Effect of d-f hybridization on the Josephson current through Eu-chalcogenides

TL;DR

This paper theoretically investigates the formation of pi Josephson junctions in superconductor/Eu-chalcogenide/superconductor structures, highlighting the role of d-f electron hybridization as an alternative to ferromagnetic metals for qubit applications.

Contribution

It demonstrates that pi junctions can be realized through d-f hybridization in Eu-chalcogenides, avoiding dissipation issues associated with ferromagnetic metals.

Findings

Pi junctions form with finite d-f hybridization.

D-f hybridization enables pi coupling without ferromagnets.

Potential for low-dissipation qubit applications.

Abstract

A superconducting ring with a pi junction made from superconductor/ferromagnetic-metal/superconductor (S-FM-S) exhibits a spontaneous current without an external magnetic field in the ground state. Such pi ring provides so-called quiet qubit that can be efficiently decoupled from the fluctuation of the external field. However, the usage of the FM gives rise to strong Ohmic dissipation. Therefore, the realization of pi junctions without FM is expected for qubit applications. We theoretically consider the possibility of the pi coupling for S/Eu-chalcogenides/S junctions based on the d-f Hamiltonian. By use of the Green's function method we found that pi junction can be formed in the case of the finite d-f hybridization between the conduction d and the localized f electrons.