Europhys. Lett.
Volume 70, Number 2, April 2005
Page(s) 225 - 231
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 18 March 2005
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 $\chem{Pr}$2-x$\chem{Ce}$x $\chem{CuO_4}$

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. Homes4

1  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

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

We report the temperature dependence of the infrared-visible conductivity of $\chem{Pr}$2-x$\chem{Ce}$x $\chem{CuO_4}$ 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 $x\sim0.17$. 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 $\chem{Ce}$ concentration.

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