Josephson junctions with negative second harmonic in the current-phase relation: properties of novel varphi-junctions

TL;DR

This paper explores Josephson junctions with a dominant negative second harmonic in their current-phase relation, leading to continuous 0-pi transitions and the potential realization of varphi junctions, with analysis of their properties and experimental detection methods.

Contribution

It introduces the concept of varphi junctions with negative second harmonic and analyzes their unique properties and experimental signatures.

Findings

Negative second harmonic causes continuous 0-pi transitions.

Varphi junctions can be realized with negative second harmonic.

Proposed experimental techniques for observing these junctions.

Abstract

Several recent experiments revealed a change of the sign of the first harmonic in the current-phase relation of Josephson junctions (JJ) based on novel superconductors, e.g., d-wave based or JJ with ferromagnetic barrier. In this situation the role of the second harmonic becomes dominant and it determines the scenario of a 0-pi transition. We discuss different mechanisms of the second harmonic generation and its sign. If the second harmonic is negative the 0-pi transition becomes continuous and the realization of the so-called varphi junction is possible. We study the unusual properties of such a novel JJ and analyze the possible experimental techniques for their observation.