Nernst effect in ultrathin FeSe/SrTiO₃ grown by PLD

Ultrathin FeSe films on oxides have attracted much attention because superconductivity is enhanced by the interface effects compared to bulk form [1].

In FeSe/STO₃ grown by molecular beam epitaxy, the pseudo-gap phenomenon below 70 K was reported, which was interpreted in terms of superconducting fluctuations [2]. The enhancement of superconductivity was also achieved using pulsed laser deposition (PLD) [3]. However, the superconducting fluctuations were not investigated for the PLD-grown films.

In this study, we performed the Nernst effect measurement on ultrathin FeSe/SrTiO₃ grown by PLD. A 4-layer film shows a superconducting transition with a T_c^onset of 27 K and zero resistance below 8.4 K at 0 T. The transverse thermoelectric coefficient α_xy increases below T^* ~1.1×T_c^onset, and a peak structure is observed at low temperatures. Furthermore, magnetic field dependence of α_xy changes from linear to non-linear below T^*. These results indicate that superconducting fluctuations persist up to T^* ~1.1×T_c^onset, which is similar to bulk superconductivity in Fe(Se, Te) thin films [4]. These results provide valuable insights into the nature of the interface-enhanced superconductivity in FeSe/oxide systems.

[1]. Q. Y. Wang et al., Chin. Phys. Lett. 29, 037402 (2012).

[2]. B. Faeth et al., Phys. Rev. X 11, 021054 (2021).

[3]. T. Kobayashi et al., Supercond. Sci. Technol. 35, 07LT01 (2022).

[4]. F. Nabeshima et al., Phys. Rev. B 97, 024504 (2018).