QUANTUM-INTERFERENCE PHENOMENA IN POINT CONTACTS BETWEEN 2 SUPERCONDUCTORS

A point contact, weakly connecting two superconductors, can be represented by an ideal Josephson junction (is = i1 sinφ{symbol}) and an effective resistance (Rn = V/in; V = = -( h {combining short stroke overlay}/2e)(∂φ{symbol}/∂t)) shunted in parallel to it. By solving the equation i = is + in = = i1 sin φ{symbol}(t) - (1/Rn)( h {combining short stroke overlay}/2e)(∂φ{symbol}(t)/∂t) = constant, the d.c. current (t̄) - d.c. voltage (V̄) characteristic for a single point contact is found to be V(t) = Rn√(i2 - i21), independent of the magnetic field B⊥. The relationship between d.c. current (ī), d.c. voltage (V̄) and magnetic field (B⊥) is also derived for a double junction, taking the self-inductance (L) of the area (O) embraced by the contacts into account. If πLi1 ≪ h/2e then the self-induced flux is ignored and the current i=2i1sinφtcos e h {combining short stroke overlay} B⊥O - 1 Rn h {combining short stroke overlay} 2e ∂φ{symbol} ∂t = constant and ovbar|V(t) = Rn√(i2 - i2c(B⊥)) for ic = 2i1 |cos(e/ h {combining short stroke overlay}) B⊥ O|. This result explains the observed voltage oscillations in the resistive-superconductive region as a function of the external magnetic field B⊥ when the applied current is constant and exceeds the critical value. If the self-induced flux is taken into account it is impossible to give a simple analytical solution and numerical methods are used. The total magnetic flux enclosed appears to be approximately quantized: B⊥ O + Licirc ≈ n h/2e, giving rise to a circulating current (icirc) which adds to the applied current in one of the contacts and subtracts in the other. The modulation in the critical current is approximately given by ic ≈ 2i1 - (2/L) |n h/2e - B⊥ O|, when πLi1 ≪h/2e. The relationship between ī, V̄ and B⊥ is in agreement with experiment and can be represented by a corrugated surface periodic in B⊥. © 1969.