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.
@article{arxiv.0708.2624,
title = {Josephson junctions with negative second harmonic in the current-phase relation: properties of novel varphi-junctions},
author = {E. Goldobin and D. Koelle and R. Kleiner and A. Buzdin},
journal= {arXiv preprint arXiv:0708.2624},
year = {2007}
}