In-plane optical spectroscopy study on FeSe epitaxial thin film grown on SrTiO$_3$ substrate

TL;DR

This study uses in-plane optical spectroscopy to analyze FeSe thin films on SrTiO3, revealing unique low-frequency conductivity features and stronger electron correlations compared to iron pnictides, with no evidence of SDW order in optical data.

Contribution

First in-plane optical spectroscopy investigation of FeSe epitaxial thin films on SrTiO3, highlighting distinct low-frequency conductivity and correlation effects without SDW signatures.

Findings

Presence of two Drude components in conductivity

Smaller plasma frequency indicating stronger correlations

No optical evidence of SDW order in thick FeSe films

Abstract

We perform in-plane optical spectroscopy measurement on (00l) FeSe thin-film grown on SrTiO$_3$ substrate by pulsed laser deposition method. The study indicates that the low frequency conductivity consists of two Drude components, a broad one which takes up most of the spectral weight and a very narrow one roughly below 100-150 \cm. The narrow Drude component locates at so low frequencies that no such behavior was observed in iron pnictides. The overall plasma frequency is found to be smaller than the FeAs based compounds, suggesting a stronger correlation effect. Similar to iron pnictides, a temperature-induced spectral weight transfer is observed for FeSe. However, the relevant energy scale is lower. Additionally, different from a recent ARPES measurement which revealed a spin density wave (SDW) order at low temperature for FeSe thin films grown on SrTiO$_3$ substrate, no signature of the band structure reconstruction arising from the formation of the SDW order is seen by optical measurement in the thick FeSe films.