High critical temperature in a superlattice of quantum wires

Abstract

Here we report experimental evidence that the high T_c superconductivity in a cuprate perovskite occurs in a superlattice of Josephson coupled quantum wires. We show that this particular heterostructure provides the physical mechanism raising T_c from the low temperature range T_c<23K to the high temperature range 30K<T_c<150K by amplification of the critical temperature of the homogeneous CuO₂ plane by a factor ∼10. The structure of the high T_c superconducting CuO₂ plane in Bi₂Sr₂CaCu₂O_8+y (Bi2212) at the mesoscopic level (10–100 Å) has been determined. The superconducting plane is decorated by a plurality of parallel superconducting stripes of width L defined by the domain walls formed by stripes of width W characterized by a short Cu-O(apical) distance and large tilting ∼ 110° of the distorted square pyramids. We have measured the width of the domain walls W=11±1 Å and of the stripes L=14±1 Å. The critical parameters raising T_c are: 1) the Fermi level is near the bottom of the second subband of the stripes, with k_2y=2π/L, formed by the quantum size effect and 2) W is of the order of the superconducting coherence length ξ₀.