Evidence for superconductivity in Li-decorated monolayer graphene

TL;DR

This study provides experimental evidence that lithium decoration induces superconductivity in monolayer graphene, demonstrated by a pairing gap and enhanced electron-phonon coupling observed via ARPES.

Contribution

First experimental observation of superconductivity in Li-decorated monolayer graphene confirmed by a pairing gap and increased electron-phonon interaction.

Findings

Observation of a temperature-dependent pairing gap of ~0.9 meV.

Enhanced electron-phonon coupling up to λ ≈ 0.58.

Superconducting transition temperature estimated at ~5.9 K.

Abstract

Monolayer graphene exhibits many spectacular electronic properties, with superconductivity being arguably the most notable exception. It was theoretically proposed that superconductivity might be induced by enhancing the electron-phonon coupling through the decoration of graphene with an alkali adatom superlattice [Profeta et al. Nat. Phys. 8, 131-134 (2012)]. While experiments have indeed demonstrated an adatom-induced enhancement of the electron-phonon coupling, superconductivity has never been observed. Using angle-resolved photoemission spectroscopy (ARPES) we show that lithium deposited on graphene at low temperature strongly modifies the phonon density of states, leading to an enhancement of the electron-phonon coupling of up to $\lambda\!\simeq\!0.58$. On part of the graphene-derived $\pi^*$-band Fermi surface, we then observe the opening of a $\Delta\!\simeq\!0.9$ meV temperature-dependent pairing gap. This result suggests for the first time, to our knowledge, that Li-decorated monolayer graphene is indeed superconducting with $T_c\!\simeq\!5.9 K$.