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Avoided Quantum Criticality in YBa2Cu3Oy and La2-xSrxCuO4

J. E. Sonier, F. D. Callaghan, Y. Ando, R. F. Kiefl, J. H. Brewer, C. V. Kaiser, V. Pacradouni, S. -A. Sabok-Sayr, X. F. Sun, S. Komiya, W. N. Hardy, D. A. Bonn, R. Liang

cond-mat.supr-conarXiv:cond-mat/0610051

Abstract

Spin-glass magnetism confined to individual weakly interacting vortices is detected in two different families of high-transition-temperature (Tc) superconductors, but only in samples on the low-doping side of the low-temperature normal state metal-to-insulator crossover (MIC). Our findings unravel the mystery of the MIC, but more importantly identify the true location of the field-induced quantum phase transition (QPT) in the superconducting state. The non-uniform appearance of magnetism in the vortex state favours a surprisingly exotic phase diagram, in which spatially inhomogeneous competing order is stabilized at the QPT, and an `avoided' quantum critical point (QCP) is realized at zero magnetic field.

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