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TT: Tiefe Temperaturen

TT 3: Schwere Fermionen

TT 3.2: Talk

Monday, March 26, 2001, 09:45–10:00, A

Metamagnetism in heavy-Fermion systems — •D. Meyer and W. Nolting — Lehrstuhl Festkörpertheorie, Institut für Physik, Humboldt-Universität zu Berlin

We investigate the periodic Anderson model using dynamical mean-field theory in combination with the modified perturbation theory. In the vicinity of the ferromagnetic phase [1], a metamagnetic transition from a low- to a high-magnetization state is found with increasing fields. This is similar to the behaviour of several heavy-Fermion materials as e.g. CeRu₂Si₂ and UPt₃. For a certain range of field strengths, two self-consistent solutions exist, corresponding to the low- and the high-magnetization state. The former is, however, always the thermodynamically stable one. The metamagnetic transition, which occurs only for strong coupling strengths, is accompanied by striking correlations effects: the quasiparticle weight z_↑ (aligned with the field) vanishes at the transition. In contrary to this, z_↓ shows only a small step being finite in all cases. This manifests itself in the density of states as disappearance of the Kondo resonance for the spin-↑ channel. The vanishing quasiparticle weight should correspond to the experimentally seen maximum in the effective mass. Increasing the temperature, the transition becomes less pronounced and finally, vanishes. Our results also indicate a relation of the metamagnetic transition to possible magnetic-field induced valence transitions.

[1] D. Meyer, W. Nolting, Phys. Rev. B 62, 5657 (2000)