Superconducting Fluctuations, Pseudogap and Phase Diagram in Cuprates

TL;DR

This study uses pulsed magnetic fields to analyze superconducting fluctuations and the pseudogap in cuprates, revealing that the pseudogap is not due to preformed pairs and proposing a disorder-inclusive phase diagram.

Contribution

It provides new measurements of the pseudogap and SCF disappearance temperatures, clarifies their relationship, and introduces a phase diagram including disorder effects.

Findings

T* is smaller than T'c near optimal doping, indicating the pseudogap is not from preformed pairs.

Disorder influences both T* and T'c, affecting the phase diagram.

The phase diagram incorporating disorder explains various observations in cuprates.

Abstract

We report transport measurements using pulsed magnetic fields to suppress the superconducting fluctuations (SCF) conductivity in a series of YBa_2Cu_3O_(6+x) samples. These experiments allow us altogether to measure the temperature T'c at which SCF disappear, and the pseudogap temperature T*. While the latter are consistent with previous determinations of T*, we find that T'c is slightly larger than similar data taken by Nernst measurements. A careful investigation near optimal doping shows that T* becomes smaller than T'c, which is an unambiguous evidence that the pseudogap cannot be assigned to preformed pairs. Studies of the incidence of disorder on both T'c and T* allow us to propose a phase diagram including disorder which explains most observations done in other cuprate families, and to discuss the available knowledge on the pseudogap line in the phase diagram.