Reappearance of first Shapiro step in narrow topological Josephson junctions

Daniel Rosenbach*, Tobias W. Schmitt, Peter Schüffelgen, Martin P. Stehno, Chuan Li, Michael Schleenvoigt, Abdur R. Jalil, Gregor Mussler, Elmar Neumann, Stefan Trellenkamp, Alexander A. Golubov, Alexander Brinkman, Detlev Grützmacher, Thomas Schäpers

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

In Josephson junctions, a supercurrent across a nonsuperconducting weak link is carried by electron-hole bound states. Because of the helical spin texture of nondegenerate topological surface states, gapless bound states are established in junctions with topological weak link. These have a characteristic 4π-periodic current phase relation (CφR) that leads to twice the conventional Shapiro step separation voltage in radio frequency-dependent measurements. In this context, we identify an attenuated first Shapiro step in (Bi0.06Sb0.94)2Te3 (BST) Josephson junctions with AlOx capping layer. We further investigate junctions on narrow, selectively deposited BST nanoribbons, where surface charges are confined to the perimeter of the nanoribbon. Within these junctions, previously identified signatures of gapless bound states are absent. Because of confinement, transverse momentum sub-bands are quantized and a topological gap opening is observed. Surface states within these quantized sub-bands are spin degenerate, which evokes bound states of conventional 2π-periodic CφR within the BST nanoribbon weak link.

Original languageEnglish
Article numbereabf1854
JournalScience advances
Volume7
Issue number26
DOIs
Publication statusPublished - 23 Jun 2021

Keywords

  • UT-Gold-D

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