arXiv subjects

F. M. D. Pellegrino

Publications and source records attributed to F. M. D. Pellegrino.

At least 19 recordsLinked to original sources

arXiv2026

Hybrid light-matter excitations and spontaneous time-reversal symmetry breaking in two-dimensional Josephson Junctions

In the context of hybrid superconductor-semiconductor systems, Josephson junctions based on two-dimensional materials, such as graphene, offer promising opportunities because of their scalability and gate-tunable electronic properties. In this work, we investigate the inductive coupling between a quantum LC resonator and a superconducting loop embedding a short, ballistic, planar Josephson junction, with the graphene-based case as a representative example. Within a mean-field formalism, we analyze how the properties of the global system depend on the light-matter interaction coupling, the Fermi level of the two-dimensional material, and temperature. Our findings reveal that the current-phase relation can show features indicative of spontaneous time-reversal symmetry breaking. Furthermore, starting from the mean-field theory, we determine the low-energy spectrum of collective hybridized light-matter excitations.

cond-mat.mes-hall↗

arXiv2026

From Valley Filtering to Superconducting Diode Effect in Spin-Orbit Coupled Graphene Junctions

We study the transport properties of proximitized graphene, which can acquire a spin-orbit coupling by the proximity effect with a substrate. We focus on the ballistic and zero temperature limits, making use of a tight-binding procedure based on the KWANT Python package. We first find key results on valley-filtering properties and asymmetric edge transport in spin-orbit coupled graphene single junctions, and then move to the analysis of the superconducting transport in a graphene Josephson junction, in the short junction limit. We study the relative contribution of edge modes for different edge terminations and some degree of edge disorder, and also analyze the magnetic interference pattern that arises when threading the junction with a perpendicular magnetic field. We find residual supercurrent at high magnetic fluxes, due to the localized nature of transport in the junction, and a strong non-reciprocal transport that leads to a significant Josephson diode effect.

cond-mat.mes-hall↗

arXiv2026

Quantum Batteries in two-dimensional material-based Josephson Junctions

We investigate the solid-state implementation of a Dicke-like quantum battery consisting of a two-dimensional material-based Josephson junction inductively coupled to a resonator, using graphene as a representative example. In this configuration, Andreev bound states naturally act as non-interacting, energetically non-degenerate two-level systems, and the setup allows for both single-photon and two-photon resonant processes. The coupling between the LC-circuit flux and the supercurrent through the junction gives rise to peculiar longitudinal interaction terms that have no counterpart in the conventional Dicke model. These additional couplings can enhance energy storage for a proper range of parameters. The proposed architecture also enables an alternative, but equivalent, charging protocol that relies on tuning the superconducting phase difference across the junction.

cond-mat.mes-hall↗

arXiv2026

Fokker-Planck approach to thermal fluctuations in antiferromagnetic systems

We develop a Fokker-Planck approach to describe the dynamics of staggered magnetization and thermal fluctuations in a two-dimensional antiferromagnetic system with uniaxial anisotropy. Beginning with a classical model for the antiferromagnetic system, we incorporate a Landau-Lifshitz-Gilbert equation augmented by Langevin fields to account for thermal fluctuations, and we derive the Fokker-Planck equation governing the probability distribution function of the spin configuration. Employing the mean-field approximation, we derive the equations of motion for the spin polarization and the two-time spin-spin correlation functions. The methodology is applied to the study of spin-wave dynamics and to the formulation of a phenomenological model for resistance fluctuations in two-dimensional antiferromagnetic semiconductors.

cond-mat.mes-hall↗

arXiv2022

A non-perturbative no-go theorem for photon condensation in approximate models

Equilibrium phase transitions between a normal and a photon condensate state (also known as superradiant phase transitions) are a highly debated research topic, where proposals for their occurrence and no-go theorems have chased each other for the past four decades. Recent no-go theorems have demonstrated that gauge invariance forbids second-order phase transitions to a photon condensate state when the cavity-photon mode is assumed to be {\it spatially uniform}. However, it has been theoretically predicted that a collection of three-level systems coupled to light can display a first-order phase transition to a photon condensate state. %{It has also been recently shown that truncation of the Hilbert space of the matter system can affect the gauge invariance of the theory. However, it is always possible to obtain approximate Hamiltonians obeying the gauge principle in the truncated Hilbert space.} Here, we demonstrate a general no-go theorem valid also for truncated, gauge-invariant models which forbid first-order as well as second-order superradiant phase transitions in the absence of a coupling with a magnetic field. In particular, we explicitly consider the cases of interacting electrons in a lattice and $M$-level systems.

cond-mat.mes-hall↗

arXiv2022

Tunable interface states between Floquet-Weyl semimetals

Weyl semimetals and nodal line semimetals are characterized by linear electronic bands touching at zero-dimensional points and one-dimensional lines, respectively. Recently, it has been predicted that nodal line semimetals can be driven into tunable Floquet-Weyl semimetals by circularly polarized light. Here, we study the occurrence of interface states between two regions of a nodal line semimetal shined by two beams of light with opposite circular polarizations. Within a minimal model, we find remarkable modifications of the energy structure by tuning the polarized light, such as the possible generation of van Hove singularities. Moreover, by adding a $δ$-doping of magnetic impurities along the interfacial plane, we show the occurrence of a switchable and topologically non-trivial, vortex-like pseudo-spin pattern of the interface states.

cond-mat.mes-hall↗

arXiv2020

Theory of Photon Condensation in a Spatially-Varying Electromagnetic Field

The realization of equilibrium superradiant quantum phases (photon condensates) in a spatially-uniform quantum cavity field is forbidden by a "no-go" theorem stemming from gauge invariance. We here show that the no-go theorem does not apply to spatially-varying quantum cavity fields. We find a criterion for its occurrence that depends solely on the static, non-local orbital magnetic susceptibility $χ_{\rm orb}(q)$, of the electronic system (ES) evaluated at a cavity photon momentum $\hbar q$. Only 3DESs satisfying the Condon inequality $χ_{\rm orb}(q)>1/(4π)$ can harbor photon condensation. For the experimentally relevant case of two-dimensional (2D) ESs embedded in quasi-2D cavities the criterion again involves $χ_{\rm orb}(q)$ but also the vertical size of the cavity. We use these considerations to identify electronic properties that are ideal for photon condensation. Our theory is non-perturbative in the strength of electron-electron interaction and therefore applicable to strongly correlated ESs.

cond-mat.mes-hall↗

arXiv2019

Cavity QED of Strongly Correlated Electron Systems: A No-go Theorem for Photon Condensation

In spite of decades of work it has remained unclear whether or not superradiant quantum phases, referred to here as photon condensates, can occur in equilibrium. In this Letter, we first show that when a non-relativistic quantum many-body system is coupled to a cavity field, gauge invariance forbids photon condensation. We then present a microscopic theory of the cavity quantum electrodynamics of an extended Falicov-Kimball model, showing that, in agreement with the general theorem, its insulating ferroelectric and exciton condensate phases are not altered by the cavity and do not support photon condensation.

cond-mat.mes-hall↗

arXiv2019

Coherent trapping in small quantum networks

We consider a three-node fully connected network (Delta network) showing that a coherent population trapping phenomenon occurs, generalizing results for the Lambda network known to support a dark state. Transport in such structures provides signatures of detrapping, which can be triggered by external controls. In the presence of an environment it turns out to be sensitive to its Markovianity. Adiabatic modulation of the system's parameters may yield coherent population transfer, analogous to the stimulated Raman adiabatic passage phenomenon. Robustness of this protocol against non-adiabatic transitions is studied. Coherent nanostructures where these phenomena are relevant for quantum transport and quantum protocols are suggested.

cond-mat.mes-hall↗

arXiv2019

Speedup of adiabatic multiqubit state-transfer by ultrastrong coupling of matter and radiation

Ultrastrongly coupled quantum hardware may increase the speed of quantum state processing in distributed architectures, allowing to approach fault-tolerant threshold. We show that circuit QED architectures in the ultrastrong coupling regime, which has been recently demonstrated with superconductors, may show substantial speedup for a class of adiabatic protocols resilient to the main source of errors, namely the interplay of dynamical Casimir effect and cavity losses.

quant-ph↗

arXiv2019

Photon pair production by STIRAP in ultrastrongly coupled matter-radiation systems

Artificial atoms (AA) offer the possibility to design physical systems implementing new regimes of ultrastrong coupling (USC) between radiation and matter, where previously unexplored non-perturbative physics emerges. While experiments so far provided only spectroscopic evidence of USC, we propose the dynamical detection of virtual photon pairs in the dressed eigenstates, which is a "smoking gun" of the very existence of USC in nature. We show how to coherently amplify this channel to reach 100% efficiency by operating advanced control similar to stimulated Raman adiabatic passage (STIRAP).

cond-mat.mes-hall↗

arXiv2018

Prospects for the detection of electronic pre-turbulence in graphene

Based on extensive numerical simulations, accounting for electrostatic interactions and dissipative electron-phonon scattering, we propose experimentally realizable geometries capable of sustaining electronic pre-turbulence in graphene samples. In particular, pre-turbulence is predicted to occur at experimentally attainable values of the Reynolds number between 10 and 50, over a broad spectrum of frequencies between 10 and 100 GHz.

cond-mat.mes-hall↗

arXiv2018

Measuring Hall Viscosity of Graphene's Electron Fluid

Materials subjected to a magnetic field exhibit the Hall effect, a phenomenon studied and understood in fine detail. Here we report a qualitative breach of this classical behavior in electron systems with high viscosity. The viscous fluid in graphene is found to respond to non-quantizing magnetic fields by producing an electric field opposite to that generated by the classical Hall effect. The viscous contribution is large and identified by studying local voltages that arise in the vicinity of current-injecting contacts. We analyze the anomaly over a wide range of temperatures and carrier densities and extract the Hall viscosity, a dissipationless transport coefficient that was long identified theoretically but remained elusive in experiment. Good agreement with theory suggests further opportunities for studying electron magnetohydrodynamics.

cond-mat.mes-hall↗

arXiv2017

Superballistic flow of viscous electron fluid through graphene constrictions

Electron-electron (e-e) collisions can impact transport in a variety of surprising and sometimes counterintuitive ways. Despite strong interest, experiments on the subject proved challenging because of the simultaneous presence of different scattering mechanisms that suppress or obscure consequences of e-e scattering. Only recently, sufficiently clean electron systems with transport dominated by e-e collisions have become available, showing behavior characteristic of highly viscous fluids. Here we study electron transport through graphene constrictions and show that their conductance below 150 K increases with increasing temperature, in stark contrast to the metallic character of doped graphene. Notably, the measured conductance exceeds the maximum conductance possible for free electrons. This anomalous behavior is attributed to collective movement of interacting electrons, which 'shields' individual carriers from momentum loss at sample boundaries. The measurements allow us to identify the conductance contribution arising due to electron viscosity and determine its temperature dependence. Besides fundamental interest, our work shows that viscous effects can facilitate high-mobility transport at elevated temperatures, a potentially useful behavior for designing graphene-based devices.

cond-mat.mes-hall↗

arXiv2014

Theory of integer quantum Hall polaritons in graphene

We present a theory of the cavity quantum electrodynamics of the graphene cyclotron resonance. By employing a canonical transformation, we derive an effective Hamiltonian for the system comprised of two neighboring Landau levels dressed by the cavity electromagnetic field (integer quantum Hall polaritons). This generalized Dicke Hamiltonian, which contains terms that are quadratic in the electromagnetic field and respects gauge invariance, is then used to calculate thermodynamic properties of the quantum Hall polariton system. Finally, we demonstrate that the generalized Dicke description fails when the graphene sheet is heavily doped, i.e. when the Landau level spectrum of 2D massless Dirac fermions is approximately harmonic. In this case we `integrate out' the Landau levels in valence band and obtain an effective Hamiltonian for the entire stack of Landau levels in conduction band, as dressed by strong light-matter interactions.

cond-mat.mes-hall↗

arXiv2012

Effect of uniaxial strain on plasmon excitations in graphene

Uniaxial strain is known to modify significantly the electronic properties of graphene, a carbon single layer of atomic width. Here, we study the effect of applied strain on the composite excitations arising from the coupling of charge carriers and plasmons in graphene, i.e. the plasmarons. Specifically, we predict that the plasmaron energy dispersion, which has been recently observed experimentally in unstrained graphene, is shifted and broadened by applied uniaxial strain. Thus, strain constitutes an additional parameter which may be useful to tune graphene properties in plasmaronic devices.

cond-mat.mes-hall↗

arXiv2012

Resonant modes in strain-induced graphene superlattices

We study tunneling across a strain-induced superlattice in graphene. In studying the effect of applied strain on the low-lying Dirac-like spectrum, both a shift of the Dirac points in reciprocal space, and a deformation of the Dirac cones is explicitly considered. The latter corresponds to an anisotropic, possibly non-uniform, Fermi velocity. Along with the modes with unit transmission usually found across a single barrier, we analytically find additional resonant modes when considering a periodic structure of several strain-induced barriers. We also study the band-like spectrum of bound states, as a function of conserved energy and transverse momentum. Such a strain-induced superlattice may thus effectively work as a mode filter for transport in graphene.

cond-mat.mes-hall↗

arXiv2011

Ballistic transport properties across nonuniform strain barriers in graphene

We study the effect of uniaxial strain on the transmission and the conductivity across a strain-induced barrier in graphene. At variance with conventional studies, which consider sharp barriers, we consider a more realistic, smooth barrier, characterized by a nonuniform, continuous strain profile. Our results are instrumental towards a better understanding of the transport properties in corrugated graphene.

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