Berlin 2015 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 47: Superconductivity: Higgs Modes in Condensed Matter and Quantum Gases (joint session TT/ DY/ MA/ O)

DY 47.3: Vortrag

Donnerstag, 19. März 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 Gorshunov^1,3,4, 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.