Quantum oscillations in an overdoped high-Tc superconductor

Abstract

As well as their elevated superconducting transition temperatures (Tcs), the copper-oxide superconductors display a variety of novel physical properties that have inspired many theories to explain their electronic ground state. One topic of note is the nature of the metallic phase in these compounds, in particular, how coherent electronic states or quasiparticles emerge from the antiferromagnetic insulator with doping — the addition of trace amounts of impurities. Vignolle et al. report the observation of quantum oscillations, that is, oscillations in the electrical and magnetic response as a function of magnetic field, in the overdoped superconductor Tl2Ba2CuO6+δ. These oscillations point to the existence of a large Fermi surface of well-defined quasiparticles covering two-thirds of the Brillouin zone. The measurements confirm the applicability of a generalized Fermi-liquid picture to the overdoped side of the superconducting dome and mean that the important charge carriers involved in superconductivity are essentially similar to those found in normal metals. This paper reports the observation of quantum oscillations in the overdoped superconductor Tl2Ba2CuO6+δ that show the existence of a large Fermi surface of well-defined quasiparticles covering two-thirds of the Brillouin zone. These measurements firmly establish the applicability of a generalized Fermi-liquid picture on the overdoped side of the superconducting dome. The nature of the metallic phase in the high-transition-temperature (high-Tc) copper oxide superconductors, and its evolution with carrier concentration, has been a long-standing mystery1. A central question is how coherent electronic states, or quasiparticles, emerge from the antiferromagnetic insulator with doping. Recent quantum oscillation experiments on lightly doped copper oxides have shown evidence for small pockets of Fermi surface2,3,4,5, the formation of which has been associated with the opening of the pseudogap—an anisotropic gap in the normal state excitation spectrum of unknown origin1. As the doping is increased, experiments suggest that the full Fermi surface is restored6,7, although the doping level at which the pseudogap closes and the nature of the electronic ground state beyond this point have yet to be determined. Here we report the observation of quantum oscillations in the overdoped superconductor Tl2Ba2CuO6+δ that show the existence of a large Fermi surface of well-defined quasiparticles covering two-thirds of the Brillouin zone. These measurements confirm that, in overdoped superconducting copper oxides, coherence is established at all Fermi wavevectors, even near the zone boundary where the pseudogap is maximal and electronic interactions are strongest; they also firmly establish the applicability of a generalized Fermi-liquid picture on the overdoped side of the superconducting phase diagram.