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Link visio : https://univ-grenoble-alpes-fr.zoom.us/j/95896774614?pwd=ekJFc0RnSDlPWUpXcERraTk5RVc5dz09
Meeting ID : 958 9677 4614
Secret code : 147934
The defence will be in French.
The Higgs mode is an electronic excitation characteristic of the superconducting state. It is not coupled to electric charge, light or spin, making direct observation of this mode impossible. Recent work, on which the work presented in this thesis is based, shows that it is nevertheless possible to detect a signature of its existence via the coupling between superconductivity and another electronic order : the charge density wave. As a perfect mathematical analogue of the Higgs boson for high energy physics, the Higgs mode is very important both for the understanding of superconductivity and its interactions, and for physics beyond the standard model of particle physics. The objective of this thesis was to explore systems with coupling between several electronic orders, different from those known in the literature, in order to extend our knowledge on the observability mechanism of the Higgs mode. To this end, I have studied several compounds belonging to the A15 and cuprate families using Raman spectroscopy. This work is distinguished by the study of very low energy excitations (<100 meV) under extreme conditions of temperature (≈ 10 K) and magnetic field (up to 30 T). Our study shed light on new signatures with a remarkable dependence on magnetic field, temperature and doping. Through a thorough analysis of the obtained Raman
spectra and a review of the literature, hypotheses about the nature of these new excitations are proposed in this manuscript. Nevertheless, many questions remain unanswered. This work therefore opens the way to many additional experiments required in order to understand the observed new phenomena.
Thesis supervisor:
Matteo D’Astuto
Institut Néel
Co-thesis supervisor:
Marie-Aude Méasson
Institut Néel
Jury Members :
M. Matthieu Le Tacon
KIT, Referee
Mme Paulina Plochocka
LNCMI-Toulouse, Referee
M. Yannick Klein
Sorbonne Université, Examiner
M. Thierry Klein
Université Grenoble Alpes, Examiner
M. Ingo Schienbein
Université Grenoble Alpes, Guest member
