Polarization Controlled Supercurrent in Ferroelectric Josephson Junction

TL;DR

This work demonstrates all-electrical control of the supercurrent in a ferroelectric-based Josephson junction by exploiting polarization reversal in a S-I-FE-I-S stack. Using a WKB tunneling framework paired with Landauer transport, the authors show that breaking inversion symmetry via asymmetric barriers or FE thickness shifts the electrostatic potential $U^{es}$, yielding large, tunable changes in the critical current $J_c$ and an on-off efficiency $\eta$ approaching $0.9$ for realistic parameters. They derive a compact linear relation $J_c(P) \approx \frac{e\Delta_0}{4h}\kappa\,(1+\theta P)$ with $\eta(P) \approx |\theta P|$ for small $P$, enabling rapid design estimates. The results position ferroelectric Josephson junctions as electrically programmable superconducting switches suitable for cryogenic memory and logic without relying on magnetic components.

Abstract

Josephson junctions are essential devices in superconducting electronics and quantum computing hardware. Here we predict electrical control of the supercurrent in composite superconductor-insulator-ferroelectric-insulator-superconductor (S-I-FE-I-S) Josephson junctions. Inversion symmetry broken by unequal dielectric barrier thicknesses and/or potentials converts ferroelectric polarization reversal into a substantial change of the critical current. With a WKB tunneling model we obtain non-volatile switching of the critical current with on-off efficiency up to 0.9 for physically realistic parameters. This can be achieved by optimizing the thicknesses and potential barriers of the insulating layers, as well as the thickness and dielectric constant of the ferroelectric layer. We also derive a compact linear expression for the critical current valid for small polarizations. Our results identify ferroelectric Josephson junctions as electrically programmable superconducting current switches for cryogenic memory and logic applications.

Figures (6)

• Figure 1: S-I-FE-I-S composite ferroelectric junction. Top: Geometry and electrostatic potential $U^{es}$ for opposite polarization directions (blue vs. red). Bottom: An asymmetric potential barrier profile $U^{b}$ in the dielectric state.
• Figure 2: Potential profiles. Ferroelectric (yellow) and dielectric (blue) layers. Blue (solid) and red (dashed) curves: total potentials for opposite polarization directions (arrows). (a) Symmetric junction: $l_1=l_2=0.5$ nm, $U_1^b=U_2^b=0.15$ eV. (b) Barrier-asymmetric: $l_1=l_2=0.5$ nm, $U_1^b=0.15$ eV, $U_2^b=0.4$ eV. (c) Thickness-asymmetric: $U_1^b=U_2^b=0.15$ eV, $l_1=1.5$ nm, $l_2=0.5$ nm. (d) Strongly asymmetric: $l_1=1.5$ nm, $l_2=0.5$ nm, $U_1^b=0.15$ eV, $U_2^b=0.4$ eV.
• Figure 3: Polarization dependence. (a) Averaged critical current density $\bar{J}_c$ and (b) on-off efficiency $\eta$ vs polarization $P$. Solid black: symmetric junction of Fig. \ref{['fig:potentials']}. Dotted blue: barrier asymmetry [Fig. \ref{['fig:potentials']}]. Dashed red: thickness asymmetry [Fig. \ref{['fig:potentials']}]. Dash-dot yellow: combined strong asymmetry [Fig. \ref{['fig:potentials']}].
• Figure 4: Tunable on-off efficiency at fixed $|P|=5$ µC/cm^2. (a) $\eta$ vs $l_1,l_2$ for $U_1^b=U_2^b=0.15$ eV. (b) $\eta$ vs $U_1^b,U_2^b$ for $l_1=l_2=1.0$ nm. (c) $\eta$ vs thickness difference $l_2-l_1$ and barrier difference $U_2^b-U_1^b$ at fixed $l_1+l_2=2$ nm and $U_1^b+U_2^b=1$ eV. (d) Line cuts of (c): $\eta$ vs $l_2-l_1$ for $U_2^b-U_1^b=0$ (solid black), $+0.6$ eV (dotted blue), and $-0.6$ eV (dashed red).
• Figure 5: Dependence on ferroelectric thickness, dielectric constant and screening length. (a) $\eta$ vs. ferroelectric thickness $d$ for a strongly asymmetric junction in Fig. \ref{['fig:potentials']} and dielectric constants $\varepsilon_f=800$ (solid black), $400$ (dotted blue), $200$ (dashed red), $100$ (dash-dot yellow). The screening length $\delta=0.1$ nm. (b) $\eta$ vs. screening length $\delta$ and $\varepsilon_f$ for $d=2$ nm.