The Onsager relations applied to electronic transport state that the
conductance of a two-terminal conductor is an even function of the
magnetic field. However, breakings of this symmetry may take place in
the nonlinear regime. We find that magnetic-field asymmetries indeed
arise in mesoscopic systems out of equilibrium but, interestingly, only
as a consequence of the charge response of the conductor, thus being a
pure interaction effect [1]. We illustrate this result for two types of
conductors: a quantum Hall bar with an antidot and a ballistic chaotic
cavity connected to quantum point contacts. For the latter, we obtain
through random matrix theory an asymmetry in the fluctuations of the
nonlinear conductance. A metallic diffusive cavity has been recently
treated [2] whereas experiments are currently in progress [3].
[1] D. Sanchez and M. Buttiker, condmat/0404387 (unpublished).
[2] B. Spivak and A. Zyuzin, cond-mat/0404408 (unpublished).
[3] D.M. Zumbuhl, C.M. Marcus, M. Hanson, and A.C. Gossard, in
preparation (2004).