Upper critical field, Hall effect and magnetoresistance in the iron-based layered superconductor LaO$_{0.9}$F$_{0.1-δ}$FeAs

Abstract

By using a two-step method, we successfully synthesized the iron based new superconductor LaO$_{0.9}$F$_{0.1-\delta}$FeAs. The resistive transition curves under different magnetic fields were measured, leading to the determination of the upper critical field $H_{c2}^{ab}(T)$ of this new superconductor. The value of $H_{c2}^{ab}$ at zero temperature is estimated to be about 50 Tesla, corresponding to $\xi_{ab}\approx 80 \AA$ and $\xi_{c}\approx 8 \AA$ assuming an anisotropy of about 10. In addition, the Hall effect and magnetoresistance were measured in wide temperature region. A negative Hall coefficient R_H$ has been found implying a dominant conduction by electron-like charge carriers in this material. The charge carrier density determined at 100K is about 9.8E20/cm^3, which is close to the cuprate superconductors. It is further found that the magnetoresistance does not follow the Kohler's law. Meanwhile, the Hall coefficient, the resistivity at 0T, and magnetoresistance all have an anomalous property at about 240K, which may be induced by the multi-band effect or by some exotic scattering mechanism.