arXiv subjects

B. Tanatar

Publications and source records attributed to B. Tanatar.

At least 19 recordsLinked to original sources

arXiv2026

Quadratic pair-breaking absorption edge from Anderson localization in a superconducting wire

We show that Anderson localization fundamentally reshapes dissipative superconducting electrodynamics, replacing the linear Mattis--Bardeen pair-breaking onset with a parametrically weaker quadratic Mott edge while leaving the quasiparticle spectrum unchanged. We derive this behavior for a weakly disordered single-channel wire with a spatially uniform $s$-wave pair potential using a Nambu-space extension of the Berezinskii diagram technique that resums elastic impurity scattering to all orders. Conservation of the Bogoliubov branch collapses the Nambu diagram hierarchy onto an exactly solvable localization problem. The localization length remains equal to its normal-state value, whereas the localization time diverges at the gap edge. The new absorption edge results from the product of the superconducting pair-creation coherence factor and the Mott-suppressed current matrix elements between localized orbitals, which generates the characteristic double logarithm. Localization also reduces the Hebel--Slichter coherence peak. The resulting theory provides an all-orders benchmark for microwave and spin-relaxation experiments on localized superconducting nanowires.

cond-mat.supr-con↗

arXiv2026

Impact of spin-orbit coupling on electron correlation corrections to the density of states in anisotropic conductors

We study Altshuler-Aronov-type interaction corrections to the single-particle density of states (DOS) in a strongly anisotropic 2D conductor with an open Fermi surface (FS) and weak disorder, in the presence of coexisting Rashba and Dresselhaus spin-orbit couplings (SOCs) constrained to the longitudinal direction. The low-energy band consists of two warped sheets weakly tunnel-coupled transversely; SOC splits the sheets into helicity branches with a fixed spin axis. Working in a Matsubara space, we compute the exchange contribution in the diffusion channel with dynamically screened Coulomb interaction and an impurity ladder. The resulting DOS anomaly exhibits a dimensional crossover governed by the transverse coupling scale $\varepsilon_c$. Close to the Fermi level ($|\varepsilon-\varepsilon_F|<\varepsilon_c$), the system behaves two-dimensionally, featuring a logarithmic DOS dip whose magnitude is enhanced by intrinsic SOCs. Further from the Fermi level ($|\varepsilon-\varepsilon_F|\!>\!\varepsilon_c$), the system behaves quasi-one-dimensionally, featuring a sharper square-root singularity whose amplitude is remarkably enhanced by the SOCs. Notably, we identify a critical SOC strength at which these spin-orbit effects exactly cancel the electron-correlation correction, perfectly restoring the unperturbed density of states. Furthermore, increasing the SOC beyond this critical point inverts the sign of the anomaly entirely, yielding a positive DOS correction. This sign reversal fundamentally alters the energy dependence, such that at energies beyond $\varepsilon_F + \varepsilon_c$, the positive correction decays to smaller values as energy increases, opposite to the standard negative correction. This contrasting trend provides a distinct spectroscopic signature of SOC-modulated correlation effects.

cond-mat.mes-hall↗

arXiv2026

Localization Transitions in a Half-Filled Helical Aubry-Andr\'e Model

We study localization in a one-dimensional quasiperiodic lattice obtained by extending the Aubry-Andr\'e model with an additional $N$th-neighbor hopping term of strength $J_{N}$. This long-range tunneling couples successive windings of an effective helical chain and introduces a second control parameter beyond the quasiperiodic potential strength $\Delta$. Working with noninteracting fermions (typically at half filling), we diagnose the delocalization-localization transition using extensions of the modern theory of polarization. Specifically, we compute the polarization amplitudes of the many-body Slater-determinant ground state and construct a geometric Binder cumulant from polarization amplitudes. The critical potential where the localization transition happens is extracted from the sign change (zero crossing) of the geometric Binder cumulant. We map critical potential as a function of $J_N$ and the helical range $N$, finding that stronger helical hopping generally stabilizes the extended phase (shifting critical potential upward), while the $N$-dependence can display pronounced commensurability-induced spikes. We further compare the geometric Binder cumulant with the Fermi gap, which remains near zero at small values of potential and opens in the same parameter regime where the geometric Binder cumulant departs from extended phase. Finally, to take a controlled thermodynamic limit along Fibonacci system sizes, we employ a Zeckendorf-shift construction that fixes the many-body sector consistently as system size goes to infinity.

cond-mat.dis-nn↗

arXiv2025

Reentrant Localization Transition in a Quasiperiodic Thue-Morse Chain

We investigate single-particle localization in a dimerized Su--Schrieffer--Heeger (SSH) chain with a quasiperiodic onsite potential masked by the deterministic Thue--Morse sequence. Using exact diagonalization, we map the localization behavior as a function of the quasiperiodic potential strength and hopping dimerization through the correlation dimension, inverse participation ratio, and normalized participation ratio. For appropriate hopping ratios, increasing the potential strength drives the mid-spectrum states through a localized--multifractal--localized sequence, producing a reentrant recovery of participation before localization is restored at stronger modulation. Energy-resolved diagnostics show that this recovery is concentrated in the central spectral region rather than occurring uniformly throughout the spectrum. Extrapolations of the generalized dimensions to the thermodynamic limit reveal a systematic moment-dependent hierarchy in the reentrant window, accompanied by a broadened thermodynamic-limit singularity spectrum. Real- and momentum-space diagnostics provide complementary evidence for multifractal scaling in this regime, while two-size crossings yield finite-size estimates of the reentrant boundaries. Comparisons with random, globally balanced, pair-canceling, and block-permuted masks show that short-range sign anticorrelation promotes reentrance when it is aligned with the dominant SSH hopping bonds. The resulting reduction of the onsite mismatch across the strong bonds provides an effective-dimer interpretation of the reentrant response, while longer-range Thue--Morse correlations modify its location and strength.

cond-mat.dis-nn↗

arXiv2025

Localization Properties of a Disordered Helical Chain

We study the localization properties of the quasiperiodic one-dimensional helical chain with two tunneling paths: nearest-neighbor and a long-range hop that connects sites of consecutive helical turns. Using exact diagonalization, we quantify localization employing the inverse participation ratio (IPR) and the normalized participation ratio (NPR), and combine them into a single measure to create a phase map. The resulting diagrams reveal three regimes: a completely extended phase, a completely localized phase, and a mixed domain where localized and extended states coexist. In the diagrams, we investigate the behaviors of tightly and loosely wound helices and examine a special case where the number of sites per turn is a Fibonacci number. For moderate numbers of sites per helical turn, the mixed region is broad and also shifts with the long-range coupling. When the turn size is a Fibonacci number, the phase boundary becomes nearly horizontal and the mixed region fades out, effectively recovering the standard Aubry-Andr\'e model behavior.

cond-mat.dis-nn↗

arXiv2025

Localization and persistent currents in a quasiperiodic disordered helical lattice

We investigate localization and persistent currents in a helical tight-binding lattice subject to two independent magnetic fluxes and a quasiperiodic on-site potential. Working with non-interacting, spinless fermions under periodic boundary conditions, we solve the model by exact diagonalization and study localization with both inverse and normalized participation ratios. We identify boundaries separating extended, mixed, and localized regimes by constructing a diagram incorporating potential strength and inter-ring coupling. In the metallic regime, persistent currents flowing around both the toroidal and poloidal directions show oscillations whose amplitude decays as disorder grows and vanishes past the localization threshold; in the localized regime, currents become flux-insensitive. We demonstrate that tuning magnetic fluxes, hopping strengths, or quasiperiodic potential amplitudes provides control over the critical disorder threshold. Our results suggest a versatile platform for disorder-and flux-controlled switching between conductive and insulating states.

cond-mat.dis-nn↗

arXiv2025

Floquet Non-Bloch Formalism for a Non-Hermitian Ladder: From Theoretical Framework to Topolectrical Circuits

Periodically driven systems intertwined with non-Hermiticity opens a rich arena for topological phases that transcend conventional Hermitian limits. The physical significance of these phases hinges on obtaining the topological invariants that restore the bulk-boundary correspondence, a task well explored for static non-Hermitian (NH) systems, while it remains elusive for the driven scenario. Here, we address this problem by constructing a generalized Floquet non-Bloch framework that analytically captures the spectral and topological properties of time-periodic NH systems. Employing a high-frequency Magnus expansion, we analytically derive an effective Floquet Hamiltonian and formulate the generalized Brillouin zone for a periodically driven quasi-one-dimensional system, namely, the Creutz ladder with a staggered complex potential. Our study demonstrates that the skin effect remains robust (despite the absence of non-reciprocal hopping) across a broad range of driving parameters, and is notably amplified in the low-frequency regime due to emergent longer-range couplings. We further employ a symmetric time frame approach that generates chiral-partner Hamiltonians, whose invariants, when appropriately combined, account for the full edge-state structure. To substantiate the theoretical framework, we propose a topolectrical circuit (TEC) that serves as a viable experimental setting. Apart from capturing the skin modes, the proposed TEC design faithfully reproduces the presence of distinct Floquet edge states, as revealed through the voltage and impedance profiles, respectively. Thus, our work not only offers a theoretical framework for exploring NH-driven systems, but also provides an experimentally feasible TEC architecture for realizing these phenomena stated above in a laboratory.

cond-mat.mes-hall↗

arXiv2024

Gap Anisotropy in Layered Superconductors Due to Rashba and Dresselhaus Spin-Orbit Interactions

The theory of layered superconductors is extended in the presence of Rashba and Dresselhaus spin-orbit interactions (SOIs). Using the intralayer BCS-like pairing interaction and employing the Gor'kov formalism, we obtain analytical expressions for the temperature Green's functions and determine the gap function $\Delta$ which becomes complex in the presence of SOIs. In the absence of SOIs, $\Delta$ is isotropic at both zero and finite temperatures, but it becomes anisotropic even in the presence of a single SOI. This anisotropy is related to the extra $\cos{k_z}$ factors in which the $k_z$ momentum along the $z$ direction contributes to the magnitude of the gap function. It is also found that SOIs suppress $\Delta$ at both zero and finite temperatures, and for certain critical values of SOIs and beyond $\Delta$ vanishes. Analytical expressions for the critical values of SOIs at zero temperature are obtained. Additionally, how the BCS equation for layered superconductors changes in the presence of SOIs is determined.

cond-mat.supr-con↗

arXiv2024

Anomalous Lifetime of Quasiparticles in Fermi Liquids as a Precursor of the Density-Wave Instability

We analytically study the inelastic lifetime of quasiparticles due to particle-particle interactions in a three-dimensional Fermi liquid approaching a density-wave instability. Using the G$_0$W approximation, we find that the softening of the dielectric function significantly enhances the quasiparticle decay rate near the instability. While the zero-temperature quasiparticle lifetime at the Fermi surface generally follows a $|\varepsilon_k-\varepsilon_{\rm F}|^{-\alpha}$ divergence with $\alpha=2$, we observe $\alpha=0.5$ at the instability point and $\alpha=1$ within the density-wave phase. Moreover, we demonstrate that the renormalization constant $Z$ is substantially suppressed as the instability is approached, enhancing the effective mass. We extend our analysis to ultra-cold Rydberg-dressed Fermi liquids, where the soft-core interactions promote density-wave instability, and find that our numerical G$_0$W results are in excellent agreement with our analytic predictions for quasiparticle lifetime, renormalization constant, and effective mass.

cond-mat.str-el↗

arXiv2024

Mutual dipolar drag in a bilayer Fermi gas

We consider two-dimensional spin-polarized dipolar Fermi gases confined in a double-layer system and calculate the momentum transfer between the layers as a function of temperature to investigate the transport properties of the system. We use the Hubbard approximation to describe the correlation effects and the screening between the dipoles within a single layer. The effective interlayer interaction between the dipoles across the layers is obtained by the random-phase approximation. We calculate the interaction strength and the layer separation distance dependence of the drag rate, and we show that there is a critical distance below which the system is unstable. In addition, we calculate the typical behavior of the collective modes related to the density fluctuations.

cond-mat.quant-gas↗

arXiv2022

The transition from Bose-Einstein condensate to supersolid states in Rydberg-dressed gases beyond Bogoliubov approximation

In this paper, we study Bose-Einstein condensation of Rydberg-dressed atoms considering finite range interactions. We use Hartree-Fock-Bogoliubov approximation based on Mean-Field approach. Moreover, within this approximation modified by the finite-range character of the two-body interaction we shall obtain analytical expressions for thermodynamic quantities of Rydberg-dressed Bose gas. The imaginary part of the quasiparticle spectrum of a BEC signals the instability of the roton mode with respect to the formation of supersolid state. Our theory predicts a second-order quantum phase transition from BEC to supersolid phase for Rydberg-dressed bosons in three dimensions.

cond-mat.quant-gas↗

arXiv2021

Density and pseudo-spin rotons in a bilayer of soft-core bosons

We study the dynamics of a bilayer system of bosons with repulsive soft-core Rydberg-dressed interactions within the mean-field Bogoliubov-de Gennes approximation. We find roton minima in both symmetric and asymmetric collective density modes of the symmetric bilayer. Depending on the density of bosons in each layer and the spacing between two layers, the homogeneous superfluid phase becomes unstable in either (or both) of these two channels, leading to density and pseudo-spin-density wave instabilities in the system. Breaking the symmetry between two layers, either with a finite counterflow or a density imbalance renormalizes the dispersion of collective modes and makes the system more susceptible to density-wave instability.

cond-mat.quant-gas↗

arXiv2021

Metal-insulator transitions in bilayer electron-hole systems in transition metal dicalcogenides

We investigated metal-insulator transitions for double layer two-dimensional electron hole systems in transition metal dicalcogenides (TMDC) stacked on opposite sides of thin layers of boron nitride (BN). The interparticle interaction is calculated by including the screening due to the polarization charges at different interfaces, including that at the encapsultion and the substrate of experimental structures. We compute and compare the energies of the metallic electron-hole plasma and the newly proposed insulating exciton solid with fixed-node diffusion Monte Carlo simulation including the high valley degeneracy of the electron bands. We found that for some examples of current experimental structures, the transition electron/hole density is in an accessible range of g x 10^12 /cm*2 with g between 4.1 and 14.5 for spacer thicknesses between 2.5 and 7.5 nm. Our result raise the possibility of exploiting this effect for logic device applications.

cond-mat.mes-hall↗

arXiv2020

Rydberg-dressed Fermi liquid: correlations and signatures of droplet crystallization

We investigate the effects of many-body correlations on the ground-state properties of a single component ultra-cold Rydberg-dressed Fermi liquid with purely repulsive inter-particle interactions, in both three and two spatial dimensions. We have employed the Fermi-hypernetted-chain Euler-Lagrange approximation and observed that the contribution of the correlation energy on the ground-state energy becomes significant at intermediate values of the soft-core radius and large coupling strengths. For small and large soft-core radii, the correlation energy is negligible and the ground-state energy approaches the Hartree-Fock value. The positions of the main peaks in static structure factor and pair distribution function in the homogeneous fluid phase signal the formation of quantum droplet crystals with several particles confined inside each droplet.

cond-mat.quant-gas↗

arXiv2020

Reentrant Localization Transition in a Quasiperiodic Chain

Systems with quasiperiodic disorder are known to exhibit localization transition in low dimension. After a critical strength of disorder all the states of the system become localized, thereby ceasing the particle motion in the system. However, in our analysis we show that in a one dimensional dimerized lattice with staggered quasiperiodic disorder, after the localization transition some of the localized eigenstates become extended for a range of intermediate disorder strengths. Eventually, the system undergoes a second localization transition at a higher disorder strength leading to all states localized. We also show that the two localization transitions are associated with the mobility regions hosting the single particle mobility edges. We establish this re-entrant localization transition by analyzing the eigenspectra, participation ratios and the density of states of the system.

cond-mat.quant-gas↗

arXiv2020

Quantum turnstile regime of nanoelectromechanical systems

The effects of a turnstile operation on the current-induced vibron dynamics in nanoelectromechanical systems (NEMS) are analyzed in the framework of the generalized master equation. In our simulations each turnstile cycle allows the pumping of up to two interacting electrons across a biased mesoscopic subsystem which is electrostatically coupled to the vibrational mode of a nanoresonator. The time-dependent mean vibron number is very sensitive to the turnstile driving, rapidly increasing/decreasing along the charging/discharging sequences. This sequence of heating and cooling cycles experienced by the nanoresonator is due to specific vibron-assisted sequential tunneling processes along a turnstile period. At the end of each charging/discharging cycle the nanoresonator is described by a linear combination of vibron-dressed states $s_{\nu}$ associated to an electronic configuration $\nu$. If the turnstile operation leads to complete electronic depletion the nanoresonator returns to its equilibrium position, i.e.\,its displacement vanishes. It turns out that a suitable bias applied on the NEMS leads to a slow but complete cooling at the end of the turnstile cycle. Our calculations show that the quantum turnstile regime switches the dynamics of the NEMS between vibron-dressed subspaces with different electronic occupation numbers. We predict that the turnstile control of the electron-vibron interaction induces measurable changes on the input and output transient currents.

cond-mat.mes-hall↗

arXiv2019

Josephson current between two $p$-wave superconducting nanowires in the presence of Rashba spin-orbit interaction and Zeeman magnetic fields

Josephson current between two one-dimensional nanowires with proximity induced $p$-wave superconducting pairing is calculated in the presence of Rashba spin-orbit interaction, in-plane and normal magnetic fields. We show that Andreev retro-tunneling is realized by means of three channels. The main contribution to the Josephson current gives a scattering in a conventional particle-hole channel, when an electron-like quasiparticle reflects to a hole-like quasiparticle with opposite spin yielding a current which depends only on the order parameters' phase differences $\varphi$ and oscillates with $4\pi$ period. Second anomalous particle-hole channel, corresponding to the Andreev reflection of an incident electron-like quasiparticle to an hole-like quasiparticle with the same spin orientation, survives only in the presence of the in-plane magnetic field. The contribution of this channel to the Josephson current oscillates with $4\pi$ period not only with $\varphi$ but also with orientational angle of the in-plane magnetic field $\theta$ resulting in a magneto-Josephson effect. Third anomalous particle-particle channel, which represents a reflection of an electron-like (hole-like) quasiparticle to a electron-like (hole-like) quasiparticle with opposite spin-orientation, oscillates only with the in-plane magnetic field orientation angle $\theta$. We present a detailed theoretical analysis of both DC and AC Josephson effects in such a system showing contributions from all these channels and discuss experiments which can test our theory.

cond-mat.supr-con↗

arXiv2019

Superfluid weight and polarization amplitude in the one-dimensional bosonic Hubbard model

We calculate the superfluid weight and the polarization amplitude for the one-dimensional bosonic Hubbard model focusing on the strong-coupling regime. Other than analytic calculations we apply two methods: variational Monte Carlo based on the Baeriswyl wave function and exact diagonalization. The former gives zero superfluid response at integer filling, while the latter gives a superfluid response at finite hopping. From the polarization amplitude we derive the variance and the associated size scaling exponent. Again, the variational study does not produce a finite superfluid weight at integer filling (size scaling exponent is near one), but the Fourier transform of the polarization amplitude behaves in a similar way to the result of exact diagonalization, with a peak at small hopping, and suddenly decreasing at the insulator-superfluid transition. On the other hand, exact diagonalization studies result in a finite spread of the total position which increases with the size of the system. In the superfluid phase the size scaling exponent is two as expected. Importantly, our work addresses the ambiguities that arise in the calculation of the superfluid weight in variational calculations, and we comment on the prediction of Anderson about the superfluid response of the model at integer filling.

cond-mat.quant-gas↗