For a diatomic linear chain, the phonon dispersion relation
has two branches, according to the + and - sign in the
equation below:
There are two atoms in the unit cell with masses 
and 
, and the
force constant of the nearest-neighbor interaction is given by f. In Figure
2.3 the frequency is plotted for various values of 
,
with the effective mass, 
, kept constant.
Figure 2.3: Phonon dispersion relation for a diatomic chain for 
(solid line), 
and 
. The frequency scale is set by
.
(a) Calculate the sound velocity.
(b) Show that for 
, the result is equivalent to the dispersion
curve of the single-atom chain.
Laszlo Mihaly
Thu Oct 31 13:23:11 EST 1996
Cover Page
.
