1106.2283 (L. Jiao et al.)

Upper critical field and thermally activated flux flow in single
crystalline Tl$_{0.58}$Rb$_{0.42}$Fe$_{1.72}$Se$_2$    [PDF]

L. Jiao, Y. Kohama, J. L. Zhang, H. D. Wang, B. Maiorov, F. F. Balakirev, Y. Chen, L. N. Wang, T. Shang, M. H. Fang, H. Q. Yuan

The upper critical field $\mu_0H_{c2}(T_c)$ of
Tl$_{0.58}$Rb$_{0.42}$Fe$_{1.72}$Se$_2$ single crystals has been determined by
means of measuring the electrical resistivity in both a pulsed magnetic field
($\sim$60T) and a DC magnetic field ($\sim$14T). It is found that $H_{c2}$
linearly increases with decreasing temperature for $\textbf{H}$$\parallel$$c$,
reaching $\mu_0H_{c2}^{\textbf{H}\parallel c}(0\textrm{K})\simeq60$ T. On the
other hand, a larger $\mu_0H_{c2}(0\textrm{K})$ with a strong convex curvature
is observed for $\textbf{H}$$\perp$$c$ ($\mu_0H_{c2}^{\textbf{H}\perp
c}$(18K)$\simeq$60T). This compound shows a moderate anisotropy of the upper
critical field around $T_c$, but decreases with decreasing temperature.
Analysis of the upper critical field based on the Werthamer-Helfand-Hohenberg
(WHH) method indicates that $\mu_0H_{c2}(0\textrm{K})$ is orbitally limited for
$\textbf{H}$$\parallel$$c$, but the effect of spin paramagnetism may play an
important role on the pair breaking for $\textbf{H}$$\perp$$c$. All these
experimental observations remarkably resemble those of the iron pnictide
superconductors, suggesting a unified scenario for the iron-based
superconductors. Moreover, the superconducting transition is significantly
broadened upon applying a magnetic field, indicating strong thermal fluctuation
effects in the superconducting state of
Tl$_{0.58}$Rb$_{0.42}$Fe$_{1.72}$Se$_2$. The derived thermal activation energy
for vortex motion is compatible with those of the 1111-type iron pnictides.

View original: http://arxiv.org/abs/1106.2283