Lattice contributions to the anisotropic dielectric response of rare-earth langasites

We investigate the phonon spectrum of pure and rare-earth substituted langasites. For electric fields oriented along the c axis, a strong low-frequency phonon is observed, softening at lower temperature in all samples studied. The dielectric contribution and temperature dependence of this mode is th...

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Bibliographic Details
Published in:Physical review. B 2021-07, Vol.104 (2), p.1, Article 024106
Main Authors: Bergen, L., Weymann, L., Wettstein, J., Kuzmenko, A. M., Mukhin, A. A., Mill, B. V., Pimenov, A., Constable, E.
Format: Article
Language:English
Subjects:
Absorption spectra
Dielectrics
Electric fields
Low temperature
Phonons
Rare earth elements
Softening
Structural stability
Substitutes
Temperature dependence
Terahertz frequencies
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Summary:We investigate the phonon spectrum of pure and rare-earth substituted langasites. For electric fields oriented along the c axis, a strong low-frequency phonon is observed, softening at lower temperature in all samples studied. The dielectric contribution and temperature dependence of this mode is the primary source of the large [ɛ ( 0 ) ∼ 100] static dielectric permittivity observed in these systems. Softening of this mode with increasing mass of the rare-earth substitutes further suggests that langasites are close to a structural instability at low temperatures. The application of a magnetic field to a diluted Ho-langasite sample reveals a shift in the strong absorption band at THz frequencies associated with this soft lattice mode, suggesting spin-lattice effects may also be at play in these systems.
ISSN:2469-9950
2469-9969
DOI:10.1103/PhysRevB.104.024106