Jukka Vayrynen: Non-Reciprocal and Topological Phenomena in Superconductors

Date and Time
Location
Elings Hall, Room 1605
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Quantum Foundry and Microsoft Station Q jointly hosted seminar

 

Abstract:

I will discuss two topics related to superconducting devices, discussed in recent preprints [1-2]. In the first part of the talk, I will discuss the so-called superconducting diode effect originating from two different mechanisms. The first one is an intrinsic one that can be realized for example in the proximitized edge states of a topological insulator. The second mechanism is an extrinsic one but is also relevant for superconducting heterostructures. The latter mechanism is based on formation of interfacial Josephson vortices and may explain some recent experiments [2]. In the second part of the talk, I will discuss a mesoscopic 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, where the effective impurity "spin" transforms under the orthogonal group SO(M) stemming from the non-local topological ground state degeneracy of the island. In [2], we introduce a physically motivated N-channel generalization of the topological Kondo model, finding signatures of non-Fermi liquid (NFL) physics and emergent anyons. We complement previous bosonization approaches by using the large-N limit and obtain an NFL fixed point at weak coupling. We predict conductances and impurity entropies that can be observed in mesoscopic devices. Besides enriching quantum impurity physics, our work may be relevant for topological quantum computation based on Majorana states.

[1]    Supercurrent non-reciprocity and vortex formation in superconductor heterostructures,  Sundaresh, Vayrynen, Lyanda-Geller, Rokhinson, arXiv:2207.03633.

[2]    Multichannel topological Kondo effect, Li, Oreg, Vayrynen, arXiv:2207.10105.