Ortho-II band folding in YBa$_2$Cu$_3$O$_7-$δ$$ films revealed by angle-resolved photoemission

We present an angle-resolved photoelectron spectroscopy study of YBa2Cu3O7-δ films in situ grown by pulsed laser deposition. We have successfully produced underdoped surfaces with ordered oxygen vacancies within the CuO chains resulting in a clear ortho-II band folding of the Fermi surface. This indicates that order within the CuO chains affects the electronic properties of the CuO2 planes. Our results highlight the importance of having not only the correct surface carrier concentration, but also a very well ordered and clean surface in order that photoemission data on this compound be representative of the bulk.