Quasiparticle energy spectrum in ferromagnetic Josephson weak links

TL;DR

This paper calculates the quasiparticle energy spectrum in ferromagnetic Josephson weak links, revealing how bound states and zero-energy states depend on barrier properties and phase difference, impacting the ground state and spin polarization.

Contribution

It provides analytical conditions for the appearance of zero-energy bound states and spin-polarized ground states in ferromagnetic Josephson junctions, advancing understanding of their spectral properties.

Findings

Large peaks in DOS due to Andreev reflection correspond to spin-split bound states.

Zero-energy states appear only outside the weak link ground state.

Conditions for zero-energy states and spin-polarized ground states are derived analytically.

Abstract

The quasiparticles energy spectrum in clean ferromagnetic weak links between conventional superconductors is calculated. Large peaks in DOS, due to a special case of Andreev reflection at the ferromagnetic barrier, correspond to spin-splitt bound states. Their energies are obtained as a function of the barrier thickness, exchange field strength, and of the macroscopic phase difference $\phi$ at the link, related to the Josephson current. In the ground state, $\phi$ can be 0 or $\pi$, depending on the ferromagnetic barrier influence. Conditions for the appearence of the zero-energy bound states (ZES) and for the spin polarized ground state (SPGS) are obtained analytically. It is shown that ZES appear only outside the weak link ground state.