RF wave mixing with sliding charge-density waves

We report I–V curves of quasi one-dimensional charge-density wave (CDW) conductors under simultaneous impacts of rf voltage at two frequencies, F and f, with F ≫ f. We find that each Shapiro step (ShS) induced by F-irradiation behaves as a “host” surrounded with “satellites” induced by f-irradiation, e.g., by ShSs at the CDW currents corresponding to F ± f. The subharmonic “hosts” are surrounded with subharmonic “satellites,” e.g., by ShSs at the CDW currents corresponding to F/2 ± f/2. The hosts and satellites show oscillations of their widths as a function of rf amplitude. We demonstrate that each satellite can be treated as a conventional ShS, if its host ShS is taken as a reference point at which the CDW is resting. Thus, with the help of rf irradiation one can emulate CDW samples with tunable threshold voltages and extremely coherent sliding modes.