2015/12/20 by Bing Cheng, Liang Wu, N. J. Laurita +4 · 48 citations
Physics and Astronomy · #Condensed matter physics #Context (archaeology) #Density of states #Dissipation #Mesoscopic physics #Optical conductivity #Physics #Physics of Superconductivity and Magnetism #Quantum mechanics #Quantum tunnelling #Quasiparticle #Superconducting and THz Device Technology #Superconductivity #Superconductivity in MgB2 and Alloys #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.93.180511
published in Physical review. B./Physical review. B 93(18) (American Physical Society) · 5 pages, 3 figures in main text; 7 pages, 4 figures in SI
arxiv created 2015/12/20 · openalex publication_date 2016/05/26 · arxiv updated 2016/06/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
Superconductivity in disordered systems close to an incipient localization transition has been an area of investigation for many years, but many fundamentally important aspects are still not understood. It has been noted that in such highly disordered superconductors, anomalous spectral weight develops in their conductivity near and below the superconducting gap energy. In this work we investigate the low frequency conductivity in disordered superconducting NbN thin films close to the localization transition with time-domain terahertz spectroscopy. In the normal state, strong deviations from the Drude form due to incipient localization are found. In the superconducting state we find substantial spectral weight at frequencies well below the superconducting gap scale derived from tunneling. We analyze this spectral weight in the context of a model of disorder induced broadening of the quasiparticle density of states. We find that aspects of the optical and tunneling data can be consistently modeled in terms of this effect of mesoscopic disorder, showing that in this disorder and frequency range, quasiparticle effects and not collective modes are the source of low energy absorption. Interestingly, we also find that as a function of frequency the optical conductivity recovers to the normal state value much faster than any model predicts. This points to the nontrivial interplay of superconductivity and disorder close to localization.