Prof. dr Oleg Derzhko, Acad.Sci. of Ukraine

Rigorous and numerical results for low-temperature thermodynamics of some flat-band Hubbard models

We consider some frustrated lattices which have one-electron states localized on isolated trapping cells or, in other words, which support a dispersionless (flat) one-electron band. We study the repulsion Hubbard model on these lattices and construct exact many-electron ground states for a wide range of low electron densities. We calculate the degeneracy of these states and, as a result, we obtain closed-form expressions for the low-temperature thermodynamic quantities around a particular value of the chemical potential. We illustrate our general arguments in some detail for a specific example, i.e. for the sawtooth Hubbard chain [1]. [1] O. Derzhko, A. Honecker, and J. Richter, Phys.Rev. B 76, 220402(R) (20007).