Half-quantum fluxoid features in the magnetotransport of Sr₂RuO₄ micro rings

Sr₂RuO₄ is a leading candidate for spin-triplet superconductors with an equal-spin pairing state. For such a state, an unusual fluxoid state, the half-quantum fluxoid (HQF), can be realized because the Cooper pairs have an additional degree of freedom in its superconducting order parameter. Although the observation of HQF in Sr₂RuO₄ micro rings using magnetic torque has been reported [1], detection with other experimental technique is still desired [2].
Our goal is to observe possible HQF using magnetoresistance measurements to reproduce the first discovery as well as to try to utilize the phenomenon for research toward manipulation of Majorana quasiparticles. We fabricated micro rings of Sr₂RuO₄ using the focused ion beam technique and observed magnetoresistance oscillations that show good agreement with theoretical simulations for the Little-Parks oscillations. With careful analysis of the data, features that can be attributed to HQF were observed under additional in-plane magnetic fields [3].
[1] J. Jang et al., Science 331, 186 (2011).
[2] X. Cai et al., Phys. Rev. B 87, 081104(R) (2013).
[3] Y. Yasui et al., Phys Rev. B (R) (2017); arXiv:1710.11348.