Pressure effects on a low carrier density metal's infrared response

We have performed pressure and temperature dependent infrared studies of semi-metal bismuth. Along with other semi-metals such as graphite and antimony, bismuth is a material of much current interest due to the interesting properties resulting from an extremely low carrier density, small effective mass, and long mean free path. A novel optical setup has been developed to measure low temperature infrared responses at pressures of up to 17kbar. We observe massive changes in bismuth's optical and infrared conductivity as a function of temperature and pressure. We discuss the origin of these changes both in terms of simple band structure effects, as well as in terms of the correlation effects that are expected in this very low-carrier density metal.