96,436 research outputs found
The Hawking-Page phase transitions in the extended phase space in the Gauss-Bonnet gravity
In this paper, the Hawking-Page phase transitions between the black holes and
thermal anti-de Sitter (AdS) space are studied with the Gauss-Bonnet term in
the extended phase space, in which the varying cosmological constant plays the
role of an effective thermodynamic pressure. The Gauss-Bonnet term exhibits its
effects via introducing the corrections to the black hole entropy and Gibbs
free energy. The global phase structures, especially the phase transition
temperature and the Gibbs free energy , are systematically
investigated, first for the Schwarzschild-AdS black holes and then for the
charged and rotating AdS black holes in the grand canonical ensembles, with
both analytical and numerical methods. It is found that there are terminal
points in the coexistence lines, and decreases at large electric
potentials and angular velocities and also decreases with the Gauss-Bonnet
coupling constant .Comment: 13 pages, 13 figure
Competing electronic orders on Kagome lattices at van Hove filling
The electronic orders in Hubbard models on a Kagome lattice at van Hove
filling are of intense current interest and debate. We study this issue using
the singular-mode functional renormalization group theory. We discover a rich
variety of electronic instabilities under short range interactions. With
increasing on-site repulsion , the system develops successively
ferromagnetism, intra unit-cell antiferromagnetism, and charge bond order. With
nearest-neighbor Coulomb interaction alone (U=0), the system develops
intra-unit-cell charge density wave order for small , s-wave
superconductivity for moderate , and the charge density wave order appears
again for even larger . With both and , we also find spin bond order
and chiral superconductivity in some particular
regimes of the phase diagram. We find that the s-wave superconductivity is a
result of charge density wave fluctuations and the squared logarithmic
divergence in the pairing susceptibility. On the other hand, the d-wave
superconductivity follows from bond order fluctuations that avoid the matrix
element effect. The phase diagram is vastly different from that in honeycomb
lattices because of the geometrical frustration in the Kagome lattice.Comment: 8 pages with 9 color figure
Exact solution of the one-dimensional Hubbard model with arbitrary boundary magnetic fields
The one-dimensional Hubbard model with arbitrary boundary magnetic fields is
solved exactly via the Bethe ansatz methods. With the coordinate Bethe ansatz
in the charge sector, the second eigenvalue problem associated with the spin
sector is constructed. It is shown that the second eigenvalue problem can be
transformed into that of the inhomogeneous XXX spin chain with arbitrary
boundary fields which can be solved via the off-diagonal Bethe ansatz method.Comment: published version, 15 pages, no figur
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