A A Katanin

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Using the one-loop functional renormalization group technique, we evaluate the self-energy in the weak-coupling regime of the 2D t-t(') Hubbard model. At van Hove (vH) band fillings and at low temperatures, the quasiparticle weight along the Fermi surface (FS) continuously vanishes on approaching the (pi,0) point where the quasiparticle concept is invalid.(More)
Isotropic S = 1/2 quasi-one-dimensional antiferromagnets are considered within the bosonization method. The 1/z ⊥-corrections to the interchain mean-field theory (where z ⊥ is the number of nearest neighbors in transverse to chain directions) are obtained for the ground-state sublattice magnetization S 0 and Neel temperature T N. The corrections to T N make(More)
Phase diagrams of the two-dimensional one-band t-tЈ Hubbard model are obtained within the two-patch and temperature-cutoff many-patch renormalization group approaches. At small tЈ and at van Hove band fillings antiferromagnetism dominates, while with increasing tЈ or changing filling antiferromagnetism is replaced by d-wave superconductivity. Near tЈϭt/2(More)
The phase diagram of the two-dimensional extended one-band U-V-J Hubbard model is considered within a mean-field approximation and two-and many-patch renormalization-group ͑RG͒ approaches near the Van Hove band fillings. At small tЈ and JϾ0, mean-field and many-patch RG approaches give similar results for the leading spin-density-wave ͑SDW͒ instability,(More)
By means of the dynamical vertex approximation (DΓA) we include spatial correlations on all length scales beyond the dynamical mean-field theory (DMFT) for the half-filled Hubbard model in three dimensions. The most relevant changes due to nonlocal fluctuations are (i) a deviation from the mean-field critical behavior with the same critical exponents as for(More)
We consider a quantum two-dimensional O(N) ⊗ O(2)/O(N − 2) ⊗ O(2) diag nonlin-ear sigma model for frustrated spin systems and formulate its 1/N-expansion which involves fluctuating scalar and vector fields describing kinematic and dynamic interactions , respectively. The ground state phase diagram of this model is obtained within the 1/N-expansion and 2+ε(More)
We discuss the low-temperature behavior of the electronic self-energy in the vicinity of a ferromagnetic instability in two dimensions within the two-particle self-consistent approximation, functional renormalization group and Ward-identity approaches. Although the long-range magnetic order is absent at T > 0, the self-energy has a non-Fermi liquid form at(More)
We consider the two-dimensional t-t ′ Hubbard model with the Fermi level being close to the van Hove singularities. The phase diagram of the model is discussed. In a broad energy region the self-energy at the singularity points has a nearly-linear energy dependence. The corresponding correction to the density of states is proportional to ln 3 |ε|. Both(More)
The systems exhibiting quantum phase transitions (QPT) are investigated within the Ising model in the transverse field and Heisenberg model with easy-plane single-site anisotropy. Near QPT a correspondence between parameters of these models and of quantum φ 4 model is established. A scaling analysis is performed for the ground-state properties. The(More)
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