Ultrafast Dynamics Evidence of High Temperature Superconductivity in Single Unit Cell FeSe on SrTiO3

TL;DR

This study uses ultrafast spectroscopy to confirm high-temperature superconductivity in single-unit-cell FeSe on SrTiO3, revealing a Tc of about 68K and supporting a phonon-mediated pairing mechanism.

Contribution

It provides the first ultrafast dynamics evidence confirming high Tc in 1UC FeSe/STO and elucidates the role of the capping layer and phonons in the superconductivity mechanism.

Findings

Superconducting Tc is approximately 68K.

Identification of a coherent acoustic phonon mode.

Support for phonon-mediated pairing mechanism.

Abstract

The recent observation of high-temperature superconductivity in one unit cell thick FeSe on SrTiO3 (1UC FeSe/STO)1 initiated a new pathway to realizing even higher transition temperature (Tc) superconductors and established a promising different paradigm to understand the mechanism of high temperature superconductivity2-10. However, independent confirmation on the high Tc value, the role of capping layer in reducing Tc, and the underlying mechanism of the novel superconductivity remain open questions11. Here we report a time-resolved study of the excited state ultrafast dynamics of 1UC FeSe/STO protected by 2UC FeTe capping layer, and identify the superconducting Tc to be 68 (-5/+2) K. We found a coherent acoustic phonon mode in the capping layer, which provides an additional decay channel to the gluing bosons and explains the reduced Tc value. Our investigation supports the phonon pairing scenario.