Multichannel charge Kondo effect and non-Fermi liquid fixed points in conventional and topological superconductor islands

TL;DR

This paper investigates the multichannel charge Kondo effect in superconducting islands, revealing distinct non-Fermi liquid fixed points for conventional and topological cases, with implications for experimental detection.

Contribution

It demonstrates that conventional and topological superconducting islands map to different multichannel charge Kondo problems, providing new platforms to study non-Fermi liquid behavior.

Findings

Different low-temperature fixed points for conventional and topological islands.

High crossover temperature in topological case enhances experimental feasibility.

Transport signatures distinguish between charge-$2e$ and charge-$e$ transfer mechanisms.

Abstract

We study multiterminal Majorana and conventional superconducting islands in the vicinity of the charge degeneracy point using bosonization and numerical renormalization group. Both models map to the multichannel charge Kondo problem, but for noninteracting normal leads they flow to different non-Fermi liquid fixed points at low temperatures. We compare and contrast both cases by numerically obtaining the full crossover to the low temperature regime and predict distinctive transport signatures. We attribute the differences between both types of islands to a crucial distinction of charge-$2e$ and charge-$e$ transfer in the conventional and topological case, respectively. In the conventional case, our results establish s-wave islands as a new platform to study the intermediate multichannel Kondo fixed point. In the topological setup the crossover temperature to non-Fermi liquid behavior is relatively high as it is proportional to level broadening and the transport results are not sensitive to channel coupling anisotropy, moving away from the charge degeneracy point or including a small Majorana hybridization, which makes our proposal experimentally feasible.