Evidence of the Ortho II band folding in of YBa2Cu3O7-$\delta $ underdoped surface

Fermi surface and low energy electronic structure of YBa2Cu3O7-$\delta $ (Y123) is investigated using angle-resolved photoemission spectroscopy (ARPES) on pulsed laser deposition (PLD) in situ grown films. By PLD, the Y123 surface is carefully controlled to produce underdoped surfaces with ordered oxygen vacancies within the CuO chains. The resulting Fermi surface displays a clear Ortho II band folding, showing how order within the CuO chains strongly affect the electronic properties of the superconducting CuO2 planes. Until now, the Ortho II band folding has not been detected by ARPES measurements. This present approach opens the door to systematic studies in the remaining question concerning the ambiguous nature of the pseudogap phase for high-temperature cuprates.