Pure nematic state in iron-based superconductor

TL;DR

This study demonstrates the existence of a pure electronic nematic state in thin FeSe films, free from lattice distortions, highlighting its origin from electronic degrees of freedom and its implications for understanding nematicity in superconductors.

Contribution

It provides conclusive evidence of a pure electronic nematic state in FeSe thin films, distinct from bulk behavior, advancing the understanding of nematicity's origin and its role in superconductivity.

Findings

No structural phase transition detected below 90 K.

Nematic state confirmed by resistivity and ARPES measurements.

Pure nematicity originates from electronic degrees of freedom.

Abstract

Lattice and electronic states of thin FeSe films on LaAlO$_3$ substrates are investigated in the vicinity of the nematic phase transition. No evidence of structural phase transition is found by x-ray diffraction below $T^\ast \sim 90$ K, while results obtained from resistivity measurement and angle-resolved photoemission spectroscopy clearly show the appearance of a nematic state. These results indicate formation of a pure nematic state in the iron-based superconductor and provide conclusive evidence that the nematic state originates from the electronic degrees of freedom. This pure nematicity in the thin film implies difference in the electron-lattice interaction from bulk FeSe crystals. FeSe films provide valuable playgrounds for observing the pure response of "bare" electron systems free from the electron-lattice interaction, and should make important contribution to investigate nematicity and its relationship with superconductivity.