Suppression of Magnetic Order by Pressure in BaFe2As2

We performed the dc resistivity and the ZF 75As-NMR measurement of BaFe2As2 under high pressure. The T-P phase diagram of BaFe2As2 determined from resistivity anomalies and the ZF 75As-NMR clearly revealed that the SDW anomaly is quite robust against P.Comment: 2 pages, 2 figure

Microwave Penetration Depth and Quasiparticle Conductivity in PrFeAsO_1-y Single Crystals : Evidence for a Full-Gap Superconductor

In-plane microwave penetration depth $\lambda_{ab}$ and quaiparticle conductivity at 28 GHz are measured in underdoped single crystals of the Fe-based superconductor PrFeAsO$_{1-y}$ ($T_c\approx 35$ K) by using a sensitive superconducting cavity resonator. $\lambda_{ab}(T)$ shows flat dependence at low temperatures, which is incompatible with the presence of nodes in the superconducting gap $\Delta({\bf k})$. The temperature dependence of the superfluid density demonstrates that the gap is non-zero ($\Delta/k_BT_c\gtrsim 1.6$) all over the Fermi surface. The microwave conductivity below $T_c$ exhibits an enhancement larger than the coherence peak, reminiscent of high-$T_c$ cuprate superconductors.Comment: 4 pages, 3 figures. Version accepted for publication in Phys. Rev. Lett. For related results of hole-doped 122 system, see arXiv:0810.350

Uniform Mixing of High-Tc Superconductivity and Antiferromagnetism on a Single CuO2 Plane in Hg-based Five-layered Cuprate

We report a site selective Cu-NMR study on under-doped Hg-based five-layered high-$T_{\rm c}$ cuprate HgBa2Ca4Cu5Oy with a Tc=72 K. Antiferromagnetism (AF) has been found to take place at TN=290 K, exhibiting a large antiferromagnetic moment of 0.67-0.69uB at three inner planes (IP's). This value is comparable to the values reported for non-doped cuprates, suggesting that the IP may be in a nearly non-doped regime. Most surprisingly, the AF order is also detected with M(OP)=0.1uB even at two outer planes (OP's) that are responsible for the onset of superconductivity (SC). The high-Tc SC at Tc = 72 K can uniformly coexist on a microscopic level with the AF at OP's. This is the first microscopic evidence for the uniform mixed phase of AF and SC on a single CuO2 plane in a simple environment without any vortex lattice and/or stripe order.Comment: 4 pages, 4 figures. To be published in Phys.Rev.Let

A New Iron Pnictide Oxide (Fe2As2)(Ca5(Mg,Ti)4Oy) and a New Phase in Fe-As-Ca-Mg-Ti-O system

A new layered iron arsenide oxide (Fe2As2)(Ca5(Mg,Ti)4Oy) and its structural derivative were found in the Fe-As-Ca-Mg-Ti-O system. The crystal structure of (Fe2As2)(Ca5(Mg,Ti)4Oy) is identical to that of (Fe2As2)(Ca5(Sc,Ti)4Oy), which was reported in our previous study. The lattice constants of this compound are a = 3.86(4) A and c = 41.05(2) A. In addition, another phase with a thicker blocking layer was found. The structure of the compound and its derivative was tentatively assigned through STEM observation as (Fe2As2)(Ca8(Mg,Ti)6Oy) with sextuple perovskite-type sheets divided by a rock salt layer. The interlayer Fe-Fe distance of this compound is ~30 A. The compound and its derivative exhibited bulk superconductivity, as found from magnetization and resistivity measurements.Comment: 9 pages, 7 figure