band linearity in their dispersions. Interestingly, while the response does not depend on the tilting of a type-I node, it is a decreasing function of the same in type-II mWSMs. We also reveal that the frequency independence can be destroyed either by going beyond a certain cutoff frequency under lattice regularization or by going to a higher-order Weyl phase. The predicted signatures of OPI beyond the ordinary WSM could be experimentally exploited, leading to effective access as well as distinguishing between different nontrivial Weyl topologies.

cond-mat.mes-hall↗

arXiv2024

Role of strong correlation and spin-orbit coupling in $\textrm{LuB}_{4}$: a first principle study

The recent observation of magnetization plateaus in rare-earth metallic tetraborides has drawn a lot of attention to this class of materials. In this work, we investigate the electronic structure of one such canonical system $\textrm{LuB}_{4}$, using first-principle density functional theory, together with strong Coulomb correlation and spin-orbit coupling (SOC) effects. The electronic band structures show that $\textrm{LuB}_{4}$ is a non-magnetic correlated metal with completely filled $4f$ shell. The projected density of states (DOS) shows a continuum at the Fermi level (FL), arising mainly from hybridized Lu $d$ and B $p$ orbitals, along with some discrete peaks, well separated from the continuum. These peaks arise mainly due to core-level Lu $s$, $p$ and $4f$ atomic orbitals. Upon inclusion of SOC, the discrete peak arising due to Lu $p$ is split into two peaks with $j = 1/2$, $j = 3/2$ while the peak arising due to Lu $4f$ orbitals splits into two peaks with $j = 5/2$ and $j = 7/2$. These peaks will give rise to multiplet structure in core level X-ray photo-emission spectroscopy. Inclusion of strong correlation effects pushes the Lu $4f$ peak away from the FL while the qualitative features remain intact.

cond-mat.str-el↗

arXiv2024

Signature of nodal topology in nonlinear quantum transport across junctions in Weyl and multi-Weyl semimetals

We investigate quantum transport through a rectangular potential barrier in Weyl semimetals (WSMs) and multi-Weyl semimetals (MSMs), within the framework of Landauer-Büttiker formalism. Our study uncovers the role of nodal topology imprinted in the electric current and the shot noise. We find that, in contrast to the finite odd-order conductance and noise power, the even-order contributions vanish at the nodes. Additionally, depending on the topological charge ($J$), the linear conductance ($G_1$) scales with the Fermi energy ($E_F$) as $G_1^{E_F>U}\propto E_F^{2/J}$. We demonstrate that the $E_F$-dependence of the second-order conductance and shot noise power could quite remarkably distinguish an MSM from a WSM depending on the band topology, and may induce several smoking gun experiments in nanostructures made out of WSMs and MSMs. Analyzing shot noise and Fano factor, we show that the transport across the rectangular barrier follows the sub-Poissonian statistics. Interestingly, we obtain universal values of Fano factor at the nodes unique to their topological charges. The universality for a fixed $J$, however, indicates that only a fixed number of open channels participate in the transport through evanescent waves at the nodes. The proposed results can serve as a potential diagnostic tool to identify different topological systems in experiments.

cond-mat.mes-hall↗

arXiv2023

Large circular photogalvanic effect in the noncentrosymmetric magnetic Weyl semimetal CeAlSi

The recent discovery of the Weyl semimetal CeAlSi with simultaneous breaking of inversion and time-reversal symmetries has opened up new avenues for research into the interaction between light and topologically protected bands. In this work, we present a comprehensive examination of the shift current and injection current responsible for the circular photogalvanic effect in CeAlSi using first-principles calculations. Our investigation identifies a significant injection current of 4 mA/V$^2$ over a broad range in the near-infrared region of the electromagnetic spectrum, exceeding previously reported findings. In addition, we explored several externally controllable parameters to further enhance the photocurrent. A substantial boost in the injection current is observed when applying uniaxial strain along the $c$ axis of the crystal: a 5% strain results in a remarkable 64% increment. The exceptional photocurrent response in CeAlSi suggests that magnetic non-centrosymmetric Weyl semimetals may provide promising opportunities for novel photogalvanic applications.

cond-mat.mes-hall↗

arXiv2023

Possible routes to superconductivity in the surface layers of V-doped Mg$_{1-δ}$Ti$_2$O$_4$ through multiple charge transfers and suppression of Jahn-Teller activity

Superconductivity in the family of spinel oxides is very rare owing to their robust Mott-insulating nature. About half a century ago, LiTi$_2$O$_4$ became the first reported spinel compound to show superconductivity with a 12K transition temperature. Since then, several unsuccessful attempts were made to enhance the T$_c$ of this family of materials. However, a very recent experiment [arXiv:2209.02053] has reported superconductivity at a higher temperature (below 16K), in the V-doped Mg$_{1-δ}$Ti$_2$O$_4$ thin surface layer while its bulk counterpart remains Mott insulating. The superconducting T$_c$ of this material is significantly higher compared to other engineered MgTi$_2$O$_4$ thin films grown on different substrates. From our first-principles analysis, we have identified that Mg-depletion significantly reduces Jahn-Teller (JT) activity and antiferromagnetic superexchange at the surface layer of V-doped MgTi$_2$O$_4$ due to considerable charge transfer between various ions. The combined effect of a degraded antiferromagnetic order and reduced JT activity weakens the Mottness of the system, leading to the emergence of superconductivity at higher temperatures.

cond-mat.supr-con↗

arXiv2023

Magneto-Transport and High-Resolution Angle-Resolved Photoelectron Spectroscopy Studies of Palladium Doped Bi$_{2}$Te$_{3}$

We have performed magneto-transport and high-resolution angle-resolved photoelectron spectroscopy (ARPES) measurements on palladium (Pd) doped topological insulator Pd$_{x}$Bi$_{2}$Te$_{3}$ (0 $\leq$ x $\leq$ 0.20) single crystals. We have observed unusually high values of magnetoresistance ($\sim$ 1500%) and mobility ($\sim$ 93000 cm$^{2}$V$^{-1}$s$^{-1}$) at low temperatures for pristine Bi2Te3 that decrease on Pd doping. The Shubnikov-de Haas (SdH) oscillations have been detected for x = 0.05, 0.10, confirming the presence of 2D topological surface states (TSSs) for these samples. The Hall measurement shows the crossover from n-type charge carriers in pristine Bi$_{2}$Te$_{3}$ to p-type charge carriers upon Pd doping. The ARPES measurements show that the conduction band crosses the Fermi level for pristine Bi$_{2}$Te$_{3}$, and the Dirac point of the TSSs and bulk-derived valence bands indicated shift to lower binding energy upon Pd doping in a rigid-band-like way up to x $\sim$0.10. Based on the comparison of the parameters obtained from the SdH and ARPES measurements, the reduction in the kF value in the magneto-transport measurements likely due to the band bending induced by the Schottky barrier.

cond-mat.str-el↗

arXiv2023

Kondo frustration via charge fluctuations: a route to Mott localisation

We propose a minimal effective impurity model that captures the phenomenology of the Mott-Hubbard metal-insulator transition (MIT) of the half-filled Hubbard model on the Bethe lattice in infinite dimensions as observed by dynamical mean field theory (DMFT). This involves extending the standard Anderson impurity model Hamiltonian to include an explicit Kondo coupling $J$, as well as a local on-site correlation $U_b$ on the conduction bath site connected directly to the impurity. For the case of attractive local bath correlations ($U_{b}<0$), the extended Anderson impurity model (e-SIAM) sheds new light on several aspects of the DMFT phase diagram. For example, the $T=0$ metal-to-insulator quantum phase transition (QPT) is preceded by an excited state quantum phase transition (ESQPT) where the local moment eigenstates are emergent in the low-lying spectrum. Long-ranged fluctuations are observed near both the QPT and ESQPT, suggesting that they are the origin of the quantum critical scaling observed recently at high temperatures in DMFT simulations. The $T=0$ gapless excitations at the QCP display particle-hole interconversion processes, and exhibit power-law behaviour in self-energies and two-particle correlations. These are signatures of non-Fermi liquid behaviour that emerge from the partial breakdown of the Kondo screening.

cond-mat.str-el↗

arXiv2023

Possible realization of hyperbolic plasmons in a few-layered rhenium disulfide

The in-plane structural anisotropy in low-symmetric layered compound rhenium disulfide ($\text{ReS}_2$) makes it a candidate to host and tune electromagnetic phenomena specific for anisotropic media. In particular, optical anisotropy may lead to the appearance of hyperbolic plasmons, a highly desired property in optoelectronics. The necessary condition is a strong anisotropy of the principal components of the dielectric function, such that at some frequency range, one component is negative and the other is positive, i.e., one component is metallic, and the other one is dielectric. Here, we study the effect of anisotropy in $\text{ReS}_2$ and show that it can be a natural material to host hyperbolic plasmons in the ultraviolet frequency range. The operating frequency range of the hyperbolic plasmons can be tuned with the number of $\text{ReS}_2$ layers.

cond-mat.mtrl-sci↗

arXiv2023

Frustration shapes multi-channel Kondo physics: a star graph perspective

We study the overscreened multi-channel Kondo (MCK) model using the recently developed unitary renormalization group (URG) technique. Our results display the importance of ground state degeneracy in explaining various important properties like the breakdown of screening and the presence of local non-Fermi liquids. The impurity susceptibility of the intermediate coupling fixed point Hamiltonian in the zero-bandwidth (or star graph) limit shows a power-law divergence at low temperature, signalling its critical nature. Despite the absence of inter-channel coupling in the MCK fixed point Hamiltonian, the study of mutual information between any two channels shows non-zero correlation between them. A spectral flow analysis of the star graph reveals that the degenerate ground state manifold possesses topological quantum numbers. The low energy effective Hamiltonian obtained upon adding a finite non-zero conduction bath dispersion to the star graph Hamiltonian for both the two and three-channel cases displays the presence of local non-Fermi liquids arising from inter-channel quantum fluctuations. Discontinuous behaviour is observed in several measures of ground state entanglement, signalling the underlying orthogonality catastrophe associated with the degenerate ground state manifold. We extend our results to underscreened and perfectly screened MCK models through duality arguments. A study of channel anisotropy under renormalisation flow reveals a series of quantum phase transitions due to the change in ground state degeneracy. Our work thus presents a template for the study of how a degenerate ground state manifold arising from symmetry and duality properties in a multichannel quantum impurity model can lead to novel multicritical phases at intermediate coupling.

cond-mat.str-el↗