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Millimeter and Submillimeter Wave Spectroscopy of Solids focuses on
the experimental methods and recent experimental results which are
currently employed in the millimeter wave spectral range. Time
dome, Fourier transform, coherent source and resonant techniques
are discussed by leading authorities in the field. The usefulness
of the methods is discussed by reviewing experimental results on
metals and semiconductors. Recent experiment covering modern topics
such as correlation on metals, superconductors and confined quantum
systems are also discussed. The volume is aimed at physicists,
engineers and materials scientists interested in the dynamics of
solid matter.
The dynamical properties of solids have recently attracted renewed
interest in connection with the increasing understanding of phase
transitions and re lated phenomena. In particular, soft modes or,
more generally, phonon 'anom alies' seem to play an important role
in structural and electronic phase tran sitions, such as
ferroelectric or superconducting transitions. The understanding of
the mechanisms responsible for the occurrence of unusually low
frequencies in phonon spectra requires a detailed analysis of the
microscopic forces governing the lattice vibrations. Of particular
importance is the influence of the electron lattice interaction in
the adiabatic approximation which in many cases is the origin of
peculiarities in the phonon self-energy. In this work the
vibrational spectra of pure non-metals and of those con taining
point defects are investigated. ' In these materials the
interrelation be tween the pseudo-harmonic forces (determining the
phonon dispersion re lations) and the non-linear anharmonic and
electron-phonon forces (as they act in infrared and Raman spectra)
is most obvious and can be quantitatively analysed in terms of
appropriate models. The main task is to arrive at a physically
correct treatment of electronic degrees of freedom, as for example
in an electronic 'shell' model, which leads to the description of
phonon spectra in terms of long-range polarizabilities and
short-range deformabilities. The pur pose of our review is to
stimulate further investigations which, we hope, will result in
explicit relations between the parameters of the semi-microscopic
models and the matrix elements from the electronic band structure."
159 elements only between states which differ in one of the
single-electron wave functions, in short, HeR induces only
one-electron transitions. The matrix elements 1mn and Pmn reduce to
matrix elements between the single-electron wave functions. We are
interested primarily in crystalline solids for which the band model
is a good approximation. The Bloch single-electron wave function in
this model has the form: N'I ili-';; U. r.;;) ( (1.14) ""nk r, =e
nh\r , where n is the band index and U (r) has the periodicity of
the lattice. The form of the Bloch function follows from the
translational symmetry of the crystal, and the matrix elements
between Bloch states are subject to the condition of wave-vector
conservation: k'=k, for
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