Browsing by Author "Blumberg, G."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Critical quadrupole fluctuations and collective modes in iron pnictide superconductors
    (American Physical Society, 2016) Thorsmølle, V.K.; Khodas, M.; Yin, Z.P.; Zhang, Chenglin; Carr, S.V.; Dai, Pengcheng; Blumberg, G.
    The multiband nature of iron pnictides gives rise to a rich temperature-doping phase diagram of competing orders and a plethora of collective phenomena. At low dopings, the tetragonal-to-orthorhombic structural transition is closely followed by a spin-density-wave transition both being in close proximity to the superconducting phase. A key question is the nature of high-Tc superconductivity and its relation to orbital ordering and magnetism. Here we study the NaFe1−xCoxAs superconductor using polarization-resolved Raman spectroscopy. The Raman susceptibility displays critical enhancement of nonsymmetric charge fluctuations across the entire phase diagram, which are precursors to a d-wave Pomeranchuk instability at temperature θ(x). The charge fluctuations are interpreted in terms of quadrupole interorbital excitations in which the electron and hole Fermi surfaces breathe in-phase. Below Tc, the critical fluctuations acquire coherence and undergo a metamorphosis into a coherent in-gap mode of extraordinary strength.
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Raman scattering study of NaFe0.53Cu0.47As
    (American Physical Society, 2018) Zhang, W.-L.; Song, Y.; Wang, W.-Y.; Cao, C.-D.; Dai, P.-C.; Jin, C.-Q.; Blumberg, G.
    We use polarization-resolved Raman scattering to study lattice dynamics in NaFe0.53Cu0.47As single crystals. We identify four A1g phonon modes, at 126, 172, 183, and 197 cm−1, and four B3g phonon modes at 101, 139, 173, and 226 cm−1(D4h point group). The phonon spectra are consistent with the Ibam space group, which confirms that the Cu and Fe atoms form a stripe order. The temperature dependence of the phonon spectra suggests weak electron-phonon and magnetoelastic interactions.
  • Thumbnail Image
    Item
    Superconductivity and electronic fluctuations in Ba1−xKxFe2As2 studied by Raman scattering
    (American Physical Society, 2017) Wu, S.-F.; Richard, P.; Ding, H.; Wen, H.-H.; Tan, Guotai; Wang, Meng; Zhang, Chenglin; Dai, Pengcheng; Blumberg, G.
    Using polarization-resolved electronic Raman scattering we study underdoped, optimally doped, and overdoped Ba1−xKxFe2As2 samples in the normal and superconducting states. We show that low-energy nematic fluctuations are universal for all studied doping ranges. In the superconducting state, we observe two distinct superconducting pair-breaking peaks corresponding to one large and one small superconducting gap. In addition, we detect a collective mode below the superconducting transition in the B2g channel and determine the evolution of its binding energy with doping. Possible scenarios are proposed to explain the origin of the in-gap collective mode. In the superconducting state of the underdoped regime, we detect a reentrance transition below which the spectral background changes and the collective mode vanishes.