Quantum oscillations and the Fermi surface in an underdoped high-Tc superconductor

• Published in: Nature (London) 2007-05, Vol.447 (7144), p.565-568
• Main Authors: Doiron-Leyraud, Nicolas, Proust, Cyril, LeBoeuf, David, Levallois, Julien, Bonnemaison, Jean-Baptiste, Liang, Ruixing, Bonn, D. A., Hardy, W. N., Taillefer, Louis
• Format: Article
• Language: English
• Subjects: Condensed Matter; Copper; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Humanities and Social Sciences; letter; Magnetic fields; Materials science; multidisciplinary; Oxides; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physical properties; Physics; Quantum theory; Science; Science (multidisciplinary); Superconductivity; Superconductors; Temperature
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature05872

Superconductivity pair Two papers in this issue report notable contributions towards an understanding of high-temperature superconductivity, still an elusive goal after more than 20 years of intensive research. Doiron-Leyraud et al . report the observation of a Fermi surface in a high-temperature superconductor, a phenomenon regarded as the classic signature of a metal. Gomes et al . tackled the long-standing question of whether the gap in the electronic energy spectrum at temperatures above the critical temperature of a high-temperature superconductor is associated with electron pairing. They find that it is. With these two elegant experimental papers adding some solid new data to the mix, it is the turn of the theorists to work out the implications for superconductivity mechanisms. The observation of quantum oscillations in the electrical resistance of YBa 2 Cu 3 O 6.5 , 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. Despite twenty years of research, the phase diagram of high-transition-temperature superconductors remains enigmatic 1 , 2 . A central issue is the origin of the differences in the physical properties of these copper oxides doped to 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 copper oxides 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 copper oxide YBa 2 Cu 3 O 6.5 , 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. Two possible interpretations are discussed: either a small pocket is part of the band structure specific to YBa