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

Area of Science:

• Condensed Matter Physics
• Quantum Superconductivity
• Materials Science

Background:

• Josephson junctions with Majorana fermions are predicted to show a 4π-periodic current-phase relation.
• A key experimental signature of this 4π periodicity is the absence of odd steps in Shapiro step experiments.
• Missing odd Shapiro steps have been experimentally observed and often attributed to topological superconductivity.

Purpose of the Study:

• To investigate the disappearance of odd Shapiro steps in Josephson junctions.
• To determine if this phenomenon is exclusively indicative of topological superconductivity.
• To explore alternative explanations for missing odd Shapiro steps in non-topological systems.

Main Methods:

• Fabrication of Josephson junctions using InAs quantum wells.
• Experimental measurement of Shapiro steps under microwave irradiation.
• Analysis of results using a bi-modal transparency distribution model.
• Investigation of Landau-Zener transitions and their dependence on junction transparency and drive frequency.

Main Results:

• Missing odd Shapiro steps were observed in topologically trivial Josephson junctions.
• The phenomenon was attributed to Landau-Zener transitions in high-transparency junctions.
• The probability of Landau-Zener transitions was found to be independent of the drive frequency.
• A bi-modal transparency distribution model successfully described the disappearance of odd steps with few 4π-periodic modes.

Conclusions:

• Missing odd Shapiro steps in Josephson junctions do not exclusively indicate topological superconductivity.
• High junction transparency leading to Landau-Zener transitions can mimic signatures of topological superconductivity.
• Careful consideration of junction properties is crucial when investigating 4π-periodic Josephson junctions and their relation to topological states.