Abstract
The building of superconductor/graphene hybrid structure has attracted a lot of attention in recent years as it provides an exciting platform to study the novel superconducting proximity effect in graphene and has promise in potential device applications. Here we report an experimental investigation on the fabrication of MgB2/graphene bilayer films. The fabrication process consists of two major steps: the transfer of monolayer graphene grown on copper foil to the target substrate, and then the deposition of MgB2 thin film on transferred graphene with a hybrid physical-chemical vapor deposition technique. The obtained MgB2 film on graphene shows a continuous film surface with prevailing c-axis orientation, and displays a narrow superconducting transition with high transition temperature Tc at 36 K, close to the value of 39 K in bulk MgB2. The decent crystalline property and high Tc of the film demonstrate the effectiveness of the present method in producing the MgB2/graphene hybrid structure, which lays a foundation for further exploring the proximity effect in graphene and developing related superconducting devices such as the Josephson junctions to work at relatively high temperatures.
Highlights
Since the first extraction through mechanical cleavage, graphene, a single atomic layer of carbon, has remained the subject of intense study owing to its exceptional properties and high promise in various practical applications.[1,2] By bringing graphene in contact with a superconductor, superconductivity may be induced in graphene via the proximity effect, i.e., the extension of superconducting correlations from the superconductor into graphene
By transferring chemical vapor deposition (CVD)-grown monolayer graphene from Cu foil to the 6H-SiC substrate, MgB2 thin film has been deposited on graphene/SiC with the use of the hybrid physical-chemical vapor deposition (HPCVD) technique
The deposited film shows predominant c-axis orientation with well-connected grains, and displays superconducting transition within 3 K at mid-point T c of 36 K, illustrating the effectiveness of the present method in obtaining MgB2/graphene hybrid with decent properties
Summary
Since the first extraction through mechanical cleavage, graphene, a single atomic layer of carbon, has remained the subject of intense study owing to its exceptional properties and high promise in various practical applications.[1,2] By bringing graphene in contact with a superconductor, superconductivity may be induced in graphene via the proximity effect, i.e., the extension of superconducting correlations from the superconductor into graphene. As a matter of fact, concerning MgB2, a lot of efforts have been devoted to using it to make superconducting devices or circuits in order to take advantage of its high T c.18–21 In this respect, the MgB2/graphene hybrid would offer a new route, for instance, to fabricate MgB2/normal metal/MgB2 Josephson junctions.[22] Another notable feature of MgB2, which sets it apart from many other superconductors including the high-T c cuprate materials, is that it is a multiband superconductor.[23,24] in MgB2 there are two σ-bands and two π-bands crossing the Fermi level, resulting in four sheets of the Fermi surface and two groups of superconducting gaps, namely the σ- and π-gaps.[23,24,25,26] This multigap superconductivity has shown to lead to many properties of MgB2 markedly different from that in conventional single-gap superconductors and, the presence of new physical phenomena that do not exist in single-gap superconductors.[18,27] For instance, novel vortex patterns not unattainable in single-gap superconductors, such as the vortex stripes or clusters and fractional vortices, have been experimentally or theoretically explored for MgB2.28,29 the research on multigap or multicomponent superconductivity has recently evolved into a fascinating field owing to the rich emergent quantum effects exhibited therein.[30] In light of this, the MgB2/graphene hybrid may provide a unique platform to explore possible new physics in the proximity effect in graphene resulting from the multigap superconductivity of MgB2. It demonstrates the feasibility to obtain MgB2/graphene hybrid structure with high T c, which is critical to both investigating the proximity effect in graphene at relatively high temperatures and developing related superconducting devices such as the high operating-temperature Josephson junctions
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