Refrigeration using magnetocaloric and electrocaloric effects in a Fermi-Hubbard optical dimer exposed to a heat bath
We consider a Fermi–Hubbard dimer exposed to external electromagnetic fields and a Fermi gas bath under the assumptions of a repulsive two-particle interaction and the half-filling condition. Using the exact diagonalization method, it was found that the entropy and heat capacity rapidly rise within distinct localized regions of the magnetic and electric fields at low temperatures. The behavior of the magnetic (electric) Grüneisen ratio denotes that the direction of the external field determines the magnetization or demagnetization (polarization or depolarization) due to the magnetocaloric (electrocaloric) effect among the lattice particles at a given temperature. At the same time, the isothermal entropic change as a function of the temperature indicates that refrigeration is optimized when the electric field along the line joining the two sites of the optical lattice is assisted by a transverse magnetic field.