Events in Physics
Gordon Davies
Lifetimes of Vibrations
Impurities in crystals often create local vibrational modes - vibrations that are at frequencies too high to travel through the lattice and so are localised on the impurity. These Local Vibration Modes can often be seen in infrared absorption spectra as sharp lines. The LVM lines are invaluable in characterising the chemical nature and the structure of the impurity. The LVM lines have this importance because they are relatively sharp, with linewidths of a few wavenumbers.
What limits how sharp the lines can be? If the crystals have low impurity content and are made of one isotope, the limit to the linewidth is the lifetime of the excited state of the vibration, working through the uncertainty principle.
In this talk the vibrations of oxygen in crystalline silicon and germanium are used as (non-mathematical) examples to illustrate the different decay mechanisms of LVMs.