Numerical-Diagonalization Study of Spin Gap Issue of the Kagome Lattice   Heisenberg Antiferromagnet
  We study the system size dependence of the singlet-triplet excitation gap in the $S=1/2$ kagome-lattice Heisenberg antiferromagnet by numerical diagonalization. We successfully obtain a new result of a cluster of 42 sites. The two sequences of gaps of systems with even-number sites and that with odd-number sites are separately analyzed. Careful examination clarifies that there is no contradiction when we consider the system to be gapless. 
Hiroki Nakano and Toru Sakai
cond-mat.mtrl-sci cond-mat.stat-mech cond-mat.str-el