@misc{oai:repo.qst.go.jp:00066591,
 author = {Sakai, Toru and Nakano, Hiroki and Sakai, Toru},
 month = {Nov},
 note = {The S=1/2 kagome-lattice antiferromagnet is one of interesting frustrated quantum spin systems. The systems exhibit the quantum spin liquid behavior. The spin gap is an important physical quantity to characterize the spin liquid behavior. Whether the S=1/2 kagome-lattice antiferromagnet is gapless or has a finite spin gap, is still unsolved issue. We propose one of good methods to determine whether the spin excitation is gapless or gapped, based on the finite-size scaling analysis of the spin susceptibility calculated by the numerical diagonalization. The present analysis indicates that the kagome-lattice antiferromagnet is gapless, as well as the triangular-lattice antiferromagnet. 
[1]H. Nakano and T. Sakai, J. Phys. Soc. Jpn., 2011, 80, 053704
[2]T. Sakai and H. Nakano,  Phys. Rev. B, 2011, 83, 100405(R).
[3]H. Nakano and T. Sakai, J. Phys. Soc. Jpn., 2015, 84, 063705., YIPQS Long-Term and Nishinomiya-Yukawa Memorial Workshop Novel Quantum States in Condensed Matter 2017},
 title = {Quantum Spin Liquid of the Kagome- and Triangular-Lattice Antiferromagnets and Related Materials},
 year = {2017}
}