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Magnetic Moment Screening in the Correlated Kondo Lattice Model
Peter Thalmeier,Mohammad Siahatgar,Burkhard Schmidt,Gertrud Zwicknagl 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.10
The local moments, magnetic correlations and susceptibility in the 2D half-filled correlated Kondo lattice model are studied. We calculate their dependence on the control parameters given by local exchange coupling JK and Coulomb repulsion U. Exact diagonalization (ED) approach for ground state properties as well as finite temperature Lanczos method (FTLM) for the uniform susceptibility are employed for small tiles on the square lattice. The competition of on-site screening and induced inter-site correlations leads to non-monotonic local moment dependence on U for weak Kondo coupling JK. In the large U limit the numerical results are compared to those of the analytical bond operator method in mean field treatment. The variation of the Kondo temperature scale with U is obtained from the temperature dependence of the susceptibility. A monotonic increase with U is found.
Self-energy effects and electron–phonon coupling in Fe–As superconductors
Choi, K-Y,Lemmens, P,Eremin, I,Zwicknagl, G,Berger, H,Sun, G L,Sun, D L,Lin, C T IOP Pub 2010 Journal of Physics, Condensed Matter Vol.22 No.11
<P>Doping and temperature dependent studies of optical phonon modes in Fe-122 pnictides are performed using Raman scattering experiments and compared with model calculations to elucidate the role of electron-phonon and spin-phonon interaction in this family of compounds. The frequency and linewidth of the B(1g) mode at around 210 cm(-1) is highlighted as appreciable anomalies at the superconducting and spin density wave transitions are observed that strongly depend on composition. We give estimates of the electron-phonon coupling related to this renormalization and calculate the phonon self-energy on the basis of a four-band model comparing different symmetries of the order parameters. In addition, we observe a pronounced quasi-elastic Raman response for the undoped compound, suggesting persisting magnetic fluctuations in the spin density wave state.</P>