Browsing by Author "Song, Y."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Correlation-driven metal-insulator transition in proximity to an iron-based superconductor
    (American Physical Society, 2017) Charnukha, A.; Yin, Z.P.; Song, Y.; Cao, C.D.; Dai, Pengcheng; Haule, K.; Kotliar, G.; Basov, D.N.
    We report the direct spectroscopic observation of a metal to correlated-insulator transition in the family of iron-based superconducting materials. By means of optical spectroscopy we demonstrate that the excitation spectrum of NaFe1−xCuxAs develops a large gap with increasing copper substitution. Dynamical mean-field theory calculations show a good agreement with the experimental data and suggest that the formation of the charge gap requires an intimate interplay of strong on-site electronic correlations and spin-exchange coupling, revealing the correlated Slater-insulator nature of the antiferromagnetic ground state. Our calculations further predict the high-temperature paramagnetic state of the same compound to be a highly incoherent correlated metal. We verify this prediction experimentally by showing that the doping-induced weakening of antiferromagnetic correlations enables a thermal crossover from an insulating to an incoherent metallic state. Redistribution of the optical spectral weight in this crossover uncovers the characteristic energy of Hund's-coupling and Mott-Hubbard electronic correlations essential for the electronic localization. Our results demonstrate that NaFe1−xCuxAs continuously transitions from the typical itinerant phases of iron pnictides to a highly incoherent metal and ultimately a correlated insulator. Such an electronic state is expected to favor high-temperature superconductivity.
  • 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.