The emerging two-dimensional ferromagnetic materials present atomic layer thickness and a perfect interface feature, which have become an attractive research direction in the field of spintronics for low power and deep nanoscale integration. However, it has been proven to be extremely challenging to achieve a room-temperature ferromagnetic candidate with well controlled dimensionality, large-scale production, and convenient heterogeneous integration. Here, we report the growth of wafer-scale two-dimensional Fe3GeTe2 integrated with a topological insulator of Bi2Te3 by molecular beam epitaxy, which shows a Curie temperature (T c ) up to 400 K with perpendicular magnetic anisotropy. Dimensionality-dependent magnetic and magnetotransport measurements find that T c increases with decreasing Fe3GeTe2 thickness in the heterostructures, indicating an interfacial engineering effect from Bi2Te3. The theoretical calculation further proves that the interfacial exchange coupling could significantly enhance the intralayer spin interaction in Fe3GeTe2, hence giving rise to a higher T c . Our results provide great potential for the implementation of high-performance spintronic devices based on two-dimensional ferromagnetic materials.

Polarization arbitrary manipulated terahertz (THz) pulses with a prescribed amplitude temporal evolution and deposited electric‐field vectors can promote many disruptive technologies and enable enormous applications in polarization‐sensitive THz spectroscopy and imaging, ultrafast THz optospintronics, information encryption, and space exploration. However, the severe shortage of dynamically tunable THz polarization devices has impeded the proliferation of THz science and technology. Herein, a method of efficient generation and arbitrary manipulation of chiral THz waves in the topological insulator (TI)–iron (Fe) heterostructures through delicately engineering the linear photogalvanic effect (LPGE) and spin‐to‐charge conversion (SCC) effect induced by femtosecond laser pulses is proposed and demonstrated. Utilizing the intrinsic merits of optical‐controlled LPGE and magnetic field direction‐adjusted SCC effect, the TI–Fe can radiate chiral THz waves with arbitrarily tailored chirality and ellipticity. To verify the capability of such a novel chiral THz source, helical substructure associates THz circular dichroism spectroscopy is implemented on several (bio)materials, exemplified by the beetle exoskeletons. Furthermore, ultrafast switching between two THz chirality states can be realized by a double‐pulse excitation scheme. Such versatile chiral THz emitters with high efficiency and easy integration may have some disruptive applications.

Arbitrary manipulation of broadband terahertz waves with flexible polarization shaping at the source has great potential in expanding numerous applications, such as imaging, information encryption, and all-optical coherent control of terahertz nonlinear phenomena. Topological insulators featuring unique spinmomentum-locked surface state have already exhibited very promising prospects in terahertz emission, detection, and modulation, which may lay a foundation for future on-chip topological insulator-based terahertz systems. However, polarization-shaped terahertz emitters based on topological insulators with an arbitrarily manipulated temporal evolution of the amplitude and the electric-field vector direction have not yet been explored. We systematically investigated the terahertz radiation from topological insulator Bi 2 Te 3 nanofilms driven by femtosecond laser pulses and successfully realized the generation of efficient chiral terahertz waves with controllable chirality, ellipticity, and principal axis. The convenient engineering of the chiral terahertz waves was interpreted by a photogalvanic effect (PGE)-induced photocurrent, while the linearly polarized terahertz waves originated from linear PGE-induced shift currents. Our work not only provides further understanding of femtosecond coherent control of ultrafast spin currents but also describes an effective way to generate spin-polarized terahertz waves at the source.

The ultrafast optoelectronic response in topological insulators (TIs) has been recognized as one of the keys for applications on quantum computing and high-speed devices, which thus has attracted great attention recently. In this work, we systematically investigate the ultrafast transient terahertz emission excited by femtosecond laser pulses in Bi2Te3 with terahertz emission spectroscopy serving as an ultrafast and contactless detector. The nonlinear terahertz emission surpasses the terahertz emission from the sum of the drift and diffusion current contributions even at oblique incidence with an incident angle up to 70°, manifesting remarkable surface nonlinear effects on TIs. Quantitatively comprehensive microscopic analysis of the nonlinear terahertz emission origins indicates the 120°-periodic azimuth-angle dependence, which reveals a microscopic picture that the nonlinear current flows along the Bi-Te bonds. Our exploration not only enhances the microscopic understanding of the nonlinear responses in TIs on a femtosecond timescale but also lays a foundation for their applications on high-speed and low-power-consumption devices and systems.

Future information technologies for low‐dissipation quantum computation, high‐speed storage, and on‐chip communication applications require the development of atomically thin, ultracompact, and ultrafast spintronic devices in which information is encoded, stored, and processed using electron spin. Exploring low‐dimensional magnetic materials, designing novel heterostructures, and generating and controlling ultrafast electron spin in 2D magnetism at room temperature, preferably in the unprecedented terahertz (THz) regime, is in high demand. Using THz emission spectroscopy driven by femtosecond laser pulses, optical THz spin‐current bursts at room temperature in the 2D van der Waals ferromagnetic Fe3GeTe2 (FGT) integrated with Bi2Te3 as a topological insulator are successfully realized. The symmetry of the THz radiation is effectively controlled by the optical pumping incidence and external magnetic field directions, indicating that the THz generation mechanism is the inverse Edelstein effect contributed spin‐to‐charge conversion. Thickness‐, temperature‐, and structure‐dependent nontrivial THz transients reveal that topology‐enhanced interlayer exchange coupling increases the FGT Curie temperature to room temperature, which provides an effective approach for engineering THz spin‐current pulses. These results contribute to the goal of all‐optical generation, manipulation, and detection of ultrafast THz spin currents in room‐temperature 2D magnetism, accelerating the development of atomically thin high‐speed spintronic devices.