Polarization of spontaneous magnetic field and magnetic fluctuations in $s+is$ anisotropic multiband superconductors

Abstract

We show that multiband superconductors with broken time-reversal symmetry can produce spontaneous currents and magnetic fields in response to the local variations of pairing constants. Considering the iron pnictide superconductor Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ as an example we demonstrate that both the point-group symmetric $s+is$ state and the C${}_4$-symmetry breaking $s+id$ states produce in general the same magnitudes of spontaneous magnetic fields. In the $s+is$ state these fields are polarized mainly in ab crystal plane, while in the $s+id$ state their ab-plane and c-axis components are of the same order. The same is true for the random magnetic fields which are produced by the order parameter fluctuations near the critical point of the time-reversal symmetry breaking phase transition. Our findings can be used as a direct test of the $s+is/s+id$ dichotomy and the additional discrete symmetry breaking phase transitions with the help of muon spin relaxation experiments.

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• Demonstration of $\mathbb{C}{P}^2$ skyrmions in three-band superconductors by self-consistent solutions to a Bogoliubov-de Gennes model
• Effects of intercomponent couplings on the appearance of time-reversal symmetry breaking fermion quadrupling state in two-component London models
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• Effective model and Magnetic Properties of the Resistive Electron Quadrupling State
• Chiral p-wave superconductors have complex coherence and magnetic field penetration lengths
• Magnetic field behaviour in $s+is$ and $s+id$ superconductors: twisting of applied and spontaneous fields
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