[1] Dagotto E et al 1992 Phys. Rev. B 45 5744

[2]Neaf F and Wang X 2000 Phys. Rev. Lett. 84 1320

[3]White S R et al 1994 Phys. Rev. Lett. 73 886

[4]Azuma M et al 1994 Phys. Rev. Lett. 73 3463

[5]Japaridze G I and Pogosyan E 2006 cond-mat/0603153v1

[6]Luca Capriotti et al 2004 Phys. Rev. Lett. 93
17

[7]Liu G H, Wang H L, and Tian G S 2008 Phys. Rev. B
77 214418

[8]Guo J L, Wang X L, and Song H S 2007 Chin. Phys.
Lett. 24 1448

[9]Liu Z S, Divis Martin, and Sechovsk\'{y Vladimir 2007
Chin. Phys. Lett. 24 1448

[10]Affleck I 1989 J. Phys.C: Cond. Matt. l 3047

[11]Greven M et al 1996 Phys. Rev. Lett. 77 1865

[12]Almeida J et al 2007 Phys. Rev. B 76 184428

[13]Haldane F D M 1982 Phys. Lett. A 93 464

[14]Schollw\"ock 2005 Rev. Mod. Phys. 77 259

[15]White S R 1992 Phys. Rev. Lett. 69 2863

[16]White S R 1993 Phys. Rev. B 48 10345

[17]Keisuke Totsukat et al 1995 J. Phys. C: Condens.
Matter 7 4895

[18]Kohno M, Takahashi M and Hagiwara M 1998 Phys. Rev.
B 57 1046

[19]Den Nijs M P M and Rommelse K 1989 Phys. Rev. B
40 4709

[20]White S R and Huse David A 1993 Phys. Rev. B
48 6

[21]F\'ath G, Legeza \"O and S\'olyom J 2001 Phys. Rev.
B 63 134403

[22]Zhu N S, Wang X Q and Chen C F 2000 Phys. Rev. B
63 012401

[23]Hung H H et al 2006 Phys. Rev. B 73 224433

[24]Hida K 1992 Phys. Rev. B 45 2207