  Chiral molecules ionized by circularly polarized fields produce a
photoelectron current orthogonal to the polarization plane. This current has
opposite directions for opposite enantiomers and provides an extremely
sensitive probe of molecular handedness. Recently, such photoelectron currents
have been measured in the strong-field ionization regime, where they may serve
as an ultrafast probe of molecular chirality. Here we provide a mechanism for
the emergence of such strong-field photoelectron currents in terms of two
propensity rules that link the properties of the initial electronic chiral
state to the direction of the photoelectron current.
