Absence of gross static inhomogeneity in cuprate superconductors
Physical Review B
Recent scanning tunnelling microscopy (STM) studies on Bi_2Sr_2CaCu_2O_8+δ (Bi-2212) revealed the presence of severe inhomogeneity with length scale L_0 ≈ξ_0, the coherence length. Other studies have been interpreted in terms of mesoscale or nanoscale phase segregation. Here we analyze heat capacity and NMR data on Bi-2212 and (Y,Ca)Ba_2Cu_3O_7-δ and find no evidence for phase segregation or gross inhomogeneity. For Bi-2212 the coherence scale L_0 increases with doping from 5 to 17ξ_0 and the
... le density inhomogeneity decreases from 0.028 to 0.005 holes/Cu. We conclude that STM measurements considerably overstate the inhomogeneity in bulk Bi-2212.