Tailoring Josephson Coupling through Superconductivity-Induced Nonequilibrium

The distinctive quasiparticle distribution existing under nonequilibrium in a superconductor-insulator-normal metal-insulator-superconductor mesoscopic line is proposed as a novel tool to control the supercurrent intensity in a long Josephson weak link. We present a description of this system in the framework of the diffusive-limit quasiclassical Green-function theory and take into account the effects of inelastic scattering with arbitrary strength. Supercurrent enhancement and suppression, including a marked transition to a $\pi$ junction, are striking features leading to a fully tunable structure.

Figure 1

Scheme of the Josephson transistor. The supercurrent $I_J$ (along the white dashed line) is tuned by applying a bias $V_C$ across the SINIS symmetric line connected to the center of the weak link. All normal wires are assumed quasi-one-dimensional.

Figure 2

(a) Supercurrent vs control voltage $V_C$ at different temperatures ($T$) for $\varphi =\pi /2$ and $T_c^C=0.2T_c^J$ (see text). Bias regions labeled (I), (II), and (III) indicate supercurrent enhancement due to quasiparticle cooling, high-voltage $\pi$ state and low-voltage $\pi$ state in the high-temperature regime, respectively. These are qualitatively explained in (b), (c), and (d), where hatched areas represent the contribution to supercurrent arising in such bias ranges (see text).

Figure 3

Supercurrent vs $V_C$ for various ${\mathcal{K}}_{\mathrm{coll}}$ with $T=0.1T_c^C$ and $T_c^C=0.2T_c^J$. Insets show the distribution function at $e{V}_C=1.5{\Delta }_C$ (left) and $e{V}_C=2.5{\Delta }_C$ (right) calculated for the same ${\mathcal{K}}_{\mathrm{coll}}$ values.

Figure 4

(a) Power dissipated in the SINIS line vs $V_C$ calculated for various ratios $T_c^C/T_c^J$ and $T=0.01T_c^J$. (b) Noise power $\mathcal{S}$ vs $V_C$ calculated for the same parameters as in (a). (c) Differential current gain ${\mathbf{G}}_I$ vs $V_C$ for $T_c^C/T_c^J=0.2$. The inset shows ${\mathbf{G}}_I$ in the high-bias region. In all these calculations we set ${\mathcal{K}}_{\mathrm{coll}}=0$ and $T_c^J=9.26\mathrm{K}$ (Nb).