  The optical properties of layered tungsten ditelluride have been measured
over a wide temperature and frequency range for light polarized in the $a$-$b$
planes. A striking low-frequency plasma edge develops in the reflectance at low
temperature where this material is a perfectly compensated semimetal. The
optical conductivity is described using a two-Drude model which treats the
electron and hole pockets as separate electronic subsystems. At low
temperature, one scattering rate collapses by over two orders of magnitude,
while the other also undergoes a significant, but less dramatic, decrease; both
scattering rates appear to display the quadratic temperature dependence
expected for a Fermi liquid. First principles electronic structure calculations
reveal that the low-lying optical excitations are due to direct transitions
between the bands associated with the electron and hole pockets.
