Abstract
The optical properties of a large, detwinned single crystal of have been examined over a wide frequency range above and below the structural and magnetic transition at . Above the real part of the optical conductivity and the two infrared-active lattice modes are almost completely isotropic; the lattice modes show a weak polarization dependence just above . For , the optical conductivity due to the free-carrier response is anisotropic, being larger along the axis than the axis below meV; above this energy the optical conductivity is dominated by the interband contributions, which appear to be isotropic. The splitting of the low-energy infrared-active mode below is clearly observed, and the polarization modulation of the new modes may be used to estimate that the crystal is detwinned. The high-frequency mode, with a threefold increase in strength of the lower branch below and the nearly silent upper branch, remains enigmatic.
- Received 3 July 2020
- Accepted 30 September 2020
DOI:https://doi.org/10.1103/PhysRevB.102.155135
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