Spin degeneracy and conductance fluctuations in open quantum dots

The dependence of conductance fluctuations on parallel magnetic field is us ed as a probe of spin degeneracy in open GaAs quantum dots. The variance of fluctuations at high parallel field is reduced from the low-field variance (with broken time-reversal symmetry) by factors ranging from roughly 2 in a 1 mum(2) dot to greater than 4 in 8 mum(2) dots. The factor of 2 is expec ted for Zeeman splitting of spin-degenerate channels. A possible explanatio n for the larger suppression based on field-dependent spin-orbit scattering is proposed.