19 research outputs found
Maintaining the quality of Western Australia\u27s oat harvest
WESTERN AUSTRALIA deservedly enjoys the reputation of being a producer of oats of high milling quality.
Because of this, we have been able to develop valuable export markets which pay a premium for our oats.
For some time Ballidu has been rated as the best milling oat in W.A.
The work reported in this article indicates that other recommended varieties are equal to or better than Ballidu for milling
Quadratic operators used in deducing exact ground states for correlated systems: ferromagnetism at half filling provided by a dispersive band
Quadratic operators are used in transforming the model Hamiltonian (H) of one
correlated and dispersive band in an unique positive semidefinite form coopting
both the kinetic and interacting part of H. The expression is used in deducing
exact ground states which are minimum energy eigenstates only of the full
Hamiltonian. It is shown in this frame that at half filling, also dispersive
bands can provide ferromagnetism in exact terms by correlation effects .Comment: 7 page
One-dimensional Kondo lattice at partial band filling
An effective Hamiltonian for the localized spins in the one-dimensional Kondo
lattice model is derived via a unitary transformation involving a bosonization
of delocalized conduction electrons. The effective Hamiltonian is shown to
reproduce all the features of the model as identified in various numerical
simulations, and provides much new information on the ferro- to paramagnetic
phase transition and the paramagnetic phase.Comment: 11 pages Revtex, 1 Postscript figure. To appear in Phys. Rev. Let
Ordering of localized moments in Kondo lattice models
We describe the transition from a ferromagnetic phase, to a disordered para-
magnetic phase, which occurs in one-dimensional Kondo lattice models with
partial conduction band filling. The transition is the quantum order-disorder
transition of the transverse-field Ising chain, and reflects double-exchange
ordered regions of localized spins being gradually destroyed as the coupling to
the conduction electrons is reduced. For incommensurate conduction band
filling, the low-energy properties of the localized spins near the transition
are dominated by anomalous ordered (disordered) regions of localized spins
which survive into the paramagnetic (ferromagnetic) phase. Many interesting
properties follow, including a diverging susceptibility for a finite range of
couplings into the paramagnetic phase. Our critical line equation, together
with numerically determined transition points, are used to determine the range
of the double-exchange interaction. Models we consider are the spin 1/2 Kondo
lattices with antiferromagnetic (Kondo) coupling, with ferromagnetic (Hund's
rule) coupling, and the Kondo lattice with repulsive interactions between the
conduction electrons.Comment: 18 pages, 6 embedded eps figures. To appear in Phys Rev
Phase diagram of the anisotropic Kondo chain
We establish the phase diagram of the one-dimensional anisotropic Kondo
lattice model at T=0 using a generalized two-dimensional classical Coulomb gas
description. We analyze the problem by means of a renormalization group (RG)
treatment. We find that the phase diagram contains regions of paramagnetism,
partial and full ferromagnetic order.Comment: Final version to appear in Physical Review Letter
Effect of disorder on quantum phase transitions in anisotropic XY spin chains in a transverse field
We present some exact results for the effect of disorder on the critical
properties of an anisotropic XY spin chain in a transverse field. The continuum
limit of the corresponding fermion model is taken and in various cases results
in a Dirac equation with a random mass. Exact analytic techniques can then be
used to evaluate the density of states and the localization length. In the
presence of disorder the ferromagnetic-paramagnetic or Ising transition of the
model is in the same universality class as the random transverse field Ising
model solved by Fisher using a real space renormalization group decimation
technique (RSRGDT). If there is only randomness in the anisotropy of the
magnetic exchange then the anisotropy transition (from a ferromagnet in the
direction to a ferromagnet in the direction) is also in this universality
class. However, if there is randomness in the isotropic part of the exchange or
in the transverse field then in a non-zero transverse field the anisotropy
transition is destroyed by the disorder. We show that in the Griffiths' phase
near the Ising transition that the ground state energy has an essential
singularity. The results obtained for the dynamical critical exponent, the
typical correlation length, and the temperature dependence of the specific heat
near the Ising transition agree with the results of the RSRGDT and numerical
work.Comment: 22 pages, RevTeX + epsf, 4 figure