The observation of quantum oscillations in the electrical resistance of YBa2Cu3O6.5, is reported, establishing the existence of a well-defined Fermi surface in the ground state of underdoped copper oxides (once superconductivity is suppressed by a magnetic field). The low oscillation frequency reveals a Fermi surface made of small pockets, in contrast to the large cylinder characteristic of the overdoped regime.
- Nicolas Doiron-Leyraud
- Cyril Proust
- Louis Taillefer