Dynamics and distribution of doped holes in the CuO2 plane of slightly doped Y1-y CayBa2Cu3O 6 studied by Cu(1) NQR

Cu(1) nuclear quadrupole resonance (NQR) in slightly doped YBCO6: Ca compounds allows us to study the incidence of doped holes on the antiferromagnetic state. Distributions of transverse (1/ T2) and longitudinal (1/ T1) relaxation rates of the NQR are found at low temperature, which allows us to determine a fraction of doped holes which are localized. We conclude that the holes doped in the CuO2 plane by Ca2+ → Y3+ substitution are distributed homogeneously in the CuO2 plane above 70 K and move freely in the plane. We establish that the reduction in hole mobility from metallic to variable-range hopping induces the differentiation of Cu(1) nuclei. At lower T the holes' motion slows down and we estimate that the holes localize finally in restricted regions (4-6 lattice constants) in the Coulomb potential of the Ca2+ ions. © 2009 The American Physical Society