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

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 Tc, and returns to higher fields above Tc. 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.