113 research outputs found
Pressure dependence of two-level systems in disordered atomic chain
The dependence of two-level systems in disordered atomic chain on pressure,
both positive and negative was studied numerically. The disorder was produced
through the use of interatomic pair potentials having more than one energy
minimum. It was found that there exists a correlation between the energy
separation of the minima of two-level systems Delta and the variation of this
separation with pressure. The correlation may have either positive or negative
sign, implying that the asymmetry of two-level systems may in average increase
or decrease with pressure depending on the interplay of different interactions
between atoms in disordered state. The values of Delta depend on the sign of
pressure.Comment: 5 pages, 5 figure
Unrestricted slave-boson mean-field approximation for the two-dimensional Hubbard model
The Kotliar-Ruckenstein slave-boson scheme is used to allow for an
unrestricted variation of the bosonic and fermionic fields on the saddle-point
level. Various inhomogeneous solutions, such as spin polarons and domain walls
are discussed within the two-dimensional Hubbard model and compared with
results of unrestricted Hartree-Fock (HF) calculations. We find that the
present approach drastically reduces the polarization of these states and leads
to increased delocalized wave functions as compared to the HF model. The
interaction between two spin polarons turns out to be attractive over a wide
range of the on-site repulsion U. In addition we obtain the crossover from
vertical to diagonal domain walls at a higher value of U than predicted by HF.Comment: 6 pages, 8 figures, Accepted for publication in Phys. Rev.
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