Frequency-dependent transport through a spin chain

Motivated by potential applications in spintronics, we study frequency-dependent spin transport in nonitinerant one-dimensional spin chains. We propose a system that behaves as a capacitor for the spin degree of freedom. It consists of a spin chain with two impurities a distance d apart. We find that at low energy (frequency), the impurities flow to strong coupling, thereby effectively cutting the chain into three parts, with the middle island containing a discrete number of spin excitations. At finite frequency, spin transport through the system increases. We find a strong dependence of the finite-frequency characteristics both on the anisotropy of the spin chain and the applied magnetic field. We propose a method to measure the finite-frequency conductance in this system.