Raman scattering study of electronic and magnetic excitations in La 2x Sr x CuO 4 Masayuki Udagawa a, * , Norio Ogita a , Shigenobu Sakita b , JunÕya Hori b , Fumihiko Nakamura c , Takashi Suzuki c , Toshizo Fujita c a Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521, Japan b Venture Business Laboratory of Hiroshima University, Higashi-Hiroshima 739-8527, Japan c Graduate School of ADSM, Hiroshima University, Higashi-Hiroshima 739-8526, Japan Abstract Electronic and magnetic excitations with A 1g -symmetry have been investigated by the polarized Raman scattering in the energy region between 0 and 4000 cm 1 for La 2x Sr x CuO 4 (x ¼ 0, 0.1, 0.113, 0.15, 0.22). In the bða; aÞ  b polarization both magnetic and electronic excitations are allowed, while only electronic excitation for bðc; cÞ  b. In x 6 0:15, the in- tensity of bða; aÞ  b is larger than that of bðc; cÞ  b due to the additional existence of the magnetic excitation, however, both spectra become the same for x ¼ 0:22. This result is the experimental evidence that dynamical magnetic fluctuation disappears in the over-doped region in La 2x Sr x CuO 4 . Ó 2003 Elsevier Science B.V. All rights reserved. Keywords: La 2x Sr x CuO 4 ; Raman scattering; Magnetic excitation; Electronic excitation 1. Introduction Recently, magnetic interaction models seem to be accepted as a pairing mechanism for high-T c supercon- ductors. However, the recent report of photoemission pointed out the importance of electron–phonon inter- action [1]. Furthermore, our Raman scattering results reported the existence of electron–phonon coupling in K 2 NiF 4 -type crystals and also the correlation between T c and electron–phonon coupling parameter for LSCO [2,3]. These recent reports suggest that the electron– phonon mechanism cannot be excluded. Thus, to un- derstand the mechanism, new experiments for the magnetic excitations are necessary. In this report, we have investigated the propagation-direction dependence of the magnetic and electronic excitations in the wide energy region by Raman scattering. Such a measure- ment has not been reported, since the most of the measurements have been done on only the c-plane. 2. Experimental The single crystals of La 2x Sr x CuO 4 (x ¼ 0, 0.1, 0.113, 0.15, 0.22) were grown by a traveling-solvent floating-zone method. After the surface polish, the samples were annealed in O 2 at 920 °C for 50 h and 500 °C for 50 h, in order to minimize strains and to obtain the better oxygen stoichiometric specimens. In the Raman scattering measurements, an Ar þ laser light with a wavelength of 514.5 nm was employed as the incident beam and its output power was 12.5 mW. The scattered light into nearly backward direction was analyzed by a triple monochromator (JASCO model NR-1800), and the analyzed light was detected by a CCD multi-channel detector (Princeton Instrument model LN/CCD-576E). In this experiment, we studied two different polar- ization geometries of bða; aÞ  b and bðc; cÞ  b with the same A 1g -symmetry. In the symbol of k i ðp i ; p s Þk s , k and p are * Corresponding author. E-mail address: udagawa@hiroshima-u.ac.jp (M. Udag- awa). 0921-4534/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02469-3 Physica C 388–389 (2003) 315–316 www.elsevier.com/locate/physc