2016/08/31 by Egor Babaev, Johan Carlstrom, Mihail Silaev +1
Physics and Astronomy · #cond-mat.supr-con
paper · pdf · doi:10.1016/j.physc.2016.08.003
published as Physica C 533, 20-35 (2017) · v2: Missing value for a coupling constant for Fig 2(d) added. Prepared for the proceedings of Vortex IX conference, Rhodes 12-17 September 2015. Updates and supersedes the Vortex VII proceedings contribution arXiv:1110.2744
arxiv created 2017/02/26 · arxiv updated 2017/02/28
In general a superconducting state breaks multiple symmetries and, therefore, is characterized by several different coherence lengths ξi, i=1,...,N. Moreover in multiband material even superconducting states that break only a single symmetry are nonetheless described, under certain conditions by multi-component theories with multiple coherence lengths. As a result of that there can appear a state where some coherence lengths are larger and some are smaller than the magnetic field penetration length λ: ξ1≤ ξ2... < √(2)λ<ξM≤...ξN. That state was recently termed "type-1.5" superconductivity. This breakdown of type-1/type-2 dichotomy is rather generic near a phase transition between superconducting states with different symmetries. The examples include the transitions between U(1) and U(1)× U(1) states or between U(1) and U(1)× Z2 states. The later example is realized in systems that feature transition between s-wave and s+is states. The extra fundamental length scales have many physical consequences. In particular in these regimes vortices can attract one another at long range but repel at shorter ranges. Such a system can form vortex clusters in low magnetic fields. The vortex clustering in the type-1.5 regime gives rise to many physical effects, ranging from macroscopic phase separation in domains of different broken symmetries, to unusual transport properties.