Change of quasiparticle dispersion in crossing T_c in the underdoped cuprates

TL;DR

This paper explains the change in quasiparticle dispersion crossing T_c in underdoped cuprates as due to phase fluctuations of the superconducting order parameter, supported by theory and experiment comparison.

Contribution

It demonstrates that phase fluctuations account for the dispersion change and pseudogap behavior in underdoped cuprates, providing a unified understanding of the phenomena.

Findings

Back-turning BCS bands disappear above T_c

Pseudogap has a U-shape, not V-shape

Pseudogap closes from nodal directions and fills at anti-nodal regions

Abstract

One of the most remarkable properties of the high-temperature superconductors is a pseudogap regime appearing in the underdoped cuprates above the superconducting transition temperature T_c. The pseudogap continously develops out of the superconducting gap. In this paper, we demonstrate by means of a detailed comparison between theory and experiment that the characteristic change of quasiparticle dispersion in crossing T_c in the underdoped cuprates can be understood as being due to phase fluctuations of the superconducting order parameter. In particular, we show that within a phase fluctuation model the characteristic back-turning BCS bands disappear above T_c whereas the gap remains open. Furthermore, the pseudogap rather has a U-shape instead of the characteristic V-shape of a d_{x^2-y^2}-wave pairing symmetry and starts closing from the nodal k=(pi/2,pi/2) directions, whereas it rather fills in at the anti-nodal k=(pi,0) regions, yielding further support to the phase fluctuation scenario.