Temperature-Dependent Fermi Gap Opening in thec(6×4)–C60/Ag(100)Two-Dimensional Superstructure

High-resolution angle-integrated photoemission of one monolayer of $\mathrm{C}{}_{60}$ chemisorbed on Ag(100) shows the reversible opening of a gap at the Fermi level at temperatures $25\le T\le 300\mathrm{K}$. The gap reaches a maximum value of $\approx 10\mathrm{meV}$ at $T\le 70\mathrm{K}$. This finding is the first evidence of an electronic phase transition in $\mathrm{C}{}_{60}$ monolayers and has implications on the ongoing debate about surface superconductivity in $\mathrm{C}{}_{60}$-based bulk materials.