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

doi:10.1126/sciadv.abf1854

Reappearance of first Shapiro step in narrow topological Josephson junctions

Sci Adv. 2021 Jun 23;7(26):eabf1854. doi: 10.1126/sciadv.abf1854. Print 2021 Jun.

Authors

Daniel Rosenbach^{1

2

3}, Tobias W Schmitt^{4

5}, Peter Schüffelgen^{4

2}, Martin P Stehno⁶, Chuan Li⁷, Michael Schleenvoigt⁴, Abdur R Jalil⁴, Gregor Mussler^{4

2}, Elmar Neumann⁸, Stefan Trellenkamp⁸, Alexander A Golubov⁷, Alexander Brinkman⁷, Detlev Grützmacher^{4

2}, Thomas Schäpers^{4

2

3}

Affiliations

¹ Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany. d.rosenbach@utwente.nl.
² Helmholtz Virtual Institute for Topological Insulators (VITI), Forschungszentrum Jülich, 52425 Jülich, Germany.
³ JARA-Fundamentals of Future Information Technology, Jülich-Aachen Research Alliance, Forschungszentrum Jülich and RWTH Aachen University, Aachen, Germany.
⁴ Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany.
⁵ JARA-FIT Institute Green IT, RWTH Aachen University, 52062 Aachen, Germany.
⁶ Physikalisches Institut EP3, University of Würzburg, Am Hubland 97070, Würzburg, Germany.
⁷ MESA+ Institute for Nanotechnology, University of Twente, 7500AE Enschede, The Netherlands.
⁸ Helmholtz Nano Facility (HNF), Forschungszentrum Jülich, 52425 Jülich, Germany.

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 (Bi_0.06Sb_0.94)₂Te₃ (BST) Josephson junctions with AlO _x 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.

Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).