Topological two-parameter charge pump in a one-dimensional semiconductor nanowire superlattice

Abstract

We study a possible topological charge pump in a traditional two-parameter pump device, which is based on a one-dimensional (1D) semiconductor nanowire with Rashba spin-orbit interaction. The 1D nanowire has a superlattice structure through periodic folding and the pumping parameters are the two time-dependent Zeeman fields with a phase lag $\ensuremath{\varphi}$ between them. It is shown that the Zeeman field can open an energy gap of the nanowire superlattice and the system enters into a topological state. There are two electron charges pumped out adiabatically in a pumping cycle if the Fermi energy resides in the energy gap and $\ensuremath{\varphi}$ is not close to $n\ensuremath{\pi}$ ($n$, an integer). This originates from the topologically protected interface state forming between the two pumping sources, which evolves with time, resulting in electron charges from one end transported to the other end of the wire. The quantized current direction can be modulated by some system parameters such as the Fermi energy, pumping phase, and the local potential of the device via gate voltage.