Berlin 2018 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 94: Correlated Electrons: Other Theoretical Topics

TT 94.8: Vortrag

Donnerstag, 15. März 2018, 17:15–17:30, H 3010

Heisenberg-like model for correlated electrons and quantum spin fluctuations near magnetic instabilities — •Evgeny Stepanov — Radboud University, Institute for Molecules and Materials, 6525AJ Nijmegen, The Netherlands

Theory of magnetism and magnetic interactions is the one of the most attractive areas of physics nowadays. Nevertheless, a quantum nature of the exchange interaction that occurs between spins is not clear yet. Up to now, studies of magnetic interactions have been mostly limited to a classical description, which makes their generalization on the case of strongly correlated systems rather difficult.

Here we consider an extended Hubbard model for correlated electrons and derive a corresponding Heisenberg-like problem. Our approach is based on the Dual Boson theory, which allows to introduce quantum collective variables associated to bosonic excitations and separate charge and spin degrees of freedom. The obtained result for the exchange interaction accounts for important quantum fluctuations and improves Anderson's idea of the superexchange, which makes possible description of collective excitations in the most interesting physical regimes. Thus, the study of quantum spin fluctuations in paramagnetic (PM) phase near the PM to AFM phase transition allows to detect the antiferromagnetic ``soft'' mode and manifest the tendency of the system to the spin ordering before the actual transition to the ordered state happens. Importantly, the derived exchange interaction is expressed in terms of single-particle quantities, which can be efficiently used in realistic calculations of multiband systems.