arXiv subjects

Mehdi Biderang

Publications and source records attributed to Mehdi Biderang.

At least 19 recordsLinked to original sources

arXiv2026

Quantum Correlation Dynamics Subjected to Quantum Reset-Driven Environment

We study two central qubits interacting with a transverse-field Ising chain that serves as their environment. The environment is driven linearly in time across its quantum critical points (QCPs) and, during the evolution, is subjected to quantum reset (QR), where it is returned at random times to its initial state. We investigate how such QR of the environmental spin chain modifies the dynamics of entanglement and quantum discord between the qubits. Our results show that in the strong-coupling regime, entanglement and discord exhibit pronounced revivals within the interval bounded by the Ising QCPs, but these revivals diminish as the QR rate increases. In contrast, weak coupling leads to a monotonic reduction of quantum correlations. Numerically, we find that the revival peaks of concurrence decay and scale exponentially with the QR rate, while quantum discord shows no clear scaling behavior. In the weak-coupling regime without QR, the correlations decay monotonically as the driven field crosses the second QCP. When QR is applied, however, both entanglement and discord undergo oscillatory suppression, with the oscillation period increasing as either the QR rate or the ramp time scale is reduced.

quant-ph↗

arXiv2025

Noise-Affected Dynamical Quantum Phase Transitions

We investigate the effects of uncorrelated noise on dynamical quantum phase transitions (DQPTs) in fermionic two-band models following a quantum ramp across critical points. We consider a generalized Loschmidt echo for the noise-averaged density matrix $\bar\rho$, which is a mixed state in general, as well as the pure state Loschmidt echo calculated for each noise realization with the average performed over the corresponding return rates. $\bar\rho$ can be obtained from a master equation and we show that for two-band models noise destroys its coherences which typically drives $\bar\rho$ towards the completely mixed state which is an attractive fixed point. DQPTs are thus always smoothed out for finite noise. For single noise realizations, on the other hand, we find that DQPTs under certain conditions are always present irrespective of the noise level. This leads to remarkable stable though slightly broadened DQPT-like features in the averaged return rate. We illustrate our results for the XY model by considering a noisy ramp as well as noise in the energy levels of the final Hamiltonian.

cond-mat.stat-mech↗

arXiv2025

Influence of Fermi Surface Geometry and Van Hove Singularities on the Optical Response of Sr$_2$RuO$_4$

Motivated by the sensitivity of Sr$_2$RuO$_4$ to Fermi surface reconstructions under strain, we investigate how Fermi surface geometry and Van Hove singularities influence the optical Hall response and polar Kerr effect. Within a three-orbital model, we explore the impact of chemical potential and interlayer hopping on superconducting pairing and response functions. We find that $d_{x^2-y^2}$ and $d_{x^2-y^2}+ig$ symmetries are the leading candidates for the quasi-2D orbital, while a chiral $p$-wave state in the quasi-1D orbitals is essential for generating an accessible Kerr angle. The Lifshitz transition is shown to affect coherence factors and density-of-states peaks, producing sharp signatures in $T_c$ and optical transport. Inter-orbital charge transfer further enhances these effects by modifying the balance between quasi-1D and quasi-2D contributions. These results provide a framework for interpreting Kerr effect experiments in multi-orbital superconductors.

cond-mat.supr-con↗

arXiv2024

Quantum Many-Body Theory for kq-Deformed Particles

We present a comprehensive quantum many body theory for kq deformed particles, offering a novel framework that relates particle statistics directly to effective interaction strength. Deformed by the parameters k and q, these particles exhibit statistical behaviors that interpolate between conventional bosonic and fermionic systems, enabling us to model complex interactions via statistical modifications. We develop a generalized Wick's theorem and extended Feynman diagrammatic tailored to kq-particles, allowing us to calculate two types of Green functions. Explicit expressions for these Green functions are derived in both direct and momentum spaces, providing key insights into the collective properties of kq-deformed systems. Using a random phase approximation (RPA), we estimate the dielectric function for q-fermion gas, and analyze the Friedel oscillations, the plasmon excitations, and the energy loss function. Our results demonstrate that the effective interaction is tuned by the value of q, so that a non interacting limit is obtained as q goes to zero, where the Friedel as well as the plasma oscillations disappear. There is an optimal value of q, the plasma frequency, as well as the energy loss function show an absolute maximum, and the effective interaction changes behavior.

cond-mat.stat-mech↗

arXiv2024

$T_c$ and the elastocaloric effect of Sr$_2$RuO$_4$ under $\langle 110 \rangle$ uniaxial stress: no indications of transition splitting

There is considerable evidence that the superconductivity of Sr2RuO4 has two components. Among this evidence is a jump in the shear elastic modulus $c_{66}$ at the critical temperature $T_c$, observed in ultrasound measurements. Such a jump is forbidden for homogeneous single-component order parameters, and implies that $T_c$ should develop as a cusp under the application of shear strain with $\langle 110 \rangle$ principal axes. This shear strain should split the onset temperatures of the two components, if they coexist, or select one component if they do not. Here, we report measurements of $T_c$ and the elastocaloric effect of Sr2RuO4 under uniaxial stress applied along the $[110]$ lattice direction. Within experimental resolution, we resolve neither a cusp in the stress dependence of $T_c$, nor any second transition in the elastocaloric effect data. We show that reconciling these null results with the observed jumps in $c_{66}$ requires extraordinarily fine tuning to a triple point of the Ginzburg-Landau parameter space. In addition, our results are inconsistent with homogeneous time reversal symmetry breaking at a temperature $T_2 \leq T_c$ as identified in muon spin relaxation experiments.

cond-mat.supr-con↗

arXiv2024

Stacking of charge-density waves in 2H-NbSe$_2$ bilayers

We employ ab-initio electronic structure calculations to investigate the charge-density waves and periodic lattice distortions in bilayer 2H-NbSe$_2$. We demonstrate that the vertical stacking can give rise to a variety of patterns that may lower the symmetry of the charge-density waves exhibited separately by the two composing 1H-NbSe$_2$ monolayers. The general tendency to a spontaneous symmetry breaking observed in the ground state and the first excited states is shown to originate from a non-negligible inter-layer coupling. Simulated images for scanning tunnelling microscopy (STM) as well as diffraction/scattering patterns show signatures of the different stacking orders. This may not only be useful to reinterpret past experiments on surfaces and thin films, but may also be exploited to devise ad-hoc experiments for the investigation of the stacking order in 2H-NbSe$_2$. We anticipate that our analysis does not only apply to the 2H-NbSe$_2$ bilayer, but is also relevant for thin films and bulk, whose smallest centro-symmetric component is indeed the bilayer. Finally, our results illustrate clearly that the vertical stacking is not only important for 1T structures, as exemplified by the metal-to-insulator transition observed in 1T-TaS$_2$, but seems to be a general feature of metallic layered transition metal dichalcogenides as well.

cond-mat.str-el↗

arXiv2024

Entangled Photon Generation through Cooper Pair Recombination in a Noncentrosymmetric Quantum Well

We explore theoretically the generation of entangled two-photon pairs by Cooper pair recombination in a noncentrosymmetric [001]-quantum well superconductor, driven by a forward-biased p-n junction with a superconducting layer which exhibits admixture Rashba and Dresselhaus spin-orbit couplings. We show that the highest achievable purity of entangled photon pairs emerges within scenarios involving pure singlet Cooper pairs, specifically, the conventional $s$-wave gap function. Our results highlight the importance of minimizing the charge-carrier level concentration and balancing the magnitudes of Rashba and Dresselhaus spin-orbit couplings to achieve entangled states with enhanced purity, which can be realized by reducing the amplitudes of antisymmetric spin-orbit couplings. In addition to purity concerns, to explore the distribution of two-photon states, we compare their population across entangled pairs for potential superconducting pairings.

quant-ph↗

arXiv2023

Thermodynamic geometry of a system with unified quantum statistics

We examine the thermodynamic characteristics of unified quantum statistics as a novel framework that undergoes a crossover between Bose-Einstein and Fermi-Dirac statistics by varying a generalization parameter $\delta$. We find an attractive intrinsic statistical interaction when $\delta\le0.5$ where the thermodynamic curvature remains positive throughout the entire physical range. For $0.5 < \delta < 1$ the system exhibits predominantly Fermi-like behavior at high temperatures, while at low temperatures, the thermodynamic curvature is positive and the system behaves like bosons. As the temperature decreases further, the system undergoes a transition into the condensate phase. We also report on a critical fugacity ($z = Z^*$) defined as the point at which the thermodynamic curvature changes sign, i.e. for $z< Z^*$ ($z > Z^*$), the statistical behavior resembles that of fermions (bosons). Also, we extract the variation of statistical behaviour of the system for different values of generalization parameter with respect to the temperature. We evaluate the critical fugacity and critical $\delta$ dependent condensation temperature of the system. Finally, we investigate the specific heat as a function of temperature and condensation phase transition temperature of the system for different values of generalization parameter in different dimensions.

cond-mat.stat-mech↗

arXiv2023

Polar Kerr Effect in Multiband Spin-Orbit Coupled Superconductors

We undertake a theoretical analysis to probe the Kerr spectrum within the superconducting phase of strontium ruthenate, where the Kerr rotation experiments demonstrate the existence of a superconducting state with broken time reversal symmetry. We find that spin-orbit coupling changes the hybridization along the Fermi surface's diagonal zone mainly affects Hall transport. We show that the dominant Hall response arises mainly from the quasi-1D orbitals $d_{yz}$ and $d_{xz}$, linked to their hybridization, while other contributions are negligible. This establishes that, the breaking of time reversal symmetry of quasi-1D orbitals can account for the existence of the Kerr angle, irrespective of the order symmetry specific to the $d_{xy}$ orbital. Moreover, the optical Hall conductivity and Kerr angle estimated for the hypothesised superconducting orders also closely match the experimental findings, providing important novel insight on the role of the spin-orbit coupling, hybridization, and emergent order.

cond-mat.supr-con↗

arXiv2023

Microscopic Insights into London Penetration Depth: Application to CeCoIn$^{}_{5}$

We propose a comprehensive theoretical formulation of magnetic penetration depth, $\lambda(T)$, based on the microscopic calculations for a general superconducting gap symmetry. Our findings admit the significant role of band structure and Fermi surface topology together with the symmetry of superconducting order parameter. We employ our findings pertaining to the heavy-fermion superconductor CeCoIn$_5$ to explore both local and non-local behaviors in response to an external magnetic field across varying temperatures. Our calculations in the low-temperature regime offer compelling macroscopic evidence of the nodal character within the superconducting state with $d_{x^2-y^2}$ symmetry. Furthermore, our findings align with the characteristics of London-type superconductivity, holding significant implications for upcoming experiments.

cond-mat.supr-con↗

arXiv2022

Topological Superconductivity in Sn/Si(111) driven by non-local Coulomb interactions

Superconductivity was recently observed in boron-doped ($\sqrt{3}\times\sqrt{3}$)Sn/Si(111). The material can be described by an extended Hubbard model on a triangular lattice. Here, we use the random-phase approximation to investigate the charge and spin fluctuations as well as the superconducting properties of the system with respect to filling and the relative strength of the extended versus the on-site Hubbard interactions. Our calculations reveal that near half-filling and weak extended Hubbard interactions, the superconducting ground state exhibits chiral $d$-wave pairing. Far from half-filling and for stronger nearest-neighbor Coulomb interactions, the system shows chiral $p$-wave (hole-doping) and $f$-wave (electron-doping) pairings. The dependence of the pairing symmetry on the extended Hubbard interactions suggests that charge fluctuations play an important role in the formation of Cooper pairs. Finally, the temperature dependence of the Knight shift is calculated for all observed superconducting textures and put forward as an experimental method to examine the symmetry of the superconducting gap function.

cond-mat.supr-con↗

arXiv2021

Proximity-driven ferromagnetism and superconductivity in the triangular Rashba-Hubbard model

Bilayer Moiré structures are a highly tunable laboratory to investigate the physics of strongly correlated electron systems. Moiré transition metal dichalcogenides at low-energies, in particular, are believed to be described by a single narrow band Hubbard model on a triangular lattice with spin-orbit coupling. Motivated by recent experimental evidence for superconductivity in twisted bilayer materials, we investigate the possible superconducting pairings in a two-dimensional single band Rashba-Hubbard model. Using a random-phase approximation in the presence of nearest and next-nearest neighbor hopping, we analyze the structure of spin fluctuations and the symmetry of the superconducting gap function. We show that Rashba spin-orbit coupling favors ferromagnetic fluctuations which strengthen triplet superconductivity. If parity is violated due to the absence of spatial inversion symmetry, singlet (d-wave) and triplet (p-wave) channels of superconductivity will be mixed. Moreover, we show that time-reversal symmetry can be spontaneously broken leading to a chiral superconducting state. Finally, we consider quasiparticle interference as a possible experimental technique to observe the superconducting gap symmetry.

cond-mat.supr-con↗

arXiv2021

Momentum space imaging of locally noncentrosymmetric superconductors

The failure of spatial inversion symmetry in noncentrosymmetric materials introduces two different types of spin-independent and spin-dependent electron hopping. The spin-dependent term can be translated into a quasi-spin-orbit coupling and may affect the electronic structure. In the locally noncentrosymmetric crystals, the presence of a sublattice degree of freedom generates a distinction between the inter- and intra-sublattice hopping integrals. The spin-dependent part of the former (latter), which is even (odd) under parity, is called symmetric (antisymmetric) quasi-spin-orbit coupling. Here, we show the consequences of such quasi-spin-orbit couplings on the electronic band structure and study their characteristic features via the quasiparticle interference method. We extend our discussions to a realistic class of materials, known as transition metal oxides.

cond-mat.supr-con↗

arXiv2020

Spin and charge order in doped spin-orbit coupled Mott insulators

We study a two-dimensional single band Hubbard Hamiltonian with antisymmetric spin-orbit coupling. We argue that this is the minimal model to understand the electronic properties of locally non-centrosymmetric transition-metal (TM) oxides such as Sr$_2$IrO$_4$. Based on exact diagonalizations of small clusters and the random phase approximation, we investigate the correlation effects on charge and magnetic order as a function of doping and of the TM-oxygen-TM bond angle $θ$. For small doping and $θ$ $\lesssim$ $15^\circ$ we find dominant commensurate in-plane antiferromagnetic fluctuations while ferromagnetic fluctuations dominate for $θ$ $\gtrsim$ $25^\circ$. Moderately strong nearest-neighbor Hubbard interactions can also stabilize a charge density wave order. Furthermore, we compare the dispersion of magnetic excitations for the hole-doped case to resonant inelastic X-ray scattering data and find good qualitative agreement.

cond-mat.str-el↗

arXiv2019

Superconductivity of mixed parity and frequency in an anisotropic spin-orbit coupling

We illuminate the superconducting phases in [001]-grown-noncentrosymmetric quantum wells with an anisotropic spin-orbit coupling in the presence of on-site Hubbard interaction. Within the random phase approximation, we investigate the spin-fluctuation-mediated pairing in the presence of Rashba/Dresselhaus antisymmetric spin-orbit couplings. Although the existence of spatial inversion symmetry desires a dominant d-wave pairing for all filling levels, a broken inversion symmetry generates antisymmetric spin-orbit coupling and mixes the even- and odd-parity in the superconducting gap. We study the symmetry of the mixed-parity gap for various strengths of Hubbard interaction. Besides, we consider a superconductor-ferromagnet junction to survey the modifications of superconducting order parameters and observe an admixture of even- and odd-frequencies due to the ferromagnet exchange field.

cond-mat.supr-con↗

arXiv2018

Drumhead surface states and their signatures in quasiparticle scattering interference

We consider a two-orbital tight-binding model defined on a layered three-dimensional hexagonal lattice to investigate the properties of topological nodal lines and their associated drumhead surface states. We examine these surface states in centrosymmetric systems, where the bulk nodal lines are of Dirac type (i.e., four-fold degenerate), as well as in non-centrosymmetric systems with strong Rashba and/or Dresselhaus spin-orbit coupling, where the bulk nodal lines are of Weyl type (i.e., two-fold degenerate). We find that in non-centrosymmetric systems the nodal lines and their corresponding drumhead surface states are fully spin polarized due to spin-orbit coupling. We show that unique signatures of the topologically nontrivial drumhead surface states can be measured by means of quasiparticle scattering interference, which we compute for both Dirac and Weyl nodal line semimetals. At the end, we analyze the possible crystal structures with a symmetry that supports flat surface states which are effectively ringlike.

cond-mat.str-el↗

arXiv2018

Edge currents as a probe of the strongly spin-polarized topological noncentrosymmetric superconductors

Recently the influence of antisymmetric spin-orbit coupling has been studied in novel topological superconductors such as half-Heuslers and artificial hetero-structures. We investigate the effect of Rashba and/or Dresselhaus spin-orbit couplings on the band structure and topological properties of a two-dimensional noncentrosymetric superconductor. For this goal, the topological helical edge modes are analyzed for different spin-orbit couplings as well as for several superconducting pairing symmetries. To explore the transport properties, we examine the response of the spin-polarized edge states to an exchange field in a superconductor-ferromagnet heterostructure. The broken chiral symmetry causes the uni-directional currents at opposite edges.

cond-mat.supr-con↗

arXiv2017

Mixed-pairing superconductivity in 5d Mott insulators with antisymmetric exchange

We investigate the potential existence of a superconducting phase in $5d$ Mott insulators with an eye to hole doped Sr$_2$IrO$_4$. Using a mean-field method, a mixed singlet-triplet superconductivity, $d + p$, is observed due to the antisymmetric exchange originating from a quasi-spin-orbit-coupling. Our calculation on ribbon geometry shows possible existence of the topologically protected edge states, because of nodal structure of the superconducting gap. These edge modes are spin polarized and emerge as zero-energy flat bands, supporting a symmetry protected Majorana states, verified by evaluation of winding number and $\mathbb{Z}_2$ topological invariant. At the end, a possible experimental approach for observation of these edge states and determination of the superconducting gap symmetry are discussed based on the quasi-particle interference (QPI) technique.

cond-mat.supr-con↗