Upper critical field in the electron-doped layered superconductor ZrNCl0.7: Magnetoresistance studies

Abstract

We report magnetoresistance measurements of layered superconductor ZrNCl0.7 at high magnetic fields (H) as high as 27T and temperatures (T) as low as 0.5K. The T dependence of the upper critical field Hc2(T) for Hc and Hc was obtained. Hc2(T) starts to increase with a gentle slope near Tc(0) followed by a steep slope with decreasing T, implying the dimensional crossover of the interplane coherence length from three dimensional to two dimensional (2D). The Hc2(T) is found to be anisotropic for the field direction, where the slope of Hc2′=(dHc2 dT) near H1T can be estimated as Hc2′-22.1kOeK and Hc2′-4.9kOeK for Hc and Hc, respectively. The obtained anisotropy parameter γ4.5 gives evidence for the 2D characteristic of the superconducting state in ZrNCl0.7. © 2005 The American Physical Society.