Quantum oscillations and the Fermi surface in an underdoped high-Tc superconductor (original) (raw)

Despite twenty years of research, the phase diagram of high-temperature superconductors remains enigmatic 1 , 2 . A central question is: what makes the physical properties of these copper oxides so dramatically different on opposite sides of the superconducting region? In the overdoped regime, the material behaves as a reasonably conventional metal, with a large Fermi surface 3 , 4 . The underdoped regime, however, is highly anomalous and appears to have no coherent Fermi surface, but only disconnected "Fermi arcs" 5 , 6 . The fundamental question, then, is whether underdoped cuprates have a Fermi surface, and if so, whether it is topologically different from that seen in the overdoped regime. Here we report the observation of quantum oscillations in the electrical resistance of the oxygen-ordered cuprate YBa 2 Cu 3 O 6.5 , establishing the existence of a well-defined Fermi surface in the ground state of underdoped cuprates, once superconductivity is suppressed by a magnetic field. The low oscillation frequency reveals a Fermi