Large Second-Order Josephson Effect in Planar Superconductor-Semiconductor Junctions

Abstract

We investigate the current-phase relations of Al/InAs-quantum well planar Josephson junctions fabricated using nanowire shadowing technique. Based on several experiments, we conclude that the junctions exhibit an unusually large second-order Josephson harmonic, the $\sin (2\phi )$ term. First, superconducting quantum interference devices (dc-SQUIDs) show half-periodic oscillations, tunable by gate voltages as well as magnetic flux. Second, Josephson junction devices exhibit kinks near half-flux quantum in supercurrent diffraction patterns. Third, half-integer Shapiro steps are present in the junctions. Similar phenomena are observed in Sn/InAs quantum well devices. We perform data fitting to a numerical model with a two-component current phase relation. Analysis including a loop inductance suggests that the sign of the second harmonic term is negative. The microscopic origins of the observed effect remain to be understood. We consider alternative explanations which can account for some but not all of the evidence.

Written using The Block Method. Data on Zenodo DOI: https://doi.org/10.5281/zenodo.6416083 v2: Added block "Non-identical negative and positive switching currents" and Figs.S4, S5. v3: Added Figs. 6, S6-S9, simulations with both inductive and second harmonic effects

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Cited by in corpus (13)

• Tunable second harmornic in altermagnetic Josephson junctions
• Direct measurement of a $\sin (2\phi )$ current phase relation in a graphene superconducting quantum interference device
• Microwave-assisted unidirectional superconductivity in Al-InAs nanowire-Al junctions under magnetic fields
• Non-Hermitian superconducting diode effect
• Influence of capacitance and thermal fluctuations on the Josephson diode effect in asymmetric higher-harmonic SQUIDs
• Tunable superconducting diode effect in higher-harmonic InSb nanosheet interferometers
• Missing odd-order Shapiro steps do not uniquely indicate fractional Josephson effect
• Fractional positional jumps in stochastic systems with tilted periodic double-well potentials
• Relations between normal state nonreciprocal transport and the superconducting diode effect in the trivial and topological phases
• Effect of 2${}^{\text{nd}}$ harmonic current--phase relation on a behavior of a Josephson Traveling Wave Parametric Amplifier
• Diode effect in Shapiro steps in an asymmetric SQUID with a superconducting nanobridge
• Ubiquitous missing first Shapiro step in Al-InSb nanosheet Josephson junctions
• Strongly anharmonic flux-tunable transmon based on InAs-Al 2D heterostructure