Berlin 2015 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 85: Superconductivity: Higgs Modes in Condensed Matter and Quantum Gases (jointly with DY, MA, O)
TT 85.3: Talk
Thursday, March 19, 2015, 10:15–10:30, H 2053
THz Investigations of the Higgs Amplitude Mode in Superconducting Thin Films — •Martin Dressel1, Uwe S. Pracht1, Daniel Sherman2, Aviad Frydman2, Boris Gorshunov1,3,4, Pratap Raychaudhuri5, Nandini Trivedi6, and Assa Auerbach7 — 11. Phys. Inst., Universtät Stuttgart — 2Phys. Dept., Bar Ilan University, Ramat Gan, Israel — 3General Physics Inst, RUS, Moscow, Russia — 4Moscow Inst. Phys. and Techn., Dolgoprudny, Russia — 5Tata Inst. Fund. Res., Mumbai, India — 6Phys. Dept., Ohio State University, Columbus, U.S.A. — 7Phys. Dept., Technion, Haifa, Israel
We have measured thin superconducting films of various degrees of disorder by THz spectroscopy in order to investigate the optical conductivity at low temperatures. While the properties of weakly disordered superconductors, such as NbN or InO, can be well described by the BCS theory, significant deviations are observed as disorder increases towards the superconductor-insulator transition. On both sides of the transition, tunneling spectroscopy determines a finite pairing gap 2Δ. In contrast, the threshold frequency for the dynamical conductivity, which in BCS theory is associated with the gap, vanishes critically toward the superconductor insulator transition. Here we can identify an excess optical spectral weight below 2Δ as the first unambiguous evidence of a well-defined Higgs amplitude mode observed in a superconductor.