Superfluid density and strange metallicity in the overdoped regime of the cuprate Bi-2201

Identifying the origin of cuprate high-temperature superconductivity remains one of the outstanding challenges of modern condensed matter physics. Key to this challenge is to understand why both the superconducting transition temperature Tc and superfluid density trace out a dome as a function of doping. This project focusses on the overdoped side of the dome in what is known as the strange metal regime, characterized by anomalous transport, maximal (Planckian) dissipation and strong electron correlations. Our comprehensive study of the single-layered cuprate Bi2201 within this regime has provided compelling evidence for the coexistence of two distinct charge sectors; one conventional and Fermi-liquid-like, the other non-Fermi-liquid-like and defined by an anomalous T-linear resistivity and this ‘Planckian’ dissipation. Given the presence of these two charge sectors, the crucial question is which sector contributes most to the superfluid density? The prospect of having a superfluid condensate composed exclusively of these Planckian carriers would represent a new paradigm for high-temperature superconductivity. In order to provide a definitive answer to this question, we seek to carry out the first detailed investigation of the superfluid density across the strange metal regime via μSR measurements of the in-plane penetration depth in Bi2201. This proposal represents the first stage of this project, focussing on two well-characterized single crystals with different Tc values.