Nonuniversal conductance steps in mesoscopic quantum wires

While the dc conductance in mesoscopic quantum wires is generally found to be quantized in units of ${2e}^{2}/h$, recent experiments on perfect quantum wires at low temperatures have revealed nonuniversal conductance steps ${(2e}^{2}/h)\ensuremath{\nu}$ with $\ensuremath{\nu}<1$. We argue that this surprising behavior may be attributed to the fact that transitions into occupied states below the Fermi level remain possible in open dc systems, where electrons can always diffuse further away.