We investigated the transport properties of BaFe 2 As 2 single crystals before and after annealing with BaAs powder. The annealing remarkably improves transport properties, in particular, the magnitude of residual resistivity, which decreases by a factor of more than 10. From the resistivity measurement on detwinned crystals, we found that the anisotropy of the in-plane resistivity is remarkably diminished after annealing, indicative of dominant contributions to the charge transport from the carriers with isotropic and high mobility below magnetostructural transition temperature T s and the absence of nematic state above T s . We found that the Hall resistivity shows strong nonlinearity against magnetic field, and the magnetoresistance becomes very large at low temperatures. These results give evidence for the manifestation of multiple carriers with distinct characters in the ordered phase below T s . By analyzing the magnetic-field dependences, we found that at least three carriers equally contribute to the charge transport in the ordered phase, which is in good agreement with the results of recent quantum oscillation measurements.

The kagome-bilayer material Fe(3)Sn(2) has recently been shown to be an example of a rare class of magnet-a frustrated ferromagnetic metal. While the magnetism of Fe(3)Sn(2) appears to be relatively simple at high temperature, with localized moments parallel to the c-axis (T(C) = 640 K), upon cooling the competing exchange interactions and spin frustration become apparent as they cause the moments to become non-collinear and to rotate towards the kagome plane, forming firstly a canted ferromagnetic structure and then a re-entrant spin glass (T(f) approximately equal 80 K). In this work we show that Fe(3)Sn(2) possesses an unusual anomalous Hall effect. The saturated Hall resistivity of Fe(3)Sn(2) is 3.2 µΩ cm at 300 K, almost 20 times higher than that of typical itinerant ferromagnets such as Fe and Ni. The anomalous Hall coefficient R(s) is 6.7 × 10(-9) Ω cm G(-1) at 300 K, which is three orders of magnitude larger than that of pure Fe, and obeys an unconventional scaling with the longitudinal resistivity, ρ(xx), of R(s) is proportional to ρ(xx)(3.15). Such a relationship cannot be explained by either the conventional skew or side-jump mechanisms, indicating that the anomalous Hall effect in Fe(3)Sn(2) has an extraordinary origin that is presumed to be related to the underlying frustration of the magnetism. These findings demonstrate that frustrated ferromagnets, whether based on bulk materials or on artificial nanoscale structures, can provide new routes to room temperature spin-dependent electron transport properties suited to application in spintronics.

We have performed electrical resistivity measurements of a polycrystalline sample of FeSe 0.25 Te 0.75 , which exhibits superconductivity at T c ∼ 14 K, in magnetic fields up to 55 T to determine the upper critical field µ 0 H c2 . In this compound, very large slopes of µ 0 H c2 at the onset, the mid-point, the zero-resistivity temperatures on superconductivity are determined to be −13.7, −10.1, and −6.9 T/K, respectively. The observed µ 0 H c2 (T )s of this compound are considerably smaller than those expected from the Werthamer-Helfand-Hohenberg model, manifesting the Pauli limiting behavior. These results suggest that this compound has a large Maki parameter, but it is smaller than that calculated for a weakcoupling superconductor, indicating a large superconducting gap of this compound as a strong-coupling superconductor.Recent discovery of superconductivity at T c = 26 K in the iron-based LaFeAsO 1−x F x 1 (abbreviated as the 1111-system) has attracted a considerable attention of condensed matter scientists due to an unusual interplay of superconductivity and magnetism arising from ubiquitous magnetic element Fe. In general, it has been believed that materials containing the magnetic elements are difficult to occur the superconductivity. By substitution of La atoms for other lanthanoid atoms, T c increases with increasing lanthanoid atomic number and shows a maximum value of T c = 55 K for Sm atoms. As well as the CuO 2 layers in the high-T c cuprate superconductors, the Fe-P n (P n = P, As) layers in iron oxypnictides are responsible for the superconductivity, and the Ln-O (Ln = lanthanoid) layers provide charge carriers.The electrical structure of a high-T c cuprate superconductor has been explained by the single band model, but it is difficult to understand the mechanism of its superconductivity due to the strongly electron correlation effects. While the electron correlation on an iron-based su- *

Unconventional features of relativistic Dirac/Weyl quasi-particles in topological materials are most evidently manifested in the 2D quantum Hall effect (QHE), whose variety is further enriched by their spin and/or valley polarization. Although its extension to three dimensions has been long-sought and inspired theoretical proposals, material candidates have been lacking. Here we have discovered valley-contrasting spin-polarized Dirac fermions in a multilayer form in bulk antiferromagnet BaMnSb 2 , where the out-of-plane Zeeman-type spin splitting is induced by the in-plane inversion symmetry breaking and spin-orbit coupling (SOC) in the distorted Sb square net. Furthermore, we have observed well-defined quantized Hall plateaus together with vanishing interlayer conductivity at low temperatures as a hallmark of the half-integer QHE in a bulk form.The Hall conductance of each layer is found to be nearly quantized to 2(N+1/2)e 2 /h with N being the Landau index, which is consistent with two spin-polarized Dirac valleys protected by the strong spin-valley coupling. arXiv:2001.08683v1 [cond-mat.str-el] 23 Jan 2020 Researches of topological materials have currently been one of the central topics of the condensed matter physics. Their topologically non-trivial electronic structure leads to the relativistic quasiparticles, Dirac/Weyl fermions, whose most prominent feature is seen in QHE in 2D systems[1], such as the relativistic QHE in graphene[2, 3] and topological insulator films[4]. The half-integer quantization of the Hall plateaus and the zero-energy Landau level forming at the charge neutral Dirac point were experimentally clarified, which are associated with the Berry phase of Dirac fermions and hence have no analog in conventional 2D systems. More recently, the variety of QHE in topological materials has been further expanded by utilizing the spin and/or valley polarization in the system[5-19K21851, JP19H05173) and the Asahi Glass Foundation. The synchrotron radiation experiments were performed at the BL25SU of SPring-8 with the approval of the Japan Synchrotron

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