Missing Shapiro steps in topologically trivial Josephson junction on InAs quantum well

Abstract

Josephson junctions hosting Majorana fermions have been predicted to exhibit a 4π periodic current phase relation. One experimental consequence of this periodicity is the disappearance of odd steps in Shapiro steps experiments. Experimentally, missing odd Shapiro steps have been observed in a number of materials systems with strong spin-orbit coupling and have been interpreted in the context of topological superconductivity. Here we report on missing odd steps in topologically trivial Josephson junctions fabricated on InAs quantum wells. We ascribe our observations to the high transparency of our junctions allowing Landau-Zener transitions. The probability of these processes is shown to be independent of the drive frequency. We analyze our results using a bi-modal transparency distribution which demonstrates that only few modes carrying 4π periodic current are sufficient to describe the disappearance of odd steps. Our findings highlight the elaborate circumstances that have to be considered in the investigation of the 4π Josephson junctions in relationship to topological superconductivity.

Fractional AC Josephson effect in a topological insulator proximitized by a self-formed superconductor

“…Suppression of the first and third Shapiro steps due to Landau-Zener transitions (LZTs) between upper and lower ABS branches near φ = π (Fig. 1(e)) has been predicted [47,48] and recently observed in a lateral Josephson junction based on a topologically trivial InAs weak link [13], enabled by exceptionally high interface transparency. The probability of an LZT is…”

“…Therefore the suppression of higher odd Shapiro steps is a crucial step in eliminating the ambiguity surrounding claims of 4π periodicity. Landau-Zener transitions suppress the expression of the first and higher odd Shapiro steps, but only in devices with near-unity interface transparency between superconductor and weak link [13], offering a clear-cut way to rule out this mechanism.…”

Spin-resolved spectroscopy of helical Andreev bound states

“…These expressions, which are compatible with Eqs. (38) and (45), merely differ by a global phase and they clearly satisfy |r ee ← | 2 = |r ee → | 2 . The scattering processes are distinctively different in case (ii), displayed in Fig.…”

“…Unfortunately, experimental signatures of these phenomena can be obscured by non-topological effects [45][46][47]. It is therefore an open question how to directly probe the existence of hABSs and thus the topological origin of the JJ [48,49].…”

Quasiparticle trapping at vortices producing Josephson supercurrent enhancement

“…For example, the zero-bias conductance peak can be attributed to the Andreev bound state (ABS) [13][14][15][16][17] or weak anti-localization [18]. In addition, the missing odd integer Shapiro steps can be explained by non-adiabatic dynamics such as the Landau-Zener transition of the highly transparent Josephson junctions [19]. These recent criticisms indicate that thorough experimental study and careful data treatment to identify the origin of the novel superconducting transport phenomena are of great importance, significantly, for the establishment of not only TSC and MF physics but also the development of superconducting device physics.…”