HIGH CRITICAL-TEMPERATURE BY RESONANT QUANTUM CONFINEMENT - EVIDENCE FOR POLARONS ORDERING AT T-ASTERISK-APPROXIMATE-TO-1.5T(C) IN BI-2212 AND LA-214 BY EXAFS

The temperature dependence of local Cu site conformations in single-domain crystals of Bi2Sr2CaCu2Os8+y (Bi-2212) and La1.85Sr0.15CuO4 (La-214) has been determined by EXAFS (Extended X-ray Absorption Fine Structure), a fast (10(-15) S) and local probe. Two sets of Cu site conformations characterized by the Cu-O(apical) bond distances and tilting of copper square plane have been found at T < T* similar to 1.5T(c). The difference between the long and short Cu-O(apical) distance appeared to be 0.17 Angstrom and 0.12 Angstrom at T < T* in Bi-2212 and La-214 systems, respectively. The polarons are associated with the short Cu-O(apical) bond distance. The ratio between the number of short and the total number of Cu-O(apical) bonds (N-short/N-tot similar to 0.42 in both systems) is a measure of the relative area of distorted and undistorted domains. By using this result we have been able to show the polaronic nature of the one-dimensional structural anharmonic modulation of the CuO2 plane in Bi-2212 where the polarons have dimension W = (11 +/- 1) Angstrom at T < T* = 1.4T(c) and are condensed into a one-dimensional generalized Wigner charge density wave (CDW). It appears that superconductivity is stabilized at high temperature by resonant quantum confinement in a superlattice of stripe width L where k(Fx) similar to k(Fy) similar to pi/L.