Proximity coupling in superconductor-graphene heterostructures

Abstract

This review discusses the electronic properties and the prospective research directions of superconductor-graphene heterostructures. The basic electronic properties of graphene are introduced to highlight the unique possibility of combining two seemingly unrelated physics, superconductivity and relativity. We then focus on graphene-based Josephson junctions, one of the most versatile superconducting quantum devices. The various theoretical methods that have been developed to describe graphene Josephson junctions are examined, together with their advantages and limitations, followed by a discussion on the advances in device fabrication and the relevant length scales. The phase-sensitive properties and phase-particle dynamics of graphene Josephson junctions are examined to provide an understanding of the underlying mechanisms of Josephson coupling via graphene. Thereafter, microscopic transport of correlated quasiparticles produced by Andreev reflections at superconducting interfaces and their phase-coherent behaviors are discussed. Quantum phase transitions studied with graphene as an electrostatically tunable 2D platform are reviewed. The interplay between proximity-induced superconductivity and the quantum-Hall phase is discussed as a possible route to study topological superconductivity and non-Abelian physics. Finally, a brief summary on the prospective future research directions is given.

Nonlocal Andreev entanglements and triplet correlations in graphene with spin-orbit coupling

“…As a consequence, one can imagine a heterostructure made of a single s-wave superconductor and multiple nonsuperconducting electrodes in which an electron and hole excitation from different electrodes are coupled by means of a nonlocal Andreev process [7,[10][11][12][13]. This idea has so far motivated numerous theoretical and experimental endeavours to explore this entangled state in various geometries and materials [12,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Nonetheless, the nonlocal Andreev process is accompanied by an elastic cotunneling current that makes it practically difficult to detect unambiguously the signatures of nonlocal entangled state [10,11,[13][14][15][16][17].…”

Local density of states in clean two-dimensional superconductor–normal metal–superconductor heterostructures

“…From Eq. (38) we can see that the superconducting phase difference depends on the y position of the incoming and outgoing Green's function at the SN interface (x = −L/2). The averaged LDOS over all trajectories, see Eq.…”

“…In fact, the proximity superconductivity in graphene systems has been intensively investigated since its early days [37] and has recently been reviewed in Ref. [38]. Remarkably, a two-dimensional interference pattern has been predicted in warped Fermi-surface proximitized in two-dimensions [39] or in the presence of boundaries [40].…”

Higgs modes in proximized superconducting systems

“…Two new Higgs modes with the frequencies depending on both the primary and induced gaps in the hybrid structure are shown to appear due to the coherent electron transfer between the superconductor and the normal metal. Altogether these three modes determine the long-time asymptotic behavior of the superconducting order parameter disturbed either by the electromagnetic pulse or the quench of the system parameters and, thus, are of crucial importance for the dynamical properties and restrictions on the operating frequencies for superconducting devices based on the proximity effect used, e.g., in quantum computing, in particular, with topological low-energy excitations.The progress of modern nanotechnology opens new horizons for engineering superconducting correlations in various hybrid structures and creating, in fact, novel types of artificial superconducting materials with controllable properties [1][2][3][4][5][6][7][8][9][10][11]. The proximity phenomenon arising in a non-superconducting material from the electron exchange with a primary superconductor can generate the induced superconducting ordering in a wide class of materials, including unconventional ones [1][2][3][4][5][8][9][10][11].…”

“…The progress of modern nanotechnology opens new horizons for engineering superconducting correlations in various hybrid structures and creating, in fact, novel types of artificial superconducting materials with controllable properties [1][2][3][4][5][6][7][8][9][10][11]. The proximity phenomenon arising in a non-superconducting material from the electron exchange with a primary superconductor can generate the induced superconducting ordering in a wide class of materials, including unconventional ones [1][2][3][4][5][8][9][10][11]. The resulting superconducting state in these materials can controllably reveal the exotic properties very rarely found in natural metals or alloys and strongly different from the ones of the primary superconductor.…”