Correlation between unconventional superconductivity and strange metallicity revealed by operando superfluid density measurements
Ruozhou Zhang, Mingyang Qin, Chenyuan Li, Zhanyi Zhao, Zhanyi Zhao, Zhongxu Wei, Juan Xu, Xingyu Jiang, Wenxin Cheng, Qiuyan Shi, Xuewei Wang, Jie Yuan, Yangmu Li, Qihong Chen, Tao Xiang, Subir Sachdev, Zixiang Li, Kui Jin, Zhongxian Zhao, Zhongxian Zhao
Abstract
Strange-metal behavior has been observed in superconductors ranging from cuprates to pressurized nickelates, but its relationship to unconventional superconductivity remains elusive. Here, we perform operando superfluid density measurements on ion-gated FeSe films. We observe a synchronized evolution of the superconducting condensate and the strange-metal phase with electron doping, from which a linear scaling between zero-temperature superfluid density and strange-metal resistivity coefficient is further established. The scaling also applies to different iron-based and cuprate superconductors despite their distinct electronic structures and pairing symmetries. Such a correlation can be reproduced in a theoretical calculation on the two-dimensional Yukawa-Sachdev-Ye-Kitaev model by considering a cooperative effect of quantum critical fluctuation and disorder. These findings suggest that a common mechanism may govern both the Cooper pair condensation and the normal-state strange metallicity in unconventional superconductors.