Crossover temperatures in the normal-state phase diagram of high-Tc superconductors

Abstract

The widespread reference to phase diagrams for the high-Tc superconductors that involve two crossover temperatures TL and TU extending across the underdoped normal-state region is critically examined in the light of NMR and heat capacity data. We conclude that, in both the q=(0,0) and q=(π,π) response, there is only one crossover temperature, best described as the pseudogap energy scale rather than a well-defined onset temperature. This has a strong, linearly decreasing dependence on hole concentration. The lower crossover temperature, TL, commonly determined from 63T1T, is shown to be an artefact of convoluting the pseudogap energy scale with an intrinsic linear T dependence arising, in the nearly antiferromagnetic Fermi-liquid model, from the characteristic spin-fluctuation frequency, ωsf. We conclude that models constructed on the two-crossover temperatures scenario need to be reexamined.

Source-reported materials — not catalogue approval

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