Issue
EPL
Volume 84, Number 3, November 2008
Article Number 37005
Number of page(s) 4
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI http://dx.doi.org/10.1209/0295-5075/84/37005
Published online 24 October 2008
EPL, 84 (2008) 37005
DOI: 10.1209/0295-5075/84/37005

Hall coefficient and Hc2 in underdoped LaFeAsO0.95F0.05

Y. Kohama1, 2, Y. Kamihara3, 4, S. Riggs1, F. F. Balakirev1, T. Atake2, M. Jaime1, M. Hirano3, 4 and H. Hosono3, 4

1   MPA-NHMFL, Los Alamos National Laboratory - Los Alamos, NM 87545, USA
2   Materials and Structures Laboratory, Tokyo Institute of Technology - Mail-Box: R3-7, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
3   ERATO-SORST, Japan Science and Technology Agency in Frontier Research Center, Tokyo Institute of Technology - Mail-Box: S2-13, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
4   Frontier Research Center, Tokyo Institute of Technology - Mail-Box: S2-13, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan

ykohama@lanl.gov

received 24 June 2008; accepted in final form 23 September 2008; published November 2008
published online 24 October 2008

Abstract
The electrical resistivity and Hall coefficient of LaFeAsO0.95F0.05 polycrystalline samples were measured in pulsed magnetic fields up to $\mu$0H = 60 T from room temperature to 1.5 K. The resistance of the normal state shows a negative temperature coefficient (d$\rho$ / dT < 0) below 70 K for this composition, indicating insulating ground state in underdoped LaFeAsO system in contrast to heavily doped compound. The charge carrier density obtained from Hall effect can be described as constant plus a thermally activated term with an energy gap $\Delta$ E = 630 K. The upper critical field, Hc2, estimated from resistivity measurements, exceeds 75 T with zero-field Tc = 26.3 K, suggesting an unconventional nature for superconductivity.

PACS
74.25.Fy - Transport properties (electric and thermal conductivity, thermoelectric effects, etc.).
74.70.-b - Superconducting materials.

© EPLA 2008