1. J.E. Hoffman, E.W. Hudson, K.M. Lang, V. Madhavan, S.H. Pan, H. Eisaki, S. Uchida, and J.C. Davis, Science 295 (2002) 466.
2. B. Lake, H.M.R. Rnnow, N.B. Christensen, G. Aeppli, K. Lefmann, D.F. McMorrow, P. Vorderwisch, P. Smeibidl, N. Mangkorntong, T. Sasagawa, M. Nohara, H. Takagi, T.E. Mason, Nature 415 (2002) 299.
3. B. Khaykovich, Y.S. Lee, S. Wakimoto, K.J. Thomas, R. Erwin, S.-H. Lee, M.A. Kastner, and R..J. Birgeneau, cond-mat/0112505.
4. 2. M. Vojta and S. Sachdev, Phys. Rev. Lett. 83 (1999) 3916
5. 3. M. Vojta, Y. Zhang and S. Sachdev, Phys. Rev. B62 (2000) 6721