arXiv subjects

Juan F. P. Mosquera

Publications and source records attributed to Juan F. P. Mosquera.

3 recordsLinked to original sources

arXiv2026

Ultrafast dynamics of excitons in black phosphorus

Excitons are key quasiparticles determining the optical properties of solids. As such, they can be utilized to coherently control the electronic structure of materials using optical femtosecond pulses. Identifying the decoherence mechanism during the early non-equilibrium dynamics is crucial to achieve light-induced band-structure engineering in semiconductors. Here, we generate excitons in the direct band gap semiconductor black phosphorus with a resonant mid-infrared photoexcitation. Using time- and angle-resolved photoemission spectroscopy, we track their complex ultrafast dynamics on the few-picosecond time scale. We develop a quantum-kinetic theoretical framework to model the decoherence of excitons into dark excitons via phonon scattering. By combining simulation and experiment, we quantify key parameters describing the early dynamics of the excitons. Our work highlights phonon-mediated intravalley scattering as a fundamental limitation for coherent exciton phenomena in single-valley semiconductors.

cond-mat.mtrl-sci↗

arXiv2025

Electronic-nuclear entanglement in Born-Oppenheimer wave functions and beyond

We analyze the entanglement between electronic and nuclear motions in molecular wave functions, by using different widely used ansatzes in molecular Hamiltonian models (H$^+_2$ in 1D and the Shin-Metiu model); namely, i) Born-Oppenheimer separation in both adiabatic and ii) diabatic pictures and beyond it, iii) using a Born-Huang expansion, which involves non-adiabatic couplings in the solution. Any molecule can be considered a bipartite system in terms of electronic and nuclear halfspaces. Accordingly, the Schmidt decomposition theorem can be applied to each molecular ansatz to find a much shorter representation in terms of Schmidt basis and to estimate the entanglement content through the calculation of von Neumann entropies. Although here we justify that the ground BO vibronic state of any molecule may be regarded as an almost separable and non-entangled state, this property worsens with the vibrational excitation, which increases the entanglement monotonically. The interlace between electronic and nuclear wave functions for each vibronic state becomes even more critical for those electronic excited states whose electronic wave functions change drastically with the molecular geometry. We find that the entanglement may be quantified by the variation of the electronic wave function along the different nuclear geometries, and that the nuclear wave function indeed plays the role of a tester. In addition, the presence of avoided crossings among the potential energy curves brings about a strong enhancement of entanglement in the Born-Oppenheimer adiabatic picture, which instead is much reduced in a diabatic picture. Finally, the Born-Huang expansion uncovers some synergistic vibronic states whose entanglement content is larger than that of any Born-Oppenheimer component in the superposition.

quant-ph↗

arXiv2024

Topological phase transitions via attosecond x-ray absorption spectroscopy

We present a numerical experiment that demonstrates the possibility to capture topological phase transitions via an x-ray absorption spectroscopy scheme. We consider a Chern insulator whose topological phase is tuned via a second-order hopping. We perform time-dynamics simulations of the out-of-equilibrium laser-driven electron motion that enables us to model a realistic attosecond spectroscopy scheme. In particular, we use an ultrafast scheme with a circularly polarized IR pump pulse and an attosecond x-ray probe pulse. A laser-induced dichroism-type spectrum shows a clear signature of the topological phase transition. We are able to connect these signatures with the Berry structure of the system. This work extend the applications of attosecond absorption spectroscopy to systems presenting a non-trivial topological phase.

physics.optics↗