Evidence of a Precursor Superconducting Phase at Temperatures as High as 180 K in RBa2Cu3O7-delta (R = Y, Gd, Eu) Superconducting Crystals from Infrared Spectroscopy

Abstract

We show that a multilayer analysis of the infrared c-axis response of RBa2Cu3O7-delta (R = Y, Gd, Eu) provides important new information about the anomalous normal-state properties of underdoped cuprate high temperature superconductors. In addition to competing correlations which give rise to a pseudogap that depletes the low-energy electronic states below T* >> T-c, it enables us to identify the onset of a precursor superconducting state below T-ons > T-c. We map out the doping phase diagram of T-ons which reaches a maximum of 180 K at strong underdoping and present magnetic field dependent data which confirm our conclusions.