Condensed Matter Seminars

I will discuss mesoscopic topological superconductors that can be used to realize quantum impurity models with orthogonal or symplectic symmetries [1-2]. The first one uses a topological superconductor that hosts many (M>2) Majorana zero modes. Such an "M-Majorana island" coupled to normal metal leads realizes a novel type of topological Kondo effect with SO(M) symmetry, stemming from the non-local topological ground state degeneracy of the island. A physically motivated N-channel generalization of the model enables a perturbative large-N limit which we use to obtain a non-Fermi liquid fixed point at weak coupling [1]. In [2], we propose a Majorana-free setup that uses k spinful zero-energy Andreev bound states and can be mapped to a Kondo impurity with Sp(2k) symmetry. We predict conductances and impurity entropies that can be potentially observed in mesoscopic devices. Qualitative difference is found between the conductances of single- and multichannel models, arising from different fusion outcomes of charge current operators [3]. Besides enriching the understanding of quantum impurity and correlations physics, our work may be relevant for topological quantum computation. 

[1] Multichannel topological Kondo effect, by Li, Oreg, Vayrynen, PRL 130, 066302 (2023)

[2] Topological symplectic Kondo effect, by Li, Konig, Vayrynen, PRB 107, L201401 (2023)

[3] Multichannel topological Kondo models and their low-temperature conductances, by Li, Konig, Vayrynen, arXiv:2507.11682 (2025)