Evidence for a generic quantum transition in high-Tc cuprates

Abstract

We study the low-energy spin fluctuations and superfluid density of a series of pure and Zn-substituted high-Tc superconductors (HTS) using the muon spin relaxation and ac-susceptibility techniques. At a critical doping state, pc, we find (i) simultaneous abrupt changes in the magnetic spectrum and in the superconducting ground state and (ii) that the slowing down of spin fluctuations becomes singular at T=0. These results provide experimental evidence for a quantum transition that separates the superconducting phase diagram of HTS into two distinct ground states.