Kondo temperature definition

A requirement of all theories for heavy fermion compounds is the existence of a large AT ( p) due to the f electrons. Figure 19.12 shows the low-temperature ultraviolet photoemission spectra from UBcia and UPt3 [73]. The high N( p), narrow f-peak is definitely observed with bandwidths of about 0.1S eV. Further analysis of the data yields a true bandwidth of 0.07S eV, which is extremely narrow, but much broader than the 0.001 eV needed to explain the enormous y-values. In order to find the expected narrower bands, and/or to observe a theoretically predicted Kondo temperature of 10-20 K, data of this type must be... 

Fig. 27. Resistivity p(T) (a), thermoelectric power S(T) and Lorenz number L T) (b), calculated with LNCA techniques for a sixfold degenerate Anderson lattice model in the Kondo regime (Cox and Grewe 1988). Impurity results, scaled with concentration are shown for comparison. The resistivity results exhibit the logarithmic increase with decreasing temperature and the coherence-derived decrease below T = to the residual value due to impurities, which is quadratic in the Fermi liquid regime T < T. S(T ) is positive definite for the simple model situation chosen.

The reader is cautioned to observe, however, that existing theories for the various physical properties of Kondo systems do not provide a self-consistent definition for the characteristic temperature as defined by the temperatures of the typically broad anomalies in the thermoelectric power, electrical resistivity, heat capacity and magnetic susceptibility. Thus the values of the characteristic temperature inferred from different measurements may differ by as much as an order of magnitude. 

In the event that the amount of hybridization is too strong for the exchange hamiltonian to be an adequate starting point for a theoretical description of the Kondo-like anomalies in the physical properties, the characteristic temperature is often identified with a spin fluctuation temperature T,f which has the obvious definition Tsf = h/keTsf. In this view, Tjt, rather than Tk, is a boundary which separates high temperature (compared to Tsf) magnetic behavior from low temperature nonmagnetic behavior. 

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