Observation of surface-state transport in ultrathin Sb

We report magnetotransport studies of ultrathin Sb films. Sb has been identified as a topologically nontrivial element; as a semimetal, however, the interior states dominate the transport in bulk samples. In the ultrathin films studied here, quantum confinement suppresses the interior transport such that surface transport accounts for about $15%$ of the conduction in 10-bilayer-thick Sb structures. For thicknesses between 5 and 16 bilayers, the conduction increases linearly with film thickness, extrapolating to a finite remnant conductivity at zero film thickness. Weak antilocalization (WAL) is observed at low magnetic fields with thickness independent values of the phase breaking length and prefactor ($\ensuremath{\alpha}$) implying surface transport coupled to residual interior conduction. At high fields we see an evolution of the magnetoresistance (MR) field dependence from parabolic to sublinear as a function of film thickness. The data are reproduced by a simple model combining parallel parabolic MR from the interior and WAL from the surface.