Observation of tunneling gap in epitaxial ultrathin films of pyrite-type copper disulfide

TL;DR

This study uses scanning tunneling microscopy to observe a persistent symmetric tunneling gap in epitaxial ultrathin CuS2 films, revealing novel matter states at the two-dimensional limit.

Contribution

First observation of a tunneling gap in epitaxial ultrathin pyrite-type copper disulfide films grown by molecular beam epitaxy.

Findings

Tunneling gap persists up to ~15 K

Gap degrades with increasing temperature

Gap diminishes with increasing film thickness

Abstract

We report scanning tunneling microscopy investigation on epitaxial ultrathin films of pyrite-type copper disulfide. Layer by layer growth of CuS2 films with a preferential orientation of (111) on SrTiO3(001) and Bi2Sr2CaCu2O8+{\delta} substrates is achieved by molecular beam epitaxy growth. For ultrathin films on both kinds of substrates, we observed symmetric tunneling gap around Fermi level that persists up to ~ 15 K. The tunneling gap degrades with either increasing temperature or increasing thickness, suggesting new matter states at the extreme two dimensional limit.