Two-dimensional Dirac semimetal phase in undoped one-monolayer FeSe film

Abstract

In the one-monolayer FeSe film on SrTiO${}_{3}$, which is a new member of high-temperature superconductor family, there exists two competing proposals on the nature of the ground state in the parent undoped film: strongly correlated insulator (as in copper-oxide superconductors) versus moderately correlated metal (as in iron-based superconductors). Here, the authors provide experimental evidence for the metallic nature by performing $i\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ angle-resolved photoemission spectroscopy on an undoped one-monolayer FeSe film prepared by careful post-growth annealing. The authors demonstrate the materialization of an ideal two-dimensional Dirac electron system, where only the Dirac-cone band crosses the Fermi level, unlike in the multilayer counterpart.