arXiv subjects

Jorge Cervantes-Villanueva

Publications and source records attributed to Jorge Cervantes-Villanueva.

6 recordsLinked to original sources

arXiv2026

Nonequilibrium dynamics of high energy transitions in monolayer WSe$_{2}$

High-energy optical transitions in monolayer transition-metal dichalcogenides exhibit characteristics that are markedly distinct from those of lower-lying band-edge excitons. These differences arise from the involvement of electronic states located at regions of the Brillouin zone that are displaced from the $K$ valleys. In this work, we investigate the ultrafast dynamics of these high-energy excitations by employing broadband ultrafast transient absorption spectroscopy spanning the visible to ultraviolet spectral range. We observe that the formation and relaxation dynamics of one of the high energy transitions display a distinct behavior compared to the lower-energy excitonic resonances, developing on a significantly slower timescale. First-principles calculations of the excitonic landscape allow us to account for this delayed response and attribute it to the phonon-mediated formation of momentum-dark excitons.

cond-mat.mtrl-sci↗

arXiv2026

Coherent Ultrafast Excitonic Oscillations in Monolayer WS$_2$

Monolayer transition metal dichalcogenides are a suitable platform for studying excitonic coherence in the light-matter coupling regime. We present an ab initio time-dependent GW-Bethe-Salpeter equation (GW-BSE) investigation of coherent excitonic dynamics in monolayer WS$_2$. By solving the coherent coupling between the A, A$^{*}$, and B excitons under linearly polarized pump fields, we identify the microscopic origin of the resulting oscillatory dynamics and rationalize it using an effective theoretical model. Our results provide the interpretation of recently reported coherent excitonic phenomena in monolayer WS$_2$ (Nano Lett. 24, 8117 (2024)). Building on this first-principles time-resolved framework, we propose a tailored pump-probe scheme that enables the controlled generation and regeneration of coherent oscillations between excitonic states. These findings establish a predictive route for controlling excitonic coherence in two-dimensional materials, with direct relevance for ultrafast optoelectronic switches and solid-state quantum logic devices.

cond-mat.mtrl-sci↗

arXiv2025

Detection of a coherent excitonic state in the layered semiconductor BiI$_{3}$

The measurement and manipulation of the coherent dynamics of excitonic states constitute a forefront research challenge in semiconductor optics and in quantum coherence-based protocols for optoelectronic technologies. Layered semiconductors have emerged as an ideal platform for the study of exciton dynamics with accessible and technologically relevant energy and time scales. Here, we investigate the sub-picosecond exciton dynamics in a van-der-Waals semiconductor upon quasi-resonant excitation, and achieve to single out an incipient coherent excitonic state. Combining broadband transient reflectance spectroscopy and simulations based on many-body perturbation theory, we reveal a transient enhancement of the excitonic line intensity that originates from the photoinduced coherent polarization that is phase-locked with the interacting electromagnetic field. This finding allows us to define the spectral signature of a coherent excitonic state and to experimentally track the dynamical crossover from coherent to incoherent exciton, unlocking the prospective optical control of an exciton population on the intrinsic quantum-coherence timescale.

cond-mat.mtrl-sci↗

arXiv2024

Unveiling exciton formation: exploring the early stages in time, energy and momentum domain

Resolving the early-stage dynamics of exciton formation following non-resonant photoexcitation in time, energy, and momentum is quite challenging due to their inherently fast timescales and the proximity of the excitonic state to the bottom of the conduction band. In this study, by combining time- and angle-resolved photoemission spectroscopy with \mathit{ab initio} numerical simulations, we capture the timing of the early-stage exciton dynamics in energy and momentum, starting from the photoexcited population in the conduction band, progressing through the formation of free excitons, and ultimately leading to their trapping in lattice deformations. The chosen material is bismuth tri-iodide ($BiI_3$), a layered semiconductor with a rich landscape of excitons in the electronic structure both in bulk and in monolayer form. The obtained results, providing a full characterization of the exciton formation, elucidate the early stages of the physical phenomena underlying the operation of the ultrafast semiconductor device.

cond-mat.mtrl-sci↗

arXiv2023

Physics of excitons in layered BiI$_{3}$. Effects of dimensionality and crystal anisotropy

We carry out a detailed theoretical study of the electronic and optical properties of bulk and monolayer bismuth triiodide (BiI$_{3}$), a layered metal halide, using the ab initio GW+BSE scheme with a full spinorial formulation. We discuss in detail the effects due to the change of dimensionality and the role of spin-orbit coupling. Moreover, we compute the exciton dispersion by solving the BSE at finite momentum, also analysing transverse (TE) and longitudinal (LE) excitons, and the L-T splitting at $\bf{q}\approxΓ$. The results provide a reference for future experimental measurements. In addition, the interplay between spin-orbit coupling and large binding energy, together with the role of quantum confinement, confirm that BiI$_{3}$ is an interesting material for opto-electronic applications and show that it is a good candidate for the study of exciton dynamics.

cond-mat.mtrl-sci↗

arXiv2023

Strong Coupling of Coherent Phonons to Excitons in Semiconducting Monolayer MoTe$_2$

The coupling of the electron system to lattice vibrations and their time-dependent control and detection provides unique insight into the non-equilibrium physics of semiconductors. Here, we investigate the ultrafast transient response of semiconducting monolayer 2$H$-MoTe$_2$ encapsulated with $h$BN using broadband optical pump-probe microscopy. The sub-40-fs pump pulse triggers extremely intense and long-lived coherent oscillations in the spectral region of the A' and B' exciton resonances, up to $\sim$20% of the maximum transient signal, due to the displacive excitation of the out-of-plane $A_{1g}$ phonon. Ab-initio calculations reveal a dramatic rearrangement of the optical absorption of monolayer MoTe$_2$ induced by an out-of-plane stretching and compression of the crystal lattice, consistent with an $A_{1g}$-type oscillation. Our results highlight the extreme sensitivity of the optical properties of monolayer TMDs to small structural modifications and their manipulation with light.

cond-mat.mes-hall↗