Spintronic terahertz emission with manipulated polarization (STEMP)

Coherent polarization control of terahertz emission from graphene under excitation of two-color co-circularly polarized laser fields

Coherent polarization control of terahertz (THz) emission is crucial for applications in the THz field. Here, we demonstrate that the polarization of THz waves emitted from graphene through quantum interference can be coherently controlled by varying the relative phase between the co-circularly polarized laser fields. The polarization state of the THz wave emitted from graphene remains linearly polarized, while its direction can be arbitrarily changed by varying the relative phase. This work not only achieves the coherent polarization control of the THz waves emitted from graphene but also promotes the fundamental research of THz photonics in graphene.

Electric-field control of nonlinear THz spintronic emitters

Energy-efficient spintronic technology holds tremendous potential for the design of next-generation processors to operate at terahertz frequencies. Femtosecond photoexcitation of spintronic materials generates sub-picosecond spin currents and emission of terahertz radiation with broad bandwidth. However, terahertz spintronic emitters lack an active material platform for electric-field control. Here, we demonstrate a nonlinear electric-field control of terahertz spin current-based emitters using a single crystal piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) that endows artificial magnetoelectric coupling onto a spintronic terahertz emitter and provides 270% modulation of the terahertz field at remnant magnetization. The nonlinear electric-field control of the spins occurs due to the strain-induced change in magnetic energy of the ferromagnet thin-film. Results also reveal a robust and repeatable switching of the phase of the terahertz spin current. Electric-field control of terahertz spintronic emitters with multiferroics and strain engineering offers opportunities for the on-chip realization of tunable energy-efficient spintronic-photonic integrated platforms.