Study on fluctuations of interface-enhanced superconductivity in ultrathin FeSe/SrTiO3 by the Nernst effect

TL;DR

This study uses the Nernst effect to explore superconducting fluctuations in ultrathin FeSe/SrTiO3 films, revealing that fluctuations occur only near the transition temperature and suggesting the pseudogap originates from non-superconducting states.

Contribution

It provides new insights into the nature of superconducting fluctuations and the origin of the pseudogap in ultrathin FeSe/SrTiO3 films using Nernst effect measurements.

Findings

Superconducting fluctuations are observed only below approximately 1.2 times the transition temperature.

Normal state Nernst signals resemble bulk FeSe, indicating limited electron transfer.

The pseudogap likely arises from electronic states other than superconductivity.

Abstract

Ultrathin FeSe films on SrTiO3 substrate show interface-enhanced superconductivity. However, how the superconductivity is established including superconducting fluctuations remains unclear. This study investigates the Nernst effect, which is sensitive to superconducting fluctuations, in ultrathin FeSe films on SrTiO3. Temperature dependence of Nernst signals in the normal state is similar to bulk FeSe, suggesting that the electrons of SrTiO3 are transferred only to a few layers near the FeSe/SrTiO3 interface. The Nernst effect caused by SC fluctuations was observed only below T ~ 1.2 Tconset within our measurement resolution, which is similar to other Fe chalcogenide systems. Our results suggest that the pseudogap in monolayer FeSe/STO possibly originates in other electronic states rather than superconductivity.