Quasiparticles bands

The complexity of our angular distribution spectra do not permit reliable extraction of mixing ratios for the I+I-l transitions in the Trgg 2 band. Assuming that these are pure Ml, a 10 fold increase in the experimental B(M1)/B(E2) is observed between the one and three quasiparticle bands. 

Origin and theory of unstable moments and quasiparticle bands... 

A different approach was used by Razafimandimby et al. (1984), d Am-brumenil and Fidde (1985) and Fulde et al. (1988) for the Kondo lattice to calculate quasiparticle bands. They start from the observation, Nozieres (1974), that for r a Fermi liquid description can be used for the scattering by Kondo ions. Its phase shift is assumed to have a resonant behaviour around the Fermi energy, with T defining the energy scale. A periodic lattice of resonant scattering centers then leads to narrow quasipartiele bands, whieh have been caleulated within the KKR formalism. In the simplest approximation they are equivalent to those obtained from the mean-field approximation of the Anderson lattice. The method of Razafimandimby et al. has been used for a realistic... 

It is suggestive that the narrow Kondo resonance states of individual 4f impurities will form heavy quasiparticle bands in a periodic lattice of 4f ions. A satisfactory microscopic theory of heavy-band formation has yet to be developed. The Hamiltonian of eq. (107) can be generalized to the lattice by introducing a Bose field h,- at every lattice site. However, in this model it is no longer practicable to restrict to physical states with = 1 at every site. The most successful approach so far consists in a mean-field approximation for the Bose field (Coleman 1985, 1987, Newns and Read 1987) that is valid for large N and r < It can be applied both for the impurity and the lattice model. It starts from the observation that in the limit with QJN= fixed, the rescaled... 

The first equation shows that the center of the quasiparticle bands lies at an energy above the original conduction band Fermi level. This should be compared with the position Tg = aT of the Kondo resonance in the impurity model. The second equation simply results from the charge constraint QflN = g, which is now enforced only on the average in contrast to the impurity model. The occupation f(0) is obtained by setting equal to the actual value of 1 IN. The quasiparticle bands are the result of a hybridization with an effective strength K Here r iT) is the average fraction of sites without f occupation,... 

Fig. 44. Transitions across hybridization gaps of the quasiparticle band structure (a) can, depending on the position of the chemical potential (assumed inside the pseudogap for this calculation), and on the other band-structure features, give rise to pronounced structures in the non-local interaction part Y = x K of the Stoner denominator [compare eqs. (19) and (20)] at small wavevectors (b). In (b) a = y/ir with y defined in eq. (20) is varied somewhat around its proper value of (Grewe and Welslau 1988) to exhibit the strong tendency towards a magnetic instability occurring for Y(9 it> i/ = 0) = l.

T. Miyake, and S. Saito, Quasiparticle band structure of carbon nanotubes. Physical Review B, 2003. 68(15) p. 155424. 

The calculation of realistic quasiparticle bands proceeds in several steps as schematically summarized in fig. 4. The first step is a standard LDA band structure calculation by means of which the effective single-particle potentials are self-consistently generated. The calculation starts, like any other ab-initio calculation, from atomic potentials and structure information. In this step, no adjustable parameters are introduced. The effective potentials and hence the phase shifts of the conduction states are determined from first principles to the same level as in the case of ordinary metals. The f-phase shifts at the lanthanide and actinide sites, on the other hand, are described by a resonance type expression... 

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