In this study, we report the ultrafast excitation and dynamics of the carrier and photocurrent in a 3D typical topological insulator Sb2Te3. We utilize time-resolved optical pump-THz probe spectroscopy to explore the nonequilibrium carrier dynamics of Sb2Te3. The electron system undergoes an ultrafast relaxation and releases through intra-band and inter-band scattering. Additionally, THz emission spectroscopy is employed to investigate the different ultrafast photocurrents in Sb2Te3 through tuning the polarization of excitation pulses and rotating the sample's azimuthal angle. We distinguish the different ultrafast photocurrents driven by the linear photogalvanic effect, circular photogalvanic effect, and thermoelectric effect. Our results potentially enable an all-optical modulation of THz emission without any external bias field, which could play an important role in the development of topological insulator-based high-speed THz optoelectronic and opto-spintronic devices.

We observe terahertz (THz) emission in Mn3Sn, Mn3Sn/Pt, and Mn3Sn/Co films excited by a femtosecond laser pulse. In the Mn3Sn film and Mn3Sn/Pt heterostructures, the THz emission originates from both magnetic-dipole and superdiffusive transient spin current with different proportions. Our results unambiguously demonstrate that THz emission can be controlled by the spin structure of Mn3Sn. The (0001)-orientated Mn3Sn produces stronger THz emission than the (112¯0)-orientated counterpart because for the latter one, only half of the kagome planes of Mn3Sn are parallel to the field, which can be controlled by the external magnetic field. In the Mn3Sn/Co heterostructure, the Mn3Sn layer serves as a spin-to-charge converter. The (112¯0)-orientated Mn3Sn emits larger THz signals than (0001)-orientated Mn3Sn due to the anisotropic inverse spin Hall effect, determined by the relative relation between spin, charge current, and the kagome plane of Mn3Sn. The spin structure dependent THz radiations in noncollinear antiferromagnetic metal Mn3Sn provide versatility for both spintronics and THz optics.

We report the broadband emission of terahertz (THz) pulse in metallic patterned ferromagnetic heterostructures CoFeB/Pt based on inverse spin-Hall effect, by illuminating a train of linearly polarized 120-fs-wide laser pulses at 800 nm. The spatial-temporal distribution of charge currents by changing the length of the subwavelength rectangular metal blocks allows for not only effectively controlling the magnitude, but subtly tuning the center frequency and bandwidth of the emitted THz pulses. Our results will open new avenues for the study of modulated spintronic-based THz emitters.

Recently, ferromagnetic/nonmagnetic heavy metal heterostructures have been intensively investigated as terahertz (THz) emitters. The interconversion of spin‐to‐charge dynamics plays a central role for efficient emission of THz electromagnetic pulses. However, a direct observation of spin–charge interconversion in antiferromagnetic (AFM) materials occurring on the sub‐picosecond time scale remains a challenge. Herein, the magnetic‐field‐, pump‐fluence‐, and polarization‐dependent THz emission behaviors by a femtosecond optical pump in cobalt (Co)/Mn2Au nanometer heterostructure are experimentally investigated. The Co/Mn2Au bilayer generates sizable THz signals, whereas the Mn2Au/Pt bilayer does not show any THz emission. In addition, the thickness‐ and temperature‐dependent THz emission measurements indicate a direct relation between the THz amplitude and the conductivity of AFM Mn2Au layer. The results obtained will not only promote the fundamental understanding of ultrafast spin–charge interconversion in Co/Mn2Au heterostructures, but also provide a possibility of spectroscopic‐based spin current detector at THz‐frequency range.

Recently, ferromagnetic (FM) heterostructures have been demonstrated to emit THz radiation induced by femtosecond laser pulses. In such spintronic THz emitters, an in-plane external magnetic field is technological required to assist the orientations of the magnetization, which could be an obstacle for practical micro-electrooptic applications. Here, as a proof-of-concept, THz generation is based on the inverse spin Hall effect of the FM/Ta within a magnetic tunneling junction (MTJ) without external magnetic field. Furthermore, THz emission can be engineered by modulating of the tunneling conductivity within a photoexcited MTJ as the relative magnetizations of two FM layers change their alignments.