Two-dimensional (2D) anisotropic materials have garnered significant attention in the realm of anisotropic optoelectronic devices due to their remarkable electrical, optical, thermal, and mechanical properties. While extensive research has delved into the optical and electrical characteristics of these materials, there remains a need for further exploration to identify novel materials and structures capable of fulfilling device requirements under various conditions. Here, we employ heterojunction interface engineering with black phosphorus (BP) to disrupt the C₃ rotational symmetry of monolayer WS₂. The resulting WS₂/BP heterostructure exhibits pronounced anisotropy in exciton emissions, with a measured anisotropic ratio of 1.84 for neutral excitons. Through a comprehensive analysis of magnetic-field-dependent and temperature-evolution photoluminescence spectra, we discern varying trends in the polarization ratio, notably observing a substantial anisotropy ratio of 1.94 at a temperature of 1.6 K and a magnetic field of 9 T. This dynamic behavior is attributed to the susceptibility of the WS₂/BP heterostructure interface strain to fluctuations in magnetic fields and temperatures. These findings provide valuable insights into the design of anisotropic optoelectronic devices capable of adaptation to a range of magnetic fields and temperatures, thereby advancing the frontier of material-driven device engineering.

Moiré superlattices, arising from the controlled twisting of van der Waals homostructures at specific angles, have emerged as a promising platform for quantum emission applications. Concurrently, the manipulation of strain provides a versatile strategy to finely adjust electronic band structures, enhance exciton luminescence efficiency, and establish a robust foundation for two-dimensional quantum light sources. However, the intricate interplay between strain and moiré potential remains partially unexplored. Here, we introduce a meticulously designed fusion of strain engineering and the twisted 2L-WSe₂/2L-WSe₂ homobilayers, resulting in the precise localization of moiré excitons. Employing low-temperature photoluminescence spectroscopy, we unveil the emergence of highly localized moiré-enhanced emission, characterized by the presence of multiple distinct emission lines. Furthermore, our investigation demonstrates the effective regulation of moiré potential depths through strain engineering, with the potential depths of strained and unstrained regions differing by 91%. By combining both experimental and theoretical approaches, our study elucidates the complex relationship between strain and moiré potential, thereby opening avenues for generating strain-induced moiré exciton single-photon sources.

Exploiting the valley degrees of freedom as information carriers provides new opportunities for the development of valleytronics. Monolayer transition metal dichalcogenides (TMDs) with broken space-inversion symmetry exhibit emerging valley pseudospins, making them ideal platforms for studying valley electronics. However, intervalley scattering of different energy valleys limits the achievable degree of valley polarization. Here, we constructed WSe₂/yttrium iron garnet (YIG) heterostructures and demonstrated that the interfacial magnetic exchange effect on the YIG magnetic substrate can enhance valley polarization by up to 63%, significantly higher than that of a monolayer WSe₂ on SiO₂/Si (11%). Additionally, multiple sharp exciton peaks appear in the WSe₂/YIG heterostructures due to the strong magnetic proximity effect at the magnetic–substrate interface that enhances exciton emission efficiency. Moreover, under the effect of external magnetic field, the magnetic direction of the magnetic substrate enhances valley polarization, further demonstrating that the magnetic proximity effect regulates valley polarization. Our results provide a new way to regulate valley polarization and demonstrate the promising application of magnetic heterojunctions in magneto-optoelectronics.

Moiré superlattices in van der Waals structures have emerged as a powerful platform for studying the novel quantum properties of two-dimensional materials. The periodic moiré patterns generated by these structures lead to the formation of flat mini-bands, which alter the electronic energy bands of the material. The resulting flat electronic bands can greatly enhance strong correlative interactions between electrons, leading to the emergence of exotic quantum phenomena, including moiré phonons and moiré excitons. While extensive research has been conducted on the exotic quantum phenomena in twisted bilayers of transition metal dichalcogenides (TMDs), and the regulatory effect of stacked layers on moiré excitons remains unexplored. In this study, we report the fabrication of a twisted WSe₂/WSe₂/WSe₂ homotrilayer with two twist angles and investigate the influence of stacked layers on moiré excitons. Our experiments reveal multiple moiré exciton splitting peaks in the twisted trilayer, with moiré potential depths of 78 and 112 meV in the bilayer and trilayer homostructures, respectively. We also observed the splitting of the moiré excitons at 90 K, indicating the presence of a deeper moiré potential in the twisted trilayer. Moreover, we demonstrate that stacked layers can tune the moiré excitons by manipulating temperature, laser power, and magnetic field. Our results provide a new physical model for studying moiré superlattices and their quantum properties, which could potentially pave the way for the development of quantum optoelectronics.

Recently, the discovery of a variety of moiré-related properties in the twisted vertical stacking of two different monolayers has attracted considerable attention. The introduction of small twist angles in transition metal dichalcogenide (TMD) heterostructures leads to the emergence of moiré potentials, which provide a fascinating platform for the study of strong interactions of electrons. While there has been extensive research on moiré excitons in twisted bilayer superlattices, the capture and study of moiré excitons in homostructure superlattices with layer-coupling effects remain elusive. Here, we present the observation of moiré excitons in the twisted 1L-WSe₂/1L-WSe₂ and 1L-WSe₂/2L-WSe₂ homostructures with various layer-coupling interactions. The results reveal that the moiré potential increases (~ 260%) as the number of underlying layers decreases, indicating the effect of layer coupling on the modulation of the moiré potential. The effects of the temperature and laser power dependence as well as valley polarization on moiré excitons were further demonstrated, and the crucial spectral features observed were explained. Our findings pave the way for exploring quantum phenomena and related applications of quantum information.

The formation of moiré superlattices in twisted van der Waals (vdW) homostructures provides a versatile platform for designing the electronic band structure of two-dimensional (2D) materials. In graphene and transition metal dichalcogenides (TMDs) moiré systems, twist angle has been shown to be a key parameter for regulating the moiré superlattice. However, the effect of the modulation of the twist angle on moiré potential and interlayer coupling has not been the subject of experimental investigation. Here, we report the observation of the modulation of moiré potential and intralayer excitons in the WS₂/WS₂ homostructure. By accurately adjusting the torsion angle of the homobilayers, the depth of the moiré potential can be modulated. The confinement effect of the moiré potential on the intralayer excitons was further demonstrated by the changing of temperature and valley polarization. Furthermore, we show that a detection of atomic reconstructions by the low-frequency Raman mapping to map out inhomogeneities in moiré lattices on a large scale, which endows the uniformity of interlayer coupling. Our results provide insights for an in-depth understanding of the behaviors of moiré excitons in the twisted van der Waals homostructure, and promote the study of electrical engineering and topological photonics.

Vertically stacked transition metal dichalcogenide (TMD) heterostructures provide an opportunity to explore optoelectronic properties within the two-dimensional limit. In such structures, spatially indirect interlayer excitons (IXs) can be generated in adjacent layers because of strong Coulomb interactions. However, due to the complexity of the multilayered heterostructure (HS), the capture and study of the IXs in trilayer type-II HSs have so far remained elusive. Here, we present the observation of the IXs in trilayer type-II staggered band alignment of MoS₂/MoSe₂/WSe₂ van der Waals (vdW) HSs by photoluminescence (PL) spectroscopy. The central energy of IX is 1.33 eV, and the energy difference between the extracted double peaks is 23 meV. We confirmed the origin of IX through PL properties and calculations by the density functional theory, we also studied the dependence of the IX emission peak on laser power and temperature. Furthermore, the polarization-resolved PL spectra of HS were also investigated, and the maximum polarizability of the emission peak of WSe₂ reached 11.40% at 6 K. Our findings offer opportunities for the study of new physical properties of excitons in TMD HSs and therefore are valuable for exploring the potential applications of TMDs in optoelectronic devices.

Moiré superlattices are formed by a lattice mismatch or twist angle in two-dimensional materials, which can generate periodical moiré potentials leading to strong changes in the band structure, resulting in new quantum phenomena. However, the experimental engineering of in-situ deformation of moiré heterostructures remains deficient. Here, we demonstrate a dynamic local deformation of the twisted heterostructures using a diamond anvil cell (DAC), enabling in-situ dynamic modulation of moiré potential in twisted WS₂–WSe₂ heterostructures at room temperature. Deformation of the twisted heterostructure increases the moiré potential, causing a red shift of the moiré exciton resonance, and observed the red shift of the intralayer exciton resonance up to 16.3 meV (less than 1.1 GPa). The blue shift of the interlayer excitons of twisted WS₂–WSe₂ heterostructures shows an evident transition of the pressure sensitive exciton, induced by the dominant effect of modifying the band structure on optical properties. Combined with the spectral changes of pressurized Raman, which further demonstrated that the DAC can efficiently regulate the interlayer coupling. Our results offer an effective strategy for in-situ dynamic modulation of moiré potential, providing a promising platform for the development of novel quantum devices.

Van der Waals heterostructures have recently emerged, in which two distinct transitional metal dichalcogenide (TMD) monolayers are stacked vertically to generate interlayer excitons (IXs), offing new opportunites for the design of optoelectronic devices. However, the bilayer heterostructure with type-II band alignment can only produce low quantum yield. Here, we present the observation of interlayer neutral excitons and trions in the MoSe₂/MoS₂/MoSe₂ trilayer heterostructure (Tri-HS). In comparison to the 8 K bilayer heterostructure, the addition of a MoSe₂ layer to the Tri-HS can significantly increase the quantum yield of IXs. It is believed the two symmetrical type-II band alignments formed in the Tri-HS could effectively promote the IX radiation recombination. By analyzing the photoluminescence (PL) spectrum of the IXs at cryogenic temperature and the power dependence, the existence of the interlayer trions was confirmed. Our results provide a promising platform for the development of more efficient optoelectronic devices and the investigation of new physical properties of TMDs.

Interlayer excitons (IX_S) are electron–hole pairs bound in the spatial separation layer by the Coulomb effect, and their lifetime is several orders of magnitude longer than that of direct excitons, providing an essential platform for long-lived exciton devices. The recent emergence of the van der Waals heterostructure (HS), which combines two layers of different transitional metal dichalcogenides (TMDs), has created new opportunities for IX research. Herein, we demonstrate the observation of double indirect interlayer excitons in the MoSe₂/WSe₂ HS using photoluminescence (PL) spectroscopy. The intensities of the two peaks are essentially the same, and the energy difference is 22 meV, which is perfectly in line with the calculation result of density functional theory. Furthermore, the experience of variable excitation power also proves that the splitting of the IXs originates from the conduction band spin-splitting of MoSe₂. The observation results provide a promising platform for further exploring the new physical properties and optoelectronic phenomena of TMD HS.