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TT: Fachverband Tiefe Temperaturen
TT 79: Correlated Electrons - Poster Session
TT 79.48: Poster
Wednesday, April 2, 2014, 15:00–19:00, P2
Strongly correlated system on frustrated lattices: Beyond the flat-band scenario — •J. Richter1, O. Derzhko2, O. Krupnitska2, and T. Krokhmalskii2 — 1University Magdeburg, Germany — 2Institute for Condensed Matter Physics, Ukraine
We consider the spin-1/2 antiferromagnetic Heisenberg model at high magnetic fields as well as the Hubbard model at low electron density on some frustrated lattices with almost dispersionless lowest one-particle band. Eliminating high-energy degrees of freedom we construct low-energy effective Hamiltonians which are much simpler than the initial ones. Based on the effective-model description we examine the low-temperature properties of the considered frustrated quantum Heisenberg antiferromagnets in the high-field regime. We also apply our approach to describe azurite. Interesting features of these highly frustrated spin models consist in a steep increase of the entropy at very small temperatures T and a characteristic extra low-T peak in the specific heat. The most prominent effect for spin models is the existence of a magnetic-field driven Berezinskii-Kosterlitz-Thouless phase transition occurring in the two-dimensional model [1].
For the Hubbard model we discuss the existence of ground-state ferromagnetism. While for the considered model for a completely flat band the ground state is paramagnetic, we find a transition to ground-state ferromagnetism driven by the on-site repulsion in case that the band becomes dispersive. We present the ground-state phase diagram for the Hubbard model on the frustrated diamond chain at 1/6 electron filling.
O.Derzhko et al., Phys. Rev. B 88, 094426 (2013)