Qdev Seminar by Katharina Laubscher, University of Basel

RKKY interaction at helical edges of topological superconductors

In this work, we study spin configurations of classical magnetic impurities placed close to the edge of a two-dimensional helical topological superconductor. First, we demonstrate that the spin of a single magnetic impurity close to the edge of the topological superconductor tends to align along the edge due to a strong magnetic anisotropy caused by the helical Majorana edge states. Next, we compute the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic impurities placed close to the edge. We show that, in the limit of large inter-impurity distances, the RKKY interaction between the two impurities is mainly mediated by the Majorana edge states and leads to a ferromagnetic alignment of both spins along the edge. Since the above effects are absent in trivial superconductors without edge states, we argue that spectroscopy of dilute magnetic impurities can serve as a powerful tool to probe topological superconductors by detecting the magnetic anisotropy induced by the gapless edge states.

Reference: K. Laubscher, D. Miserev, V. Kaladzhyan, D. Loss, and J. Klinovaja, arXiv:2203.08137 (2022).