Thermodynamics of correlated electrons in a magnetic field

We simulate the Hubbard-Hofstadter model using the numerically exact and unbiased determinant quantum Monte Carlo (DQMC) algorithm. We report the field and Hubbard interaction strength dependence of charge compressibility, fermion sign, local moment, magnetic structure factor, and specific heat. We find that some features of the non-interacting magnetic band structure are preserved in the presence of Hubbard repulsion and coexists with the Mott gap at half filling. We also find that incompressible regions of the phase diagram correspond to regions of improved fermion sign. At half filling, in the intermediate to strong coupling regime, we see that strong magnetic field delocalizes electrons and reduces the effect of Hubbard interaction on low-energy properties of the system.