Green's function approach to the magnetic properties of the kagome antiferromagnet

The $S=1\mathrm{/}2$ Heisenberg antiferromagnet is studied on the kagom'e lattice by using a Green’s function method based on an appropriate decoupling of the equations of motion. Thermodynamic properties as well as spin-spin correlation functions are obtained and characterize this system as a two-dimensional quantum spin liquid. Spin-spin correlation functions decay exponentially with distance down to low temperature and the calculated missing entropy at T=0 is found to be $0.46\ln 2$. Within the present scheme, the specific heat exhibits a single peak structure and a $T^2$ dependence at low temperature.