Current-voltage relation for asymmetric ballistic superconducting junctions

Magnus Hurd; Supriyo Datta; Philip F. Bagwell

doi:10.1103/PhysRevB.54.6557

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Current-voltage relation for asymmetric ballistic superconducting junctions

Magnus Hurd, Supriyo Datta, Philip F. Bagwell

DOI 10.1103/PhysRevB.54.6557 · Physical Review B

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Abstract

We calculate the dc current-voltage (I−V) relation for a ballistic superconductor-normal metal-superconductor (S1NS2) junction, where the two superconducting contacts have different energy gaps (Δ2>~Δ1>~0). Several new features appear in the I−V relation as it evolves from a NS junction (Δ1=0) to the symmetric SNS junction (Δ1=Δ2). The dc current I0 flowing at small voltages is I0=4eΔ1h, and is different from the critical current Ic. The differential conductance changes abruptly at eV=Δ2−Δ1 due to the loss of a single Andreev reflection from the larger-gap superconductor. Finally, the voltages Δn at which subharmonic gap structures appear in the I−V relation for temperatures kBT≃Δ2 depend on both energy gaps Δ1 and Δ2. We find a systematic way to classify this subgap structure.