arXiv subjects

Guy Vosco

Publications and source records attributed to Guy Vosco.

3 recordsLinked to original sources

arXiv2026

Application of the exact-factorization density-functional perturbation approach to pentacene crystal and monolayer MoS2

Non-adiabatic effects arising from electron-phonon interactions are often neglected within the Born-Oppenheimer (BO) approximation, which assumes that electronic states adjust instantaneously to nuclear motion. The exact factorization (EF) formalism provides a rigorous framework for treating such effects beyond the adiabatic regime and has recently been adapted to density functional theory (DFT) in the harmonic limit. Building on these foundations, we previously introduced an EF-based perturbative scheme, the EF density-functional perturbation theory (EF-DFPT), that enables the computation of phonon-driven non-adiabatic (NA) corrections to Kohn-Sham (KS) electronic states, up to second order in nuclear displacements. Here, we present the first implementation and application of EF-DFPT to extended periodic materials, focusing on its impact on experimentally relevant observables. Using the pentacene molecular crystal and monolayer MoS2 as representative soft- and stiff-mode systems, respectively, we demonstrate how NA electron-phonon interactions modify the static dielectric response. We show that these modifications originate from the combined effect of NA phonon-dressed electronic wavefunctions and second-order NA energy renormalizations. The resulting behavior is strongly material dependent: NA effects are negligible in monolayer MoS2, whereas in pentacene they lead to pronounced long-range screening effects associated with soft vibrational modes and enhanced electron-phonon coupling.

cond-mat.mtrl-sci↗

arXiv2025

Exciton-Exciton Annihilation Mediated by Many-Body Coulomb and Phonon Interactions: An Ab Initio Study

Exciton-exciton annihilation (EEA), in which two excitons interact to generate high-energy excitations, is an important non-radiative channel in light-induced excited-state relaxation. When efficient, this process offers an alternative route to exciton emission, potentially allowing extended energetically excited particles' lifetime and coherence. These properties are significant in designing and understanding materials-based quantum devices, particularly for low-dimensional semiconductors. Here, we present a first-principles framework to compute EEA mechanisms and rates using many-body perturbation theory within the GW and Bethe-Salpeter Equation (GW-BSE) formalism. Our method explicitly accounts for Coulomb-driven and phonon-assisted exciton-exciton scattering by explicitly evaluating the interaction channels between the constituent electrons and holes composing the BSE excitons. We apply this framework to monolayer WSe$_2$ and explore the $A$, $B$ excitation manifolds, finding picosecond-scale annihilation between bright and dark states, cross valleys, and cross peak manifolds. These channels become allowed due to scattering into free electron-hole pairs across the Brillouin zone. Our results supply new insights into non-radiative exciton relaxation mechanisms in two-dimensional materials, providing a predictive and general tool for modeling these interactions in excitonic materials.

cond-mat.mtrl-sci↗

arXiv2025

Ab-initio density-matrix approach to exciton coherence: phonon scattering, Coulomb interactions and radiative recombination

Relaxation processes following light excitation in semiconductors are key in materials-based quantum technology applications. These processes are broadly studied in atomically thin transition metal dichalcogenides (TMDs), quasi-two-dimensional excitonic semiconductors in which atomistic design allows for tunable excited-state properties, such as relaxation lifetimes and photo-induced coherence. In this work, we present a density-matrix-based approach to compute exciton relaxation within a many-body ab initio perspective. We expand our previously developed Lindblad density-matrix formalism to capture multi-channel electron-hole pair relaxation processes, including phonon and Coulomb scattering as well as radiative recombination, and study their effect on the time-resolved excited-state propagation. Using monolayer MoSe$_2$ as a prototypical example, we examine many-body effects on the time-dependent dynamics of photoactive excitations, exploring how the electron-hole pair interactions are reflected in variations of the excitation energy, spectral signature, and state coherence. Our method supplies a detailed understanding of exciton relaxation mechanisms in realistic materials, offering a previously unexplored pathway to study excited-state dynamics in semiconductors from first principles.

cond-mat.mtrl-sci↗