High pressure growth and electron transport properties of superconducting SmFeAsO_1−xH_x single crystals

Abstract

We report the single crystal growth and characterization of the highest T c ironbased superconductor SmFeAsO 1−x H x . Some sub-millimeter-sized crystals were grown using the mixture flux of Na 3 As + 3NaH + As at 3.0 GPa and 1473 K. The chemical composition analyses confirmed 10% substitution of hydrogen for the oxygen site (x = 0.10), however, the structural analyses suggested that the obtained crystal forms a multidomain structure. By using the FIB technique we fabricated the single domain SmFeAsO 0.9 H 0.10 crystal with the T c of 42 K, and revealed the metallic conduction in in-plane (ρ ab ), while semiconducting in the out-of-plane (ρ c ). From the in-plane Hall coefficient measurements, we confirmed that the dominant carrier of SmFeAsO 0.9 H 0.10 crystal is an electron, and the hydride ion occupied at the site of the oxygen ion effectively supplies a carrier electron per iron following the equation: O 2− → H − + e − . S. Iimura et al., Particularly, the iron pnictides family consists of various structures by inserting alkali metal cation, alkaline earth metal cation, positively charged PbO-type layer, or perovskite-type block between the FePn layers to compensate the neutrality. A prototypical REFeAsO-type (RE = rare earth) material, abbreviated as 1111-type, crystallizes in a tetragonal lattice at room temperature (space group P4/nmm, a ~ 4 Å, c ~ 8-9 Å, and Z = 2), in which the conducting [FeAs] − and insulating [REO] + layers stack alternately along the crystallographic c axis (Fig. 1a). On cooling, they undergo a tetragonal-orthorhombic transition at T ~ 150 K, accompanying a paramagneticantiferromagnetic (PM-AFM) transition just below the structural transition temperature [4,5]. Superconductivity appears if the AFM is suppressed by doping carriers or applying pressure (see x = 0 in Fig. 1b).Carrier doping mode in 1111-type is categorized into four from a view of doping site and carrier polarity. Substitution for the site in conducting layer is called "direct doping", while that in insulating layer is called "indirect doping". Among those methods, the indirect electron doping has intensively been studied because it induces

Anisotropy of the transport properties of NdFeAs(O,F) thin films grown on vicinal substrates

“…under-doped regime) 10 , and LiFeAs 8 . For all OP samples, on the other hand, the temperature-dependent ρ c (T ) was metallic, which differs from the reports on PrFeAsO 0.7 12 , SmFeAs(O,F) 13 and SmFeAsO 0.9 H 0.1 14 single crystals. To identify the reason of this difference, it is desired to measure ρ c (T ) using NdFeAs(O,F) single crystals.…”

High Jc and low anisotropy of hydrogen doped NdFeAsO superconducting thin film

“…1d). It is reported that the c-axis lattice parameter decreases with increasing hydrogen content x in LnFeAsO1-xHx [7,10,11] with a rate of Dc/Dx~-2-3×10 -3 Å/at.%. The lattice parameter c of our NdFeAs(O,H) film determined by x-ray diffraction (XRD) was 8.437±0.003 Å, which also supports the lattice shrinkage due to hydrogen doping although the value was slightly shorter than the average value evaluated from TEM.…”

“…The growth of LnFeAs(O,H) opens new opportunities to explore how heavily electron doping influences the superconducting properties. However, most of the studies have been carried out on polycrystals [7,8] or tiny single crystals [10], on which measurements of the transport critical current density are rather complicated. The successful growth of LnFeAs(O,H) epitaxial thin films gives a great opportunity to explore the intrinsic physical properties by electrical transport measurements especially for critical current characteristics, since thin films are the ideal platform for such investigations.…”

Superconductivity at 48 K of heavily hydrogen-doped SmFeAsO epitaxial films grown by topotactic chemical reaction using CaH2

“…Although small size crystals with maximum at ~400 μm were reported recently [14], it is very difficult to grow enough large-size single crystals of H-doped Sm1111, which restricts further detailed investigations on the superconducting mechanism and the electronic band structure by experimental methods such as angle-resolved photoemission spectroscopy.…”