6 papers
Spin-3/2 models on the Cayley tree -- optimum ground state approach
H. Niggemann, J. Zittartz
We present a class of optimum ground states for spin-3/2 models on the Cayley tree with coordination number 3. The interaction is restricted to nearest neighbours and contains 5 co…
Optimum ground states for spin-3/2 ladders with two legs
H. Niggemann, J. Zittartz
We construct the exact ground state for an antiferromagnetic spin-3/2 model on the two-leg ladder as an optimum ground state. The ground state contains a discrete parameter "sigma"…
Mixed Heisenberg Chains. II. Thermodynamics
H. Niggemann, G. Uimin, J. Zittartz
We consider thermodynamic properties, e.g. specific heat, magnetic susceptibility, of alternating Heisenberg spin chains. Due to a hidden Ising symmetry these chains can be decompo…
Mixed Heisenberg Chains. I. The Ground State Problem
H. Niggemann, G. Uimin, J. Zittartz
We consider a mechanism for competing interactions in alternating Heisenberg spin chains due to the formation of local spin-singlet pairs. The competition of spin-1 and spin-0 stat…
Quantum phase transition in spin-3/2 systems on the hexagonal lattice - optimum ground state approach
H. Niggemann, A. Klümper, J. Zittartz
Optimum ground states are constructed in two dimensions by using so called vertex state models. These models are graphical generalizations of the well-known matrix product ground s…
Optimum ground states for spin- chains
H. Niggemann, J. Zittartz
We present a set of {\em optimum ground states} for a large class of spin- chains. Such global ground states are simultaneously ground states of the local Hamiltonian,…