The nature of the broken time reversal symmetry (BTRS) state in Sr2RuO4 remains elusive, and its relation to superconductivity remains controversial. There are various universal predictions for the BTRS state when it is associated with a multicomponent superconducting order parameter. In particular, in the BTRS superconducting state, spontaneous fields appear around crystalline defects, impurities, superconducting domain walls and sample surfaces. However, this phenomenon has not yet been experimentally demonstrated for any BTRS superconductor. Here, we aimed to verify these predictions for Sr2RuO4 by performing muon spin relaxation (μSR) measurements on Sr2−yLayRuO4 single crystals at ambient pressure and stoichiometric Sr2RuO4 under hydrostatic pressure. The study allowed us to conclude that spontaneous fields in the BTRS superconducting state of Sr2RuO4 appear around non-magnetic inhomogeneities and, at the same time, decrease with the suppression of Tc. The observed behaviour is consistent with the prediction for multicomponent BTRS superconductivity in Sr2RuO4. The results of the work are relevant to understanding BTRS superconductivity in general, as they demonstrate, for the first time, the relationship among the superconducting order parameter, the BTRS transition, and crystal-structure inhomogeneities.
@article{arxiv.2512.24585,
title = {Origins of spontaneous magnetic fields in Sr$_2$RuO$_4$},
author = {Yongwei Li and Rustem Khasanov and Stephen P. Cottrell and Naoki Kikugawa and Yoshiteru Maeno and Binru Zhao and Jie Ma and Vadim Grinenko},
journal= {arXiv preprint arXiv:2512.24585},
year = {2026}
}