SKM 2023 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 53: Graphene

TT 53.1: Vortrag

Donnerstag, 30. März 2023, 15:00–15:15, HSZ 204

Andreev and normal reflections processes in gated bilayer graphene — •Panch Ram¹, Detlef Beckmann², Romain Danneau², and Wolfgang Belzig¹ — ¹Fachbereich Physik, Universität Konstanz, D-78457 Konstanz, Germany — ²Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany

We present our theoretical study of the Andreev and normal reflections processes in a bilayer graphene normal-superconductor junction where gate fields are applied (equal and opposite). Gating can induce a gap in the dispersion of the graphene layer. We employ the Dirac-Bogoliubov-de Gennes equation for the low-energy gated bilayer graphene Hamiltonian and calculate the Andreev and normal reflections probabilities using the scattering theory, and also obtain the differential conductance within the Blonder-Tinkham-Klapwijk formalism [1, 2]. We observe the Andreev retro-reflection (specular-reflection) below (above) the Fermi energy when the bias voltage is within the superconducting gap [3]. Interestingly, both retro-reflection as well as specular reflection are strongly modified in the presence of the gate field. For small gate field, they can be tuned to either specular or retro Andreev reflection by changing the Fermi energy. Moreover, we find double Andreev reflections and double normal reflections (specular and retro) when the gate field becomes comparable to the interlayer coupling strength.
[1] A. F. Andreev, Sov. Phys. JETP 19, 1228 (1964)
[2] G. E. Blonder et al., Phys. Rev. B 25, 4515 (1984)
[3] C. W. J. Beenakker, Phys. Rev. Lett. 97, 067007 (2006)