Spin functional renormalization group for dimerized quantum spin systems

We investigate dimerized quantum spin systems using the functional renormalization group approach proposed by Krieg and Kopietz [Phys. Rev. B 99, 060403(R) (2019)] which directly focuses on physical correlation functions avoids representation of spins in terms fermionic or bosonic auxiliary operators. Starting from decoupled dimers as initial condition for flow equations, we obtain spectrum triplet excitations well magnetization paramagnetic, ferromagnetic, thermally disordered phases at all temperatures. Moreover, compute full phase diagram a weakly coupled system three dimensions, including correct mean field critical exponents two points.