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Modelling of carrier dynamics and ultra-fast spectroscopy in two-dimensional materials - FAST-2DMAT

The goal of our project is to quantitatively determine the carrier dynamics of monolayer TMDs, using a fully ab initio approach. From the knowledge of the carrier dynamics we can simulate many observables from ultra-fast spectroscopy, such as time-dependent Kerr rotation, time-dependent photo-luminescence and transient absorption.

We solve the Kadanoff-Baym equations using an ab initio approach. We include several dissipation mechanisms, relevant in solid-state systems, such as the electron-phonon interaction, the electron-electron scattering, and the radiative recombination of electron and holes. We are able to describe the interaction with a pump pulse.


Electron-phonon interaction in two-dimensional semiconductors

The interaction of the electron with the lattice vibrations is responsible of many phenomena in semiconductor materials. For instance, the bandgap dependence on temperature is explained as an effect of the electron-phonon interaction. Moreover, the excited states as the excitons also change the binding energy when temperature changes.


Theory of resonant Raman spectroscopy in transition metal dichalcogenides

Raman spectroscopy is a widely used technique for the characterization of materials. When the energy of the laser excitation matchs with the bandgap we are in the resonant Raman scattering. In semiconductors with stronly bound excitons (binding energies in the range of 0.1-0.5 eV) we expect strong excitonic effects on the Raman tensor.

Excitons in two-dimensional materials

Semiconductors 2D materials are known for its small dielectric screening of the Coulomb interaction and the large binding energies of the bound excitons hosted in such materials. We explore 2D materials as hexagonal boron nitride (hBN), transition metal dichalcogenides (TMDs) as MoS2, MoSe2, WSe2, WS2, and other 2D semiconductors as InSe, GaSe. We work in the framework of the Bethe-Salpeter equation, using the wave functions of electrons and holes, obtained from abi-inito software as Quantum Espresso and AB INIT.