arXiv subjects

Francesca Maria Marchetti

Publications and source records attributed to Francesca Maria Marchetti.

10 recordsLinked to original sources

arXiv2026

Room-temperature tuning and probing of Fermi polarons in atomically thin semiconductors on a plasmonic metasurface

The Fermi polaron, arising from interactions between a mobile impurity and a degenerate Fermi sea, is a many-body quasiparticle that provides a sensitive probe of strongly correlated electronic phases in atomically thin semiconductors. In doped transition-metal dichalcogenides, the attractive and repulsive polaron branches are well established in monolayers. However, extending active control and quantitative, branch-resolved probing to stacked geometries has remained elusive because spectral quenching and weak optical contrast restrict access to Fermi polaron signatures. Here, we integrate electron-doped WS$_2$ flakes from monolayer to quadrilayer with a strain-tunable plasmonic metasurface, enabling high-contrast scattering readout at room temperature through coupling between Fermi polaron resonances and surface plasmons. This platform enables quantitative extraction of polaron branch spectral weights and coupling strengths across different layer numbers. We uncover a systematic thickness dependence of the spectral-weight distribution and demonstrate continuous and fully reversible spectral-weight transfer between attractive and repulsive branches in bilayers and quadrilayers, with near-complete transfer achieved in bilayers. By identifying layer number and strain as complementary control parameters for Fermi polarons, our results establish metasurface-enabled scattering spectroscopy as a practical route to resolve and manipulate many-body resonances in stacked van der Waals semiconductors, bridging idealized monolayer polaron physics and device-relevant architectures.

cond-mat.mes-hall↗

arXiv2026

Very strong light-matter coupling in patterned GaAs heterostructures

The very strong light-matter coupling regime enables the non-perturbative modification of matter properties via light. Using a patterned GaAs/AlGaAs waveguide with twelve wide quantum wells, we demonstrate hybridization of heavy- and light-hole excitons within a single polariton state and show that, at finite magnetic field, the presence of the light-hole exciton suppresses coupling to the heavy-hole Rydberg excitons and unbound scattering states. We develop a fully microscopic theory that accounts for the combined effects of the magnetic field and light-matter coupling on the excitons, providing an accurate description of the experimental results beyond a perturbative coupled-oscillator framework. This identifies quantum well width as a key control parameter for engineering the light-induced hybridization of matter wave functions in polaritons, which, in turn, can play a crucial role in the optical non-linearities.

cond-mat.mes-hall↗

arXiv2026

Magnetic-field driven hybridization of heavy- and light-hole Rydberg excitons in GaAs quantum wells

We present a combined theoretical and experimental study of ground and excited Rydberg exciton states in wide GaAs quantum wells exposed to a magnetic field in the Faraday geometry. We employ a multiband exciton model based on the Luttinger Hamiltonian, which captures valence-band mixing between heavy- and light-hole states induced by both the quantum well confinement and the magnetic field, and we develop an efficient numerical approach to solve for both ground- and excited-state excitons. The method treats Coulomb interactions, magnetic confinement, and band mixing on an equal footing, enabling a systematic characterization of exciton energies, oscillator strengths, and orbital composition. We show that band hybridization increases with magnetic field and is significantly more pronounced for higher excited states, where it sets in at lower fields and strongly modifies their properties. The theoretical predictions are validated by polarization-resolved magneto-reflectance measurements up to 9 T on GaAs/Al$_{0.4}$Ga$_{0.6}$As quantum wells of 20 nm width. We find excellent agreement for both the diamagnetic shift and Zeeman splitting of the ground state and the first four Rydberg excitons. Our results demonstrate that valence-band mixing plays a crucial role in determining the magnetic-field dependence of excited exciton states and must be properly included for a quantitative description of magneto-excitons in wide GaAs quantum wells.

cond-mat.mes-hall↗

arXiv2026

Optical properties of Fermi polarons in a GaInP/MoSe2 monolayer heterostructure

Engineering optical properties, such as luminescence purity and charge transfer, is crucial for harnessing the application potential of atomically thin transition metal dichalcogenides (TMDCs). While electrostatic gating is widely applied to gain charge control in TMDC monolayers, charge transfer can also be engineered via coupling of TMDC monolayers at semiconductor III/V, organic, or van der Waals interfaces. This confers great advantages, such as ease in implementation and compatibility in device integration. Here, we shed light on the optical properties of many-particle complexes emerging at the GaInP/MoSe2 interface as a highly relevant material combination to manipulate the optical properties of TMDCs in integrated photonic devices. Our study verifies its nature as a type II hetero-interface, which bears the feasibility to display disorder-free photoluminescence. Through optical absorption measurements, we verify that the charged complexes acquire substantial oscillator strength. Furthermore, temperature-dependent photoluminescence, supported by a microscopic theory framework, evidences the suppression of the characteristic carrier recoil effect that was previously observed in the photoluminescence of trions in TMDCs. These phenomena allow us to identify the optical signatures at the TMDC-GaInP interface as Fermi polaron quasiparticle resonances, which are of high importance in researching Bose-Fermi mixtures in condensed matter systems.

cond-mat.mtrl-sci↗

arXiv2025

Role of impurity statistics and medium constraints in polaron-polaron interactions

We consider the behavior of a small density of mobile impurities (polarons) immersed in a quantum gas, a generic scenario that can be realized in cold atomic gases, liquid helium mixtures, and doped semiconductors. We present a unified theoretical framework for understanding polaron quasiparticles beyond the single-impurity limit, and we identify two key factors that control the polaron-polaron interactions: (i) the statistics of the impurities, including whether or not they are degenerate, and (ii) the constraints on the medium response, i.e., whether the medium density or chemical potential is held fixed. By constructing wave functions for two bosonic, fermionic, or distinguishable impurities immersed in a Bose or Fermi gas, we derive rigorous results for the polaron interactions in the limit of weak impurity-medium coupling. We furthermore obtain an exact relationship between the polaron interactions at fixed medium density and at fixed chemical potential, a result which is valid for arbitrary interaction strength. Our work provides an important guide for understanding experiments, and it acts as a starting point for future strong-coupling theories of polaron interactions that capture all of the effects identified in this work.

cond-mat.quant-gas↗

arXiv2025

Quantum Droplets of Light in Semiconductor Microcavities

Quantum droplets are dilute self-bound configurations of bosons that result from the balance between a mean-field attraction and a repulsion induced by quantum fluctuations. Such droplets have been successfully realized in cold atomic gases and represent a signature of their quantum nature. Here, we predict the existence of a similar droplet phase in a solid-state system, involving polaritons formed from the strong coupling between excitons (bound electron-hole pairs) and photons in a semiconductor microcavity. We consider a spin mixture of exciton-polaritons near a biexciton Feshbach resonance, which allows one to tune the interspecies interactions to be attractive and comparable in magnitude to the intraspecies repulsion. We find that self-bound quantum droplets are achievable for realistic parameters in atomically thin semiconductors, and that they can be detected via their excitation spectrum and spatial profile. This exotic phase could potentially lead to polariton condensation at lower thresholds and it opens an alternative avenue to achieve the long-sought quantum polaritonic regime.

cond-mat.mes-hall↗

arXiv2024

Efficient calculation of trion energies in monolayer transition metal dichalcogenides

The reduced dielectric screening in atomically thin semiconductors leads to remarkably strong electron interactions. As a result, bound electron-hole pairs (excitons) and charged excitons (trions), which have binding energies in the hundreds and tens of meV, respectively, typically dominate the optical properties of these materials. However, the long-range nature of the interactions between charges represents a significant challenge to the exact calculation of binding energies of complexes larger than the exciton. Here, we demonstrate that the trion binding energy can be efficiently calculated directly from the three-body Schr\"odinger equation in momentum space. Key to this result is a highly accurate way of treating the pole of the electronic interactions at small momentum exchange (i.e., large separation between charges) via the Land\'e subtraction method. Our results are in excellent agreement with quantum Monte Carlo calculations, while yielding a substantially larger ratio of the trion to exciton binding energies than obtained in recent variational calculations. Our numerical approach may be extended to a host of different few-body problems in 2D semiconductors, and even potentially to the description of exciton polarons.

cond-mat.mes-hall↗

arXiv2018

Spectroscopic probes of quantum many-body correlations in polariton microcavities

We investigate the many-body states of exciton-polaritons that can be observed by pump-probe spectroscopy. Here, a weak-probe `spin-down' polariton is introduced into a coherent state of `spin-up' polaritons created by a strong pump. We show that the $\downarrow$ impurities become dressed by excitations of the $\uparrow$ medium, and form new polaronic quasiparticles that feature two-point and three-point many-body quantum correlations, which, in the low density regime, arise from coupling to the vacuum biexciton and triexciton states respectively. In particular, we find that these correlations generate additional branches and avoided crossings in the $\downarrow$ optical transmission spectrum that have a characteristic dependence on the $\uparrow$-polariton density. Our results thus demonstrate a way to directly observe correlated many-body states in an exciton-polariton system that go beyond classical mean-field theories.

cond-mat.quant-gas↗

arXiv2014

Interaction-Shaped Vortex-Antivortex Lattices in Polariton Fluids

Topological defects such as quantized vortices are one of the most striking manifestations of the superfluid nature of Bose-Einstein condensates and typical examples of quantum mechanical phenomena on a macroscopic scale. Here we demonstrate the formation of a lattice of vortex-antivortex pairs and study, for the first time, its properties in the non-linear regime at high polarion-density where polariton-polariton interactions dominate the behaviour of the system. In this work first we demonstrate that the array of vortex-antivortex pairs can be generated in a controllable way in terms of size of the array and in terms of size and shape of it fundamental unit cell. Then we demonstrate that polariton-polariton repulsion can strongly deform the lattice unit cell and determine the pattern distribution of the vortex-antivortex pairs, reaching a completely new behaviour with respect to geometrically generated vortex lattices whose shape is determined only by the geometry of the system.

cond-mat.quant-gas↗

arXiv1999

On the Pairing Structure of the Vacuum induced by a Magnetic Field in 2+1-dimensional Dirac Field Theory

Using a sequence of Bogoliubov transformations, we obtain an exact expression for the vacuum state of a Dirac field in 2+1 dimensions in presence of a constant magnetic field. This expression reveals a peculiar two level pairing structure for any value of the mass m greater than zero. This calculation clarifies the nature of the condensate in the lowest Landau level whose existence has been emphasized recently by a several authors.

hep-th↗