Pseudogap evidenced by Cu EPR in the normal state of Ortho-III YBa2Cu3O7-x

TL;DR

This study uses Cu EPR to identify the pseudogap onset in underdoped YBa2Cu3O7-x, linking magnetic resonance data with the phase boundary of high-temperature superconductivity.

Contribution

It demonstrates that Cu EPR signals can serve as a spectroscopic probe for the pseudogap in underdoped high-Tc superconductors, correlating EPR g factors with the pseudogap phase boundary.

Findings

Pseudogap onset temperature T* is approximately 190 K.

EPR signals originate from localized Cu2+ sites.

Empirical relationship between g factors and pseudogap established.

Abstract

The temperature dependences of g factors of underdoped YBa2Cu3O7-x (Tc approximates 86.5K) indicate that the pseudogap onset temperature T*( approximates 190 K) coincides with the phase boundary established by resistivity, Nernst effect, neutron diffraction and ultrasound measurements in YBCO phase diagram. The obtained empirical relationship between g factors and pseudogap is appropriate for the entire charactering temperature range of Ortho-III YBCO. The EPR signals are ascribed to the localized Cu2+(1) sites based on the quantitative calculations of the g factors by involving the local structures of the paramagnetic copper (1) sites. The present work provides another potential spectroscopic probe for the pseudogap in underdoped high Tc superconductors and the origin of EPR and related mechanisms in YBCO which are still controversial.