Heavy-mass state

The so far highest y-value of 8000mJ/K was observed for YbPtBi (Fisk et al. 1991, Thompson et al. 1993). This bismuthide can be classified as a very heavy-electron system. The heavy-mass state in YbPtBi is unconventional in that it develops from Bloch states in an electron subsystem with a low carrier concentration (Hundley et al. 1997, Fisk et al. 1991). 

At temperatures below 0.5 K, superconductivity has first been observed in UPt3 by Stewart et al. [21] The precise value of Tc depends on sample quality as does the temperature width of the superconducting transition. Most remarkable is the observation that the jump in the specific heat at Tc reveals that heavy-mass electrons are involved in the formation of the superconducting state. 

In both equations the second term can be large, giving a small mass. In contrast, there are no such matrix elements between wave functions for the conduction band and the heavy-hole states, so their masses remain large. 

Infrared chemiluminescence measurements142 have determined the vibrational and rotational state distributions of HF and DF from the F + H2,D2 reactions, and find substantial fractions of vibrational (066) and rotational (008) excitation. The potential surface143 appears to be predominantly repulsive but the heavy mass of the attacking atom relative to the light transferred atom channels the energy of repulsion into product vibration. This is termed mixed energy release on a repulsive potential surface. 

What we should like to have is a suitable average over the two bands and all directions, for this will give the correct density of heavy-hole states per unit energy. Since the heavy holes dominate the total density of states, the corresponding mass will be appropriate for a description of properties that depend directly on the density of states. Such values have been estimated by Lawaetz (1971) they are given in Table 6-3 and are compared with the values of nth obtained from... 

The normal, paramagnetic state 2.1. About the origin of heavy masses... 

Renormalized f phase shifts Heavy masses CEF states... 

The underlying normal heavy fermion state of UPts, which was the first system where heavy quasiparticles have directly been seen in dHvA oscillations (Taillefer and Lonzarich, 1988), has been described above. It was argued that the picture of heavy quasiparticle mass generation in 5f-metals has to be revised. This is due to a considerably different degree of localisation of 5f-electrons in different orbital states as opposed to the simple LDA picture which assumes complete delocalisation for all 5f-orbitals. 

We have ended this review with heavy-fermion systems. In fact, in terms of their hybridization, they lie intermediate between the materials discussed in sect. 4, and those discussed in sect. 5. What is extraordinaiy about the heavy-fermion compounds, and has been responsible for the great interest in them, has been the formation of a correlated state at low temperature. That the superconductivity appearing in some of these systems is intimately connected, if not driven by, the magnetic interactions is beyond doubt, although a complete theory is still lacking. The heavy-fermion state involves both the localized-like f electrons and the conduction-electron states. For example, extremely laige masses are seen in the de Haas-van Alphen experiments (Reinders et al. 1986, Taillefer and Lonzarich 1988), but these do not account for all the susceptibility a large... 

Nc is the carrier concentration at 7 = 0 in the partially filled quasiparticle conduction bands including the d electrons, and AE is the gap or pseudo gap. poiE) is the density of states (DOS) per cell and per eV In some theories it is assumed that the heavy mass quasiparticles hardly contribute to the conductivity process. However, a simple estimate shows that there are about 10 times more heavy-f-like quasiparticles within k T of Ep than d electrons, so if their effective mass would be lOOOw they would contribute about the same to the conductivity than the light weight d electrons. By imposing in order to keep the total number of heavy quasiparticles unchanged,... 

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