Gapless Spin Liquid Behavior in Two-Dimensional SolidHe3

Abstract

Direct demagnetization has been made for two-dimensional solid ${}^3\mathrm{H}\mathrm{e}$ in both the paramagnetic and the antiferromagnetic phases. The lowest temperature is about $10\mu \mathrm{K}$, judging from the observed magnetization for the paramagnetic solid ${}^3\mathrm{H}\mathrm{e}$. The magnetization of the antiferromagnetic solid ${}^3\mathrm{H}\mathrm{e}$ shows a gradual increase to about $10\mu \mathrm{K}$ for the $4/7$ phase adsorbed on both one layer of ${}^4\mathrm{H}\mathrm{e}$ and two layers of HD preplated graphite. This strongly suggests that the triangular antiferromagnet with the higher order multiple exchange has a quantum spin liquid ground state with nearly zero or extremely small spin gap less than $10\mu \mathrm{K}$.