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SYHM: Symposium Higgs Modes in Condensed Matter and Quantum Gases

SYHM 1: Higgs Modes in Condensed Matter and Quantum Gases

SYHM 1.4: Hauptvortrag

Mittwoch, 18. März 2015, 16:45–17:15, H 0105

Amplitude Higgs Mode in 2H-NbSe₂ Superconductor — •Marie-Aude Méasson¹, Romain Grasset¹, Yann Gallais¹, Max Cazayous¹, Alain Sacuto¹, Pierre Rodière², and Laurent Cario³ — ¹LMPQ, Universite Paris 7-CNRS, France — ²Institut Neel, Grenoble, France — ³IMN, Universite de Nantes, France

When a spontaneous breaking of a continuous symmetry takes place, as happens during a superconducting transition, collective excitations such as the amplitude Higgs mode of the order parameter emerge. The existence of such Higgs mode was proposed in the charge density wave (CDW) superconductor (SC) 2H-NbSe₂, after the first experimental observation by Raman scattering. The Higgs mode could be unraveled via its coupling to the coexisting charge density wave mode. We will address here the questions of the nature of this mode as well as the mechanism of its observability.

We report experimental evidences for the Higgs mode scenario in 2H-NbSe₂ using Raman scattering. By comparing 2H-NbSe₂ and its iso-structural partner 2H-NbS₂ which shows superconductivity but lacks the charge density wave order and by destroying the coexisting CDW order under high pressure in 2H-NbSe₂, we demonstrate that the superconducting mode owes its spectral weight to the presence of the coexisting charge density wave order. In addition a full spectral weight transfer between both modes operates in 2H-NbSe₂ upon entering the superconducting phase. All these observations are consistent with a superconducting Higgs mode. Intriguing symmetry dependent results under pressure will be discussed.