Ballistic-like supercurrent in suspended graphene Josephson weak links

Abstract

The interplay of the massless Dirac fermions in graphene and the Cooper pair states in a superconductor has the potential to give rise to exotic physical phenomena and useful device applications. But to date, the junctions formed between graphene and superconductors on conventional substrates have been highly disordered. Charge scattering and potential fluctuations caused by such disorder are believed to have prevented the emergence or observation of new physics. Here we propose to address this problem by forming suspended graphene-superconductor junctions. We demonstrate the fabrication of high-quality suspended monolayer graphene-NbN Josephson junctions with device mobility in excess of 150,000 cm 2 per Vs, minimum carrier density below 10 10 cm À 2 , and the flow of a supercurrent at critical temperatures greater than 2 K. The characteristics of our Josephson junctions are consistent with ballistic transport, with a linear dependence on the Fermi energy that reflects of linear dispersion of massless Dirac fermions.

Graphene-Based Josephson-Junction Single-Photon Detector

“…The rate of switching depends intimately on the JJ critical current I c , which takes on different forms as a function of temperature depending on whether the JJ is short or long and whether it is diffusive or ballistic. Superconductor-graphene-superconductor JJs have been studied in these different regimes [16][17][18][19][20][21]. However, experimental values, such as I c and the parameters in the long diffusive junction, have fallen short of theoretical expectations due to impurity doping.…”

“…Here, we propose using the graphene-based superconducting-normal-superconducting (SNS) Josephson junction (JJ) as a threshold sensor to detect single photons across an extremely wide spectrum. Since the first observation of the superconducting proximity effect in graphene [15], many advances have been made in the fabrication and performance of graphene-based JJs (GJJs) [16][17][18][19][20][21]. To emphasize feasibility with existing materials and fabrication technologies, we use measured parameters from a GJJ to calculate the performance of our proposed SPD.…”

Observation of Even Denominator Fractional Quantum Hall Effect in Suspended Bilayer Graphene

“…Graphene bilayers are attractive in this regard because their microscopic properties can be tuned by a perpendicular electric field to unbalance the two layers or to control symmetries, 23, 30-33, 48, 49 and because (as seen in this experiment) accessing the ν = -1/2 state is possible at relatively high temperature (~ 0.5 K). Another aspect is the possibility to access the 2DES in bilayer graphene readily with different kinds of contacts, including superconducting 50 and ferromagnetic ones, 51 and with scanning probes, 27,28,44 all of which can be used to investigate the nature of this even-denominator state in new ways. Our work therefore opens the path to unprecedented studies of even-denominator fractional quantum Hall effect, and raises the exciting possibility to use bilayer graphene as a suitable experimental platform for studying the physics of non-Abelian excitations.…”

Incipient Berezinskii-Kosterlitz-Thouless transition in two-dimensional coplanar Josephson junctions

“…This can be extremely useful to have further insights on the electrodynamic response and the nature of dissipation of GJJs, which need to be considered in the actual rush of more performing devices in the ballistic limit, to exploit the unique properties of Andreev reflection in graphene. [17][18][19][20][21][22][23] In Section II we report on the preparation of the sample. A consistent interpretation of the phenomenology described in Sections III-V requires frames which go bearXiv:1609.05499v1 [cond-mat.supr-con] 18 Sep 2016 yond the usual Josephson S/N/S paradigm.…”