Europhys. Lett., 70 (2), pp. 225-231 (2005)
DOI: 10.1209/epl/i2004-10480-2

Infrared properties of electron-doped cuprates: Tracking normal-state gaps and quantum critical behavior in _2-xx

A. Zimmers¹, J. M. Tomczak¹, R. P. S. M. Lobo¹, N. Bontemps¹, C. P. Hill², M. C. Barr², Y. Dagan², R. L. Greene², A. J. Millis³ and C. C. Homes<sup>4

1</sup>  Laboratoire de Physique du Solide (UPR 5 CNRS) ESPCI 10 rue Vauquelin, 75005 Paris, France
²  Center for Superconductivity Research, Department of Physics University of Maryland - College Park, MD 20742, USA
³  Physics Department, Columbia University - New York, NY 10027, USA
⁴  Department of Physics, Brookhaven National Laboratory Upton, NY 11973, USA

lobo@espci.fr

received 30 November 2004; accepted in final form 25 February 2005
published online 18 March 2005

Abstract
We report the temperature dependence of the infrared-visible conductivity of _2-xx thin films. When varying the doping from a non-superconducting film (x=0.11) to a superconducting overdoped film (x=0.17), we observe, up to optimal doping (x=0.15), a partial gap opening. The magnitude of this gap extrapolates to zero for . A model combining a spin density wave gap and a frequency- and temperature-dependent self-energy reproduces our data reasonably well, suggesting the coexistence of magnetism and superconductivity in this material and the existence of a quantum critical point at this concentration.

PACS
74.25.Gz - Optical properties.
74.72.Jt - Other cuprates, including Tl and Hg-based cuprates.
75.30.Fv - Spin-density waves.

© EDP Sciences 2005