Low-temperature density matrix renormalization group using regulated polynomial expansion

We propose a density matrix renormalization group (DMRG) technique at finite temperatures. As is the case of the ground-state DMRG, we use a single-target state that is calculated by making use of a regulated polynomial expansion. Both static and dynamical quantities are obtained after a random-sampling and averaging procedure. We apply this technique to the one-dimensional Hubbard model at half filling and find that this gives excellent results at low temperatures.