Quantum Creep in Y_{1-x}Pr_{x}Ba_{2}Cu_{3}O_{7}$ Crystals: Magnetic Relaxation and Transport

TL;DR

This study investigates magnetic relaxation and transport in underdoped Y_{1-x}Pr_{x}Ba_{2}Cu_{3}O_{7} crystals, revealing a transition from thermal to quantum flux creep around 5 K and suggesting a confinement of current below a coupling transition.

Contribution

It provides experimental evidence of a crossover from thermal to quantum flux creep in high-temperature superconductor crystals and links this to a coupling transition affecting current distribution.

Findings

Observation of thermal to quantum flux creep transition near 5 K

Identification of a coupling transition preceding quantum creep

Current confinement within a narrow layer below contacts

Abstract

We report transport and magnetic relaxation measurements in the mixed state of strongly underdoped Y_{1-x}Pr_{x}Ba_{2}Cu_{3}O_{7} crystals. A transition from thermally activated flux creep to temperature independent quantum flux creep is observed in both transport and magnetic relaxation at temperatures T * 5 K. Flux transformer measurements indicate that the crossover to quantum creep is preceded by a coupling transition. Based on these observations we argue that below the coupling transition the current is confined within a very narrow layer beneath the current contacts.