Long spin diffusion lengths in doped conjugated polymers due to enhanced exchange coupling

Abstract

Carbon-based semiconductors such as conjugated organic polymers are of potential use in the development of spintronic devices and spin-based information processing. In particular, these materials offer a low spin-orbit coupling strength due to their relatively light constituent chemical elements, which should, in principle, favour long spin diffusion lengths. However, organic polymers are relatively disordered materials and typically have a carrier mobility that is orders of magnitude lower than crystalline inorganic materials. As a result, small spin diffusion lengths of around 50 nm have typically been measured using vertical organic spin valves. Here, we report measuring spin diffusion lengths in doped conjugated polymers using a lateral spin transport device architecture, which is based on spin pumping injection and inverse spin Hall detection. The approach suggests that long spin diffusion lengths of more than 1 mu m and fast spin transit times of around 10 ns are possible in conjugated polymer systems when they have a sufficiently high spin density (around 10(20)cm(-3)). We explain these results in terms of an exchangebased spin diffusion regime in which the exchange interactions decouple spin and charge transport.