Motivated by the recent observation of the time-reversal symmetry broken state in K-doped BaFe2As2 superconducting alloys, we theoretically study the collective modes and the short time dynamics of the superconducting state with s+is-wave order parameter using an effective four-band model with two hole and two electron pockets. The superconducting s+is state emerges for incipient electron bands as a result of hole doping and appears as an intermediate state between s± (high number of holes) and s++ (low number of holes). The amplitude and phase modes are coupled giving rise to a variety of collective modes. In the s± state, we find the Higgs mode at frequencies similar to a two-band model with an absent Leggett mode, while in the s+is and s++ state, we uncover a new coupled collective soft mode. Finally we compare our results with the s+id solution and find similar behaviour of the collective modes.
@article{arxiv.1804.05662,
title = {Short-time dynamics in $s+is$-wave superconductor with incipient bands},
author = {Marvin A. Müller and Pengtao Shen and Maxim Dzero and Ilya Eremin},
journal= {arXiv preprint arXiv:1804.05662},
year = {2018}
}