arXiv subjects

Raphael F. Ribeiro

Publications and source records attributed to Raphael F. Ribeiro.

At least 19 recordsLinked to original sources

arXiv2026

Hydrogen Chemisorption and Current-Induced Spin Polarization on NbP

Topological semimetals have been proposed as electrocatalytic platforms because their surface states can connect adsorbate bonding with interfacial charge and spin responses. Here we investigate hydrogen chemisorption on NbP(001) using density functional theory and Wannier-based analyses of surface spectra, chemical bonding, and current-induced spin polarization. Comparing calculations with and without spin--orbit coupling allows us to examine nodal-line-derived surface states and Weyl Fermi arcs on the same surface. Spin--orbit coupling leaves the adsorption thermodynamics essentially unchanged but reorganizes how hydrogen bonds with the Nb- and P-derived surface orbitals. The characteristic Fermi-arc branches persist after adsorption, with H-derived spectral weight appearing within the same near-Fermi-level surface manifold. Together, these results show that chemisorbed hydrogen participates in the spin-textured surface electronic response. The accompanying adsorbate-local current-induced spin polarization points toward opportunities to connect surface chemistry with electrically controlled spin phenomena in topological semimetals.

physics.chem-ph↗

arXiv2026

Polyatomic Thermal Radiative Dissociation in Microcavities

Blackbody infrared radiative dissociation (BIRD) activates molecules through successive absorption of ambient thermal photons until the internal energy reaches a dissociation threshold. Because these radiative transition rates depend on the electromagnetic density of states (DOS), structured infrared environments provide a route to control thermal unimolecular dissociation. Here we develop a state-resolved master-equation framework for polyatomic BIRD in a planar Au/MgO multilayer cavity, where the reactive cluster $\mathrm{(H_2O)_2Cl^-}$ is studied. The cavity modifies the kinetics through the DOS sampled by anharmonic fundamental, overtone, and combination transitions. We show that MgO surface phonon polaritons produce strong near-field enhancements in the central vacuum reaction region of a microcavity. We find that short cavities with thick polar crystal layers yield the largest BIRD enhancements due to enhanced evanescent surface phonon polariton contributions. We further include collisions with a methane bath gas and show that cavity DOS engineering shifts the crossover between BIRD and collisional activation. These results establish Reststrahlen-band DOS engineering as a practical strategy for controlling polyatomic BIRD in infrared microcavities.

physics.chem-ph↗

arXiv2026

Topological advantage for adsorbate chemisorption on conjugated chains

Topological matter offers opportunities for control of charge and energy flow with implications for chemistry still incompletely understood. In this work, we study an ensemble of adsorbates with an empty frontier level (LUMO) coupled to the edges, domain walls (solitons), and bulk of a Su-Schrieffer-Heeger polyacetylene chain across its trivial insulator, metallic, and topological insulator phases. We find that two experimentally relevant observables, charge donation into the LUMO and the magnitude of adsorbate electronic friction, are significantly impacted by the electronic phase of the SSH chain and show clear signatures of the topological phase transition. Localized, symmetry-protected midgap states at edges and solitons strongly enhance electron donation relative to both the metallic and trivial phases, whereas by contrast, the metal's extended states, despite larger total DOS near the Fermi energy, hybridize more weakly with a molecular adsorbate near a particular site. Electronic friction is largest in the metal, strongly suppressed in gapped regions, and intermediate at topological edges where hybridization splits the midgap resonance. These trends persist with disorder highlighting their robustness and suggest engineering domain walls and topological boundaries as pathways for employing topological matter in molecular catalysis and sensing.

cond-mat.mes-hall↗

arXiv2025

Polaritonic control of blackbody infrared radiative dissociation

Vibrational strong light-matter coupling offers a promising approach for controlling chemical reactivity with infrared microcavities. While recent research has examined potential mechanisms for this phenomenon, many important questions remain, including what type of reactions can be modified and to what extent this modification can be achieved. In this study, we explore the dynamics of Blackbody Infrared Radiative Dissociation (BIRD) in microcavities under weak and strong light-matter interaction regimes. Using a Master equation approach, we simulate the effects of infrared field confinement and vibrational strong coupling on BIRD rates for diatomic molecules. We present a framework explaining how infrared microcavities influence BIRD kinetics, highlighting the importance of overtone transitions in the process. Our findings outline the conditions under which significant enhancement or mild suppression of BIRD rates can be achieved, offering insights into the practical limitations and new strategies for controlling chemistry within infrared resonators.

physics.chem-ph↗

arXiv2025

Collision-induced spectroscopy and radiative association in microcavities

Polariton chemistry has emerged as a new approach to directing molecular systems via strong light-matter interactions in confined photonic media. In this work, we implement a classical electrodynamics-molecular dynamics method to investigate collision-induced emission and radiative association in planar microcavities under variable light-matter coupling strength. We focus on the argon-xenon (Ar-Xe) gas mixture as a representative system, simulating collisions coupled to the confined multimode electromagnetic field. We find that while the effects of a microcavity on collision-induced emission spectra are subtle, even at extremely large coupling strengths, radiative association can be significantly enhanced in a microcavity. Our results also indicate that microcavities may be designed to induce changes in the statistical distribution of Ar-Xe complex lifetimes. These findings provide new insights into the control of intermolecular interactions and radiative kinetics with microcavities.

physics.chem-ph↗

arXiv2025

Static disorder-induced renormalization of polariton group velocity

Molecular exciton-polaritons exhibit long-range, ultrafast propagation, yet recent experiments have reported far slower propagation than expected. In this work, we implement a nonperturbative approach to quantify how static energetic disorder renormalizes polariton group velocity in strongly coupled microcavities. The method requires no exact diagonalization or master equation propagation, and depends only on measurable parameters: the mean exciton energy and its variance, the microcavity dispersion, and the Rabi splitting. Using parameters corresponding to recently probed organic microcavities, we show that exciton inhomogeneous broadening slows both lower and upper polaritons, particularly when the mean exciton energy fluctuation approaches the collective light-matter coupling strength. A detailed discussion and interpretation of these results is provided using perturbation theory in the limit of weak resonance scattering. Overall, our results support the view that exciton-phonon interactions likely dominate the recent experimental observations of polariton slowdown in disordered media.

quant-ph↗

arXiv2024

Theory of vibronic adsorbate-surface Fano resonances

Inspired by recent visible pump - infrared probe spectra reported for molecular catalysts adsorbed to quantum dots, we introduce a theory of non-equilibrium vibronic Fano resonances arising from the interference of quantum dot excited-state intraband transitions and infrared vibrational excitations of a molecular adsorbate. Our theory suggests a superexchange mechanism for the observed Fano resonances where charge-transfer states mediate the effective interaction between molecular vibrations and near-resonance quantum dot intraband transitions. We present a perturbative treatment of the effective adsorbate-quantum dot vibronic interaction and employ it to construct a two-reservoir Fano model that enables us to capture key experimental trends, including the relationship between the Fano asymmetry factor, quantum dot size, and the distance between the molecular adsorbate and the quantum dot. We focus on adsorbate-quantum dot species, but our theory's implications are shown to be generic for molecules adsorbed to materials with resonant strong mid-infrared electronic transitions.

physics.chem-ph↗

arXiv2024

Coherent transient exciton transport in disordered polaritonic wires

Excitation energy transport can be significantly enhanced by strong light-matter interactions. In the present work, we explore intriguing features of coherent transient exciton wave packet dynamics on a lossless disordered polaritonic wire. Our main results can be understood in terms of the effective exciton group velocity, a new quantity we obtain from the polariton dispersion. Under weak and moderate disorder, we find that the early wave packet spread velocity is controlled by the overlap of the initial exciton momentum distribution and its effective group velocity. Conversely, when disorder is stronger, the initial state is nearly irrelevant, and red-shifted cavities support excitons with greater mobility. Our findings provide guiding principles for optimizing ultrafast coherent exciton transport based on the magnitude of disorder and the polariton dispersion. The presented perspectives may be valuable for understanding and designing new polaritonic platforms for enhanced exciton energy transport.

quant-ph↗

arXiv2023

Vibrational polariton transport in disordered media

Chemical reactions and energy transport phenomena have been experimentally reported to be significantly affected by strong light-matter interactions and vibrational polariton formation. These quasiparticles exhibit nontrivial transport phenomena due to the long-range correlations induced by the photonic system and elastic and inelastic scattering processes driven by matter disorder. In this article, we employ the Ioffe-Regel criterion to obtain vibrational polariton mobility edges and to identify distinct regimes of delocalization and transport under variable experimental conditions of light-matter detuning, disorder, and interaction strength. Correlations between the obtained trends and recent observations of polariton effects on reactivity are discussed, and essential differences between transport phenomena in organic electronic exciton and vibrational polaritons are highlighted. Our transport diagrams show the rich diversity of transport phenomena under vibrational strong coupling and indicate that macroscopic delocalization is favored at negative detuning and large light-matter interaction strength. We also find the surprising feature that, despite the presence of dephasing-induced inelastic scattering processes, macroscopic lower polariton delocalization and wave transport are expected to persist experimentally, even in modes with small photonic weight.

physics.chem-ph↗

arXiv2023

Chemical equilibrium under vibrational strong coupling

We introduce a theory of chemical equilibrium in optical microcavities, which allows us to relate equilibrium reaction quotients in different electromagnetic environments. Our theory shows that in planar microcavities under strong coupling with polyatomic molecules, hybrid modes formed between all dipole-active vibrations and cavity resonances contribute to polariton-assisted chemical equilibrium shifts. To illustrate key aspects of our formalism, we explore a model SN2 reaction within a single-mode infrared resonator. Our findings reveal that chemical equilibria can be shifted in either direction of a chemical reaction, depending on the oscillator strength and frequencies of reactant and product normal-modes. Polariton-induced zero-point energy changes provide the dominant contributions, though the effects in single-mode cavities tend to diminish quickly as the temperature and number of molecules increase. Our approach is valid in generic electromagnetic environments and paves the way for understanding and controlling chemical equilibria with microcavities.

physics.chem-ph↗

arXiv2023

Theoretical Analysis of Exciton Wave Packet Dynamics in Polaritonic Wires

We present a comprehensive study of exciton wave packet evolution in disordered lossless polaritonic wires. Our simulations reveal signatures of ballistic, diffusive, and subdiffusive exciton dynamics under strong light-matter coupling and identify the typical timescales associated with the transitions between these qualitatively distinct transport phenomena. We determine optimal truncations of the molecular subsystem and radiation field required for generating reliable time-dependent data from computational simulations at affordable cost. The time evolution of the photonic part of the wave function reveals that many cavity modes contribute to the dynamics in a non-trivial fashion. Hence, a sizable number of photon modes is needed to describe exciton propagation with reasonable accuracy. We find and discuss an intriguingly common lack of dominance of the photon mode on resonance with the molecular system both in the presence and absence of disorder. We discuss the implications of our investigations to the development of theoretical models and analysis of experiments where coherent intermolecular energy transport and static disorder play an important role.

quant-ph↗

arXiv2021

Strong light-matter interaction effects on molecular ensembles

Despite the potential paradigm breaking capability of microcavities to control chemical processes, the extent to which photonic devices change properties of molecular materials is still unclear, in part due to challenges in modeling hybrid light-matter excitations delocalized over many length scales. We overcome these challenges for a photonic wire under strong coupling with a molecular ensemble. Our simulations provide a detailed picture of the effect of photonic wires on spectral and transport properties of a disordered molecular material. We find stronger changes to the probed molecular observables when the cavity is redshifted relative to the molecules and energetic disorder is weak. These trends are expected to hold also in higher-dimensional cavities, but are not captured with theories that only include a single cavity-mode. Therefore, our results raise important issues for future experiments and model building focused on unraveling new ways to manipulate chemistry with optical cavities.

physics.chem-ph↗

arXiv2021

Generalization of the Tavis-Cummings model for multi-level anharmonic systems

The interaction between anharmonic quantum emitters (e.g., molecular vibrations) and confined electromagnetic fields gives rise to quantum states with optical and chemical properties that are different from those of their precursors. The exploration of these properties has been typically constrained to the first excitation manifold, the harmonic approximation, ensembles of two-level systems [Tavis-Cummings (TC) model], or the anharmonic single-molecule case. The present work studies, for the first time, a collective ensemble of identical multi-level anharmonic emitters and their dipolar interaction with a photonic cavity mode. The permutational properties of the system allow identifying symmetry classified submanifolds in the energy spectrum. Notably, in this approach, the number of particles, typically in the order of several millions, becomes only a parameter from the operational standpoint, and the size of the dimension of the matrices to diagonalize is independent of it. The formalism capabilities are illustrated by showing the energy spectrum structure, up to the third excitation manifold, and the calculation of the photon contents as a permutationally invariant quantity. Emphasis is placed on (a) the collective (superradiant) scalings of light-matter couplings and the various submanifolds of dark (subradiant) states with no counterpart in the single-molecule case, as well as (b) the delocalized modes containing more than one excitation per molecule with no equivalent in the TC model. We expect these findings to be applicable in the study of non-linear spectroscopy and chemistry of polaritons.

physics.optics↗

arXiv2020

Enhanced optical nonlinearities under strong light-matter coupling

Optical microcavities and metallic nanostructures have been shown to significantly modulate the dynamics and spectroscopic response of molecular systems. We present a study of the nonlinear optics of a model consisting of $N$ anharmonic multilevel systems (e.g., Morse oscillators) undergoing collective strong coupling with a resonant infrared microcavity. We find that, under experimentally accessible conditions, molecular systems in microcavities may have nonlinear phenomena significantly intensified due to the high quality of polariton resonances and the enhanced microcavity electromagnetic energy density relative to free space. Particularly large enhancement of multiphoton absorption happens when multipolariton states are resonant with bare molecule multiphoton transitions. In particular, our model predicts two-photon absorption cross section enhancements by several orders of magnitude relative to free space when the Rabi splitting $Ω_R$ is approximately equal to the molecular anharmonic shift $2Δ$. Our results provide rough upper bounds to resonant nonlinear response enhancement factors as relaxation to dark states is treated phenomenologically. Notably, ensembles of two-level systems undergoing strong coupling with a cavity (described by the Tavis-Cummings model) show no such optical nonlinearity enhancements, highlighting the rich phenomenology afforded by multilevel anharmonic systems. Similar conclusions are expected to hold for excitonic systems that share features with our model (e.g., molecular dyes with accessible S_0 -> S_1 -> S_2 transitions) and strongly interact with a UV-visible cavity.

physics.chem-ph↗

arXiv2019

Manipulating Optical Nonlinearities of Molecular Polaritons by Delocalization

Optical nonlinearities - how light-matter interactions are influenced by previous interactions with photons, are key resources in the contemporary photonics toolbox, relevant to quantum gate operations and all-optical switches. Optical nonlinearities of materials are often controlled at the microscopic level by chemical modification, which makes on-the-fly manipulation of such response challenging. Tunability of optical nonlinearities in the mid-IR is even less developed, hindering its applications in chemical sensing or IR photonic circuitry. Here, we report control of vibrational polariton coherent nonlinearities by manipulation of macroscopic parameters such as cavity longitudinal length or molecular concentration. These emergent nonlinearities last for the lifetime of the cavity mode, and subsequently evolve into the response determined by an incoherent population of dark reservoir modes. The observed phenomena arise due to the nonlinear macroscopic polarization stemming from strong coupling between microscopic molecular excitations and a macroscopic photonic cavity mode.

cond-mat.mtrl-sci↗

arXiv2019

Resonant catalysis of thermally-activated chemical reactions via vibrational polaritons

In the regime of ensemble vibrational strong coupling (VSC), a macroscopic number $N$ of molecular transitions couple to each resonant cavity mode, yielding two hybrid light-matter (polariton) modes, and a reservoir of $N-1$ dark states whose chemical dynamics are essentially those of the bare molecules. This fact is seemingly in opposition to the recently reported modification of thermally activated ground electronic state reactions under VSC. Here, we provide a VSC Marcus-Levich-Jortner electron transfer model that potentially addresses this paradox: while entropy favors the transit through dark-state channels, the chemical kinetics can be dictated by a few polaritonic channels with smaller activation energies. The effects of catalytic VSC are maximal at light-matter resonance, in agreement with experimental observations.

physics.chem-ph↗

arXiv2018

Remote control of chemistry in optical cavities

Manipulation of chemical reactivity often involves changing reagents or environmental conditions. Alternatively, strong coupling between light and matter offers a way to tunably hybridize their physicochemical properties and thereby change reaction dynamics without synthetic modifications to the starting material. Here, we theoretically design a polaritonic (hybrid photonic-molecular) device that supports ultrafast tuning of reaction yields even when the catalyst and its reactant are spatially separated across several optical wavelengths. We demonstrate how photoexcitation of a `remote catalyst' in an optical microcavity can control photochemistry of a reactant in another microcavity. Harnessing delocalization across the spatially separated compounds that arises from strong cavity-molecule coupling, this intriguing phenomenon is shown for the infrared-induced \textit{cis} $\rightarrow$ \textit{trans} conformational isomerization of nitrous acid (HONO). Indeed, increasing the excited-state population of the remote catalyst can enhance the isomerization efficiency by an order of magnitude. The theoretical proposal reported herein is generalizable to other reactions and thus introduces a versatile tool to control photochemistry.

quant-ph↗

arXiv2018

Polariton Chemistry: controlling molecular dynamics with optical cavities

Molecular polaritons are the optical excitations which emerge when molecular transitions interact strongly with confined electromagnetic fields. Increasing interest in the hybrid molecular-photonic materials that host these excitations stems from recent observations of their novel and tunable chemistry. Some of the remarkable functionalities exhibited by polaritons include the ability to induce long-range excitation energy transfer, enhance charge conductivity, and inhibit or enhance chemical reactions. In this review, we explain the effective theories of molecular polaritons which form a basis for the interpretation and guidance of experiments at the strong coupling limit. The theoretical discussion is illustrated with the analysis of innovative applications of strongly coupled molecular-photonic systems to chemical phenomena of fundamental importance to future technologies.

cond-mat.mes-hall↗