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Séminaire MCBT-Lanef

Mercredi 9 Septembre à 11h00,
Salle Louis Weil, E424

"Amplitude ‘Higgs’ mode in 2H-NbSe2 Superconductor"
Oratrice : Marie-Aude Méasson (Université Paris Diderot-Paris 7 Laboratoire Matériaux et Phénomènes Quantiques)


When a spontaneous breaking of a continuous symmetry takes place, as happens during a superconducting transition, collective excitations of the order parameter emerge among which the massive amplitude Higgs mode. Although the presence of the Higgs mode is fundamental to superconductivity, it remained elusive for many decades, and its presence and observability is still under debate in many contexts, from non-equilibrium conditions to disordered superconductors close to a quantum phase transition. The existence of a Higgs mode was proposed more than thirty years ago in the bulk charge density wave (CDW) superconductor (SC) 2H-NbSe2 [1,2], where a superconducting amplitude mode, or Higgs mode, could be unravelled via its coupling to the coexisting charge density wave mode. The question of the nature of this mode as well as the relationship with the CDW order and more generally the mechanism of its observability are still open to debate [3,4]. Thanks to electronic Raman scattering experiments versus temperature and hydrostatic pressure on NbSe2 and on its brother non-CDW compound NbS2 [5], we provide new evidences for the scenario of a superconducting amplitude mode or Higgs mode. Nevertheless we show that new information, especially on the pressure dependence of the ‘Higgs’ mode in different symmetries, need to be taken into account for a full model.

1. P. B. Littlewood and C. M. Varma, Phys. Rev. Lett. 47, 811(1981).
2. R. Sooryakumar and M. V. Klein, Phys. Rev. Lett. 45, 660 (1980).
3. C. M. Varma, J. Low Temp. Phys. 126, 901 (2002).
4. T. Cea and L. Benfatto, Phys. Rev. B 90, 224515 (2014).
5. M-A Méasson , Y. Gallais, M. Cazayous, B. Clair, A. Sacuto, Phys. Rev. B Rapid Com. 89, 060503R (2014).

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