Phenomenological model for the 0.7 conductance feature in quantum wires

One dimensional (1D) quantum wires exhibit a conductance feature near 0.7 x 2e^2/h in connection with many-body interactions involving the electron spin. With the possibility of exploiting this effect for novel spintronic device applications, efforts have focused on uncovering a complete microscopic theory to explain this conductance anomaly. Here we present conductance calculations based on a simple phenomenological model for a gate-dependent spin gap that are in excellent agreement with experimental data taken on ultra-low-disorder quantum wires. Taken together the phenomenology and experimental data indicate that the 0.7 feature depends strongly on the potential profile of the contact region, where the reservoirs meet the 1D wire. Microscopic explanations that may under-pin the phenomenological description are also discussed.