Electronic transport through ballistic chaotic cavities: Reflection symmetry, direct processes, and symmetry breaking

We extend previous studies on transport through ballistic chaotic cavities with spatial left-right (LR) reflection symmetry to include the presence of direct processes. We first analyze fully LR-symmetric systems in the presence of direct processes and compare the distribution w(T) of the transmission coefficient T with that for an asymmetric cavity with the same ``optical'' S matrix. We then study the problem of ``external mixing'' of the symmetry caused by an asymmetric coupling of the cavity to the outside. We first consider the case where symmetry breaking arises because two symmetrically positioned waveguides are coupled to the cavity by means of asymmetric tunnel barriers. Although this system is asymmetric with respect to the LR operation, there is an effect of the symmetry of the cavity it was constructed from. Second, we break LR symmetry in the absence of direct processes by asymmetrically positioning the two waveguides and compare the results with those for the completely asymmetric case.