Mesoscopic Josephson effect in graphene disk at magnetic field

TL;DR

This paper investigates the mesoscopic Josephson effect in a graphene disk with a magnetic field, revealing complex current-phase relations and specific product values of critical current and resistance.

Contribution

It demonstrates that mesoscopic Josephson junction features, like skewness and I_c R_N product, also occur in graphene disk geometries under magnetic fields, supported by quantum-mechanical analysis.

Findings

I_c R_N rom 1.85 \u03b4_0/ea0 at specific magnetic fields.

Skewness S 0.14 in the studied geometry.

Quantum-mechanical mode-matching analysis aligns with simpler incoherent scattering models.

Abstract

Unlike for tunneling Josephson junctions, for which the current-phase relation is given by the sine function, with the critical current ($I_c$) and normal-state resistance ($R_N$) following the relation $I_cR_N=(\pi/2)\,\Delta_0/e$ (where $\Delta_0$ is the superconducting gap and electron charge is $-e$), mesoscopic Josephson junctions show more complex current-phase relations, with the skewness $S>0$, what is related to the presence -- in case the leads are in the normal state -- of transmission probabilities taking the values comparable to $1$. Here, we show that these features also appear for a superconductor-graphene-superconductor (S-g-S) junction in the disk-shaped (Corbino) geometry, when the magnetic field is adjusted such that $I_c\rightarrow{}0$ and $R_N\rightarrow{}\infty$. In such a case, the product $I_cR_N\approx{}1.85\,\Delta_0/e$, and the skewness $S\approx{}0.14$. The results obtained from quantum-mechanical mode-matching analysis for the Dirac-Bogoliubov-De-Gennes equation are compared with simpler model assuming incoherent scattering between two circular interfaces separating the sample and the leads.