Phase Diagram of the Triangular t-J Model with Multiple Spin Exchange in the Doped-Mott Region

We study the triangular $t$-$J$ model with multiple spin exchange interactions using exact diagonalization of small clusters, as a model of monolayer liquid $^3$He. A phase where the energy spectrum suggest the behaviors of spin-charge separation is realized in the doped-Mott region due to the competition between ferromagnetic two-spin and antiferromagnetic four-spin exchange interactions. This behavior gives an interpretation of the double peaked heat capacity recently observed in monolayer liquid $^3$He adsorbed on a graphite.