Minigap and Andreev bound states in ballistic graphene

Luca Banszerus; Florian Libisch; Andrea Ceruti; Stefan Blien; Kenji Watanabe; Takashi Taniguchi; Andreas K. Hüttel; Bernd Beschoten; Fabian Hassler; Christoph Stampfer

arXiv · 2011.11471

Minigap and Andreev bound states in ballistic graphene

Luca Banszerus·Florian Libisch·Andrea Ceruti·Stefan Blien·Kenji Watanabe·Takashi Taniguchi·Andreas K. Hüttel·Bernd Beschoten·Fabian Hassler·Christoph Stampfer

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Abstract

A finite-size normal conductor, proximity-coupled to a superconductor has been predicted to exhibit a so-called minigap, in which quasiparticle excitations are prohibited. Here, we report on the direct observation of such a minigap in ballistic graphene, coupled to superconducting MoRe leads. The minigap is probed by finite bias spectroscopy through a weakly coupled junction in the graphene region and its value is given by the dimensions of the device. Besides the minigap, we observe a distinct peak in the differential resistance, which we attribute to weakly coupled Andreev bound states (ABS) located near the superconductor-graphene interface. For weak magnetic fields, the phase accumulated in the normal-conducting region shifts the ABS in quantitative agreement with predictions from tight-binding calculations based on the Bogolioubov-de Gennes equation as well as with an analytical semiclassical model.

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Luca Banszerus, Florian Libisch, Andrea Ceruti, Stefan Blien, Kenji Watanabe, Takashi Taniguchi, Andreas K. Hüttel, Bernd Beschoten, Fabian Hassler, Christoph Stampfer. 2020-11-23. Minigap and Andreev bound states in ballistic graphene. https://arxiv.org/abs/2011.11471

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