Absence of gross inhomogeneity in HTS cuprates

TL;DR

This study shows that bulk measurements do not support the presence of large-scale inhomogeneity in HTS cuprates, contrasting with STM findings that suggest nanoscale phase segregation.

Contribution

The paper provides bulk evidence against the gross inhomogeneity in HTS cuprates, challenging interpretations based solely on STM data.

Findings

Heat capacity and NMR data show no phase segregation.

Inhomogeneity decreases with doping in Bi-2212.

Bulk measurements contradict STM inhomogeneity claims.

Abstract

Recent scanning tunnelling microscopy (STM) studies on Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212) revealed the presence of severe inhomogeneity with length scale $L_0 \approx \xi_0$, 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$_2$Cu$_3$O$_{7-\delta}$ and find no evidence for phase segregation or gross inhomogeneity. For Bi-2212 the coherence scale $L_0$ increases with doping from 5 to 17$\xi_0$ and the hole density inhomogeneity decreases from 0.028 to 0.005 holes/Cu. We conclude that STM measurements considerably overstate the inhomogeneity in bulk Bi-2212.