title: Delocalized fermions in underdoped cuprate superconductors.
abstract: Low-temperature heat transport was used to investigate the ground state of high-purity single crystals of the lightly doped cuprate YBa2Cu3O6.33. Samples were measured with doping concentrations on either side of the superconducting phase boundary. We report the observation of delocalized fermionic excitations at zero energy in the nonsuperconducting state, which shows that the ground state of underdoped cuprates is a thermal metal. Its low-energy spectrum appears to be similar to that of the d-wave superconductor, i.e., nodal. The insulating ground state observed in underdoped La2-xSrxCuO4 is attributed to the competing spin-density-wave order.
authors.affiliation: Department of Physics, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Mike
authors.initials: M
authors.lastname: Sutherland
authors.forename: S Y
authors.initials: SY
authors.lastname: Li
authors.forename: D G
authors.initials: DG
authors.lastname: Hawthorn
authors.forename: R W
authors.initials: RW
authors.lastname: Hill
authors.forename: F
authors.initials: F
authors.lastname: Ronning
authors.forename: M A
authors.initials: MA
authors.lastname: Tanatar
authors.forename: J
authors.initials: J
authors.lastname: Paglione
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: Louis
authors.initials: L
authors.lastname: Taillefer
authors.forename: J
authors.initials: J
authors.lastname: DeBenedictis
authors.forename: Ruixing
authors.initials: R
authors.lastname: Liang
authors.forename: D A
authors.initials: DA
authors.lastname: Bonn
authors.forename: W N
authors.initials: WN
authors.lastname: Hardy