Polar modes and overtone states in Raman spectra of lithium tantalate crystals

The conditions for the excitation of transverse and longitudinal polar modes in the processes of Raman scattering of light in mono- and polydomain lithium tantalate single crystals are established using a backscattering geometry. The relative intensity of the overtone Raman spectrum on the longitudi...

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Bibliographic Details
Published in:Physical review. B 2021-07, Vol.104 (2), p.1, Article 024303
Main Authors: Gorelik, V. S., Pyatyshev, A. Yu
Format: Article
Language:English
Subjects:
Backscattering
Elementary excitations
Excitation
Lithium
Lithium tantalates
Quadrupoles
Raman spectra
Single crystals
Vibrational spectra
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Summary:The conditions for the excitation of transverse and longitudinal polar modes in the processes of Raman scattering of light in mono- and polydomain lithium tantalate single crystals are established using a backscattering geometry. The relative intensity of the overtone Raman spectrum on the longitudinal and transverse fundamental polar excitations is much higher in the polydomain sample. Unfortunately, the exact reason for the difference in the Raman spectra of the mono- and polydomain lithium tantalate samples is unknown. The frequencies of the two overtone bands exceeded the exact value of the overtone frequency corresponding to the fundamental longitudinal polar mode 4A1(LO), which clearly indicates the existence of bound phonon pairs (biphonons). This is consistent with theory and has been shown for both mono- and polydomain samples. On the basis of the general theory of bound states of quasiparticles, the possibility of the existence of bound states of quadrupole excitations of the antipolar type in the vibrational spectrum of a polydomain crystal of lithium tantalate is predicted.
ISSN:2469-9950
2469-9969
DOI:10.1103/PhysRevB.104.024303