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  1. Abstract

    Single crystalline BaMnSb2is considered as a 3D Weyl semimetal with the 2D electronic structure containing Dirac cones from the Sb sheet. We report experimental investigation of low-temperature cleaved BaMnSb2surfaces using scanning tunneling microscopy/spectroscopy and low energy electron diffraction. By natural cleavage, we find two terminations: one is Ba (above the orthorhombically distorted Sb sheet) and another Sb2 (at the surface of the Sb/Mn/Sb sandwich layer). Both terminations show the 2 × 1 surface reconstructions, with drastically different morphologies and electronic properties, however. The reconstructed structures, defect types and nature of the electronic structures of the two terminations are extensively studied. The quasiparticle interference (QPI) analysis is conducted at the energy range between −2 V and 2 V, although no interesting states are observed near the Fermi level, the surface-projected electronic band structures strongly depend on the surface termination above 1.6 V. The existence of defects can greatly modify the local density of states to create electronic phase separations on the surface in the order of tens of nm scale. Our observation on the atomic structures of the terminations and the corresponding electronic structures provides critical information towards an understanding of topological properties of BaMnSb2.

  2. A novel antiferromagnetic semiconductor, Eu 3 Sn 2 P 4 , has been discovered. Single crystals of Eu 3 Sn 2 P 4 were prepared using the Sn self-flux method. The crystal structure determined by single crystal X-ray diffraction shows that Eu 3 Sn 2 P 4 crystallizes in the orthorhombic structure with the space group Cmca (Pearson Symbol, oP 216). Six Sn–Sn dimers connected by P atoms form a Sn 12 P 24 crown-shaped cluster with a Eu atom located in the center. Magnetization measurements indicate that the system orders antiferromagnetically below a T N ∼14 K at a low field and undergoes a metamagnetic transition at a high field when T < T N . The effective magnetic moment is 7.41(3) μ B per Eu, corresponding to Eu 2+ . The electric resistivity reveals a non-monotonic temperature dependence with non-metallic behavior below ∼60 K, consistent with the band structure calculations. By fitting the data using the thermally activated resistivity formula, we estimate the energy gap to be ∼0.14 eV. Below T N , the resistivity tends to saturate, suggesting the reduction of charge-spin scattering.