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Studies in the quantum phase transitions of heavy fermion metals have raised the issue about the nature of the Fermi surface in antiferromagnetic heavy fermion metals [1]. Related question is also relevant to their ferromagnetic counterparts. I will describe some
recent work on the Kondo lattice model in the limit that the Kondo coupling is small compared to the RKKY exchange coupling. We map the spin-1/2 Heisenberg Hamiltonian for the local f-moment component to a quantum nonlinear sigma model; in the ferromagnetic case, there is also a Berry phase term that must be included. This leads to an effective coupling between the QNLsM fields and the conduction electrons, which are dominated by the component that corresponds to a forward-scattering of the latter. Using RG and other methods, we establish that the Fermi surfaces in both cases are small, in the sense that they do not ncorporate
the localized f-moments[2]. The implications for the global zero-temperature phase diagram[3], and for the Kondo destroying quantum criticality[4], will be discussed.
[1] S. Paschen et al, Nature 432, 881 (2004); P. Gegenwart et al, Science 315, 969 (2007); H. Shishido et al., JPSJ 74, 1103 (2005). [2] S. J. Yamamoto and Q. Si, PRL 99, 016401 (2007); to appear (2008). [3] Q. Si, Physica B378, 23-27 (2006). [4] J.-X. Zhu, S. Kirchner, R. Bulla, and Q. Si, PRL 99, 227204 (2007); M.T. Glossop and K. Ingersent, PRL 99, 227203 (2007). |
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