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Fermi surfaces and quantum oscillations in underdoped high-Tc superconductors YBa2Cu3O6.5 and YBa2Cu4O8

We study underdoped high-Tc superconductors YBa2Cu3O6.5 and YBa2Cu4O8 using first-principles pseudopotential methods with additional Coulomb interactions at the Cu atoms, and obtain Fermi-surface pocket areas in close agreement with measured Shubnikov-de Haas and de Haas-van Alphen oscillations. With antiferromagnetic order in CuO2 planes, stable in the calculations, small hole pockets are formed near the so-called Fermi-arc positions in the Brillouin zone which reproduce the low-frequency oscillations. A large electron pocket, necessary for the negative Hall coefficient, is also formed in YBa2Cu3O6.5, giving rise to the high-frequency oscillations as well. Effective masses and specific heats are also calculated and compared with measurements. Our results highlight the important role of magnetic order in the electronic structure of underdoped high-Tc superconductors.