65 research outputs found

    Optical properties of TlNi2Se2: Observation of pseudogap formation

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    The quasi-two-dimensional nickel chalcogenides TlNi2Se2TlNi_2Se_2 is a newly discovered superconductor. We have performed optical spectroscopy study on TlNi2Se2TlNi_2Se_2 single crystals over a broad frequency range at various temperatures. The overall optical reflectance spectra are similar to those observed in its isostructure BaNi2As2BaNi_2As_2. Both the suppression in R(ω)R(\omega) and the peaklike feature in σ1(ω)\sigma_1(\omega) suggest the progressive formation of a pseudogap feature in the midinfrared range with decreasing temperatures, which might be originated from the dynamic local fluctuation of charge-density-wave (CDW) instability. We propose that the CDW instability in TlNi2Se2TlNi_2Se_2 is driven by the saddle points mechanism, due to the existence of van Hove singularity very close to the Fermi energy.Comment: 5 pages, 4 figure

    Vortex dynamics in phase separated Tl0.58Rb0.42Fe1.72Se2 crystals

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    We report the critical current density Jc and the vortex dynamics in phase-separated Tl0.58Rb0.42Fe1.72Se2 crystals by performing magnetization measurements. Structural investigation reveals micro- and nanoscopic phase separation between 122 (superconducting) and 245 (not superconducting) phases. Micrometric phase separation refers to 245 islands with typical diameters of 2 µm embedded in a multiply-connected 122 superconducting network. Nanoscopic phase separation refers to 245 nanoprecipitates embedded in the 122 superconducting paths. The 245 nanoprecipitates with size comparable to the coherence length produce strong vortex pinning. It was observed that the temperature dependence of the flux creep rate presents a peak at intermediate temperatures and magnetic fields lower than 0.5 T. The peak is systematically suppressed as the magnetic field is increased, and it could be related with relaxation generated by double-kink excitations. Double-kinks are low-energy depinning excitations usually associated with strong pinning produced by correlated disorder.Fil: Haberkorn, Nestor Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Condo, Adriana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Wang, Hangdong. Zhejiang University; China. Hangzhou Normal University; ChinaFil: Mao, Qianhui. Zhejiang University; ChinaFil: Fang, Minghu. Zhejiang University; China. Collaborative Innovation Center of Advanced Microstructures; Chin

    (Sr3La2O5)(Zn1-xMnx)2As2: A Bulk Form Diluted Magnetic Semiconductor isostructural to the "32522" Fe-based Superconductors

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    A new diluted magnetic semiconductor system, (Sr3La2O5)(Zn1-xMnx)2As2, has been synthesized and characterized. 10% Mn substitution for Zn in bulk form (Sr3La2O5)Zn2As2 results in a ferromagnetic ordering below Curie temperature, TC ~ 40 K. (Sr3La2O5)(Zn1-xMnx)2As2 has a layered crystal structure identical to that of 32522-type Fe based superconductors, and represents the fifth DMS family that has a direct counterpart among the FeAs high temperature superconductor families.Comment: Accepted for publication in EP

    Metamagnetic transitions and anomalous magnetoresistance in EuAg4_4As2_2 single crystal

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    In this paper, the magnetic and transport properties were systematically studied for EuAg4_4As2_2 single crystals, crystallizing in a centrosymmetric trigonal CaCu4_4P2_2 type structure. It was confirmed that two magnetic transitions occur at T\textit{T}N1_{N1} = 10 K and T\textit{T}N2_{N2} = 15 K, respectively. With the increasing field, the two transitions are noticeably driven to lower temperature. At low temperatures, applying a magnetic field in the ab\textit{ab} plane induces two successive metamagnetic transitions. For both H\textit{H} \parallel ab\textit{ab} and H\textit{H} \parallel c\textit{c}, EuAg4_4As2_2 shows a positive, unexpected large magnetoresistance (up to 202\%) at low fields below 10 K, and a large negative magnetoresistance (up to -78\%) at high fields/intermediate temperatures. Such anomalous field dependence of magnetoresistance may have potential application in the future magnetic sensors. Finally, the magnetic phase diagrams of EuAg4_{4}As2_{2} were constructed for both H\textit{H} \parallel ab\textit{ab} and H\textit{H} \parallel c\textit{c}

    The suppression of Curie temperature by Sr doping in diluted ferromagnetic semiconductor (La1-xSrx)(Zn1-yMny)AsO

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    (La1-xSrx)(Zn1-yMny)AsO is a two dimensional diluted ferromagnetic semiconductor that has the advantage of decoupled charge and spin doping. The substitution of Sr2+ for La3+ and Mn2+ for Zn2+ into the parent semiconductor LaZnAsO introduces hole carriers and spins, respectively. This advantage enables us to investigate the influence of carrier doping on the ferromagnetic ordered state through the control of Sr concentrations in (La1-xSrx)(Zn0.9Mn0.1)AsO. 10 % Sr doping results in a ferromagnetic ordering below TC ~ 30 K. Increasing Sr concentration up to 30 % heavily suppresses the Curie temperature and saturation moments. Neutron scattering measurements indicate that no structural transition occurs for (La0.9Sr0.1)(Zn0.9Mn0.1)AsO below 300 K.Comment: Submitted to EP
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