1202.5011 (Eundeok Mun et al.)

Anisotropic $H_{c2}$ determined up to 92 T and the signature of
multi-band superconductivity in
Ca$_{10}$(Pt$_{4}$As$_{8}$)((Fe$_{1-x}$Pt$_{x}$)$_{2}$As$_{2}$)$_{5}$
superconductor    [PDF]

Eundeok Mun, Ni Ni, Jared M. Allred, Robert J. Cava, Oscar Ayala, Ross D. McDonald, Neil Harrison, Vivien S. Zapf

The upper critical fields, $H_{c2}$($T$), of single crystals of the
superconductor
Ca$_{10}$(Pt$_{4-\delta}$As$_{8}$)((Fe$_{0.97}$Pt$_{0.03}$)$_{2}$As$_{2}$)$_{5}$
($\delta$ $\approx$ 0.246) are determined over a wide range of temperatures
down to $T$ = 1.42 K and magnetic fields of up to $\mu_{0}H$ $\simeq$ 92 T. The
measurements of anisotropic $H_{c2}$($T$) curves are performed in pulsed
magnetic fields using radio-frequency contactless penetration depth
measurements for magnetic field applied both parallel and perpendicular to the
\textbf{ab}-plane. Whereas a clear upward curvature in
$H_{c2}^{\parallel\textbf{c}}$($T$) along \textbf{H}$\parallel$\textbf{c} is
observed with decreasing temperature, the $H_{c2}^{\parallel\textbf{ab}}$($T$)
along \textbf{H}$\parallel$\textbf{ab} shows a flattening at low temperatures.
The rapid increase of the $H_{c2}^{\parallel\textbf{c}}$($T$) at low
temperatures suggests that the superconductivity can be described by two
dominating bands. The anisotropy parameter, $\gamma_{H}$ $\equiv$
$H_{c2}^{\parallel\textbf{ab}}/H_{c2}^{\parallel\textbf{c}}$, is $\sim$7 close
to $T_{c}$ and decreases considerably to $\sim$1 with decreasing temperature,
showing rather weak anisotropy at low temperatures.

View original: http://arxiv.org/abs/1202.5011