5,515 research outputs found
Polymer depletion effects near mesoscopic particles
The behavior of mesoscopic particles dissolved in a dilute solution of long,
flexible, and nonadsorbing polymer chains is studied by field-theoretic
methods. For spherical and cylindrical particles the solvation free energy for
immersing a single particle in the solution is calculated explicitly. Important
features are qualitatively different for self-avoiding polymer chains as
compared with ideal chains. The results corroborate the validity of the
Helfrich-type curvature expansion for general particle shapes and allow for
quantitative experimental tests. For the effective interactions between a small
sphere and a wall, between a thin rod and a wall, and between two small spheres
quantitative results are presented. A systematic approach for studying
effective many-body interactions is provided. The common Asakura-Oosawa
approximation modelling the polymer coils as hard spheres turns out to fail
completely for small particles and still fails by about 10% for large
particles.Comment: 68 pages, 6 figure
Correlated band structure of electron-doped cuprate materials
We present a numerical study of the doping dependence of the spectral
function of the n-type cuprates. Using a variational cluster-perturbation
theory approach based upon the self-energy-functional theory, the spectral
function of the electron-doped two-dimensional Hubbard model is calculated. The
model includes the next-nearest neighbor electronic hopping amplitude and
a fixed on-site interaction at half filling and doping levels ranging
from to . Our results support the fact that a comprehensive
description of the single-particle spectrum of electron-doped cuprates requires
a proper treatment of strong electronic correlations. In contrast to previous
weak-coupling approaches, we obtain a consistent description of the ARPES
experiments without the need to introduce a doping-dependent on-site
interaction .Comment: 7 pages 4 eps figure
Phase separation and competition of superconductivity and magnetism in the two-dimensional Hubbard model: From strong to weak coupling
Cooperation and competition between the antiferromagnetic, d-wave
superconducting and Mott-insulating states are explored for the two-dimensional
Hubbard model including nearest and next-nearest-neighbor hoppings at zero
temperature. Using the variational cluster approach with clusters of different
shapes and sizes up to 10 sites, it is found that the doping-driven transition
from a phase with microscopic coexistence of antiferromagnetism and
superconductivity to a purely superconducting phase is discontinuous for strong
interaction and accompanied by phase separation. At half-filling the system is
in an antiferromagnetic Mott-insulating state with vanishing charge
compressibility. Upon decreasing the interaction strength U below a certain
critical value of roughly U=4 (in units of the nearest-neighbor hopping),
however, the filling-dependent magnetic transition changes its character and
becomes continuous. Phase separation or, more carefully, the tendency towards
the formation of inhomogeneous states disappears. This critical value is in
contrast to previous studies, where a much larger value was obtained. Moreover,
we find that the system at half-filling undergoes the Mott transition from an
insulator to a state with a finite charge compressibility at essentially the
same value. The weakly correlated state at half-filling exhibits
superconductivity microscopically admixed to the antiferromagnetic order. This
scenario suggests a close relation between phase separation and the
Mott-insulator physics.Comment: 7 pages, 8 figures, revised version to be published in Phys. Rev.
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