Low-frequency spins and the ground state in high-T-c cuprates

Panagopoulos, C., Tallon, J.L., Rainford, B.D., Cooper, J.R., Scott, C.A. and Xiang, T. (2003) Low-frequency spins and the ground state in high-T-c cuprates. Solid State Communications, 126 (1-2), 47-55. (doi:10.1016/S0038-1098(02)00667-1).

Abstract

We study the spin fluctuations of pure and Zn-substituted high temperature superconductors (HTS) using the muon spin relaxation (SR) technique. Superconductivity is found to coexist with low frequency spin fluctuations over a large region of the superconducting phase diagram. The characteristic temperature of spin fluctuations detected by SR decreases with increasing doping and vanishes above a critical doping pc~0.19 where the normal state pseudogap vanishes. Furthermore, it is at pc that our penetration depth studies show an abrupt change in the doping dependence of the superfluid density, s. For p>pc the absolute value of s is large and nearly independent of carrier concentration whereas for p<pc it drops rapidly, signalling a crossover to weak superconductivity. These results are discussed in terms of a quantum transition involving fluctuating short-range magnetic order that separates the superconducting phase diagram of HTS into two distinct ground states.

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