Wednesday, July 7, 2010

Deconstructing thermal transport in the pseudogap state

A key question concerning the cuprate superconductors is what is the relationship between the pseudogap state and superconductivity? I previously posted about some beautiful STM data that shows no change in the excitation spectrum of underdoped cuprates when the temperature increases above the transition temperature.

Similar physics is seen in ARPES data and in the thermal conductivity data shown below, taken from this PRL by Doiron-Leyraud et al.
The bottom panel shows that the zero temperature value of kappa(T)/T changes little as a function of doping. In a d-wave superconductor this quantity has a universal non-zero value that is determined by the size of the gap. The upper panel shows how the transition temperature varies with doping, vanishing below p=0.05.
It is striking that the thermal conductivity suggests that the excitation spectrum is unchanged in the non-superconducting samples.
This fact that the thermal conductivity is a powerful probe of the pseudogap state led Michael Smith and I to examine how different models for the pseudogap state (particularly arcs vs. pockets) lead to qualitatively different predictions for the thermal conductivity. Our results appeared in Phys. Rev. B this week.

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