Fractionalization in Josephson junction arrays hinged by quantum spin Hall edges

We study a superconductor-ferromagnet-superconductor (SC-FM-SC) Josephson array deposited on top of a two-dimensional quantum spin Hall insulator. The Majorana bound state at the interface between SC and FM leads to charge-e tunneling between neighboring superconductor islands, in addition to the usual charge-2e Cooper pair tunneling. Moreover, because Majorana fermions encode the information of charge number parity, an exact Z(2) gauge structure naturally emerges and leads to many new phases, including a deconfined phase where electrons fractionalize into charge-e bosons and topological defects. A deconfined SC-insulator transition has also been found.