Microscopy model of the velocity of sound in La0.5Ca0.5MnO3

In this paper, the microscopic theory of the relative change in the velocity of sound with temperature of La0.5Ca0.5MnO3 is reported. The phonon Green function is calculated using the Green function technique of Zubarev (1960 Sov. Phys.-Usp. 3 320) in the limit of zero wave vector and low temperature. The electronic Hamiltonian of the lattice model in the presence of the phonon interaction with the hybridization between the conduction electrons and l-electrons is used. The relative change in the velocity of sound at various temperatures is studied for different model parameters, namely the position of the l-level, the effective phonon coupling strength, the Coulomb interaction and the hybridization strength. The phonon anomalies observed experimentally at different temperatures are explained theoretically. An abrupt change in velocity at the Neel temperature (T-N) is clearly observed. It is observed that different parameters influence the velocity of sound and the Neel temperature increases with increase in the Coulomb interaction.