Griineisen electron parameter

Here k = is the compressibility, the averages are given by eq. (34) and y = -(din E /d In V) define electronic Griineisen parameters for a given CEF level. The close correspondence between )8 and the Schottky specific heat has been emphasized before (Ott et al. 1976, 1977, Liithi 1980a). The latter is described by a corresponding formula 1... 

We first begin with a short survey of the basic experimental evidence in sect. 4.1. The basic physical properties of the unstable-moment systems will be surveyed. In order to discuss their elastic and lattice dynamical properties that are of central interest here an outline of current theoretical concepts to describe unstable-moment systems, especially heavy-fermion compounds is given first (sect. 4.2). Because in heavy-electron compounds is much smaller than the CEF splittings they exhibit magnetoelastic anomalies as described in sect. 2. However, in addition, Griineisen parameter coupling to the heavy-electron bands leads to elastic effects below T. For a few typical Ce compounds this is studied within a microscopic model calculation in sect. 4.3. A more complete discussion... 

Microscopically, an important contribution to the Griineisen parameter coupling in HF Ce compounds comes from a strong volume dependence of the sf-hybridization strength V k) (Allen and Martin 1982, Razafimandimby et al. 1984). Therefore, sound waves of compressional character, e.g., longitudinal modes modulate the mixing term in the Hamiltonian of eq. (107) and consequently couple to electronic states. For smaU displacements one can write... 

The phenomenological Griineisen parameter electron-phonon coupling for the heavy-fermion compounds is very successful in describing the thermal expansion and temperature dependence of elastic constants. The parameters deduced from the different experiments agree with each other and they agree also with the parameters used in the microscopic description, sect. 4.3. 

On the basis of this expression, authors have determined the value ]r(T,F) = 0.57 for the electron Griineisen parameter, which is near to the theoretical value of 2/1. 

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