Surface of underdoped YBa2Cu3O7-δ as revealed by STM/STSG. Urbanik, T. Hänke, C. Hess, B. Büchner, A. Ciszewski, V. Hinkov, C. T. Lin and B. KeimerEur. Phys. J. B, 69 4 (2009) 483-489DOI: https://doi.org/10.1140/epjb/e2009-00198-y