Spectroscopy of Solids in the Far-Infrared: Studies of superconductors, magnetic materials, and ferroelectrics in this spectral region are rewarding.
The far-infrared spectral region (10-100 cm(-1)) is a fruitful one for studies of solids. The experimental obstacle of weak sources has been partially overcome in recent years by the introduction of very sensitive bolometric radiation detectors cooled by liquid helium to temperatures near 1 degrees K. Used with a mercury arc source and a simple grating monochromator, these detectors have made work in a number of areas of solid-state physics possible. Important examples of such work are, (i) demonstration of the energy gap in superconductors and measurement of gap widths in various metals; (ii) observation of magnetic resonances in ordered magnetic materials, from which precise information about exchange fields and anisotropy energies can be obtained; and (iii) demonstration of the existence of a temperature-dependent low-frequency vibrational mode associated with the Curie-law dielectric constant in certain types of ferroelectric crystals.
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