Characteristic energies, transition temperatures, and switching effects in clean SNS graphene nanostructures

Abstract

We study proximity effects in clean nanoscale superconductor-normal metal-superconductor (S$\mid$N$\mid$S) graphene heterostructures using a self-consistent numerical solution to the continuum Dirac Bogoliubov-de Gennes (DBdG) equations. We obtain results for the pair amplitude and the local density of states (DOS), as a function of doping and of the geometrical parameters determining the width of the structures. The superconducting correlations are found to penetrate the normal graphene layers even when there is extreme mismatch in the normal and superconducting doping levels, where specular Andreev reflection dominates. The local DOS exhibits peculiar features, which we discuss, arising from the Dirac cone dispersion relation and from the interplay between the superconducting and Thouless energy scales. The corresponding characteristic energies emerge in the form of resonant peaks in the local DOS, that depend strongly on the doping level, as does the energy gap, which declines sharply as the relative difference in doping between the S and N regions is reduced. We also linearize the DBdG equations and develop an essentially analytical method that determines the critical temperature $T_c$ of an \sns nanostructure self-consistently. We find that for S regions that occupy a fraction of the coherence length, $T_c$ can undergo substantial variations as a function of the relative doping. At finite temperatures and by manipulating the doping levels, the self consistent pair amplitudes reveal dramatic transitions between a superconducting and resistive normal state of the structure. Such behavior suggests the possibility of using the proposed system as a carbon-based superconducting switch, turning superconductivity on or off by tuning the relative doping levels.

13 pages, figures included

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• Spin-controlled superconductivity and tunable triplet correlations in graphene nanostructures
• Tunable Anomalous Andreev Reflection and Triplet Pairings in Spin Orbit Coupled Graphene
• Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions
• Tight-binding study of bilayer graphene Josephson junctions
• Nearly flat Andreev bound states in superconductor-topological insulator hybrid structures
• Electrical and thermal transport in a twisted heterostructure of transition metal dichalcogenide and CrI${}_3$ connected to a superconductor
• Determination of Gap Solution and Critical Temperature in Doped Graphene Superconductivity