Center for Quantum Metamaterials held a scientific seminar on the connection between superconductivity and time reversal symmetry breaking

Dr. V. A. Grinenko, researcher at the Li Zhengdao Institute of Shanghai Jiao Tong University, has told the seminar participants about the new data on spontaneous fields and clustering of vortices in the Sr2RuO4 superconductor and their explanation.

Sr 2 RuO 4  is one of the most studied unconventional superconductors with broken time reversal symmetry (BTRS) in the superconducting state [1]. However, despite 30 years of research, the connection of the BTRS state with superconductivity remains controversial. Recently, using measurements of muon spin rotation/relaxation (µSR) in the zero field (ZF), we found that the superconducting junction temperatures Tc and BTRS, TBTRS, split under the action of uniaxial stress [2,3] and do not split under the action of hydrostatic pressure or disorder [4]. On the other hand, all attempts to find thermodynamic evidence for the splitting of junctions under the action of uniaxial stress have failed [5,6]. In this report,   our new data on µSR obtained under the action of uniaxial voltage in a transverse magnetic field was presented. We investigated the field distribution in a superconducting vortex lattice in various magnetic fields and temperatures. The analysis of the field distribution is consistent with the trend towards clustering of vortices caused by the proximity to the BTRS transition. This observation indicates that the BTRS state is related to superconductivity and can be explained by the divergent coherence length of ξBTRs during the TBTRS transition. Long-range attractive and short-range repulsive inter-vortex interactions occur at ξBTRs > λSC > ξBTRs overconducting coherence length ξBTRs and penetration depth λSC [7]. Our recent study of the effect of La doping on the strength of spontaneous fields in Sr2RuO4, investigated by the ZF-µSR method was presented as well.

[1] G. M. Luke et al. Time-reversal symmetry-breaking superconductivity in Sr₂RuO₄. Nature 394, 558–561 (1998)

[2] V. Grinenko, S. Ghosh et al. Split superconducting and time-reversal symmetry-breaking transitions in Sr₂RuO₄ under stress. Nat. Phys. 17, 748–754 (2021).

[3] V. Grinenko et al., 𝜇SR measurements on Sr₂RuO₄ under ⟨110⟩ uniaxial stress. Phys. Rev. B 107, 024508 (2023).

[4] V. Grinenko et al. Unsplit superconducting and time reversal symmetry breaking transitions in Sr₂RuO₄ under hydrostatic pressure and disorder. Nat Commun 12, 3920 (2021).

[5] Y.-S. Li et al. High-sensitivity heat-capacity measurements on Sr2RuO4 under uniaxial pressure. PNAS  118 (10) e2020492118 (2021).

[6] Y.-S. Li et al. Elastocaloric determination of the phase diagram of Sr₂RuO₄. Nature 607, 276–280 (2022).

[7] E. Babaev et al. Type-1.5 superconductivity in multicomponent systems. Physica C 533, 20-35 (2017).