Free-energy density Terms Links

External stress, locally applied, can have nonlocal static effects in ferroelastics (see Fig. 4 of Ref. [7]). Dynamical evolution of strains under local external stress can show striking time-dependent patterns such as elastic photocopying of the applied deformations, in an expanding texture (see Fig.5 of Ref. [8]). Since charges and spins can couple linearly to strain, they are like internal (unit-cell) local stresses, and one might expect extended strain response in all (compatibility-linked) strain-tensor components. Quadratic coupling is like a local transition temperature. The model we consider is a (scalar) free energy density term... 

Thus when the two energy levels coexist, the density contains a term which varies periodically with time. This term has not a frequency equal to that of either of the separate values EJh or EJh but one equal to E —E jh. Thus we obtain a link between the wave-mechanical theory of the atom and the classical theory of the field which is formally very striking, though, in the light of any statistical interpretation of the electric density, it cannot be said that the problem is entirely free from mystery. 

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