Hole Distribution in (Sr,Ca,Y,La)₁₄Cu₂₄O₄₁Compounds Studied by X-ray Absorption and Emission Spectroscopy

Polarization-dependent infrared reflectivity study of Sr$_{2.5}$Ca$_{11.5}$Cu$_{24}$O$_{41}$ under pressure: Charge dynamics, charge distribution, and anisotropy

“…[8][9][10] With increasing Ca doping the total carrier concentration in the material is conserved, but the physical properties change drastically, which was attributed to a redistribution of charge carriers from the chains to the ladders with increasing Ca content. 2,7,9, [26][27][28][29][30][31][32][33][34] Because the ionic radius of Ca is smaller than that of Sr, the lattice parameter b decreases for increasing Ca content. 35 Since a similar effect occurs when external pressure is applied, 24,25 the substitution of Sr by Ca can be interpreted in terms of a chemical pressure.…”

Hole-depletion of ladders in Sr$_{14}$Cu$_{24}$O$_{41}$ induced by correlation effects

“…2) O K NEXAFS pre-edge spectra has two distinct structures, A e , centered at 527.9 eV and B e , at 529.5 eV (e is for "experiment"), in agreement with previously published room-temperature spectra. 5,6,16 The shape of the two structures is depen-dent on the polarization of the incident photon: for E a, A e is stronger than B e , while for E c (direction along the chains and the ladders) it is the opposite. For E c structure A e has a second, well resolved peak at 528.5 eV, A' e .…”

“…Determining exactly how the holes are distributed in the system is hindered by the complexity of the crystal structure of Sr 14 Cu 24 O 41 and electron correlation effects. 2,3 Room temperature optical conductivity, 4 Near-Edge X-ray Absorption Fine Structure (NEXAFS), 5 X-ray emission spectroscopy, 6 and Hall coefficient measurements 7 on Sr 14 Cu 24 O 41 estimated that at least f ive holes per f u reside in chains and at most one in ladders. High density of holes in chains is compatible with the low temperature T C ≈ 200 K 8 charge ordering with the 5-fold chain periodicity accompanying the antiferromagnetic (AF) spin-dimerization, observed by inelastic neutron scattering.…”

Real-space localization and quantification of hole distribution in chain-ladder Sr 3 Ca 11 Cu 24 O 41 superconductor

“…SCO is naturally doped with six holes per formula unit (f.u. ), and the total number of holes does not vary with isovalent Ca substitution for Sr. Several estimates of the hole distribution have been reported in literature, using different approaches such as x-ray absorption spectroscopy (XAS) ( 6 – 9 ), x-ray emission spectroscopy (XES) ( 10 ), nuclear magnetic resonance (NMR) ( 11 , 12 ), Hall effect measurements ( 13 ), infrared reflectivity ( 14 ), and bond valence sum analysis based on structural coordination data extracted from x-ray ( 15 ) or neutron ( 16 , 17 ) diffraction measurements. However, they present a wide disparity as a result of major differences in the interpretation of the results.…”