Browsing by Author "Tan, G.T."

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    In-plane electronic anisotropy resulted from ordered magnetic moment in iron-based superconductors
    (American Physical Society, 2020) Wu, S.-F.; Zhang, W.-L.; Thorsmølle, V.K.; Chen, G.F.; Tan, G.T.; Dai, P.C.; Shi, Y.G.; Jin, C.Q.; Shibauchi, T.; Kasahara, S.; Matsuda, Y.; Sefat, A.S.; Ding, H.; Richard, P.; Blumberg, G.
    We study the in-plane electronic anisotropy in the parent compounds of several families of Fe-based superconductors (BaFe2As2, EuFe2As2, NaFeAs, LiFeAs, FeSe, and LaFeAsO) by polarization-resolved Raman scattering. We measure intensity of the fully symmetric c-axis vibration of As atom mode in the XY scattering geometry and notice that the mode's intensity is significantly enhanced below the magnetostructural transition only for compounds showing magnetic ordering. In particular, we find that the intensity ratio of this As phonon in the XY vs. XX scattering geometries is proportional to the square of the ordered magnetic moment. We relate this As phonon intensity enhancement below the Néel temperature in iron pnictides to in-plane electronic anisotropy induced by the collinear spin-density wave order.
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    Phase separation, competition, and volume-fraction control in NaFe1−xCoxA
    (American Physical Society, 2014) Ma, Long; Dai, J.; Wang, P.S.; Lu, R.; Song, Yu; Zhang, Chenglin; Tan, G.T.; Dai, Pengcheng; Hu, D.; Li, S.L.; Normand, B.; Yu, Weiqiang
    We report a detailed nuclear magnetic resonance (NMR) study by combined Na23 and As75 measurements over a broad range of doping to map the phase diagram of NaFe1−xCoxAs. In the underdoped regime (x≤0.017), we find a magnetic phase with robust antiferromagnetic (AFM) order, which we denote the s-AFM phase, cohabiting with a phase of weak and possibly proximity-induced AFM order (w-AFM) whose volume fraction V≃8% is approximately constant. Near optimal doping, at x=0.0175, we observe a phase separation between static antiferromagnetism related to the s-AFM phase and a paramagnetic (PM) phase related to w-AFM. The volume fraction of AFM phase increases upon cooling, but both the Néel temperature and the volume fraction can be suppressed systematically by applying a c-axis magnetic field. On cooling below Tc, superconductivity occupies the PM region and its volume fraction grows at the expense of the AFM phase, demonstrating a phase separation of the two types of order based on volume exclusion. At higher dopings, static antiferromagnetism and even critical AFM fluctuations are completely suppressed by superconductivity. Thus the phase diagram we establish contains two distinct types of phase separation and reflects a strong competition between AFM and superconducting phases both in real space and in momentum space. We suggest that both this strict mutual exclusion and the robustness of superconductivity against magnetism are consequences of the extreme two-dimensionality of NaFeAs.