Magnetic properties of proximity-induced superconducting matrix in multifilamentary wires

Abstract

Critical current densities J_cp of proximity-induced superconducting matrices in NbTi multifilamentary wires are estimated from measured twist-pitch dependence of magnetization. The values of J_cp are 2–4 orders of magnitude smaller than those of the superconducting filaments and decrease rapidly by raising temperature T and magnetic field B_e. The interfilamentary spacing d_N of submicrons results in zero screening length at measured temperatures ranging 4.5 to 8 K and the induced superconductivity is suggested to be type-II. The upper critical field B_c2p is obtained by applying the scaling law to J_cp data. B_c2p's at 4.5 K are 1.2–3.0 T for d_N = 0.20–0.59 μm. The Cooper pair penetration length K ⁻¹_N estimated from the temperature dependence of B_c2p shows the clean limit characteristic as T⁻¹ and 0.32 μm for d_N = 0.59 μm wire at 4.5 K. K ⁻¹_N estimated from the temperature dependence of J_cp agrees consistently with those from B_c2p(T).