Quantum point contact with large localized spin: fractional quantization of the ballistic conductance

We analyze the conductance of the quantum point contact containing large localized spin J. The additional plateau is formed on a ballistic conductance staircase if only one propagating channel is rendered conducting. The conductance value at this plateau is shown to depend strongly on J and decrease from 3e^2/2h to e^2/h when J increases from 1/2 to infinity, which is in a good agreement with the experimental observations [D.J. Reilly, et al, Phys. Rev. B 63, 121311 (2001)].