Measurements of thermal conductivity versus temperature over a broad range of doping in YBa2Cu3O6+x and HgBa2Can−1CunO 2n+2+δ (n=1,2,3) suggest that small domains of localized holes develop for hole concentrations near p=1/8. The data imply a mechanism for localization that is intrinsic to the CuO2-planes and is enhanced via pinning associated with oxygen-vacancy clusters.PACS numbers: 74.25.Fy, 74.25.Bt, 74.25.Dw There has been considerable recent interest in novel charge-and spin-ordered phases which may compete with superconductivity in the cuprates [1]. This stripe order is favored at CuO 2 planar hole concentrations near p=1/8 for which the modulation wavelength is commensurate with the lattice, and when an appropriate pinning potential is present. Inelastic neutron scattering results [2] suggest that stripe modulations are disordered and/or fluctuating in La 1−x Sr x CuO 4 (La-214) and YBa 2 Cu 3 O 6+x (Y-123). Nuclear magnetic and quadrupole resonance (NMR and NQR) studies [3,4] indicate the presence of localized holes in the CuO 2 planes. Whether localized holes are a general feature of cuprates and contribute to short-ranged charge/spin segregation and the normalstate pseudogap [5,6] are fundamental issues of current interest.Here we report the observation of anomalies at p=1/8 revealed in the oxygen doping dependence of thermal conductivity (κ) in Y-123 and Hg cuprates. Our principal finding is that a fraction of the doped holes in the CuO 2 planes become localized near this particular doping level. This fraction correlates with the oxygen vacancy concentration in the charge reservoir layers, consistent with the formation of nanoscale, hole-localized domains that are pinned near oxygen-vacancy clusters.Two prominent characteristics of the in-plane heat conductivity in superconducting cuprates [7] are a normalstate κ predominantly of lattice origin, and an abrupt increase in κ at T ≤ T c . To motivate our proposal that κ probes localized holes, we demonstrate for Y-123 that its magnitude and temperature derivative at T c correlate with independent measures of local structural distortions (planar Cu NQR) and the superfluid fraction (specific heat jump), respectively, throughout the underdoped regime (p ≤ 0.16). Consider data from previous work [8] that illustrate the p=1/8 features in κ (Fig. 1). The upper panel shows normal-state data, κ(p, T =100K), for an Y-123 polycrystal and the ab-plane of single crystals. The lower panel shows, for the same specimens, the dimensionless slope change in κ at T c defined as, where t = T /T c and κ s (κ n ) is the thermal conductivity in the superconducting (normal) state. Γ measures the change in scattering of heat carriers (electrons and phonons) induced by superconductivity. Both quantities exhibit local minima near p=1/8.

The ferromagnetic ground state of a Kondo lattice with a low concentration of conduction electrons is ferromagnetic. Assuming the existence of disorder in the Fermi liquid of the conduction electrons we showed that the ferromagnetic state can be suppressed by the effect of the spin fluctuations of the disordered Fermi liquid.

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