Anomalous spin excitations in a coupled spin-pseudospin model for anisotropic Hubbard ladders at quarter filling

By using the quantum Monte-Carlo and density-matrix renormalization group methods, we study the coupled spin-pseudospin Hamiltonian in one-dimension (1D) that models the charge-ordering instability of the anisotropic Hubbard ladder at quarter filling in a strong coupling limit. We here present the temperature dependence of the specific heat of the system to clarify consequences of the interplay between its spin and charge degrees of freedom. We show that there is a parameter and temperature region where the spin degrees of freedom are separated from the charge degrees of freedom and behave like a 1D antiferromagnetic Heisenberg model