Abstract
We study the coupling of the fully symmetric vibration mode of arsenic atoms to magnetism in a Ba(Fe1-xAux)2As2 system by polarization-resolved Raman spectroscopy and neutron diffraction. In this system, there are two phase transitions: a tetragonal-to-orthorhombic structural phase transition at temperature TS and a magnetic phase transition into collinear spin-density wave (SDW) state at temperature TN (≤TS). TS and TN almost coincide in the pristine compound, whereas they differ by as much as 8 K for compounds with dilute gold substitution for iron. Raman coupling to the Ag(As) phonon is forbidden for the XY scattering geometry in the tetragonal phase above TS, whereas it becomes allowed in the orthorhombic phase below TS: The emerging mode's intensity indicates the lattice orthorhombicity. We find that upon cooling below TS, first, weak Ag(As) phonon mode intensity appears in the XY scattering geometry spectra; however, the mode's intensity is significantly enhanced in the magnetic phase below TN. The Ag(As) phonon also shows an asymmetric line shape below TN and an anomalous linewidth broadening upon Au doping. We describe the anomalous behavior of the Ag(As) mode in the XY scattering geometry using a Fano model involving the Ag(As) phonon interacting with the B2g(D4h)-symmetry-like electron-hole continuum. We conclude that the temperature dependence of light coupling amplitude to the Ag(As) phonon follows the evolution of the magnetic order parameter M(T). We propose that the intensity enhancement of the Ag(As) phonon in the XY scattering geometry below TN is due to electronic anisotropy induced by the collinear SDW order parameter.
| Original language | English |
|---|---|
| Article number | 014501 |
| Journal | Physical Review B |
| Volume | 102 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jul 1 2020 |
Bibliographical note
Publisher Copyright:© 2020 American Physical Society.
Funding
We thank E. Bascones and K. Haule for discussions. The spectroscopic work conducted at Rutgers (S.-F.W., W.-L.Z., H.-H.K., and G.B.) was supported by NSF Grant No. DMR-1709161. The sample growth and characterization work conducted at ORNL (L.L. and A.S.S.) was supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. For characterization by neutron diffraction (H.-B.C.) this research used resources at the High-Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. G.B. also acknowledges partial support from QuantEmX grant from ICAM and the Gordon and Betty Moore Foundation through Grant No. GBMF5305. The work at NICPB was supported by the Estonian Research Council Grant No. PRG736 and by the European Research Council (ERC) under Grant Agreement No. 885413.
| Funders | Funder number |
|---|---|
| ICAM | |
| National Science Foundation | DMR-1709161 |
| U.S. Department of Energy | |
| Gordon and Betty Moore Foundation | GBMF5305 |
| Basic Energy Sciences | |
| Oak Ridge National Laboratory | |
| Horizon 2020 Framework Programme | 885413 |
| Division of Materials Sciences and Engineering | |
| European Research Council | |
| Eesti Teadusagentuur | PRG736 |