Transport Properties of the Iron-based Superconductor SrFe 2 (As,P) 2 in High Magnetic Fields
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Transport Properties of the Iron-based Superconductor SrFe2 (As,P)2 in High Magnetic Fields T. Kida · T. Kobayashi · S. Miyasaka · S. Tajima · M. Hagiwara
Received: 10 June 2012 / Accepted: 24 September 2012 / Published online: 3 October 2012 © Springer Science+Business Media New York 2012
Abstract We have investigated the resistive upper critical field (μ0 Hc2 ) of the ironbased superconductor SrFe2 (As1−x Px )2 (x = 0.35, Tc ∼ 29 K) in pulsed high magab (T ) exhibits the Werthamer-Helfandnetic fields of up to 52 T. For H ab, μ0 Hc2 c (T ) is almost linear against Hohenberg (WHH) like behavior. While, for H c, μ0 Hc2 T and exhibits a slightly upward curvature near Tc . The anisotropy of μ0 Hc2 decreases from 2.5 near Tc to ∼1.2 at T = 0 K monotonically. Similar isotropic behavior of μ0 Hc2 at low temperatures has also been observed in the Fe1+δ (Te,Se). We demonstrate the results of the two-band analysis for μ0 Hc2 (T ) on the present sample and discuss the anisotropy of μ0 Hc2 by comparing with those in some kinds of iron-based superconductors. Keywords Iron-based superconductors · Upper critical field · High magnetic fields
1 Introduction The discovery of high-Tc superconductivity in the iron-pnictide LaFeAs(O,F) [1] and related compounds has generated great interest in understanding the interplay of magnetism, superconductivity, and electronic structure. In most cases, the superconductivity is induced by charge doping into a stoichiometric parent compound which shows a collinear antiferromagnetic spin-density-wave (SDW) ground state [2]. For T. Kida () · M. Hagiwara KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan e-mail: [email protected] T. Kida e-mail: [email protected] T. Kobayashi · S. Miyasaka · S. Tajima Dep. Phys., Grad. Sch. Sci., Osaka University, Toyonaka, Osaka 560-0043, Japan
J Low Temp Phys (2013) 170:346–351
347
example, superconductivity in AFe2 As2 (abbreviated as the 122-system, A = alkali earth metals) is induced by hole-doping (K substitution for A) and electron-doping (Co substitution for Fe). Recently, it has been reported that substitution of isovalent P for As in the 122-system, such as AFe2 (As,P)2 (A = Ba,Sr), suppresses the SDW state and induces superconductivity without charge doping [3, 4]. The zero field resistivity of the optimally doped AFe2 (As,P)2 exhibits T -linear dependence in a wide temperature range above Tc [3–5], suggesting that a non-Fermi-liquid behavior is caused by quantum critical magnetic fluctuations close to an antiferromagnetic quantum critical point. The isovalent substituted 122-system is suitable for studying the intrinsic nature of high-Tc superconductivity in iron-based superconductors, and quantum critical phenomena in the boundary between the SDW and the superconducting states, because it is very clean, as demonstrated by the observed quantum oscillations [6]. In this study, we performed electrical resistivity measurements on a single crystal of SrFe2 (As0.65 P0.35 )2 (Tc ∼ 29 K) in high magnetic fields of up to 52 T t
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