25 July 2024
Coherent Excitonic State detected in the Layered Semiconductor BiI3
A team of researchers identifies the signature of excitonic coherence in the layered semiconductor BiI3 by combining ab initio real-time simulations and time-resolved experiments.
Layered semiconductors are promising materials for the study of exciton dynamics with accessible and technologically relevant energy and time scales. Yet, measuring and manipulating the coherent dynamics of excitonic states remain challenging. In this study, a team of researchers tracks the evolution of the exciton dynamics from a coherent to an incoherent regime in the layered semiconductor BiI3. By investigating the subpicosecond exciton dynamics in a van der Waals semiconductor upon quasi-resonant excitation, researchers identify an incipient coherent excitonic state.
«Coherent excitons are bound electron-hole pairs. They can lead to fascinating phenomena such as Bose-Einstein condensation, and could be exploited for quantum computing. However, it is crucial to understand how long they remain coherent.» says Davide Sangalli (CNR, Italy), one of the authors of the paper.
To study out-of-equilibrium coherent excitons, and their signature in transient absorption, the researchers solved the equation of motion for the time-dependent density matrix in the presence of a pump field, as recently implemented in the MaX lighthouse code Yambo.
Funded by MaX, this study brings substantial contributions to the fields of semiconductor optics and quantum-coherence-based protocols for optoelectronic technologies.
About the Yambo code
YAMBO is an open-source code released within the GPL licence that implements ground-state as well as excited-state properties in an ab initio context. The code implements MBPT, DFT and Non-Equilibrium Green's Function Theory (NEGF) in order to allow the user to calculate a wealth of physical properties: reliable band gaps, band alignments, defect quasi-particle energies, optical and non--equilibrium properties. YAMBO resorts to previously computed electronic structure, and for this reason it is interfaced with other DFT codes, among which Quantum ESPRESSO.
Reference article:
Detection of a Coherent Excitonic State in the Layered Semiconductor BiI3.