Compass-Heisenberg model on the square lattice —Spin order and elementary excitations
Max-Planck-Institut für Festkörperforschung - Heisenbergstrasse 1, D-70569 Stuttgart, Germany, EU
2 Marian Smoluchowski Institute of Physics, Jagellonian University - Reymonta 4, PL-30059 Kraków, Poland, EU
Accepted: 6 August 2010
We explore the physics of the anisotropic compass model under the influence of perturbing Heisenberg interactions and present the phase diagram with multiple quantum phase transitions. The macroscopic ground-state degeneracy of the compass model is lifted in the thermodynamic limit already by infinitesimal Heisenberg coupling, which selects different ground states with symmetry depending on the sign and size of the coupling constants —then low-energy excitations are spin waves, while the compass states reflecting columnar order are separated from them by a macroscopic gap. Nevertheless, nanoscale structures relevant for quantum computation purposes may be tuned such that the compass states are the lowest-energy excitations, thereby avoiding decoherence, if a size criterion derived by us is fulfilled.
PACS: 05.30.Rt – Quantum phase transitions / 75.10.Jm – Quantized spin models, including quantum spin frustration / 03.67.Pp – Quantum error correction and other methods for protection against decoherence
© EPLA, 2010