In the 4/7 solid phase on the 2nd layer of 3He adsorbed on the graphite, the gapless quantum spin liquid is realized, which has attracted much attention. Although theoretical analyses based on multiple-spin exchange model have been extensively done so far, it has been still remaining issue how to explain the gapless ground state as well as the large saturation filed up to 10 Tesla.
We constructed the effective model for the 4/7 phase taking account of the density fluctuations between the 2nd and 3rd layers as a key factor, which has been neglected so far [1]. We found that the 4/7 solid phase is located near the solid-liquid boundary, and hence it is strongly affected by the density fluctuations. We clarified that the saturation field is enhanced by large density fluctuations. We also pointed out that the enhanced density fluctuations significantly contribute to the realization of the quantum spin liquid, which is essentially the same origin of the gapless spin liquid emerging near the Mott transition in the Hubbard model on geometrically frustrated lattices [2,3]. We also found that holes doped into the 4/7 solid phase move coherently by zero point motions, which form the energy bands with small Fermi surface. This naturally explains the temperature and hole-density dependences of the measured heat capacity, whose origin has not been clarified [4].
[1] S. Watanabe and M. Imada: J. Phys. Soc. Jpn. 76 (2007) 113603.
[2] H. Morita, S. Watanabe and M. Imada: J. Phys. Soc. Jpn. 71 (2002) 2109.
[3] S. Watanabe: J. Phys. Soc. Jpn. 72 (2003) 2042.
[4] S. Watanabe and M. Imada: J. Phys. Soc. Jpn. 78 (2009) 033603. <- Editor's Choice!
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Last updated: May 15 2016