Properties of dirty two-band superconductors with repulsive interband interaction: Normal modes, length scales, vortices, and magnetic response

Abstract

Publisher's PDF Garaud, Julien; Corticelli, Alberto; Silaev, Mikhail; Babaev, Egor Garaud, J., Corticelli, A., Silaev, M., & Babaev, E. (2018) Disorder in two-band superconductors with repulsive interband interaction induces a frustrated competition between the phase-locking preferences of the various potential and kinetic terms. This frustrated interaction can result in the formation of an s + is superconducting state that breaks the time-reversal symmetry. In this paper we study the normal modes and their associated coherence lengths in such materials. We especially focus on the consequences of the soft modes stemming from the frustration and time-reversal symmetry breakdown. We find that two-band superconductors with such impurity-induced frustrated interactions display a rich spectrum of physical properties that are absent in their clean counterparts. It features a mixing of Leggett's and Anderson-Higgs modes, and a soft mode with diverging coherence length at the impurity-induced second-order phase transition from s ± /s ++ states to the s + is state. Such a soft mode generically results in long-range attractive intervortex forces that can trigger the formation of vortex clusters. We find that, if such clusters are formed, their size and internal flux density have a characteristic temperature dependence that could be probed in muon-spin-rotation experiments. We also comment on the appearance of spontaneous magnetic fields due to spatially varying impurities.

Chiral p -wave superconductors have complex coherence and magnetic field penetration lengths

“…there are no real coherence lengths in general. Note that for dirty isotropic multiband superconductors, the phase difference and density modes can be mixed even without breaking time reversal symmetry [12]. Our findings of the complete mixing of the order parameters and magnetic modes would apply also for that case.…”

“…These examples shows that accurate coherence length calculations are required while simple estimates can be highly misleading. Calculations of coherence and magnetic field penetration lengths have been made for isotropic multicomponent models for general interactions both in phenomenological and microscopic models [8][9][10][11][12]. The multi-component nature of these systems strongly affects only the coherence lengths, while the magnetic field penetration length is merely renormalized by intercomponent couplings.…”

Field-induced coexistence of s++ and s± superconducting states in dirty multiband superconductors

“…1). Although the physics of vortices in, and in the vicinity of, the s + is phase is very rich, it is beyond the scope of the current work and its detailed study will be addressed in a subsequent work [18].…”

Magnetic signatures of domain walls in s+is and s+id superconductors: Observability and what that can tell us about the superconducting order parameter

“…Such configurations arise when domain walls interact with pinning centers or the boundary of the sample [9]. Several proposals were made to distinguish between s + is and s + id states from various configurations of impurities [10][11][12][13][14]. In the most recent proposal [15], it was suggested that for models relevant for Ba 1−x K x Fe 2 As 2 one can distinguish between s + is and s + id superconductors.…”

“…However, determining the nature of BTRS states is an extremely difficult task. Proposed experimental signatures are vortex clustering, flux flow viscosity at the BTRS phase transition [14,16], soft collective modes close to the transition [5,6,17,18], formation of Skyrmions [9,19,20], and quasiparticle interference [7,21].…”