Title: Coupling of fully symmetric As phonon to magnetism in Ba(Fe_1-xAu_x)₂As₂

Abstract

In this work, we study the coupling of the fully symmetric vibration mode of arsenic atoms to magnetism in a $\mathrm{Ba}{\left({\mathrm{Fe}}_{1-x}{\mathrm{Au}}_x\right)}_2{\mathrm{As}}_2$ 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 $T_S$ and a magnetic phase transition into collinear spin-density wave (SDW) state at temperature $T_N$ ( $\le T_S$). $T_S$ and $T_N$ 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 $A_g$(As) phonon is forbidden for the $XY$ scattering geometry in the tetragonal phase above $T_S$, whereas it becomes allowed in the orthorhombic phase below $T_S$: The emerging mode's intensity indicates the lattice orthorhombicity. Furthermore, we find that upon cooling below $T_S$, first, weak $A_g$(As) phonon mode intensity appears in the $XY$ scattering geometry spectra; however, the mode's intensity is significantly enhanced in the magnetic phase below $T_N$. The $A_g$(As) phonon also shows an asymmetric line shape below $T_N$ and an anomalous linewidth broadening upon Au doping. We describe the anomalous behavior of the $A_g$(As) mode in the $XY$ scattering geometry using a Fano model involving the $A_g$(As) phonon interacting with the $B_{2g}(D_{4h}$)-symmetry-like electron-hole continuum. We conclude that the temperature dependence of light coupling amplitude to the $A_g$(As) phonon follows the evolution of the magnetic order parameter $M\left(T\right)$. We propose that the intensity enhancement of the $A_g$(As) phonon in the $XY$ scattering geometry below $T_N$ is due to electronic anisotropy induced by the collinear SDW order parameter.

Authors:

Wu, S. -F. ^[1]; Zhang, W. -L. ^[2]; Li, L.  ^[3];

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• Search DOE PAGES for ORCID "0000-0003-1683-8118"

Cao, H. -B.  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-5970-4980"

Kung, H. -H. ^[1]; Sefat, A. S.  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-5596-3504"

Ding, H. ^[4]; Richard, P. ^[5]; Blumberg, G.  ^[6]

• Search DOE PAGES for author "Blumberg, G."
• Search DOE PAGES for ORCID "0000-0003-0388-8327"

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+ Show Author Affiliations

1. Rutgers Univ., Piscataway, NJ (United States)
2. Rutgers Univ., Piscataway, NJ (United States); Sophia Univ., Tokyo (Japan)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
4. Chinese Academy of Sciences (CAS), Beijing (China). Beijing National Lab. for Condensed Matter Physics; Univ. of Chinese Academy of Sciences, Beijing (China)
5. Univ. de Sherbrooke, QC (Canada)
6. Rutgers Univ., Piscataway, NJ (United States); National Inst. of Chemical Physics and Biophysics, Tallinn (Estonia)

Publication Date:

Mon Jul 06 00:00:00 EDT 2020

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); Gordon and Betty Moore Foundation; Estonian Research Council; European Research Council (ERC)

OSTI Identifier:

1651257

Grant/Contract Number:  

AC05-00OR22725; GBMF5305; 885413; PRG736; DMR-1709161

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review B

Additional Journal Information:

Journal Volume: 102; Journal Issue: 1; Journal ID: ISSN 2469-9950

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Antiferromagnetism; electron-phonon coupling; unconventional superconductors; Raman spectroscopy