We demonstrate that tunneling spectra in deeply underdoped Bi2Sr2CuO6+δ (Bi2201) and Ca2CuO2Cl2 (CCOC) provide clear evidence for nanoscale phase separation (NPS), causing the gap to fill with doping rather than close. The phase separation extends over a doping range from half filling to approximately x∼0.09. Assuming the NPS is in the form of stripes, then the nodal gap -- which we model as a Coulomb gap -- arises from impurity pinning of the charged stripes, ultimately driving a metal-insulator transition.
@article{arxiv.1405.3992,
title = {Nanoscale phase separation in deep underdoped Bi$_{2}$Sr$_{2}$CuO$_{6+\delta}$ and Ca$_2$CuO$_2$Cl$_2$},
author = {Peter Mistark and Robert S. Markiewicz and Arun Bansil},
journal= {arXiv preprint arXiv:1405.3992},
year = {2015}
}