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Phys. Rev. Lett. 94, 147004 (2005) [4 pages]

Delocalized Fermions in Underdoped Cuprate Superconductors

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Mike Sutherland1,*, S. Y. Li2, D. G. Hawthorn1,†, R. W. Hill1,‡, F. Ronning1,§, M. A. Tanatar1,**, J. Paglione1,††, H. Zhang1, Louis Taillefer1,2,4, J. DeBenedictis3, Ruixing Liang3,4, D. A. Bonn3,4, and W. N. Hardy3,4
1Department of Physics, University of Toronto, Toronto, Ontario, Canada
2Département de physique et Regroupement Québécois sur les Matériaux de Pointe, Université de Sherbrooke, Sherbrooke, Québec, Canada
3Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada
4Canadian Institute for Advanced Research, Toronto, Ontario, Canada

Received 8 November 2004; published 14 April 2005

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.

© 2005 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.94.147004
DOI:
10.1103/PhysRevLett.94.147004
PACS:
74.25.Fy, 74.72.Bk, 74.72.Dn

*Present address: Cavendish Laboratory, University of Cambridge, Cambridge UK.

†Present address: Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada.

‡Present address: Department of Physics, University of Waterloo, Waterloo, Canada.

§Present address: Los Alamos National Lab, MST-10 Division, Los Alamos, NM, USA.

**Present address: Institute of Surface Chemistry, N.A.S. Ukraine.

††Present address: Department of Physics, University of California, San Diego, La Jolla, CA, USA.

 
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