Sextets in four-terminal Josephson junctions

TL;DR

This paper explores the theoretical properties of sextets, a type of multi-Cooper pair tunneling involving four-terminal Josephson junctions, highlighting their connection to Andreev bound states and potential experimental signatures.

Contribution

It introduces the concept of sextets in four-terminal Josephson junctions, analyzing their relation to ABS hybridization and providing insights for experimental detection.

Findings

Sextets involve three Cooper pairs tunneling across four terminals.

Sextets are linked to hybridized Andreev bound states.

Experimental signatures of sextets are discussed in recent hybrid structures.

Abstract

Multiterminal superconducting junctions have revitalized the investigation of the Josephson effect. One of the most interesting aspects of these hybrid systems is the occurrence of multi-Cooper pair tunneling processes that have no analog in two-terminal devices. Such correlated tunneling events are also intimately connected to the Andreev bound states (ABSs) supported by these structures. Josephson junctions with four superconducting terminals have attracted special attention because they are predicted to support ABSs with nontrivial topological properties. Here, we present a theoretical study of sextets, which are correlated tunneling processes involving three Cooper pairs and four different superconducting terminals. We investigate how sextets can be identified from the analysis of the current-phase relation, we show how sextets are connected to the hybridization of ABSs, and we discuss their existence in recent experiments on four-terminal devices realized in hybrid Al/InAs heterostructures.