Spin and Orbital Angular Momentum Polarization in Thouless Topological Charge Pumping

Abstract

Quantized charge pumping in one-dimensional chiral wires has been widely studied in the context of topological physics in a (1+1)-dimensional synthetic space, yet the role of orbital and spin degrees of freedom in such topological pumps remains largely unexplored. Here, we examine how the topologically quantized charge pump in insulators generates spin polarizations, and assess whether this mechanism may offer distinct insight into the widely known spin-selective transport in chiral wires-commonly referred to as chirality-induced spin selectivity. We performed time-dependent Schrodinger equations of multi-orbital tight-binding Hamiltonians driven by a circularly polarized electric field. Our main findings are twofold. First, the intrinsic screw-like geometry of the system generates a distinctive winding structure governed by a single control parameter, in contrast to conventional adiabatic pumping mechanisms that require at least two independently modulated parameters, thereby providing a clear interpretation of one-dimensional pumping in terms of the topological structure in a (1+1)-dimensional Brillouin zone. Second, while the energy gap remains open throughout the pumping cycle, the Berry-phase driven real-time dynamics of the charge flow induces a nonequilibrium orbital polarization. Through spin-orbit coupling, this orbital response is partially converted into spin polarization whose direction is determined by the current and chirality. On the analogy between the synthetic (1+1)- and 2-dimensional topological insulators, we suggest that non-trivial spin-orbital dynamics may accompany the anomalous quantum charge Hall states of even-dimensional real materials.