1,578 research outputs found
Critical temperature and Ginzburg region near a quantum critical point in two-dimensional metals
We compute the transition temperature and the Ginzburg temperature
above near a quantum critical point at the boundary of an
ordered phase with a broken discrete symmetry in a two-dimensional metallic
electron system. Our calculation is based on a renormalization group analysis
of the Hertz action with a scalar order parameter. We provide analytic
expressions for and as a function of the non-thermal control
parameter for the quantum phase transition, including logarithmic corrections.
The Ginzburg regime between and occupies a sizable part of
the phase diagram.Comment: 5 pages, 1 figur
Correlated hopping of electrons: Effect on the Brinkman-Rice transition and the stability of metallic ferromagnetism
We study the Hubbard model with bond-charge interaction (`correlated
hopping') in terms of the Gutzwiller wave function. We show how to express the
Gutzwiller expectation value of the bond-charge interaction in terms of the
correlated momentum-space occupation. This relation is valid in all spatial
dimensions. We find that in infinite dimensions, where the Gutzwiller
approximation becomes exact, the bond-charge interaction lowers the critical
Hubbard interaction for the Brinkman-Rice metal-insulator transition. The
bond-charge interaction also favors ferromagnetic transitions, especially if
the density of states is not symmetric and has a large spectral weight below
the Fermi energy.Comment: 5 pages, 3 figures; minor changes, published versio
What are spin currents in Heisenberg magnets?
We discuss the proper definition of the spin current operator in Heisenberg
magnets subject to inhomogeneous magnetic fields. We argue that only the
component of the naive "current operator" J_ij S_i x S_j in the plane spanned
by the local order parameters and is related to real transport of
magnetization. Within a mean field approximation or in the classical ground
state the spin current therefore vanishes. Thus, finite spin currents are a
direct manifestation of quantum correlations in the system.Comment: 4 pages, 1 figure, published versio
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