标题： 超导体在金属-绝缘体转变附近的异常高温太赫兹非线性 显示英文标题

标题： Anomalous high-temperature THz nonlinearity in superconductors near the metal-insulator transition

摘要： 强无序与超导性的相互作用是凝聚态物理长期感兴趣的话题。 在这里，我们研究了接近三维金属-绝缘体转变的超导 NbN 薄膜的非线性太赫兹响应。 对于无序最小的样品，非线性$\chi^{(3)}$响应的大小遵循超流密度的温度依赖性，如预期的那样。 相反，对于接近金属-绝缘体转变的高无序样品，$\chi^{(3)}$非线性可以持续到高达甚至清洁样品的$T_c$四倍的温度。 我们讨论了这种显著大的非线性的可能来源，包括它可能在局域化附近超导温度尺度增强而产生的可能性。 我们的工作强调了有限频率非线性太赫兹实验在检测超导关联中的重要性，即使在长程有序超导性不持续的区域也是如此。 显示英文摘要

摘要： The interplay of strong disorder and superconductivity is a topic of long-term interest in condensed matter physics. Here we explore the nonlinear THz response of superconducting NbN films close to the 3D metal-insulator transition. For the least disordered samples, the magnitude of the nonlinear $\chi^{(3)}$ response follows the temperature dependence of the superfluid density as expected. In contrast, for high disorder samples near the metal-insulator transition the $\chi^{(3)}$ nonlinearity persists to temperatures as high as even 4 times the $T_c$ of the cleanest sample. We discuss the possible origins of this remarkably large nonlinearity, including the possibility that it arises in an enhancement of the temperature scales of superconductivity close to localization. Our work highlights the importance of finite frequency nonlinear THz experiments in detecting superconducting correlations even into regions where long-range ordered superconductivity does not persist.