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Strongly correlated electron systems with lattice frustration is an area of significant scientific interest. An interplay between strong electronic localization and frustration leads to a complex phase diagram : in some special cases the spin fluctuations might be strong enough to destroy the Neel ordering. As it was suggested by Anderson this is the case for the triangular lattice, in which RVB-state may become a ground state.
We discuss an importance of a k-dependent self-energy obtained by the self-consistent scheme for the energetics of the Hubbard model on a triangular lattice. A dual fermion approach - a perturbative scheme around DMFT as a zeroth order approximation is employed. It is shown that in the certain interval of parameter U the spin liquid phase have a lower total energy than the Neel ordered state thus corresponding to a ground state. The formation of magnetic moments in Neel and spin liquid phases is also discussed. It is shown that the spectral function of the spin-liquid Mott insulator is determined by a formation of local singlets which results in an energy gap about two times larger than that of the noncollinear antiferromagnetic Neel state. |
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