Magnetic fluctuations and self--energy effects in two--dimensional itinerant systems with van Hove singularity of electronic spectrum

Abstract

We investigate a competition of tendencies towards ferromagnetic and incommensurate order in two-dimensional fermionic systems within functional renormalization group technique using temperature as a scale parameter. We assume that the Fermi surface (FS) is substantially curved, lies in the vicinity of van Hove singularity points and perform an account of the self-energy corrections. It is shown that the character of magnetic fluctuations is strongly asymmetric with respect to the Fermi level position relatively to van Hove singularity (VHS). For the Fermi level above VHS we find at low temperatures dominant incommensurate magnetic fluctuations, while below VHS level we find indications for ferromagnetic ground state. In agreement with the Mermin-Wagner theorem, at finite temperatures and in small magnetic fields we obtain rather small magnetization, which appears to be a power-law function of magnetic field. It is found that the FS curvature is slightly increased by correlation effects, and the renormalized bandwidth decreases at sufficiently low temperatures.

26 pages, 14 figures, Submitted to Physical Review B

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• Incommensurate nematic fluctuations in the two-dimensional Hubbard model
• Incommensurate nematic fluctuations in two dimensional metals
• Resummation of fluctuations near ferromagnetic quantum critical points
• Self-energy effects in functional renormalization group flows of the two-dimensional $t$-$t^{\prime }$ Hubbard model away from van Hove filling
• Correlation Effects and Non-Collinear Magnetism in the Doped Hubbard Model
• Metal-insulator transition and antiferromagnetism in the generalized Hubbard model: Treatment of correlation effects
• Ferromagnetic instability in itinerant fcc lattice electron systems with higher order van Hove singularities: Functional renormalization group study
• Incommensurate magnetic order in rare earth and transition metal compounds with local moments
• Ferromagnetism, spiral magnetic structures and phase separation in the two-dimensional Hubbard model
• Self-energy effects in the Polchinski and Wick-ordered renormalization-group approaches
• Itinerant electron metamagnetism for lattices with van Hove density-of-states singularities near the Fermi level
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