Transmission line model for channels with spin-momentum locking

We will present a simple transmission line model for channels with spin-momentum locking (SML) based on the Boltzmann formalism with four electrochemical potentials [1, 2], which can be used for both time-dependent and steady-state analysis on a wide variety of materials including topological insulators, Rashba interfaces and heavy metals. The model has two components: charge and spin which are coupled by a factor $p_0=\left(M-N\right)/\left(M+N\right)$ representing the degree of SML, where $M$ and $N$ are number of modes for forward moving up and down spins respectively. In normal metal channels ($p_0 = 0$), the charge and spin signals travel at different velocities resulting in spin charge separation. In spin-momentum locked channels, an additional spin signal accompanies the charge signal which suggests a new mechanism in such materials with possible spintronic applications. [1] Hong et al., Sci. Rep. 6, 20325 (2016). [2] Sayed et al., Sci. Rep. 6, 35658 (2016).