Eur. Phys. J. B 5, 543-550 (1998)
https://doi.org/10.1007/s100510050475

Mixed spin ladders with exotic ground states^*

Institut für Theoretische Physik, Universität Hannover, Appelstrasse 2, 30167 Hannover, Germany

Corresponding author: ^a kolezhuk@itp.uni-hannover.de

Received: 2 December 1997
Accepted: 28 January 1998
Published online: 15 October 1998

Abstract

We study the "mixed spin" isotropic ladder system having S=1 spins on one leg and S={1/2} spins on the other, with general-type exchange interactions between spins on neighboring rungs. A set of model Hamiltonians with exact ground states in the form of a certain matrix product wave function is obtained. We show that sufficiently strong frustration can lead to exotic singlet ground states with infinite (exponential) degeneracy. We also list a couple of rather simple models with nontrivial ground states, including a model with only bilinear exchange.