Supercurrent reversal in Josephson junctions based on bilayer graphene flakes

Abstract

We investigate the Josephson effect in a bilayer graphene flake contacted by two monolayer sheet deposited by superconducting electrodes. It is found that when the electrodes are attached to the different layers of the bilayer, the Josephson current is in a π state when the bilayer region is undoped and in the absence of vertical bias. Applying doping or bias to the junction reveals π − 0 transitions which can be controlled by varying the temperature and the junction length. The supercurrent reversal here is very different from the ferromagnetic Josephson junctions where the spin degree of freedom plays the key role. We argue that the scattering processes accompanied by layer and sublattice index change give rise to the scattering phases which their effect varies with doping and the bias. Such scattering phases are responsible for the π − 0 transitions. On the other hand if both of the electrodes are coupled to the same layer of the flake or the flake has AA stacking instead of common AB, the junction will be always in 0 state since layer or sublattice index is not changed.

Quantum transport across van der Waals domain walls in bilayer graphene

“…The appearance of these structures fueled theoretical and experimental investigations on the behavior of massless and massive particles in such junctions. For example, few works have investigated different domain walls that separate, for instance, different type of stacking [19][20][21] or even different number of layers [22][23][24] . These theoretical investigations showed that the transmission probabilities through SL/BL interfaces exhibits a valley-dependent asymmetry which could be used for valley-based electronic applications [25][26][27] .…”

Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions

“…In addition, the interface between the superconducting (S) and graphene (G) regions was found to be significantly more transparent than in previous experiments 9, [15][16][17][18][19][20][21][22][23][24][25][26][27] . These experimental advances may allow to verify some of the theoretical predictions for graphene-superconductor heterostructures, such as anharmonic phase-current relation of supercurrent at low temperatures in superconductor-graphenesuperconductor (SGS) junctions in monolayer [28][29][30][31] and bilayer 31,32 graphene, supercurrent quantization in quantum point contacts 33,34 , specular Andreev reflection [35][36][37][38] , detection of valley polarization 39 , interplay of strain and superconductivity [40][41][42] etc. in the near future.…”

“…in the near future. The theoretical work has mainly focused on short SGS junctions to date [32][33][34]41,43,44 , where the length of the normal region L is smaller than the superconducting coherence length ξ 0 = vF ∆0 . In addition, it was usually assumed that the width W of the junction is much larger than L. Although the long junction regime has been studied theoretically for superconductor-normal metalsuperconductor (SNS) systems [45][46][47][48][49][50][51] , the physics of long SGS junctions is less explored.…”

Inter-layer and intra-layer heat transfer in bilayer/monolayer graphene van der Waals heterostructure: Is there a Kapitza resistance analogous?

“…Depending on the structural characteristic of a graphene heterostructure, e.g. a step-like bilayer/monolayer graphene interface, compared to covalent bonds, van der Waals interactions can lead to special properties which are considerably different from those of pristine monolayer and even bilayer graphene sheets in some cases [2,3,4,5].…”