Stripe structure in the CuO2 plane of perovskite superconductors

The Cu-O pair-distribution function in a (Formula presented)(Formula presented)(Formula presented)(Formula presented) superconductor has been measured by polarized Cu K-edge extended x-ray-absorption fine structure at T<(Formula presented). The results show an anomalous long Cu-O (planar) distance, 1.96 Å, assigned to distorted (Formula presented) stripes of width W intercalated with undistorted stripes of width L. From the measurement of L=15±0.5 Å we have calculated the energies (Formula presented) of the bottom of the one-dimensional subbands of the superlattice and found that the Fermi level (Formula presented) is tuned to a “shape resonance” (Formula presented)-(Formula presented)<ħ(Formula presented), where (Formula presented) is the Debye frequency, giving the (Formula presented) amplification.