  We characterize radio frequency detection in a high-quality metallic
single-walled carbon nanotube. At a bath temperature of 77 K, only bolometric
(thermal) detection is seen. At a bath temperature of 4.2 K and low bias
current, the response is due instead to the electrical nonlinearity of the
non-ohmic contacts. At higher bias currents, the contacts recover ohmic
behavior and the observed response agrees well with the calculated bolometric
responsivity. The bolometric response is expected to operate at terahertz
frequencies, and we discuss some of the practical issues associated with
developing high frequency detectors based on carbon nanotubes.
