ABSTRACT:We report the first nitrogen-containing iron-pnictide superconductor ThFeAsN, which is synthesized by a solid-state reaction in an evacuated container. The compound crystallizes in a ZrCuSiAs-type structure with the space group P4/nmm and lattice parameters a=4.0367(1) Å and c=8.5262(2) Å at 300 K. The electrical resistivity and dc magnetic susceptibility measurements indicate superconductivity at 30 K for the nominally undoped ThFeAsN.The discovery of high-temperature superconductivity in iron based compounds 1,2 triggered enormous researches, and a lot of progresses in material and mechanism aspects have been achieved. [3][4][5] Remarkably, dozens of Fe-based superconductors (FeSCs) were discovered, which can be classified into several crystallographic types. 5 All these FeSCs necessarily contain anti-fluorite-like Fe 2 X 2 (X denotes a pnictogen or a chalcogen element) layers. Another important feature for FeSCs is that the high-temperature superconductivity is mostly induced by suppressing the spin-density wave (SDW) order in a parent compound, typically through chemical dopings or applying pressures.The (Ref. 13 ). Note that the valence of the A-site cations is either 3+ or 2+. We previously succeeded in doping a tetravalent Th 4+ ion into the A site, 9,14 which produces superconductivity with a T c up to 56 K. 9 To expand the FeSC spectrum and, possibly to further increase the T c , it is of great interest to explore a possible A 4+ Z 3 combination for the fluorite-like spacer layer in the 1111 system. and AeFX (X=Cl, Br, I). 18 This structural relation suggests that iron pnictide containing [Th 2 N 2 ] 2+ layers could be thermodynamically stable. In this Communication, we report our successful synthesis of the target material, ThFeAsN, using solid-state reactions at high temperatures. The as-prepared sample shows bulk superconductivity at 30 K without any deliberate oxygen doping.In general, nitrides are synthetically challenging, presumably because of the potential oxygen incorporation. Therefore, the precursors of Th 3 N 4 , Th metal and FeAs are carefully synthesized avoiding oxygen contamination as far as possible. First, thorium powders were produced by the reduction of thorium oxide with metal calcium. 19 The yielded thorium metal powder was consolidated into a button with silver luster using an arc furnace. After that, the button was scraped in a glove box filled with argon (99.9999%) to get clean thorium powder. Then, nearly monophasic Th 3 N 4 (possibly with trace ThN) was synthesized by the reaction with 20% excess high-purity nitrogen gas (99.999%) at 1000 C for 24 hours in an evacuated quartz ampoule. FeAs was prepared by heating the mixture of iron (99.99%) and arsenic (99.999%) powders in an evacuated quartz ampoule at 700 C for 48 hours. All the precursors had been checked by X-ray diffractions (XRD) before using [figures S1 and S2 in the Supporting Information (SI)]. Similarly, the solid-state reaction of the stoichiometric mixture of Th 3 N 4 , Th and FeAs was also carried o...

We give a further investigation of the range criterion and Low-to-High Rank Generating Mode (LHRGM) introduced in [17], which can be used for the classification of 2 × M × N states under reversible local filtering operations. By using of these techniques, we entirely classify the family of 2 × 4 × 4 states, which actually contains infinitely many kinds of states. The classifications of true entanglement of 2 × (M + 3) × (2M + 3) and 2 × (M + 4) × (2M + 4) systems are briefly listed respectively.

Mn-based ZrCuSiAs-type pnictides ThMnPnN (Pn = P, As) containing PbO-type Th 2 N 2 layers were synthesized. The crystal and magnetic structures are determined using X-ray and neutron powder diffraction. While neutron diffraction indicates a C-type antiferromagnetic state at 300 K, the temperature dependence of the magnetic susceptibility shows cusps at 36 and 52 K respectively for ThMnPN and ThMnAsN. The susceptibility cusps are ascribed to a spontaneous antiferromagneticto-antiferromagnetic transition for Mn 2+ moments, which is observed for the first time in Mn-based ZrCuSiAs-type compounds. In addition, measurements of the resistivity and specific heat suggest an abnormal increase in the density of states at the Fermi energy. The result is discussed in terms of the internal chemical pressure effect.

ThFeAsN O ([Formula: see text]) system with heavy electron doping has been studied by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility and specific heat. The non-doped compound exhibits superconductivity at [Formula: see text] K, which is possibly due to an internal uniaxial chemical pressure that is manifested by the extremely small value of As height with respect to the Fe plane. With the oxygen substitution, the T value decreases rapidly to below 2 K for [Formula: see text], and surprisingly, superconductivity re-appears in the range of [Formula: see text] with a maximum [Formula: see text] of 17.5 K at x  =  0.3. For the normal-state resistivity, while the samples in intermediate non-superconducting interval exhibit Fermi liquid behavior, those in other regions show a non-Fermi-liquid behavior. The specific heat jump for the superconducting sample of x  =  0.4 is [Formula: see text], which is discussed in terms of anisotropic superconducting gap. The peculiar phase diagram in ThFeAsN O presents additional ingredients for understanding the superconducting mechanism in iron-based superconductors.

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