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We report a possible coexistence of nontrivial topology and antiferromagnetism in the newly discovered compounds EuCdBi 2 , with magnetic Eu layer locating above and below Bi square net. The X-ray diffraction on single crystals and powder indicats that this 112-type material crystalizes in space group of I 4 / m m m , the same as SrMnBi 2 and EuMnBi 2 . Our combined measurements of magnetization, electrical transport and specific heat consistently reveal antiferromagnetic (AFM) transition of Eu 2 + moments at T N = 20 K. The Eu moments are not saturated under a field of 7 T at 1.8 K. The anisotropic susceptibility suggests the Eu moments lie in the a b plane, and a metamagnetic (MM) transition is observed near 1 T below T N . Large positive magnetoresistance (MR) present for both H   ‖   a b and H   ‖   c , which are considered to contain part contributions from Dirac bands. Hall measurements show the electron-hole compensation effect is prominent above 100 K, with a crossover of Hall resistance from negative to positive values at ∼150 K. The fitted mobility of electrons is as high as 3250 cm 2 V − 1 S − 1 at 1.8 K. Interestingly, the rapid increase of carrier density and suppression of mobility appear at around T N , indicating non-negligible interaction between Eu moments and electron/hole bands. EuCdBi 2 may provide a new platform to investigate the interplay of topological bands and antiferromagnetic order. [ABSTRACT FROM AUTHOR]

We present a broadband optical-conductivity study of superconducting single-crystalline EuFe [ABSTRACT FROM AUTHOR]

We report electrical and magnetic measurements of an optimally doped Eu(Fe0.88Ir0.12)2As2 crystal which shows superconductivity at Tsc = 22 K and magnetic ordering of the Eu2+ spins below 20 K. The results suggest that the Eu2+ spins lie flat ferromagnetically in the ab plane at Tabm = 20 K, and then tilt toward the c-axis at Ttiltm = 17.4 K. The isothermal magnetization loop at low temperatures shows both ferromagnetic behavior and superconducting characteristics, unambiguously demonstrating the coexistence of ferromagnetism and superconductivity. The upper critical field measured is remarkably reduced, as compared to other Fe-based superconductors with the same Tsc, and it exhibits abnormal temperature dependence featured by the existence of an inflection point around Tabm, where the anisotropy ratio γ (≡ H∥abc2/H∥cc2) shows a minimum value smaller than 1.0. These observations can be explained by a ferromagnetic exchange field of ∼30 T which tilts its direction toward the c-axis below Ttiltm. The strong internal field, much higher than the intrinsic lower critical field expected, leads to the absence of Meissner state, which is confirmed by the magnetic measurements under ultra-low fields. [ABSTRACT FROM AUTHOR]

In this study, we measure the in-plane transport properties of high-quality Ba(Fe0.914Co0.086)2As2 single crystals. Signatures of vortex unbinding Berezinskii–Kosterlitz–Thouless (BKT) transition are shown from both the conventional approach and the Fisher–Fisher–Huse dynamic scaling analysis, in which a characteristic Nelson–Kosterlitz jump is demonstrated. We also observe a non-Hall transverse signal exactly at the superconducting transition, which is explained in terms of guided motion of unbound vortices. [ABSTRACT FROM AUTHOR]