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Transport in superconductor-normal metal-superconductor tunneling structures: Spinful p-wave and spin-orbit-coupled topological wires

TitleTransport in superconductor-normal metal-superconductor tunneling structures: Spinful p-wave and spin-orbit-coupled topological wires
Publication TypeJournal Article
Year of Publication2017
AuthorsF.. Setiawan, W. S. Cole, J. D. Sau, and S. Das Sarma
JournalPHYSICAL REVIEW B
Volume95
Pagination174515
Date PublishedMAY 22
Type of ArticleArticle
ISSN2469-9950
Abstract

We theoretically study transport properties of voltage-biased one-dimensional superconductor-normal metal-superconductor tunnel junctions with arbitrary junction transparency where the superconductors can have trivial or nontrivial topology. Motivated by recent experimental efforts on Majorana properties of superconductor-semiconductor hybrid systems, we consider two explicit models for topological superconductors: (i) spinful p-wave, and (ii) spin-split spin-orbit-coupled s-wave. We provide a comprehensive analysis of the zero-temperature dc current I and differential conductance dI/dV of voltage-biased junctions with or without Majorana zero modes (MZMs). The presence of an MZM necessarily gives rise to two tunneling conductance peaks at voltages eV = +/-Delta(lead), i.e., the voltage at which the superconducting gap edge of the lead aligns with the MZM. We find that the MZM conductance peak probed by a superconducting lead without a BCS singularity has a nonuniversal value, which decreases with decreasing junction transparency. This is in contrast to the MZM tunneling conductance measured by a superconducting lead with a BCS singularity, where the conductance peak in the tunneling limit takes the quantized value GM = (4 - pi)2e(2)/h independent of the junction transparency. We also discuss the ``subharmonic gap structure{''}, a consequence of multiple Andreev reflections, in the presence and absence of MZMs. Finally, we show that for finite-energy Andreev bound states (ABSs), the conductance peaks shift away from the gap bias voltage eV = +/-Delta(lead) to a larger value set by the ABSs energy. Our work should have important implications for the extensive current experimental efforts toward creating topological superconductivity and MZMs in semiconductor nanowires proximity coupled to ordinary s-wave superconductors.}, %%Address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA

DOI10.1103/PhysRevB.95.174515