Ground state properties of antiferromagnetic spin-1/2 Heisenberg systems in external fields
Fledderjohann
Andreas
Fledderjohann, Andreas
aut
2001-05-23
2018-01-22
en
The present work investigates the influence of external perturbations on the ground
states of spin-1/2 antiferromagnetic Heisenberg chains and two-dimensional spin
lattices. The lifting of the well-known zero-energy excitations (soft modes) of
the unperturbed Heisenberg chain due to suitably chosen periodicities of applied
perturbations is presented. The evolution of excitation energies and transition
matrix elements is described by a complete set of differential equations and scaling
solutions for small perturbations are discussed. A variety of topic
quasi-one-dimensional spin systems (spin-Peierls chain, spin ladders in different
geometries) are then embedded in the descriptive scheme of periodically perturbed
Heisenberg chains. In particular, the energy gaps and, most noticeable, the formation
of magnetization plateaus occurring in these systems are discussed in a single
prediction scheme related to the soft mode positions of the previously unperturbed
chain. Plateaus due to various kinds of perturbations are furthermore shown to be
observable in static correlation functions of the perturbed chain. Particular emphasis
is laid on the consideration of processes of spontaneous breaking of symmetry.
The latter aspect is discussed for translationally invariant perturbations that
do not provide an explicit change of the periodicity of the spin system. The
presented investigations finally turn to two-dimensional spin systems first addressing
the formation of a non-zero staggered magnetization (long range order) for increased
two-dimensionality in terms of a translationally invariant perturbed (helical) spin
system. Finally, first stages of a present study on the formation of magnetization
plateaus in square spin lattices with frustrating diagonal couplings are given.
urn:nbn:de:hbz:468-20010694
2018-01-22T10:46:58.482Z
2018-01-22T12:05:26.291Z
published
Pub
fb08/habi2001/fledderjohann