Andreev reflection near the Dirac point at the graphene- NbSe2 junction

Abstract

Despite extensive search for about a decade, specular Andreev reflection is only recently realized in bilayer graphene-superconductor interface. However, the evolution from the typical retro type Andreev reflection to the unique specular Andreev reflection in single layer graphene has not yet been observed. We investigate this transition by measuring the differential conductance at the van der Walls interface of single layer graphene and N bSe2 superconductor. We find that the normalized conductance (GT <Tc /GT >T c) becomes suppressed as we pass through the Dirac cone via tuning the Fermi level and bias energy, which manifests the transition from retro to non-retro type Andreev reflection. The suppression indicates the blockage of Andreev reflection beyond a critical angle (θc) of the incident electron with respect to the normal between the single layer graphene and the superconductor junction. The results are compared with a theoretical model of the corresponding setup.arXiv:1606.02559v1 [cond-mat.mes-hall]

Inter-Landau-level Andreev Reflection at the Dirac Point in a Graphene Quantum Hall State Coupled to a NbSe2 Superconductor

“…The superconducting gap of NbSe 2 flake, 2∆ ∼ 2meV and T C ∼ 7K at 0T was directly characterized in our previous work ( Fig. 3a of ref [17]), which is consistent with the 0T data in Fig. 4a.…”

“…1a-top). The AR and its transition from retro to non-retro reflection has been observed [17]. More interestingly, when E F is aligned with the Dirac point, AR requires an inter-band process and is predicted to be specular ( Fig.…”

FeTe0.55Se0.45 van der Waals tunneling devices

“…Refining exfoliation-based methods is of particular interest, as flakes can be assembled into a variety of sophisticated devices using the van-der-Waals (vdW) technology [15,16,17]. When applied to proximitized graphene and to layered superconductors, stacking of vdW flakes has allowed the study of planar tunnel junctions [18,19,20,9,21], Josephson devices [22,23], and graphene-superconductor hybrids [24,25,26]. Furthermore, in thin flakes density can be tuned by ionic gating [27,28].…”

Enhanced specular Andreev reflection in bilayer graphene

“…Graphene is a semimetal whose electronic structure can be described by a Dirac Hamiltonian (with a vanishingly small mass). Andreev reflection has been studied both theoretically [8][9][10][11][12] and experimentally 13 in graphene. What makes Andreev reflection in graphene special is that it can be of two types: one where the reflected hole retraces the path of the incident electron (called retro-) and another where the reflected hole moves away not tracing back the path of the incident electron (called specular-) 9,13 .…”