Cu NMR study of a Pb-doped Bi:2201 single crystal

TL;DR

This study uses Cu NMR to investigate a Pb-doped Bi:2201 superconductor, revealing a pseudogap opening above Tc, indicating an underdoped state, and showing a high upper critical field despite low Tc.

Contribution

It provides new insights into the pseudogap behavior and magnetic field effects in Pb-doped Bi:2201 using NMR techniques.

Findings

Pseudogap opens at 20-60 K, well above Tc.

Weak magnetic field effect on Tc suggests high upper critical field.

Underdoped state indicated by discrepancy between Tc and T*.

Abstract

A 63Cu NMR study of Pb-doped Bi:2201 system, Bi1.6Pb0.4Sr2.05CuOy, is presented. Temperature dependencies of the NMR peak shift and the nuclear spin-lattice relaxation rate revealed the pseudogap that opens at T* = 20 - 60 K, way above the Tc ~ 9K measured for the orientation (H//c) and value (7 T) of the NMR experiment field. The noticeable discrepancy between Tc and T* and the behavior of Cu SLR at T > T* imply the underdoped state of the studied system. The magnetic field has a relatively weak effect on the superconductivity in the studied system, as evidenced from small (7-8 K) shift of the zero-field Tc = 16+/- 1K under the applied 7 T field. This fact suggests a high value of the upper critical field, unusual for a compound with such low Tc.