Evidence for superconductivity in Li-decorated monolayer graphene

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 G, Calandra M, Mauri F (2012) Nat Phys 8(2):131-134]. Although experiments have shown 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 λ ≃ 0.58. On part of the graphene-derived π*-band Fermi surface, we then observe the opening of a Δ ≃ 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 ≃ 5.9 K.graphene | superconductivity | ARPES

First-principles calculations of the superconducting properties in Li-decorated monolayer graphene within the anisotropic Migdal-Eliashberg formalism

“…While previous ab initio calculations have shown that the electron-phonon coupling is sufficient to yield a critical temperature in 6.7-10.3 K range using the Allen-Dynes formula [3,13,14] or the isotropic Eliashberg formalism [15], the nature of the superconducting gap has not yet been addressed. We find that, similar to bulk CaC 6 [15][16][17][18], Li-decorated monolayer graphene exhibits a single anisotropic gap in agreement with the experimental work [8].…”

“…4(a) we find T c = 5.9 K and a ratio 2∆ 0 /k B T c = 3.50, very close to the ideal BCS value of 3.53 [44]. The predicted superconducting critical temperature is in excellent agreement with the experimental estimation of 5.9 K based on measurements of the size of the superconducting gap [8]. The temperature dependence of the superconducting gap can be well fitted with a BCS model, as obtained by solving numerically the BCS gap equation [45] with ∆ 0 and T c from our first-principles calculations.…”

“…One notable application that was missing from this list was superconductivity, despite numerous theoretical predictions of either a conventional or an unconventional pairing mechanism [2][3][4][5][6][7]. Very recently, a high-resolution angle-resolved photoemission spectroscopy (ARPES) study has presented evidence supporting the appearance of a superconducting phase in Li-decorated monolayer graphene (LiC 6 ) around 5.9 K [8], within the standard phonon-mediated coupling mechanism. This work has been followed by two more studies that reported the observation of superconductivity in Ca-intercalated bilayer graphene [9] and in Caintercalated graphene laminates [10].…”

Beyond graphene

“…In June, physicists in the United States and South Korea reported "the world's thinnest light bulb," using light-emitting graphene as an ultrathin filament (15). And in September, an international team of researchers reported that, at low temperatures, the material becomes a superconductor when coated with lithium (16).…”

Entanglement spectra of superconductivity ground states on the honeycomb lattice

“…Furthermore, additional experimental progress has been made regarding evidence of superconductivity in Li-decorated monolayer graphene with a transition temperature of approximately 5.9 K [15].…”