Yuzhou Zhao

Bismuth oxyselenide (Bi ₂ O ₂ Se) has emerged as a leading semiconductor candidate for next‐generation electronics and quantum phenomena research. However, its strong ionic interlayer bonding of Se layers fundamentally restricts the full potential of this otherwise promising quasi‐two‐dimensional (2D) material. In this work, we demonstrate chlorine substitution as an effective strategy to introduce van der Waals gaps and modify the electronic structure of the system. Through comprehensive transport and angle‐resolved photoemission spectroscopy (ARPES) measurements on Bi ₆ O ₆ Se ₂ Cl ₂ single crystal, an optimal Cl‐doping compound, we show that the key electronic features, including indirect bandgap, high electron mobility, and carrier effective mass, are well preserved, while the 2D character of the system is sufficiently enhanced. First‐principles calculations attribute this selective tunability to the unique spatial separation between conductive Bi‐O layers and dopant Se/Cl layers, which enables independent optimization of interlayer coupling and intralayer transport. Remarkably, our theoretical calculations combined with experimental observations project a broad bandgap engineering across a wide range (0.8 ∼ 3.5 eV) within the Bi ₂ O ₂ Se system. Our findings not only expand the application potential of Bi ₂ O ₂ Se‐based materials in optoelectronics, nanoelectronics, and fundamental research but also highlight spatial decoupling as a viable strategy for modifying the detailed electronic structure of quasi‐2D quantum systems.

Precise twist-angle control in van der Waals (vdW) moiré superlattices enables twistronic tuning of interfacial responses and emergent quantum states, but it remains unclear how atomic registry in three-dimensional stacks is linked to interlayer coupling and whether it can produce an internal twist degree of freedom without external torque. Here, we show that, via interlayer engineering, screw-dislocation-driven multilayer spiral WS ₂ exhibits a reversible pressure-induced rotation of second-harmonic-generation polar pattern that saturates near 1 GPa, corresponding to an effective average interlayer twist of 0.2° per layer. This compression-twist coupling arises from moiré defined hierarchy of stacking energies and the associated atomic reconstruction, which together generate a spontaneous rotational torque at a slipped, metastable interface and couple the twist angle to the interlayer spacing. Our findings establish twist-degree-of-freedom manipulation in vdW crystals, opening pathways to reshape correlation-driven behaviors in moiré-of-moiré architectures and to explore chiral elasticity beyond Cauchy continuum mechanics.

The phonon dynamics of breathing kagome material Nb ₃ Br ₈ are investigated via linearly polarized Raman spectroscopy and density-functional theory.

Studies of moiré systems have explained the effect of superlattice modulations on their properties, demonstrating new correlated phases¹. However, most experimental studies have focused on a few layers in two-dimensional systems. Extending twistronics to three dimensions, in which the twist extends into the third dimension, remains underexplored because of the challenges associated with the manual stacking of layers. Here we study three-dimensional twistronics using a self-assembled twisted spiral superlattice of multilayered WS₂. Our findings show an opto-twistronic Hall effect driven by structural chirality and coherence length, modulated by the moiré potential of the spiral superlattice. This is an experimental manifestation of the noncommutative geometry of the system. We observe enhanced light–matter interactions and an altered dependence of the Hall coefficient on photon momentum. Our model suggests contributions from higher-order quantum geometric quantities to this observation, providing opportunities for designing quantum-materials-based optoelectronic lattices with large nonlinearities.

Uniaxial strain has been widely used as a powerful tool for investigating and controlling the properties of quantum materials. However, existing strain techniques have so far mostly been limited to use with bulk crystals. Although recent progress has been made in extending the application of strain to two-dimensional van der Waals (vdW) heterostructures, these techniques have been limited to optical characterization and extremely simple electrical device geometries. Here, we report a piezoelectric-based in situ uniaxial strain technique enabling simultaneous electrical transport and optical spectroscopy characterization of dual-gated vdW heterostructure devices. Critically, our technique remains compatible with vdW heterostructure devices of arbitrary complexity fabricated on conventional silicon/silicon dioxide wafer substrates. We demonstrate a large and continuously tunable strain of up to −0.15% at millikelvin temperatures, with larger strain values also likely achievable. We quantify the strain transmission from the silicon wafer to the vdW heterostructure, and further demonstrate the ability of strain to modify the electronic properties of twisted bilayer graphene. Our technique provides a highly versatile new method for exploring the effect of uniaxial strain on both the electrical and optical properties of vdW heterostructures and can be easily extended to include additional characterization techniques.

Lateral heterostructures of two-dimensional (2D) transition metal dichalcogenides offer promise as platforms for a wide variety of applications from exotic physics to environmental control. Further development and study of these heterostructures require characterization methods that assess the quality of the heterostructures. Here, we extend current characterization strategies to create photoluminescence (PL), Raman, reflection contrast, and second harmonic generation (SHG) maps of individual monolayer core-shell WS2-MoS2 lateral heterostructures that were synthesized via water vapor assisted chemical vapor transport. Together, these methods provide the correlations required to resolve the effects of excitons, trions, lattice defects, strain, and alloying. The comparisons show substantial differences, especially in the regions near and at the narrow heterointerface. Comparisons between the different spectral maps show the importance of metal alloying for understanding the electronic and spatial structures of heterostructures. The results are compared to previous work on similar lateral heterostructures created by different methods.