1. S. Sachdev, in Low Dimensional Quantum Field Theories for Condensed Matter Physicists, edited by Y. Lu, S. Lundqvist, G. Morandi (World Scientific, Singapore, 1995)
2. J. Richter, J. Schulenburg, A. Honecker, in Quantum Magnetism, edited by U. Schollwöck, J. Richter, D.J.J. Farnell, R.F. Bishop (Springer-Verlag, Berlin, 2004), Lecture Notes in Physics, Vol. 645, p. 85
3. G. Misguich, C. Lhuillier, in Frustrated Spin Systems, edited by H.T. Diep (World Scientific, Singapore, 2005), p. 229
4. R.F. Bishop, P.H.Y. Li, D.J.J. Farnell, C.E. Campbell, Phys. Rev. B 82, 024416 (2010)
5. R. Darradi, J. Richter, D.J.J. Farnell, J. Phys.: Condens. Matter 17, 341 (2005)