3 research outputs found
An Exactly Solvable Model of Generalized Spin Ladder
A detailed study of an spin ladder model is given. The ladder
consists of plaquettes formed by nearest neighbor rungs with all possible
SU(2)-invariant interactions. For properly chosen coupling constants, the model
is shown to be integrable in the sense that the quantum Yang-Baxter equation
holds and one has an infinite number of conserved quantities. The R-matrix and
L-operator associated with the model Hamiltonian are given in a limiting case.
It is shown that after a simple transformation, the model can be solved via a
Bethe ansatz. The phase diagram of the ground state is exactly derived using
the Bethe ansatz equation
Absence of overscreened Kondo effect in ferromagnetic host
We study the low temperature behavior of a boundary magnetic impurity S'=1/2
in an open ferromagnetic Takhatajian-Babujian spin-S chain. For
antiferromagnetic Kondo coupling, it is show via Bethe ansatz solution that the
impurity spin is always locked into the critical behavior the bulk. At low
temperature, a local composite of spin S-1/2 forms near the impurity site and
its contribution to specific heat is of simple power law T^{1/2}. The absence
of overscreened Kondo effect is due to the large correlation length of host
spins which is divergent near the quantum critical point.Comment: 4 pages. to appear in Phys. Rev. B1(R4A)(2000
Ghost spins and novel quantum critical behavior in a spin chain with local bond-deformation
We study the boundary impurity-induced critical behavior in an integrable
SU(2)-invariant model consisting of an open Heisenberg chain of arbitrary
spin- (Takhatajian-Babujian model) interacting with an impurity of spin
located at one of the boundaries. For or , the
impurity interaction has a very simple form which
describes the deformed boundary bond between the impurity and the
first bulk spin with an arbitrary strength . With a weak
coupling , the impurity is completely compensated,
undercompensated, and overcompensated for , and as in the
usual Kondo problem. While for strong coupling , the
impurity spin is split into two ghost spins. Their cooperative effect leads to
a variety of new critical behaviors with different values of .Comment: 16 pages revtex, no figur