  Paramagnetism or diamagnetism of a material are shown by parallel or
antiparallel directions, respectively, of the induced magnetization under the
influence of external magnetic field. Theoretical study of paramagnetic
susceptibility and diamagnetic susceptibility of non-interacting electrons
system are well described by Pauli's spin susceptibility and Landau-Peierls'
orbital susceptibility, respectively. For interacting electron systems, the
paramagnetic susceptibility has been widely studied by using Hubbard's electron
- electron interaction. However, due to its smaller value, the diamagnetic
susceptibility has not been studied. To investigate the enhancement of an
interacting electrons system, we study a generalized space and time-dependent
orbital susceptibility of conduction electron with a repulsive Hubbard's
electron - electron interaction. By using the retarded Green function
expression of the space and time-dependent orbital susceptibility, we found
that the orbital susceptibility is enhanced when Hubbard's electron - electron
interaction is negative.
