van der Waals (vdW) heterostructures, composed of stacked materials with varying symmetries, offer exceptional opportunities in electronics and optics due to their unique anisotropic properties. However, the influence of low-symmetry layer thickness on modulating anisotropic optical responses remains elusive. Here, we fabricate heterostructures by combining monolayer (1L) MoS₂ with ReS₂ layers of varying thickness, uncovering tunable optical anisotropy. The degree of excitonic line polarization increases with ReS₂ thickness, reaching saturation due to lattice relaxation at the heterostructure interface. Density functional (DFT) theory calculations confirm that the lattice reconstruction of MoS₂ is influenced by the number of low-symmetry ReS₂ layers, providing direct evidence of interlayer coupling effects. Remarkably, we observe anisotropy ratios as high as 2.01 and 2.12 for charged and neutral excitons, respectively, underscoring robust anisotropic optical behavior. Additionally, we demonstrate that external magnetic fields can effectively modulate this anisotropy, whereas temperature variations have a negligible impact on line polarization. These findings advance our understanding of the interplay between thickness, symmetry, and external stimuli in heterostructures, paving the way for designing advanced optical devices with precise polarization control.

Van der Waals heterostructures are emerging as a versatile platform for next-generation electronic and photonic devices due to their unique anisotropic properties. While extensive studies have addressed symmetry breaking in transition metal dichalcogenides (TMDCs), the influence of magnetic fields on optical anisotropy remains underexplored. Here, we present an isotropic/magnetic/anisotropic heterostructure composed of WSe₂, ReSe₂, and the magnetic material CrOCl, which induces in-plane anisotropy in monolayer WSe₂. Density functional theory (DFT) calculations reveal significant modulation of the in-plane charge density of WSe₂​ by ReSe₂​ and CrOCl, providing direct evidence of anisotropic electronic behavior. Photoluminescence measurements at 300 K and 1.7 K show strongly linearly polarized exciton emission, with magnetic fields ranging from -9 T to 9 T modulating the anisotropy. Specifically, the anisotropy is enhanced by up to 28.34% and reduced by 40.37% under different magnetic field directions. Temperature variations also influence the linear polarization, achieving anisotropy ratios of 2.34 for neutral excitons and 1.77 for charged excitons. These results underscore a robust approach to dynamically tuning optical anisotropy via magnetic and thermal controls, paving the way for advanced polarization-sensitive optoelectronic applications.

Atomically thin two-dimensional (2D) magnetic materials offer unique opportunities to enhance interactions between electron spin, charge, and lattice, leading to novel physical properties at low-dimensional scales. While extensive research has explored how breaking three-fold (C₃) rotational symmetry in transition metal dichalcogenides (TMDC) can induce optical anisotropy at heterointerfaces, the role of magnetism in modulating these anisotropic optical properties remains underexplored. Here, we engineer an antiferromagnet/semiconductor heterostructure by coupling isotropic MoWSe₂ with the low-symmetric antiferromagnet NiPS₃, introducing in-plane anisotropy in the MoWSe₂ alloy. Low-temperature photoluminescence (PL) measurements reveal a pronounced linear polarization-dependent exciton emission intensity at the MoWSe₂/NiPS₃ interface, with anisotropy ratios of 1.09 and 1.07 for charged and neutral excitons, respectively. Furthermore, applying an out-of-plane magnetic field results in a dramatic rotation of the exciton polarization direction by up to 90° at 9 T, significantly exceeding the previously reported maximum deflection of around 27°. This pronounced polarization rotation is not solely attributed to valley coherence, indicating a strong influence of the magnetic order in NiPS₃. These findings provide new insights into the role of magnetic ordering in tuning optical anisotropy in 2D materials, paving the way for the development of advanced polarization-sensitive optoelectronic and magneto-optic devices.

Dark excitons in group VI transition metal dichalcogenides (TMDCs) have garnered significant interest due to their extended charge lifetime, spin lifetime, and diffusion length compared to bright excitons, presenting exciting opportunities for quantum communication and optoelectronic devices. However, their optical insensitivity poses challenges for investigation and manipulation. Here, we employ a strain engineering approach to introduce localized strain in monolayer WSe₂ using a substrate with prepatterned holes, resulting in the hybridization of dark excitons with bright defect states. This hybridization significantly enhances photoluminescence (PL) intensity and reduces the linewidths of dark excitons by orders of magnitude. Additionally, the hybridized states exhibit unique features in temperature-dependent and linearly polarized PL spectra, with stable localization across a broad excitation power range (up to 0.4 mW) and tunable circular polarization under a magnetic field (87% at −9 T). These findings underscore strain engineering as an effective method for enhancing dark excitons and provide new insights into exciton physics in TMDCs, paving the way for advanced optoelectronic technologies.

Moiré superlattices based on twisted transition metal dichalcogenide (TMD) heterostructures have recently emerged as a promising platform for probing novel and distinctive electronic phenomena in two-dimensional (2D) materials. By stacking TMD monolayers with a small twist angle, these superlattices create a periodic modulation of the electronic density of states, leading to the formation of mini bands. These mini bands can exhibit intriguing properties such as flat bands, correlated electron behavior, and unconventional superconductivity. This review provides a comprehensive overview of recent progress in Moiré superlattices formed from twisted TMD heterostructures. It covers the theoretical principles and experimental techniques for creating and studying these superlattices, and explores their potential applications in optoelectronics, quantum computing, and energy harvesting. The review also addresses key challenges, such as improving the scalability and reproducibility of the fabrication process, emphasizing the exciting opportunities and ongoing hurdles in this rapidly evolving field.

Pressure exerts a profound influence on atomic configurations and interlayer interactions, thereby modulating the electronic and structural properties of materials. While high pressure has been observed to induce a structural phase transition in bulk PdSe₂ crystals, leading to a transition from semiconductor to metal, the high-pressure behavior of few-layer PdSe₂ remains elusive. Here, employing diamond anvil cell (DAC) techniques and high-pressure Raman spectroscopy, we investigate the structural evolution of layer-dependent PdSe₂ under high pressure. We reveal that pressure significantly enhances interlayer coupling in PdSe₂, driving structural phase transitions from an orthorhombic to a cubic phase. We demonstrate that PdSe₂ crystals exhibit distinct layer-dependent pressure thresholds during the phase transition, with the decrease of transition pressure as the thickness of PdSe₂ increases. Furthermore, our results of polarized Raman spectra confirm a reduction in material anisotropy with increasing pressure. This study offers crucial insights into the structural evolution of layer-dependent van der Waals materials under pressure, advancing our understanding of their pressure-induced behaviors.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have garnered considerable attention for their promising applications in sensors and optoelectronic devices, owing to their exceptional optical, electronic, and optoelectronic properties. However, the inherent high symmetry of TMD lattices imposes limitations on their functional versatility. Here, we present a strategy to disrupt the C₃ rotational symmetry of monolayer WSe₂ by fabricating a heterostructure incorporating WSe₂ and SiP flakes. Through comprehensive experimental investigations and first-principle calculations, we elucidate that in the WSe₂/SiP heterostructure, excitons—both neutral and charged—emanating from WSe₂ exhibit pronounced anisotropy, which remains robust against temperature variations. Notably, we observe an anisotropic ratio reaching up to 1.5, indicating a substantial degree of anisotropy. Furthermore, we demonstrate the tunability of exciton anisotropy through the application of a magnetic field, resulting in a significant reduction in the anisotropic ratio with increasing field strength, from 1.57 to 1.18. Remarkably, the change in heterojunction anisotropy ratio reaches 24.8% as the magnetic field increases. Our findings elucidate that the perturbation of the C₃ rotational symmetry of the WSe₂ monolayer arises from a non-uniform charge density distribution within the layer, exhibiting mirror symmetry. These results underscore the potential of heterostructure engineering in tailoring the properties of isotropic materials and provide a promising avenue for advancing the application of anisotropic devices across various fields.

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 Kand 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.