The Measurement of the Polaron Size in the Metallic Phase of Cuprate Superconductors

Abstract

The statistical distribution of the Cu site conformations in the Cu02 plane of Bi2Sr2CaC~208+y (Bi 2212) has been measured by a fast and local probe Cu K-edge extended X-ray absorption f i e structure ( E M S ) as a function of temperature. The Cu site conformations are frozen at T < T* = 120 K -1.4 T, in two well-defined conformations characterized by two Cu-O(apica1) bond lengths separated by 0.17 2 0.02 k The Cu site conformations with short bond 2.38 2 0.02 A have a probability of 41 f 2% at T < T* . The diffraction experiments show that the Cu site conformations exhibit a one-dimensional anharmonic modulation, with period 1, = 25 b, that has been measured by electron diffraction. These data show that the modulation is anharmonic and the plane is decorated with stripes of distorted lattice characterized by the short Cu-O(apica1) bonds of width W = 11 f 1 A at T < T* that form domain walls for the stripes of width L -1 4 2 1 A, characterized by the long Cu-O(apica1) bond. The stripes of distorted lattice run below the lines of interstitial oxygen ions in the BiO plane, playing the role of acceptors. The lattice modulation is therefore assigned to polaronic impurity states ordered in linear arrays. The measure of the width W of the stripes provides the measure of the area of the polarons S, -4a2 (a = 5.4 A) where each hole dressed by the lattice distortion spans a domain of 8 Cu sites. with the same orbital symmetry [ll giving a correlated electron gas with 1 + d i holes per Cu site. There is experimental evidence at low doping, in the insulating phase, for a second class of holes with different orbital symmetry k(a), forming a polaron gas with local density el [2-51. In the metallic phase the polarons are indicated by the local structure which diverges from the average crystallographic structure [6-131. There are experiments showing that the L_(a) holes are trapped by the negative countercharges in the rocksalt layer forming polaronic impurity 0 Les Editions de Physique

Fermi surface reconstruction of superoxygenated La2CuO4superconductors with ordered oxygen interstitials

“…[5][6][7][8] The chargespin ordering and electronic phase separation are accompanied by fluctuations of the local structure that diverges from the average structure. [9][10][11][12][13][14] The defects inserted in the spacer layers to dope the copper oxide electronic structure are an additional source for the modulation of the heterogeneous electronic states near the Fermi level. 15 Particular attention has been addressed to oxygen interstitials that are mobile because of the misfit strain between the active and spacer layers 16 inducing a contraction of the Cu-O bonds.…”

“…A first pseudogap phase with doping around 1/8 competes with a highly doped metallic phase with about 1/4 holes per Cu site well described band structure calculations, confirming previous findings of phase separation giving distinct physics beyond the superconducting dome. [10][11][12] Superoxygenated La 2 CuO 4+y , y > 0.08, provides an ideal case to study the phase separation in the optimum doping regime and the role of ordering of oxygen interstitials (O i 's). [33][34][35][36] The O i 's in the rocksalt LaO layer are mobile; because of the large tensile strain in the spacer layers.…”

Two-Dimensional Nanogranularity of the Oxygen Chains in the YBa2Cu3O6.33 Superconductor

“…Thus, the study of local features by using high resolution experimental probes assumes a paramount importance for the a deeper understanding of new complex and heterogeneous materials. Local probes such as X ray Absorption experimental methods (XANES and EXAFS) and high resolution X ray and neutron diffraction have been used for investigating structural inhomogeneity in various systems such as diborides [15][16][17] and cuprates [18][19][20]. In the last years, the possibility to focus X ray beam onto micrometric and sub-micrometric areas, has allowed to probe the local structure with high resolution in…”

Superstripes in the Low Energy Physics of Complex Quantum Matter at the Mesoscale

“…These results are opening new roadmaps toward the design of new room temperature superconductors and new electronic and magnetic functional materials. The XANES and EXAFS methods [12,13] have been applied to investigate the fast local lattice fluctuations of the Cu-O bond [14][15][16][17][18], showing that nanoscale phase separation is an essential term in the physics of …”