arXiv subjects

R. Avriller

Publications and source records attributed to R. Avriller.

13 recordsLinked to original sources

arXiv2024

Chirality and dimensionality in the ultrastrong light-matter coupling regime

We unveil the key-role of dimensionality in describing chiroptical properties of molecules embedded inside an optical Fabry-P\'erot cavity. For a 2D-layer configuration, we show that the interplay between molecular chirality and spatial dispersion of the cavity-modes, results in a gyrotropic coupling $\chi$ at the origin of a differential shift in polaritonic energy-spectra. This differential shift is proportional to $\chi$, while for 3D bulk-aggregate configurations it is shown to vanish. We interpret physically the former 2D-chiral effect by analogy with the classical Newtonian motion of a fictive particle in presence of 3D restoring force, and static magnetic field. The gyrotropic coupling is shown to directly perturbate the anholonomy angle of the classical trajectories, and the fictive particle undergoes cyclotron gyrations upon entering the ultrastrong light-matter coupling regime.

physics.optics↗

arXiv2024

Classical Approaches to Chiral Polaritonics

We provide a theoretical framework based on classical electromagnetism, to describe optical properties of Fabry-Pérot cavities, filled with multilayered and linear chiral materials. We find a formal link between transfer-matrix, scattering-matrix and Green-function approaches to compute the polarization-dependent optical transmission, and cavity-modified circular dichroism signals. We show how general symmetries like Lorentz reciprocity and time-reversal symmetry constrain the modelling of such cavities. We apply this approach to investigate numerically and analytically the properties of various Fabry-Pérot cavities, made of either metallic or helicity-preserving dielectric photonic crystal mirrors. In the latter case, we analyze the onset of chiral cavity-polaritons in terms of partial helicity-preservation of electromagnetic waves reflected at the mirrors interfaces. Our approach is relevant for designing innovative Fabry-Pérot cavities for chiral-sensing, and for probing cavity-modified stereochemistry.

physics.optics↗

arXiv2023

Stochastic Dynamics of Resonance Electronic Energy Transfer in Bi-Dimensional Overexcited Molecular Ensembles

We investigate theoretically the stochastic dynamics of Resonance Electronic Energy Transfer (RET), in a bi-dimensional overexcited ensemble of donor and acceptor molecules. We find that, after initial optical excitation of all the donors, the reaction kinetics is well-described by a non-linear mean-field theory. The latter provides a solid way to define and compute an effective rate of RET, even for disordered samples. We predict that this effective rate scales as $\left\langle R \right\rangle^α$ with $\left\langle R \right\rangle$ the average distance between individual excited donors and their nearest-neighbor acceptor molecules, and $α\in \left\lbrack -6,-2 \right\rbrack$ an exponent depending on the spatial distribution of molecular pairs in the sample. Using a kinetic Monte-Carlo approach, we show departures from this macroscopic mean-field description arising from fluctuations and spatial correlations between several molecules involved in the RET process. We expect this prediction to be relevant for both molecular science and biology, where the control and optimization of the RET dynamics is a key issue.

cond-mat.mes-hall↗

arXiv2023

Chiral Discrimination in Helicity-Preserving Fabry-Pérot Cavities

We theoretically study circular dichroism of chiral molecules embedded inside a helicity-preserving Fabry-Pérot cavity. We find an increase of the intrinsic chiroptical response of the molecules by 2 orders of magnitude and report the first clear signature of chiral cavity polaritons upon entering the regime of strong light-matter coupling. We study a cavity design based on two dielectric photonic crystal mirrors acting, in a narrow frequency range, as efficient polarization cross-converters in transmission for one polarization and almost perfect reflectors for the other polarization. We show that a Pasteur medium hosted inside such a cavity can couple efficiently to both the outside of the cavity and to the helicity-preserving mode, inheriting an enhanced chiral character. We expect such a device to be useful in the future to design ultrasensitive chiral sensors for optics and stereochemistry.

physics.optics↗

arXiv2021

Photon-Emission Statistics induced by Electron Tunnelling in Plasmonic Nanojunctions

We investigate the statistics of photons emitted by tunneling electrons in a single electronic level plasmonic nanojunction. We compute the waiting-time distribution of successive emitted photons $w(τ)$. When the cavity damping rate $κ$ is larger than the electronic tunneling rate $Γ$, we show that in the photon-antibunching regime, $w(τ)$ indicates that the average delay-time between two successive photon emission events is given by $1/Γ$. This is in contrast with the usually considered second-order correlation function of emitted photons, $g^{(2)}(τ)$, which displays the single time scale $1/κ$. Our analysis shows a relevant example for which $w(τ)$ gives independent information on the photon-emission statistics with respect to $g^{(2)}(τ)$, leading to a physical insight on the problem. We discuss how this information can be extracted from experiments even in presence of a non-perfect photon detection yield.

cond-mat.mes-hall↗

arXiv2020

Two-level system as topological actuator for nanomechanical modes

We investigate theoretically the dynamics of two quasidegenerate mechanical modes coupled through an open quantum two-level system. A mean-field approach shows that by engineering the retarded response of the two-level system with a coherent drive, the non-Hermitian mechanical spectrum exhibits an exceptional degeneracy point where the two modes coalesce. We show that this degeneracy can be exploited to manipulate the vectorial polarization of the mechanical oscillations. We find that adiabatically varying the detuning and the intensity of the drive induces a rotation of the mechanical polarization, which enables the topological and chiral actuation of one mode from the other. This topological manifestation of the degeneracy is further supported by quantum-jump Monte Carlo simulations to account for the strong quantum fluctuations due to the spontaneous emission of the two-level system. Our presentation focuses on a promising realization based on flexural modes of a carbon-nanotube cantilever coupled to a single-molecule electric dipole irradiated by a laser.

cond-mat.mes-hall↗

arXiv2018

Transient dynamics in interacting nanojunctions within self-consistent perturbation theory

We present an analysis of the transient electronic and transport properties of a nanojunction in the presence of electron-electron and electron-phonon interactions. We introduce a novel numerical approach which allows for an efficient evaluation of the non-equilibrium Green functions in the time domain. Within this approach we implement different self-consistent diagrammatic approximations in order to analyze the system evolution after a sudden connection to the leads and its convergence to the steady state. These approximations are tested by comparison with available numerically exact results, showing good agreement even for the case of large interaction strength. In addition to its methodological advantages, this approach allows us to study several issues of broad current interest like the build up in time of Kondo correlations and the presence or absence of bistability associated with electron-phonon interactions. We find that, in general, correlation effects tend to remove the possible appearance of charge bistability.

cond-mat.mes-hall↗

arXiv2015

Transient dynamics and waiting time distribution of molecular junctions in the polaronic regime

We develop a theoretical approach to study the transient dynamics and the time-dependent statistics for the Anderson-Holstein model in the regime of strong electron-phonon coupling. For this purpose we adapt a recently introduced diagrammatic approach to the time domain. The generating function for the time-dependent charge transfer probabilities is evaluated numerically by discretizing the Keldysh contour. The method allows us to analyze the system evolution to the steady state after a sudden connection of the dot to the leads, starting from different initial conditions. Simple analytical results are obtained in the regime of very short times. We study in particular the apparent bistable behavior occurring for strong electron-phonon coupling, small bias voltages and a detuned dot level. The results obtained are in remarkable good agreement with numerically exact results obtained by Quantum Monte Carlo methods. We analyze the waiting time distribution and charge transfer probabilities, showing that only a single electron transfer is responsible for the rich structure found in the short times regime. A universal scaling (independent of the model parameters) is found for the relative amplitude of the higher order current cumulants in the short times regime, starting from an initially empty dot. We finally analyze the convergence to the steady state of the differential conductance and of the differential Fano factor at the inelastic threshold, which exhibits a peculiar oscillatory behavior.

cond-mat.mes-hall↗

arXiv2012

Inelastic shot noise characteristics of nanoscale junctions from first principles

We describe an implementation of ab-initio methodology to compute inelastic shot noise signals due to electron-vibration scattering in nanoscale junctions. The method is based on the framework of non-equilibrium Keldysh Green's functions with a description of electronic structure and nuclear vibrations from density functional theory. Our implementation is illustrated with simulations of electron transport in Au and Pt atomic point contacts. We show that the computed shot noise characteristics of the Au contacts can be understood in terms of a simple two-site tight-binding model representing the two apex atoms of the vibrating nano-junction. We also show that the shot noise characteristics of Pt contacts exhibit more complex features associated with inelastic interchannel scattering. These inelastic noise features are shown to provide additional information about the electron-phonon coupling and the multichannel structure of Pt contacts than what is readily derived from the corresponding conductance characteristics.We finally analyze a set of Au atomic chains of different lengths and strain conditions and provide a quantitative comparison with the recent shot noise experiments reported by Kumar et al. [Phys. Rev. Lett. 108, 146602 (2012)].

cond-mat.mes-hall↗

arXiv2011

Detection of ultrafast oscillations in Superconducting Point-Contacts by means of Supercurrent Measurements

We present a microscopic calculation of the nondissipative current through a superconducting quantum point contact coupled to a mechanical oscillator. Using the non-equilibrium Keldysh Green function approach, we determine the current-phase relation. The latter shows that at certain phases, the current is sharply suppressed. These dips in the current-phase relation provide information about the oscillating frequency and coupling strength of the mechanical oscillator. We also present an effective two-level model from which we obtain analytical expressions describing the position and width of the dips. Our findings are of relevance for nanomechanical resonators based on superconducting materials.

cond-mat.mes-hall↗

arXiv2011

Unified description of charge transfer mechanisms and vibronic dynamics in nanoscale junctions

We propose a general framework that unifies the point of view of counting statistics of transmitted (fermionic) charges as it is commonly used in the quantum transport community to the point of view of counting statics of phonons (bosons) as it is known from the field of quantum optics. As a particular example, we study on the same footing the counting statistics of electrons transfered through a molecular junction and the corresponding population dynamics of the associated molecular vibrational mode. In the tunnel limit, non-perturbative results in the electron-phonon interaction are derived that unify complementary approaches based on rate equations or on the use of non-equilibrium Green functions.

cond-mat.mes-hall↗

arXiv2010

Nonlinear effects of phonon fluctuations on transport through nanoscale junctions

We analyze the effect of electron-phonon coupling on the full counting statistics of a molecular junction beyond the lowest order perturbation theory. Our approach allows to take into account analytically the feedback between the non-equilibrium phonon and electronic distributions in the quantum regime. We show that even for junctions with high transmission and relatively weak electron-phonon coupling this feedback gives rise to increasingly higher nonlinearities in the voltage dependence of the cumulants of the transmitted charges distribution.

cond-mat.mes-hall↗

arXiv2009

Electron-phonon interaction and full counting statistics in molecular junctions

The full counting statistics of a molecular level weakly interacting with a local phonon mode is derived. We find an analytic formula that gives the behavior of arbitrary irreducible moments of the distribution upon phonon excitation. The underlying competition between quasi-elastic and inelastic processes results in the formation of domains in parameter space characterized by a given sign in the jump of the irreducible moments. In the limit of perfect transmission, the corresponding distribution is distorted from Gaussian statistics for electrons to Poissonian transfer of holes above the inelastic threshold.

cond-mat.mes-hall↗