1063-7834/01/4310- $21.00 © 2001 MAIK “Nauka/Interperiodica” 1801 Physics of the Solid State, Vol. 43, No. 10, 2001, pp. 1801–1806. Translated from Fizika Tverdogo Tela, Vol. 43, No. 10, 2001, pp. 1729–1734. Original Russian Text Copyright © 2001 by Bolotin, Kuz’min, Knyazev, Ponosov, Thomsen. 1. INTRODUCTION The exceptionally strong dispersion of self-energies (anomalous frequency dispersion and threshold damp- ing of optical phonons) in a range of small wave vectors (q ~ 10 6 cm –1 ) recently observed during an analysis of Raman spectra of transition metals [1] raised a question as to the origin of electron excitations that determine nonadiabatic effects in electron–phonon interaction. The effects of nonadiabatic renormalization of the long-wavelength optical-phonon spectrum (anomalous dispersion and the Landau damping threshold) [2–4] in the region of q ~ ϖ 0 /v F (ϖ 0 is the phonon frequency and v F is the Fermi velocity for electrons) are based on the intraband mechanism and, hence, must exist in transi- tion (d) as well as in simple (s, p) metals. Such effects were sought for the latter metals (Zn [5–7], Cd [5], Bi, Sb [5, 7], Be [8]) while studying the temperature depen- dences of the phonon frequencies and width by using the method of inelastic light scattering. The experiments with these metals revealed an increase in energies and a narrowing of phonon lines during cooling and made it possible to estimate the contributions of anharmonism and of the electron–phonon interaction to the frequency shifts and to the damping of phonons at low tempera- tures. However, early measurements were made in a nar- row excitation energy range (2.41–2.54 eV), which did not permit study of the dependences of the phonon self- energies on their wave vector. An estimate of the thresh- old value of the wave vector q 0 ~ ϖ 0 /v F (near which the renormalization effects must increase) obtained from the available data on the average electron velocity at the Fermi surface gives the value ~1.6 × 10 5 cm –1 for zinc, while the effective value of the momentum probed in such experiments was an order of magnitude larger: ~16 × 10 5 cm –1 . In the present work, the range of exci- tation energies is considerably extended in the course of investigating the temperature dependences of the phonon frequencies and widths for the p-metal Zn with a view to obtaining information on the change in phonon parameters in the accessible range of wave vec- tors being probed, and the obtained results are com- pared with theoretical predictions and observed anom- alies in transition d metals. 2. EXPERIMENT The measurements were made on a zinc crystal with a resistivity ratio ρ 300 K /ρ 4.2 K = 560. This ensures con- servation of the wave vector so that ql  1, where l is the electron mean free path. Previous investigations were either carried out on polycrystals [5, 6] or con- tained no information on the purity of the single crys- tals under investigation [7]. The surfaces used for mea- surements were prepared by cleaving the crystal at right angles to its hexagonal axis. Since we studied backward scattering in our experiments, the obtained results cor- respond to the phonon wave vector directed along the c axis. The excitation was carried out through krypton and titanium–sapphire laser radiation (1.4–2.6 eV), which allowed us to study a fairly wide range of phonon momenta, (7–16) × 10 5 cm –1 for T = 5 K. The spectral resolution in our measurements was <1 cm –1 . The mag- nitude of the momentum being probed and its uncer- tainty as a result of absorption in the surface layer of the metal were estimated on the basis of ellipsometric mea- surements of the optical constants on the crystal under investigation at temperatures of 80 and 300 K in the energy range 0.5–3 eV, as well as on the basis of earlier Analysis of Dispersion of Long-Wavelength Optical Phonons in Zinc with the Help of Light Scattering G. A. Bolotin*, Yu. I. Kuz’min*, Yu. V. Knyazev*, Yu. S. Ponosov*, and C. Thomsen** * Institute of Metal Physics, Ural Division, Russian Academy of Sciences, ul. S. Kovalevskoœ 18, Yekaterinburg, 620219 Russia ** Institute of Solid State Physics, Technical University, Berlin, 10623 Germany e-mail: ponosov@imp.uran.ru Received November 13, 2000; in final form, February 7, 2001 Abstract—The temperature dependences (5–300 K) of the Raman spectra of E 2g phonons and optical constants in zinc single crystals are measured in the excitation energy range 1.4–2.54 eV. It is found that phonon damping decreases upon an increase in the wavelength of exciting radiation. The obtained results are compared with the dependence of the phonon width on the excitation energy (the probed wave vector of the excitations under investigation), which are presented for the first time for the transition metal osmium, as well as with the calcu- lated electron–phonon renormalization of damping, taking into account the actual distribution of wave vectors. © 2001 MAIK “Nauka/Interperiodica”. METALS AND SUPERCONDUCTORS