volume | PIER Journals

Abstract

Phonon-polariton is the coupled excitation between optical phonon and photon. The remarkable frequency vs. wavevector dispersion relation of phonon-polariton contributes to important technological applications such as tunable terahertz radiation sources and basic materials science to clarify the terahertz dynamics of condensed matter such as lattice instability in ferroelectrics. This paper studies the broadband dispersion relation of phonon-polariton between 10 cm^-1 and 1200 cm^-1 in uniaxial ferroeletric crystals, LiNbO₃ (LN) and LiTaO₃ (LT) with polar trigonal system on the basis of the observed results using THz-Raman spectroscopy, THz time domain spectroscopy, and far-infrared spectroscopy. The dispersion on the lowest-frequency TO mode with A1(z) symmetry of LN and LT crystals, which are assigned as ferroelectric soft modes, is discussed.

1. Born, M. and K. Huang, Dynamical Theory of Crystal Lattices, Oxford University Press, 1954.

2. Claus, R., L. Merten, and J. Brandmuller, Light Scattering by Phonon-polaritons, Springer-Verlag, 1975.
doi:10.1007/BFb0048910

3. Xu, Y., Ferroelectric Materials and Their Applications, North-Holland, Amsterdam, 1991.

4. Volk, T. and M. Wohlecke, Lithium Niobate: Defects, Photorefraction and Ferroelectric Switching, Springer Series in Materials Science, 2008.

5. Henry, C. H. and J. J. Hopfield, "Raman scattering by polaritons," Phys. Rev. Lett., Vol. 15, 964-966, 1965.
doi:10.1103/PhysRevLett.15.964 Google Scholar

6. Wiederrecht, G. P., T. P. Dougherty, L. Dhar, K. A. Nelson, D. E. Leaird, and A. M. Weiner, "Explanation of anomalous polariton dynamics in LiTaO₃," Ferroelectrics, Vol. 150, 103-118, 1993.
doi:10.1080/00150199308008698 Google Scholar

7. Bond, W. L., "Measurement of the refractive indices of several crystals," J. Appl. Phys., Vol. 36, 1674-1677, 1965.
doi:10.1063/1.1703106 Google Scholar

8. Kojima, S. and T. Nakamura, "Observation of low frequency polaritons in barium sodium niobate," Jpn. J. Appl. Phys., Vol. 19, L609-610, 1980.
doi:10.1143/JJAP.19.L609 Google Scholar

9. Kojima, S. and T. Mori, " Terahertz time-domain spectroscopy of infrared active soft mode and phonon-polariton dispersion," Ferroelectrics, Vol. 500, 183-202, 2016.
doi:10.1080/00150193.2016.1214522 Google Scholar

10. Kojima, S., K. Kanehara, T. Hoshina, and T. Tsurumi, "Optical phonons and polariton dispersions of congruent LiNbO₃ studied by far-infrared spectroscopic ellipsometry and Raman scattering," Jpn. J. Appl. Phys., Vol. 55, 10TC02-1-5, 2016. Google Scholar

11. Kojima, S., "Composition variation of optical phonon damping in lithium niobate crystals," Jpn. J. Appl. Phys., Vol. 32, 4373-4376, 1993.
doi:10.1143/JJAP.32.4373 Google Scholar

12. Kojima, S., H. Kitahara, M. Wada Takeda, and S. Nishizawa, "Terahertz time domain spectroscopy of phonon-polaritons in ferroelectric lithium niobate crystals," Jpn. J. Appl. Phys., Vol. 41, 7033-7037, 2002.
doi:10.1143/JJAP.41.7033 Google Scholar

13. Kojima, S., H. Kitahara, S. Nishizawa, and M. Wada Takeda, "Dielectric properties of ferroelectric lithium tantalate crystals studied by terahertz time-domain spectroscopy," Jpn. J. Appl. Phys., Vol. 42, 6238-6241, 2003.
doi:10.1143/JJAP.42.6238 Google Scholar

14. Margueron, S., A. Bartasyte, A. M. Glazer, E. Simon, J. Hlinka, I. Gregora, and J. Gleize, "Resolved E-symmetry zone-centre phonons in LiTaO₃ and LiNbO₃," J. Appl. Phys., Vol. 111, 104105-1-6, 2012.
doi:10.1063/1.4716001 Google Scholar

15. Kojima, S. and T. Nakamura, "Low frequency phonon polaritons in several ferroelectrics," Ferroelectrics, Vol. 37, 677-680, 1981.
doi:10.1080/00150198108223519 Google Scholar

16. Kojimam, S. and T. Nakamura, "Polariton-spectroscopy in several ferroelectric crystals," Ferroelectrics, Vol. 52, 171-180, 1983.
doi:10.1080/00150198308208250 Google Scholar

17. Kojima, S., H. Kitahara, S. Nishizawa, and M. Wada Takeda, "Dielectric properties of ferroelectric lithium tantalate crystals studied by terahertz time-domain spectroscopy," Jpn. J. Appl. Phys., Vol. 42, 6238-6241, 2004.
doi:10.1143/JJAP.42.6238 Google Scholar

18. Bakker, H. J., S. Hunsche, and H. Kurz, "Coherent phonon polaritons as probes of anharmonic phonons in ferroelectrics," Rev. Mod. Phys., Vol. 70, 523-536, 1998.
doi:10.1103/RevModPhys.70.523 Google Scholar

19. Crimmins, T. F., N. S. Stoyanov, and K. A. Nelson, "Heterodyned impulsive stimulated Raman scattering of phonon-polaritons in LiTaO₃ and LiNbO₃," J. Chem. Phys., Vol. 117, 2882-2896, 2002.
doi:10.1063/1.1491948 Google Scholar

20. Penna, A. F., S. P. S. Porto, and E. Wiener-Avnear, "Anomalous polariton dispersion in LiTaO₃ near T_C," Solid State Commun., Vol. 23, 377-380, 1977.
doi:10.1016/0038-1098(77)90236-8 Google Scholar

Dr. Seiji Kojima