Photo-induced phase-transitions and coherent phenomena in realistic materials: an ab-initio Many-Body approach.

ORAL · Invited

Abstract

It is widely known that a monochromatic electro-magnetic wave can travel forever without losing information. It is similarly common knowledge among experimentalists that after a material has been photo-excited an additional, induced, electric field gets super-imposed to the external probe. This field is generated by the electronic charge oscillations. The key point is that this induced field appears only after the excitation. The system, at rest, is not able to produce it. 

What makes the electrons to oscillate in phase and produce a macroscopic field is coherence.  

In this talk I will discuss the role of coherence in out-of-equilibrium phenomena. I will describe some particularly striking examples of how a photo-excited material can reveal coherent phenomena like: magnetic phase transitions, coherent phonon oscillations and the formation of a spontaneous excitonic condensate.

I will also discuss the peculiarities of these phenomena taking the equilibrium perspective. From which it will appear evident that the system reacts is non-perturbative. A dynamics extremely challenging to describe theoretically.

The final message of my talk will be that concepts taken from the equilibrium regime are, often inadequate to describe out-of-equilibrium systems. A striking example will be the Exciton. Can we really say that excitons exist as real population of bound electron-hole pairs? 

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Publication: Marini, A. Competition between the electronic and phonon–mediated scattering channels in the out–of–equilibrium carrier dynamics of semiconductors: an ab-initio approach. Journal of Physics: Conference Series 427, 1 (2013), 012003.

Perfetto, E., Sangalli, D., Marini, A., and Stefanucci, G. Pump-driven normal-to-excitonic insulator transition: Josephson oscillations and
signatures of bec-bcs crossover in time-resolved arpes. Phys. Rev. Materials 3 (2019), 2791.

Smejkal, V., Libisch, F., Molina-Sanchez, A., Trovatello, C., Wirtz, L., and Marini, A. Time-dependent screening explains the ul-
trafast excitonic signal rise in 2d semiconductors. ACS Nano 15 (2021), 1179–1185.

Trovatello, C., Miranda, H. P. C., Molina-Sánchez, A., Borrego Varillas, R., Manzoni, C., Moretti, L., Ganzer, L., Maiuri, M.,
Wang, J., Dumcenco, D., Kis, A., Wirtz, L., Marini, A., Soavi, G., Ferrari, A. C., Cerullo, G., Sangalli, D., and Conte, S. D.
Strongly coupled coherent phonons in single-layer mos 2 . ACS Nano 14 (2020), 5700–5710.

Dendzik, M.; Xian, R. P.; Perfetto, E.; Sangalli, D.; Kutnyakhov, D.; Dong, S.; Beaulieu, S.; Pincelli, T.; Pressacco, F.; Curcio, D.; Agustsson, S. Y.; Heber, M.; Hauer, J.; Wurth, W.; Brenner, G.; Acremann, Y.; Hofmann, P.; Wolf, M.; Marini, A.; Stefanucci, G.; Rettig, L. & Ernstorfer, R. Observation of an Excitonic Mott Transition Through Ultrafast Core-cum-Conduction Photoemission Spectroscopy
Phys. Rev. Lett., 2020, 125

Presenters

  • Andrea Marini

    CNR-ISM and FLASHit

Authors

  • Andrea Marini

    CNR-ISM and FLASHit

  • Davide Sangalli

    CNR-ISM and FLASHit

  • Gianluca Stefanucci

    University of Rome Tor Vergata, Univ of Roma

  • Enrico Perfetto

    Univ of Roma

  • Valerie Smejkal

    Vienna University of Technology, Institute for Theoretical Physic