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Theoretical study of the photoexcitation of dopants in superfluid helium nanodroplets




Duration: NanoX master Internship (8 months part-time in-lab immersion)
5 months full-time internship
6 months full-time internship

Latest starting date: 30/11/2023

Localisation: LCAR


Work package:
The goal of this project is to study the dynamics induced by photoexcitation or ionization of a dopant in or on a superfluid helium nanodroplet. Helium nanodroplets are large helium clusters (typically thousands to several hundred billions of atoms) exhibiting remarkable properties : very low temperature (0.4 K), superfluidity, weak interaction with the dopant, very high thermal conductivity and very fast relaxation dynamics. This makes them an exceptional environment for dynamics studies [1]. During the past few years, several dynamics experiments have been conducted on these systems using highly sophisticated techniques : real time femtosecond pump-probe experiments, velocity map imaging, ... From a theoretical point of view, it is a serious challenge to study the real time dynamics of these systems because of the strong quantum effects due to the light mass of helium. Helium density functional theory (He-DFT) and its time-dependent version (He-TDDFT), which deal with the helium density rather than the many-body helium wave function, have emerged as an optimal compromise between accuracy and the ability to work with large numbers of helium atoms [2]. We will apply them to one of the following cases: dynamics initated by photoexcitation of a dopant atom or molecule, or solvation dynamics upon sudden ionization of a dopant, or Coulomb explosion of a two-dopant system used as a probe signal. This training will be conducted in collaboration with the team of M. Barranco and M. Pi from the University of Barcelona, who are experts in the He-(TD)DFT methods, and with the experimental team of Kristensen (Aarhus, Denmark).

[1] S. Grebenev, J.P. Toennies et A.F. Vilesov, Science 279 , 2083 (1998) [2] F. Ancilotto et al., Int. Rev. Phys. Chem. 36, 621-707 (2017) [3] H. H. Kristensen, L. Kranabetter, C. A. Schouder, C. Stapper, J. Arlt, M. Mudrich and H. Stapelfeldt, Phys. Rev. Lett. 128, 093201 (2022)

Areas of expertise:
Quantum molecular dynamics; superfluid helium

Required skills for the internship:
Very good knowledge of quantum mechanics and quantum atomic and molecular dynamics; FORTRAN 90 programming skills, or at least some programming experience.