Tunable second harmornic in altermagnetic Josephson junctions

TL;DR

This paper investigates how external electric and magnetic fields influence the Josephson effect in superconductor/altermagnet/superconductor junctions, revealing controllable second harmonic effects, 0-$ ext{pi}$ transitions, and critical current enhancements.

Contribution

It demonstrates the tunability of the second harmonic and Josephson current properties via external fields in altermagnetic junctions, a novel control mechanism.

Findings

Second harmonic term causes skewed current-phase relation.

External fields induce 0-$ ext{pi}$ transitions.

Fields can enhance critical current unexpectedly.

Abstract

We study the influence of external electric and Zeeman fields on the Josephson effect in a planar superconductor/altermagnet/superconductor junction. Remarkably, we find that the current-phase relation (CPR) can be forward or backward skewed due to a pronounced second harmonic term. It decisively depends on the altermagnetic field strength. This second harmonic can be measured directly using double SQUID devices. The CPR skewness can be effectively manipulated by electric gating. Moreover, we identify two additional impacts of external electric and magnetic fields on the Josephson current: (i) Fields can induce 0-$\pi$ transitions. (ii) Fields can substantially enhance the critical current. This enhancement is surprising since supercurrents are typically suppressed by magnetic fields.