Zusammenfassung
Low-dimensional quantum spin systems have been an interesting subject in the statistical physics for a long time. The Tomonaga-Luttinger liquid of magnons in 1D spin systems is one of established theory to describe spin liquids. The recent density matrix renormalization group study on the frustrated spin chain in magnetic field revealed that the dominant spin correlation changes from the ordinary transverse antiferromagnetic component to the longitudinal
incommensurate one in the Tomonaga-Luttinger liquid in some cases1. When this change occurs, in the presence of interchain interaction, the field-induced incommensurate long-range order would be realized. In the present study, using the numerical diagonalization, finite-size scaling and level spectroscopy, we present several phase diagrams including the field-induced incommensurate order, as well as the field-induced spin gap (magnetization plateau), in some typical quasi-1D systems; the distorted diamond chain 2 and the spin ladder with the ring and/or diagonal exchange interactions 3,4. This field-induced incommensurate order can be interpreted as the Bose-Einstein condensation of magnons. We will also discuss a possibility of the supersolid.
1) N.Maeshima, K. Okunishi, K.Okamoto and T. Sakai, Phys. Rev. Lett. 93 (2004) 127203; J. Phys.: Condens. Matter. 18 (2006) 4819-4826. \\
2) H. Kikuchi, Y. Fujii, M. Chiba, S. Mitsudo, T. Idehara, T. Tonegawa,K. Okamoto, T. Sakai, T. Kuwai and H. Ohta, Phys. Rev. Lett. 94 (2005) 227201. \\
3) T. Sakai and K. Okamoto, J. Phys. Chem. Solid 66 (2005) 1450.\\
4) T. Sakai and K. Okamoto, to appear in J. Phys.: Condens. Matter.
Nutzer