Electrically Controlled 0-$π$ Oscillations and Josephson Giant Magnetoresistor with PT-Symmetric Antiferromagnetic Bilayers

Abstract

We propose that unconventional Josephson effects can typically emerge in {\it PT}-symmetric antiferromagnetic (AFM) bilayer systems. When proximitized by a conventional superconductor, these heterostructures host dominant interlayer Cooper pairing that features a distinctive spin texture enabled by the strong exchange field. Specifically, we demonstrate a novel mechanism for electrically tunable 0-$π$ oscillations in lateral Josephson junctions, controlled by an out-of-plane electric displacement field. This behavior originates from field-induced finite-momentum Cooper pairing, a hallmark of the unique layer-pseudospin structure in {\it PT}-symmetric AFM bilayers. Furthermore, we introduce a Josephson giant magnetoresistor based on these exotic spin-layer-locked Cooper pairs, in which the supercurrent exhibits a strong dependence on the internal Néel order. Our findings establish {\it PT}-symmetric AFM bilayers as a versatile platform for phase-controllable Josephson junctions and superconducting magnetic random-access memory, with promising applications in superconducting circuits and ultralow-power computing.

Figures (8)

• Figure 1: (a) A schematic picture of a lateral JJ based on $PT$-symmetric AFM bilayers. The AFM bilayers have the interlayer Néel order. The two sides of the junction are superconducting (SC) electrodes. The weak-link region has dual gates $V_{TG}$ and $V_{BG}$ with length $L_0$. (b) In $PT$-symmetric AFM bilayers, the superconducting proximity effect causes the spin-layer-locked Cooper pairs. (c) Cooper pairs can tunnel between left and right domains when their internal Néel orders are aligned, but tunneling is forbidden when the Néel orders are opposite.
• Figure 2: (a) In $PT$-symmetric AFM bilayers, an electron on the top layer has its $PT$-partner on the bottom layer, which are degenerate in energy. (b) When $V_d \neq 0$, the $PT$ symmetry is broken by lifting the band degeneracy. (c) The numerical and analytical results of the interlayer pairing gap. The numerical result is evaluated from Eq. \ref{['eq:eq_tranfer']}.
• Figure 3: (a) $0-\pi$ oscillations: The maximum Josephson current $I_s$ as a function of the $V_d$ for $L_0=40,20$. (b) The current-phase relation for $V_d=V_A$ and $V_B$, corresponding to the green and orange star in (a). (c) The $I_s$ near the $0-\pi$ transition (pink star in (a)). (d) The free energy for the three point in (d) with $0$, $\pi$, $0-\pi$ degenerate phases. Parameters for all panels: $\mu=0.5$, $\Delta_s=0.01$, $\Delta_0=0.05$ and $k_B T=0.3\Delta_s$.
• Figure 4: (a) The conventional giant magnetoresistor: for parallel magnetization, the resistance is small with bright lamp; for antiparallel magnetization, the resistance is high with dark lamp. (b) The Josephson giant magnetoresistor: A lateral JJ with $PT$-symmetric AFM bilayers configurated as antiphase domains. (c) Critical current $I_c$ as a function of $\theta$ at interlayer coupling $g=0.2$ and $0.3$. (d) The JGMR quality factor $\eta$ versus $g$ with the numerical result (blue line) and the analytical result using Eq. \ref{['eq:eq_eta']} (yellow dashed line). We set the junction length to be $L_l=L_r=3$. Parameters: $\Delta_0=0.05$, $J_{ex}=1$, $k_B T=0.2\Delta_0$, $\mu=0.15$.
• Figure 5: Schematic picture of the Andreev reflections of lateral JJ built by AFM bilayers. The Andreev reflection process involves an incoming spin-up electron from the top layer and an outgoing spin-down hole from the bottom layer.