Evolution of 4π-Periodic Supercurrent in the Presence of an In-Plane Magnetic Field

Abstract

In the presence of a 4π-periodic contribution to the current phase relation, for example in topological Josephson junctions, odd Shapiro steps are expected to be missing. While missing odd Shapiro steps have been observed in several material systems and interpreted in the context of topological superconductivity, they have also been observed in topologically trivial junctions. Here, we study the evolution of such trivial missing odd Shapiro steps in Al−InAs junctions in the presence of an in-plane magnetic field B θ . We find that the odd steps reappear at a crossover B θ value, exhibiting an in-plane field angle anisotropy that depends on spin−orbit coupling effects. We interpret this behavior by theoretically analyzing the Andreev bound state spectrum and the transitions induced by the nonadiabatic dynamics of the junction and attribute the observed anisotropy to mode-to-mode coupling. Our results highlight the complex phenomenology of missing Shapiro steps and the underlying current phase relations in planar Josephson junctions designed to realize Majorana states.

Phase-Slip Lines and Anomalous Josephson Effects in Tungsten Nanoscale Cluster-Based Topological Insulator Nanobridges: Implications for Topologically Protected Qubits and Quantum Sensors

“…14−17 Recently, several studies have provided further insight into the behavior of JJs based on topological materials, 17−20 and, in particular, have shown that signatures in the I−V properties often associated with the topological character of the superconducting state can also be observed in nontopological JJs. 17,19,20 The main challenges to realize a robust topological JJ based on heterostructures formed by a 3D TI and a SC are (i) realization of an almost ideal TI-SC interface; (ii) suppression of disorder; and (iii) fabrication of short and very narrow JJs. In this work, to overcome these challenges, we follow a very different approach from previous ones: to create the TI-SC heterostructure, we deposit tungsten (W) clusters on TI Bi 0.91 Sb 0.09 using the focused ion-beam (FIB) technique, and to form the JJ, we rely on the natural formation of phase-slip lines (PSLs), lines across which the phase of the superconducting order parameter increases at different rates.…”

“…Hybrid structures formed by a strong topological insulator (TI) and a superconductor (SC) have been theoretically predicted as a promising platform for realizing topological superconductivity. − Soon after the theoretical proposals, experiments showed that superconducting pairing can be induced on the surface states of three-dimensional (3D) TIs. − Experimental studies of Josephson junctions (JJs) based on 2D or 3D TI-SC heterostructures then showed signatures in the current voltage characteristic ( I – V ) under microwave radiation consistent with the presence of a topological superconducting state. − Over the past few years, a growing number of JJs with 3D TI weak links have been realized and displayed signs suggesting the establishment of a topological superconducting state. − Recently, several studies have provided further insight into the behavior of JJs based on topological materials, − and, in particular, have shown that signatures in the I – V properties often associated with the topological character of the superconducting state can also be observed in nontopological JJs. ,, …”