Reduction of mesoscopic conductance fluctuations due to Zeeman splitting in a disordered conductor without spin-orbit scattering

We have studied conductance fluctuations δg in a mesoscopic quasi-one-dimensional modulation-doped GaAs/AlGaAs heterojunction as a function of Fermi energy ${\mathrm{E}}_{\mathrm{F}}$ and applied magnetic field B at 1.3 K. Such a system has no, or negligibly small, spin-orbit scattering. We observe a reduction of the variance scrV(g(${\mathrm{E}}_{\mathrm{f}}$)) by a net factor of 4. This factor-of-4 reduction is a novel observation which is absent in a system with strong spin-orbit interaction and is due to the effect of the Zeeman splitting in breaking the spin degeneracy.