Graphite, graphene and the flat band superconductivity

TL;DR

This paper discusses the emergence of superconductivity in bilayer graphene and graphite, emphasizing the role of flat electronic bands at specific twist angles, which could lead to high-temperature or room-temperature superconductivity.

Contribution

It highlights the connection between flat band formation due to twisting in graphene and graphite, and the potential for high-temperature superconductivity, proposing a unified theoretical and experimental approach.

Findings

Superconductivity in bilayer graphene peaks at the magic twist angle.

Flat bands lead to a high density of states, enabling higher T_c.

Evidence suggests possible room-temperature superconductivity in graphite interfaces.

Abstract

Superconductivity with transition temperature $T_c=1.7$ K has been reported in bilayer graphene [1,2]. The main factors, which may shed light on the mechanism of the formation of this superconductivity, are the following. Superconductivity is observed in bilayer graphene, when the two layers are twisted, and the maximum of $T_c$ takes place at the "magic angle" of twist, at which the electronic band structure becomes nearly flat. The same factors have been suggested [3] to explain the experiments in graphite [4-8], which reported high-T superconductivity in highly oriented pyrolytic graphite (HOPG). The hints of room-T superconductivity are present, only when the sample contains quasi two-dimensional interfaces between the domains of HOPG. These domains should be twisted with respect to each other in order to form the flat band in electronic spectrum. This dispersionless energy spectrum has a singular density of states, which provides the transition temperature being proportional to the coupling constant instead of the exponential suppression. The graphite and its superconductivity is now becoming the mainstream. One may say that we are coming to graphite era of superconductivity. It is time to combine the theoretical and experimental efforts to reach the bulk room-T superconductivity in graphite and in similar real or artificial materials.