Two-dimensional transition metal dichalcogenides (TMDs) have intriguing physic properties and offer an exciting platform to explore many features that are important for future devices. In this work, we synthesized monolayer WS₂ as an example to study the optical response with hydrostatic pressure. The Raman results show a continuous tuning of the lattice vibrations that is induced by hydrostatic pressure. We further demonstrate an efficient pressure-induced change of the band structure and carrier dynamics via transient absorption measurements. We found that two time constants can be attributed to the capture process of two kinds of defect states, with the pressure increasing from 0.55 GPa to 2.91 GPa, both of capture processes were accelerated, and there is an inflection point within the pressure range of 1.56 GPa to 1.89 GPa. Our findings provide valuable information for the design of future optoelectronic devices.

In this work, we reported a high-performance-based ultraviolet-visible (UV-VIS) photodetector based on a TiO₂@GaO_xN_y-Ag heterostructure. Ag particles were introduced into TiO₂@GaO_xN_y to enhance the visible light detection performance of the heterojunction device. At 380 nm, the responsivity and detectivity of TiO₂@GaO_xN_y-Ag were 0.94 A/W and 4.79 × 10⁹ Jones, respectively, and they increased to 2.86 A/W and 7.96 × 10¹⁰ Jones at 580 nm. The rise and fall times of the response were 0.19/0.23 and 0.50/0.57 s, respectively. Uniquely, at 580 nm, the responsivity of fabricated devices is one to four orders of magnitude higher than that of the photodetectors based on TiO₂, Ga₂O₃, and other heterojunctions. The excellent optoelectronic characteristics of the TiO₂@GaO_xN_y-Ag heterojunction device could be mainly attributed to the synergistic effect of the type-Ⅱ band structure of the metal–semiconductor–metal heterojunction and the plasmon resonance effect of Ag, which not only effectively promotes the separation of photogenerated carriers but also reduces the recombination rate. It is further illuminated by finite difference time domain method (FDTD) simulation and photoelectric measurements. The TiO₂@GaO_xN_y-Ag arrays with high-efficiency detection are suitable candidates for applications in energy-saving communication, imaging, and sensing networks.

On-demand modification of the electronic band structures of high-mobility two-dimensional (2D) materials is of great interest for various applications that require rapid tuning of electrical and optical responses of solid-state devices. Although electrically tunable superlattice (SL) potentials have been proposed for band structure engineering of the Dirac electrons in graphene, the ultimate goal of engineering emergent quasiparticle excitations that can hybridize with light has not been achieved. We show that an extreme modulation of one-dimensional (1D) SL potentials in monolayer graphene produces ladder-like electronic energy levels near the Fermi surface, resulting in optical conductivity dominated by intersubband transitions (ISBTs). A specific and experimentally realizable platform comprising hBN-encapsulated graphene on top of a 1D periodic metagate and a second unpatterned gate is shown to produce strongly modulated electrostatic potentials. We find that Dirac electrons with large momenta perpendicular to the modulation direction are waveguided via total internal reflections off the electrostatic potential, resulting in flat subbands with nearly equispaced energy levels. The predicted ultrastrong coupling of surface plasmons to electrically controlled ISBTs is responsible for emergent polaritonic quasiparticles that can be optically probed. Our study opens an avenue for exploring emergent polaritons in 2D materials with gate-tunable electronic band structures.