Spinless fermions on frustrated lattices in a magnetic field.

The effect of a magnetic field on the kinetic energy of both a single and thermodynamic number of spinless fermions on frustrated lattices is investigated. Two topologically distinct lattices are studied. It is found that a flux of one flux quantum per site always lifts the frustration. More significantly, if the zero-field ground-state energy has lines or a plane of degeneracies in k space, then it is found that an arbitrary value of the flux lowers the single-particle energy. Furthermore, for such cases, at least one magnetic subband lies entirely below the zero-field ground-state energy. This enhances the band paramagnetism. The absolute minimum of the kinetic energy, in the thermodynamic limit, occurs when there is one flux quantum per site plus or minus one flux quantum per particle. © 1991 The American Physical Society