Localized Many-Particle Majorana Modes with Vanishing Time-Reversal Symmetry Breaking in Double Quantum Dots

TL;DR

This paper proposes a new type of many-particle Majorana modes in double quantum dots that preserve local statistics and can exist with minimal time-reversal symmetry breaking, revealing a reverse Mott-insulator transition.

Contribution

It introduces spinful many-particle Majorana modes with local operator products in a superconductor-double-quantum-dot system, highlighting their emergence with negligible Zeeman splitting and Coulomb interactions.

Findings

Identification of a reverse Mott-insulator transition with degenerate parity bands.

Majorana operators connect odd and even parity ground states via multi-operator products.

Observation of a 4% supercurrent in the even state and none in the odd state.

Abstract

We introduce the concept of spinful many-particle Majorana modes with local odd operator products, thereby preserving their local statistics. We consider a superconductor-double-quantum-dot system where these modes can arise with negligible Zeeman splitting when Coulomb interactions are present. We find a reverse Mott-insulator transition, where the even- and odd-parity bands become degenerate. Above this transition, Majorana operators move the system between the odd-parity ground state, associated with elastic cotunneling, and the even-parity ground state, associated with crossed Andreev reflection. These Majorana modes are described in terms of one, three, and five operator products. Parity conservation results in a 4% periodic supercurrent in the even state and no supercurrent in the odd state.