247 research outputs found
One-Dimensional Multi-Band Correlated Conductors and Anderson Impurity Physics
A single Anderson impurity model recently predicted, through its unstable
fixed point, the phase diagram of a two band model correlated conductor, well
confirmed by Dynamical Mean Field Theory in infinite dimensions. We study here
the one dimensional version of the same model and extract its phase diagram in
this opposite limit of reduced dimensionality. As expected for one dimension,
the Mott metal-insulator transition at half filling is replaced by a dimerized
insulator-undimerized Mott insulator transition, while away from half filling
the strongly correlated superconductivity for inverted Hund's rule exchange in
infinite dimensions is replaced by dominant pairing fluctuations. Many other
aspects of the one dimensional system, in particular the field theories and
their symmetries are remarkably the same as those of the Anderson impurity,
whose importance appears enhanced.Comment: 4 pages, 1 figur
My friend Alex M\"uller
Alex, the main discoverer of high Tc superconductivity, was also a dear
friend. Here I offer a few frank anecdotes, possibly inaccurate in some details
but heartfelt and accurate in the substance, as a personal tribute to our
friendship.Comment: To appear on Physica C Superconductivity -- K. Alex M\"uller memorial
issu
Interacting hard-core bosons and surface preroughening
The theory of the preroughening transition of an unreconstructed surface, and
the ensuing disordered flat (DOF) phase, is formulated in terms of interacting
steps. Finite terraces play a crucial role in the formulation. We start by
mapping the statistical mechanics of interacting (up and down) steps onto the
quantum mechanics of two species of one-dimensional hard-core bosons. The
effect of finite terraces translates into a number-non-conserving term in the
boson Hamiltonian, which does not allow a description in terms of fermions, but
leads to a two-chain spin problem. The Heisenberg spin-1 chain is recovered as
a special limiting case. The global phase diagram is rich. We find the DOF
phase is stabilized by short-range repulsions of like steps. On-site repulsion
of up-down steps is essential in producing a DOF phase, whereas an off-site
attraction between them is favorable but not required. Step-step correlation
functions and terrace width distributions can be directly calculated with this
method.Comment: 15 pages, 13 figures, to appear on Phys. Rev.
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