Density-Dependent Spin Polarization in Ultra-Low-Disorder Quantum Wires

There is controversy as to whether a one-dimensional (1D) electron gas can spin polarize in the absence of a magnetic field. Together with a simple model, we present conductance measurements on ultra-low-disorder quantum wires supportive of a spin polarization at $B=0$. A spin energy gap is indicated by the presence of a feature in the range $(0.5–0.7)\times 2e^2/h$ in conductance data. Importantly, it appears that the spin gap is not constant but a function of the electron density. Data obtained using a bias spectroscopy technique are consistent with the spin gap widening further as the Fermi level is increased.