Supercurrent reversal in ferromagnetic hybrid nanowire Josephson junctions

Abstract

We report supercurrent transport measurements in hybrid Josephson junctions comprised of semiconducting InAs nanowires with epitaxial ferromagnetic insulator EuS and superconducting Al coatings. The wires display a hysteretic superconducting window close to the coercivity, away from zero external magnetic field. Using a multi-interferometer setup, we measure the current-phase relation of multiple magnetic junctions and find an abrupt switch between π and 0 phases within the superconducting window. We attribute the 0 -π transition to the discrete flipping of the EuS domains and provide a qualitative theory showing that a sizable exchange field can polarize the junction and lead to the supercurrent reversal. Both 0 and π phases can be realized at zero external field by demagnetizing the wire.

Nonsinusoidal current-phase relations in semiconductor-superconductor-ferromagnetic insulator devices

“…Directly solving for the quasiparticle spectrum of the continuum model allows treating on equal footing the current carried by Andreev bound states (ABSs) and the quasi-continuum of states above the gap. Usually, the continuum current is subdominant, except for strong exchange fields, where its contribution is comparable to or even larger than the ABS one [55,[64][65][66][67].…”

“…When a spin-split ABS crosses the Fermi level, its occupation changes and provides no contribution to the current. Therefore, the residual current is entirely due to the continuum of states and has a characteristic π contribution [55].…”

“…1. Recently, such platforms have been realized experimentally in InAs nanowires coated with epitaxial Al and EuS shells [52], which exhibited signatures of spin-polarized subgap states [53,54], and supercurrent reversal [55]. We show that these hybrid materials offer a new way to control the harmonic content of the CPR by combining the gatetunable charge carriers density of the semiconductor and the adjustable magnetization of ferromagnetic insulator insets.…”

Conductance spectroscopy of Majorana zero modes in superconductor-magnetic insulator nanowire hybrid systems

“…With the aforementioned on one hand, the basic Rashba wire setup itself has further drawbacks which includes the requirement of large magnetic fields that could potentially destroy superconductivity [41][42][43][44] apart from the practicalities of precise magnetic field alignment 45 . Recently, efforts are being made towards realizing topological superconductivity with zero external magnetic fields by using proximity effects from magnetic insulators (MI) [46][47][48][49][50][51][52][53][54][55][56][57][58][59] . Recent experimental 47 and theoretical works [48][49][50][51][52]55,60 featuring this setup indicate that at very low external magnetic fields, or even zero external magnetic fields, a topological phase can emerge.…”