Magnon-induced transparency of a disordered antiferromagnetic Josephson junction

Abstract

We considered a planar Josephson junction which is composed of two s-wave superconducting contacts deposited on the top of a thin antiferromagnetic (AFM) disordered metal film. In such a system noticeable Josephson currents may be observed, if contacts are just nanometers away from each other. It is shown that the excitation of AFM by magnons results in a strong enhancement of the stationary current through much longer junctions, whose length may be comparable to the coherence length of superconducting correlations in a nonmagnetic metal. Such a current is calculated at the weak tunneling amplitude of electrons between superconducting contacts and AFM. The problem is considered for nonequilibrium Green functions in the second-order perturbation theory with respect to the electron-magnon interaction. A spin-orbit torque oscillator was taken as a possible source of long-wavelength classic magnetic waves. This work predicts a strong effect of magnons on superconducting proximity effect in AFM, with promising applications in superconducting spintronics.

Figures (5)

• Figure 1: (Color online) Two possible random walk paths of correlated electrons and Andreev-reflected holes between superconducting contacts. Dashed arrows depict absorbed and emitted magnons, while thick arrows show electron and hole spins. The interaction with magnons results in flipping spin's directions. Therefore, the total two-particle spin switches between singlet and triplet states. The latter may diffuse over relatively large distances
• Figure 2: The normalized Josephson critical current, as a function of the magnetic excitation frequency, at $k_BT=0.1\Delta$ (solid) and 0.01$\Delta$ (dashed), $l=l_c$, $\Delta_R=0.8\Delta$, $\Delta_L=1.2\Delta$
• Figure 3: The Josephson critical current, as a function of the junction length (in units of the coherence length $l_c$), at $\Omega$=1.8$\Delta$ and $k_BT/\Delta$=0.01
• Figure S1: Color online. One of the Feynman's diagrams for the disorder averaged anomalous Green function. Dashed lines show the pair correlation function of the disorder potential. The lines connect two identical lattice sites. Red arrows indicate Green functions with corrections due to absorbed (emitted) magnons. Thick dots show the tunneling of electrons between the superconductor and AFM.
• Figure S2: Color online. The suggested set up for studying the effect of magnetic excitations on the Josephson current through AFM. The electric current in the Pt layer is directed parallel to the $x$ axis. The spin-Hall current is polarized along the $z$ axis