arXiv subjects

Joaquim Telles de Miranda

Publications and source records attributed to Joaquim Telles de Miranda.

8 recordsLinked to original sources

arXiv2026

Photogalvanic transport of nonreciprocal Cooper-pair fluctuations

We develop a theory of the nonlinear optical and transport responses of two-dimensional noncentrosymmetric superconductors in the fluctuation regime above the transition temperature, encompassing the photogalvanic effect, second-harmonic generation, and the photovoltaic Hall effect. In the vicinity of the transition these responses are strongly enhanced by preformed Cooper pairs, whose nonreciprocity enters the time-dependent Ginzburg-Landau description in two physically distinct ways: through thermodynamic Lifshitz invariants, which encode an asymmetric pair spectrum, and through kinetic Lifshitz invariants, which encode an asymmetric pair relaxation and are locked to the Langevin noise by the fluctuation-dissipation theorem. We derive generalized master formulas for the paraconductivity (Aslamazov-Larkin) and the quantum-interference (Maki-Thompson) channels of the nonlinear current, valid at arbitrary drive frequency and to linear order in the nonreciprocal perturbations, and reduce them to closed-form dimensionless functions. Circular polarization discriminates sharply between the mechanisms: for reciprocal momentum-structureless noise the Aslamazov-Larkin channel is polarization insensitive and its circular photogalvanic response vanishes for any pair spectrum, whereas the Maki-Thompson channel and the nonreciprocal noise support helicity-odd rectified currents, including a fluctuation photovoltaic Hall current flowing transverse to the strain axis. Applications to Rashba-type ($C_{3v}$) and Ising-type ($D_{3h}$) superconductors demonstrate how the point-group symmetry dictates the allowed vector structures of the nonlinear currents, and how polarization analysis together with the frequency and dephasing dependences can be used to separate the individual channels experimentally.

cond-mat.supr-con↗

arXiv2026

The universality class of the first levels in low-dimensional gravity

We investigate the physics of a small group of quantum states defined above the sharply defined ground state of a chaotic ensemble. This `universality class of the first levels' (UFL) is realized in the majority of `synthetic' random matrix models but, for all we know, in only one microscopically defined system: low-dimensional gravity. We discuss the physical properties of these states, notably their exceptional rigidity against external perturbations, as quantified by the so-called quantum state fidelity. Examining these structures through the lenses of random matrix and string theory, we highlight their relevance to the physics of low-dimensional holographic principles.

hep-th↗

arXiv2026

Spectral Edge Rigidity of Quantum Chaotic States

We determine the distribution of fidelity susceptibility for chaotic eigenstates at the spectral edge of Gaussian random-matrix ensembles. Previous work showed that, in the unitary class, the characteristic susceptibility scale of edge states grows as $D^{1/3}$, rather than proportionally to $D$ as in the spectral bulk, reflecting Airy-edge level rigidity. Extending a determinant-based framework introduced for bulk states, we derive the universal edge distributions for both the orthogonal and unitary ensembles. The two symmetry classes share the scaling variable $g/D^{1/3}$ and exhibit a symmetry-dependent cubic suppression of small susceptibilities, while their algebraic large-$g$ tails reflect the corresponding symmetry-dependent level repulsion. Although eigenvector statistics retain their random-matrix form throughout the spectrum, edge rigidity makes low-lying chaotic states parametrically less sensitive to generic perturbations than bulk states. Our results establish universal, symmetry-dependent spectral-edge fidelity-susceptibility statistics in systems whose chaotic dynamics extends down to the ground state.

cond-mat.dis-nn↗

arXiv2026

Kinetic Lifshitz invariants and dynamics of nonreciprocal fluctuations in superconductors

We derive the generalized time-dependent Ginzburg-Landau theory of a disordered noncentrosymmetric superconductor from the Keldysh nonlinear sigma model, using a two-dimensional electron gas with Rashba spin-orbit coupling and an in-plane Zeeman field as a minimal model. On the thermodynamic side we construct the Lifshitz invariants of the free energy, the linear and cubic gradient terms and the momentum-odd part of the quartic vertex, and trace their dependence on disorder. These couplings are governed by a single closed-form kernel controlled by the ratio of the Dyakonov-Perel spin-relaxation rate to temperature, interpolating between the weak-relaxation regime, where the invariants are suppressed, and the relaxation-dominated regime, where the helical modulation of the order parameter saturates at a universal, disorder-independent value. This crossover reconciles conflicting results for the magnetoelectric couplings of dirty Rashba superconductors. Because the theory is formulated on the Keldysh contour, it also determines the dissipative dynamics: the relaxation rate of a fluctuation with pair momentum $\mathbf{q}$, and hence, by the fluctuation-dissipation theorem, the Langevin noise power, acquires a term odd in $\mathbf{q}$ and odd in the magnetic field. The structure of this kinetic Lifshitz invariant is dictated by Onsager reciprocity: friction and noise renormalize in lockstep, so equal-time fluctuations remain Gibbsian while the dynamics are nonreciprocal. As applications we compute the superconducting diode efficiency near $T_c$, where the cubic invariant competes with the quartic vertex and with even higher-gradient terms rendered odd by the helical shift, reversing the sign of the diode coefficient, and the fluctuation-induced magnetochiral anisotropy above $T_c$, where the current-resolved nonreciprocal resistance forms a plateau across the Gaussian regime.

cond-mat.supr-con↗

arXiv2026

Magnetochiral anisotropy in strained superconducting transition metal dichalcogenides

We present a theoretical study of nonreciprocal charge transport in two-dimensional noncentrosymmetric superconductors, taking the transition-metal dichalcogenide MoS$_2$ as a representative example. In the normal state, the magnetochiral anisotropy vanishes within the minimal band model of MoS$_2$, appearing only at subleading order in the symmetry-breaking perturbations set by trigonal warping, Ising spin-orbit coupling, and the Zeeman field. Superconductivity changes this picture qualitatively: in the vicinity of the transition, the magnetochiral anisotropy is strongly enhanced by pairing fluctuations. We evaluate the nonreciprocal current density arising from order-parameter fluctuations and quantum-interference processes -- the Aslamazov-Larkin and Maki-Thompson channels -- and show that both are governed by cubic Lifshitz invariants of the Ginzburg-Landau free energy, generically allowed once inversion and time-reversal symmetries are broken. These invariants are derived microscopically from the band model, including the effects of disorder: in the diffusive limit the warping-induced invariant is suppressed, yet the resulting response remains sizable. Strain is shown to enable additional vector components of the nonlinear current, activating the Maki-Thompson channel. Finally, invoking Onsager reciprocity, we identify kinetic Lifshitz invariants, nonreciprocal corrections to the order-parameter relaxation rate, locked to the Langevin noise by the fluctuation-dissipation theorem, and demonstrate that their contribution to the magnetochiral anisotropy is parametrically subleading near the transition.

cond-mat.supr-con↗

arXiv2026

Electrical magnetochiral anisotropy in Rashba superconductors

We theoretically investigate the role of higher-order Lifshitz invariants in nonreciprocal charge transport in two-dimensional noncentrosymmetric superconductors with Rashba spin-orbit coupling. In the superconducting state, these symmetry-allowed terms give rise to critical-current nonreciprocity, while in the normal state near the superconducting transition they generate a pronounced magnetochiral anisotropy. Using symmetry-constrained group-theoretical methods, we systematically construct the allowed Lifshitz invariants and derive the corresponding vector structure of the nonreciprocal current. To describe nonlinear transport in the fluctuation regime, we apply a generalized time-dependent Ginzburg-Landau theory that incorporates both the Aslamazov-Larkin contribution from fluctuation-induced Cooper pairs and the Maki-Thompson contribution associated with quantum interference in the Cooper channel. We further analyze the effects of disorder scattering and dephasing on the resulting nonreciprocal response.

cond-mat.supr-con↗

arXiv2024

Tensor product random matrix theory

The evolution of complex correlated quantum systems such as random circuit networks is governed by the dynamical buildup of both entanglement and entropy. We here introduce a real-time field theory approach -- essentially a fusion of the $G Σ$-functional of the SYK-model and the field theory of disordered systems -- enigneered to microscopically describe the full range of such crossover dynamics: from initial product states to a maximum entropy ergodic state. To showcase this approach in the simplest nontrivial setting, we consider a tensor product of coupled random matrices, and compare to exact diagonalization.

cond-mat.mes-hall↗

arXiv2023

Subsystem Trace-Distances of Two Random States

We study two-state discrimination in chaotic quantum systems. Assuming that one of two $N$-qubit pure states has been randomly selected, the probability to correctly identify the selected state from an optimally chosen experiment involving a subset of $N-N_B$ qubits is given by the trace-distance of the states, with $N_B$ qubits partially traced out. In the thermodynamic limit $N\to\infty$, the average subsystem trace-distance for random pure states makes a sharp, first order transition from unity to zero at $f=1/2$, as the fraction $f=N_B/N$ of unmeasured qubits is increased. We analytically calculate the corresponding crossover for finite numbers $N$ of qubits, study how it is affected by the presence of local conservation laws, and test our predictions against exact diagonalization of models for many-body chaos.

quant-ph↗