Condensed Matter Physics - Lattice Vibration : Vibration of Diatomic Linear Lattice - 01
A one-dimensional primitive diatomic lattice consists of two atoms at each basis. When it is disturbed by a monochromatic plane acoustic wave, the system vibrates with the frequency of the wave interacting with the lattice. Taking the assumptions similar to the monatomic lattice, expression for the frequency of vibration has been obtained, which is called Dispersion relation. In case of monatomic lattice, there is only one value of frequency of vibration for a single value of wave vector whereas in the case of diatomic lattice there are two values of frequency of vibrations. The allowed frequency range is split into two branches- an upper branch called Optical Branch and a lower branch called the Acoustical Branch. The acoustical branch resembles the dispersion relation for a monatomic lattice,whereas the optical branch represents an entirely different type of wave motion.