Pure Spin Currents via Antisymmetric Light.

Abstract

Pure spin currents, the flow of spin in the absence of charge flow, represent a promising route toward energy efficient next-generation electronics. Creating such currents often involves designed nanostructures, which can be challenging to create in experiment. Here, relying only on intrinsic material properties, we "shift the design" to the light pulse. Antisymmetric laser pulses, those whose vector potential changes sign when time is inverted about the pulse center, are shown to generate pure spin current at ultrafast few femtosecond times. While defects in designed nanostructures can rapidly degrade the efficiency of pure spin current generation, "light defects" from antisymmetry have only a weak effect on the robustness of the pure spin currents generated. Applied to graphene, such pulses generate pure valley currents on a few femtosecond times. Our approach thus offers a robust route toward the creation and control of pure spin and valley currents at ultrafast times.