Upper critical field of isoelectron substituted SrFe$_2$(As$_{1-x}$P$_x$)$_2

• Main Authors: Yeninas, S, Tanatar, M. A, Murphy, J, Strehlow, C. P, Ayala-Valenzuela, O. E, McDonald, R. D, Welp, U, Kwok, W. K, Kobayashi, T, Miyasaka, S, Tajima, S, Prozorov, R
• Format: Journal Article
• Language: English
• Published: 25-01-2013
• Subjects: Physics - Superconductivity
• DOI: 10.48550/arxiv.1301.6142

Phys. Rev. B 87, 094503 (2013) The upper critical field $H_{c2}$ of optimally doped iron-based
superconductor SrFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ ($x$ = 0.35, $T_c$ = 25 K)
was measured as a function of temperature down to 1.6 K for two principal
directions of magnetic field $H \parallel c$ and $H \parallel a$. Measurements
were performed in pulsed magnetic fields up to 65 T using a tunnel-diode
resonator technique on as-grown and heavy-ion irradiated single crystals, with
columnar defect density corresponding to a matching field $B\phi$ = 25 T. The
$H_{c2,c}(T)$ is close to $T$-linear, while clear saturation is observed for
$H_{c2,a}(T)$, leading to a strongly temperature dependent anisotropy parameter
$\gamma$. The linear shape of $H_{c2,c}(T)$ is very similar to that observed in
nodal KFe$_2$As$_2$ but very different from full-gap LiFeAs. Irradiation does
not introduce any additional features on $H_{c2}(T)$ line corresponding to the
matching field. Instead, it suppresses uniformly both $T_c$ and $H_{c2}$,
keeping their ratio constant.