Electronic specific heat enhancement

The large phase shifts t 2 give a large enhancement of the resistivity when transitional metals are dissolved in other metals. A survey for solid metals is given by Friedel (1956), and for solutions of Fe and Co in liquid germanium and tin by Dreirach et al (1972). The resonance will also enhance the electronic specific heat and the Pauli paramagnetism, but these quantities cannot be treated quantitatively without including correlation as shown in Chapter 3. 

Another effect of the electron-phonon interaction is a shift in the velocity of the electrons at the Fermi surface, in some ways analogous to the polaron effect in ionic crystals. Because of the wake of lattice distortion that accompanies the electron, its velocity is reduced, as it turns out, by a factor (1 -b/l). (For a discussion of this effect, and references, see Quinn, 1960, p. 58, or Harrison, 1970. p. 418ff.) The reduction in velocity corresponds to a decrease in dEldk at thc-Fermi surface and, therefore, to an increase in the density of states by the same factor. We noted in Chapter 15 that the electronic specific heat is proportional to the density of states, so we may expect an enhancement of the experimental... 

As seen from table 10.1, the electronic specific heat of both phases of La is larger than that of Lu. However, no conclusion can be drawn as to a higher density of states in La. The electronic specific heat coefficient y is proportional to the density of states times the electron-phonon enhancement factor... 

The first heavy fermion superconductor was discovered in CeCu2Si2 [19]. Common properties in a heavy fermion superconductor are large electronic specific heat coefficient, suggesting that the effective masses of the conduction electrons are 100 times higher than the static mass of an electron, and the unconventional superconductivity is difficult to explain by the BCS theory. It has been believed that the enhancement of the effective masses of conduction electrons in... 

There is also an enhancement of the electronic specific heat coefficients 7 (y(YCo2) = 33.1, 7(LuC02) = 26.6, and 7(ScCo2)= 18.4 in units of mJ (mol-Co) K ) (Ikeda et al. 1991), which in the case of ScCo2 is larger by a factor of three than that of ScNi2. 

On the other hand, the cyclotron masses of PrCue and CeCtig are twice and forty times larger than that of LaCug, respectively. No mass enhancement is found in NdCu and SmCug, as shown in fig. 98. Here, the electronic specific heat coefficients of PrCue and... 

Interpretation of the x(T) data begins with a distinction between Stoner and mass enhancements. The electronic specific-heat parameter y increases with the mass enhancement [14]. By measuring both /(T) and y at low temperatures, Sreedhar et al. [80] determined a Stoner factor S = 0.58, well below the S = 1 for a ferromagnetic instability. These nickel oxides are clearly on the itinerant-electron side of the transition from localized to itinerant... 

Okuda et al. [221] have shown that the Dehye temperature increases with x in the range 0.12 < x < 0.30, saturating at a normal value for the perovskite structure above x = 0.30, which indicates that strong electron-lattice interactions persist in the FM phase out to x = 0.30. The electronic specific heat is only slightly enhanced as x decreases to x = 0.17, but it drops sharply to zero with decreasing x in the interval 0.15 < x < 0.17 where there is a transition from itinerant to vibronic electronic behavior. 

Thermal expansion measiuements provide a lot of information not only about the crystal structure but also about phase transformations (or crossover) in the electronic states. One of the characteristics of HE com-poimds is the anomaly in specific heat C, particularly the huge value of the electronic specific heat coefficient y or large enhancement of C/T at low temperature. The specific heat at constant volume Cy is defined as... 

---