Spectrum of Andreev bound states in Josepshon junctions with a ferromagnetic insulator

TL;DR

This paper investigates the Andreev bound states in ferromagnetic-insulator based Josephson junctions, revealing how the parity of the FI-layer number influences the stability of 0 and pi states, which is crucial for quantum and classical superconducting circuits.

Contribution

It numerically analyzes the Andreev bound state spectrum in FI-based Josephson junctions, uncovering the parity-dependent stability of 0 and pi states.

Findings

Andreev spectrum depends on FI-layer parity

Pi state is more stable for odd L

0 state is more stable for even L

Abstract

Ferromagnetic-insulator (FI) based Josephson junctions are promising candidates for a coherent superconducting quantum bit as well as a classical superconducting logic circuit. Recently the appearance of an intriguing atomic-scale 0-pi transition has been theoretically predicted. In order to uncover the mechanism of this phenomena, we numerically calculate the spectrum of Andreev bound states in a FI barrier by diagonalizing the Bogoliubov-de Gennes equation. We show that Andreev spectrum drastically depends on the parity of the FI-layer number L and accordingly the pi (0) state is always more stable than the 0 (pi) state if L is odd (even).