Observation of the ghost critical field for superconducting fluctuations in a disordered TaN thin film

TL;DR

This study experimentally investigates the ghost critical field (GCF) in a disordered TaN thin film, revealing how superconducting fluctuations are suppressed by magnetic fields near the transition temperature through Hall effect and magnetoresistance measurements.

Contribution

First experimental observation and analysis of the GCF in a disordered superconducting thin film using Hall effect and magnetoresistance measurements.

Findings

Hall effect peaks track the upper critical field below T_c

GCF vanishes near T_c and reappears above T_c

Magnetoresistance data agree with theoretical models

Abstract

We experimentally study the ghost critical field (GCF), a magnetic field scale for the suppression of superconducting fluctuations, using Hall effect and magnetoresistance measurements on a disordered superconducting thin film near its transition temperature $T_c$. We observe an increase in the Hall effect with a maximum in field that tracks the upper critical field below $T_c$, vanishes near $T_c$, and returns to higher fields above $T_c$. Such a maximum has been observed in studies of the Nernst effect and identified as the GCF. Magnetoresistance measurements near $T_c$ indicate quenching of superconducting fluctuations, agree with established theoretical descriptions, and allow us to extract the GCF and other parameters. Above $T_c$ the Hall peak field is quantitatively distinct from the GCF, and we contrast this finding with ongoing studies of the Nernst effect and superconducting fluctuations in unconventional and thin-film superconductors.