Hamburg 2001 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 3: Schwere Fermionen

TT 3.5: Hauptvortrag

Montag, 26. März 2001, 10:30–11:00, A

Band Magnetism in the Two Channel Anderson Lattice Model — •Frithjof Anders — Institut für Festkörperphysik, Hochschulstr. 6, Technische Hochschule Darmstadt, 64289 Darmstadt

The two channel Anderson Model for uranium ions, comprised of a quadrupolar and a magnetic doublet, exhibits non-Fermi-liquid properties in the paramagnetic phase caused by incoherent spin scattering of a degenerate ground state. It is expected, that the residual entropy will be quenched by a phase transition. The magnetic properties of this model are investigated through the crossover from the Kondo to the weak mixed-valent regime using dynamical mean field theory. A magnetic transition is found in the crossover regime at incommensurable wave vectors. The tendency towards nearest neighbour anti-ferromagnetism is enhanced in the Kondo regime. However, a spin density wave transition, which has an increasing q-vector for a decreasing effective coupling J=V²/|є_f|, maintains the highest transition temperature T_m. At small coupling, T_m is governed by the RKKY energy scale J²ρ(0) in accordance with the Doniach criterion. We report hints to a ferro-magnetic transition in the mixed-valent regime.The origin of the competition between anti-ferromagnetism and spin density waves at small q wave-vectors are discussed. A connection to channel ordering and odd-frequency superconductivity is made.