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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 1.5: Invited Talk
Wednesday, March 18, 2015, 17:15–17:45, H 0105
The Higgs Mode in Disordered Superconductors Close to a Quantum Phase Transition — •Aviad Frydman1, Daniel Sherman1,2, Uwe S. Pracht2, Boris Gorshunov2,3, and Martin Dressel2 — 1Department of Physics, Bar Ilan University, Ramat Gan, 52900, Israel — 2Physikalisches Institut, Universität, Stuttgart, 70550 Stuttgart, Germany — 3Moscow Institute of Physics and Technology, 141700, Dolgoprudny, Moscow Region, Russia
The Higgs theory, which generates mass for elementary particles, was inspired by screening of magnetic fields in superconductors. It is somewhat disappointing that in superconductors, the Higgs-amplitude mode has not yet been observed, partially because it can rapidly decay into unpaired electrons. Nevertheless, recent theories show that if the Higgs mass could be softened below the pairing gap it should be visible in two dimensions. Such conditions can be met by tuning a superconducting film towards a quantum critical point (QCP). We report on spectroscopic studies in the terahertz frequency regime of thin superconducting films for which the superconductor to insulator transition (SIT) is tuned by disorder. Tunneling spectroscopy determines the pairing gap 2Δ which remains finite on both sides of the SIT. In contrast, the threshold frequency for dynamical conductivity, which in BCS theory is associated with the gap, vanishes critically toward the SIT. The excess optical spectral weight below 2Δ is identified as an unambiguous observation of the Higgs mode in a superconductor.