Anharmonicity and Weak Mode Assignment in La2-xSrxCuO4, with Oxygen Isotopic Substitution

E. Siranidia, D. Lampakisa, D. Pallesa, E. Liarokapisa and K. Conderb aDepartment of Physics, National Technical University, Athens 157 80, Greece bPaul Scherrer Institut (PSI) WLGA, Villigen PSI 5232, Switzerland

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Received: 04 09 2006;

The oxygen isotope effect on the first- and second-order Raman active modes of high-quality La2-xSrxCu16,18O4 (80% substitution 16O by 18O) polycrystalline compounds with x=0.00, 0.015 was investigated at low temperatures. In the second-order Raman scattering several weak and strong peaks were observed and assigned to oxygen atom vibrations. With the isotopic substitution the apex oxygen mode follows quite well the mass harmonic law at all temperatures studied, while the soft mode is anharmonic in the temperature range of 77-180 K and for higher temperatures its anharmonicity is strongly increased. The temperature dependence of the energy of the soft mode for x=0.0 shows also a modification atࣈ180 K and an abnormal behaviour atࣈ280 K, which may be related with the transition to the antiferromagnetic phase.

DOI: 10.12693/APhysPolA.111.173 PACS numbers: 78.30.-j, 31.30.Gs, 74.25.Kc, 74.72.Dn