Controlling periodic Fano resonances of quantum acoustic waves with a giant atom coupled to a microwave waveguide.

Nanoscale Fano resonances, with applications from telecommunications to ultra-sensitive biosensing, have prompted extensive research. We demonstrate that a superconducting qubit, jointly coupled to microwave waveguides and an inter-digital transducer composite device, can exhibit acoustic Fano resonances. Our analytical framework, leveraging the Taylor series approximation, elucidates the origins of these quantum acoustic resonances with periodic Fano-like interference. By analyzing the analytical Fano parameter, we demonstrate that the Fano resonances and their corresponding Fano widths near the resonance frequency of a giant atom can be precisely controlled and manipulated by adjusting the time delay. Moreover, not just the near-resonant Fano profiles, but the entire periodic Fano resonance features can be precisely modulated from Lorentz, Fano to quasi-Lorentz shapes by tuning the coupling strength of the microwave waveguide. Our analytical framework offers insights into the control and manipulation of periodic Fano resonances in quantum acoustic waves, thereby presenting significant potential for applications such as quantum information processing, sensing, and communication.

Directly Unveiling the Energy Transfer Dynamics between Alq3 Molecules and Si by Ultrafast Optical Pump-Probe Spectroscopy.

The energy transfer (ET) between organic molecules and semiconductors is a crucial mechanism for enhancing the performance of semiconductor-based optoelectronic devices, but it remains undiscovered. Here, ultrafast optical pump-probe spectroscopy was utilized to directly reveal the ET between organic Alq3 molecules and Si semiconductors. Ultrathin SiO2 dielectric layers with a thickness of 3.2-10.8 nm were inserted between Alq3 and Si to prevent charge transfer. By means of the ET from Alq3 to Si, the SiO2 thickness-dependent relaxation dynamics of photoexcited carriers in Si have been unambiguously observed on the transient reflectivity change (ΔR/R) spectra, especially for the relaxation process on a time scale of 200-350 ps. In addition, these findings also agree with the results of our calculation in a model of long-range dipole-dipole interactions, which provides critical information for developing future optoelectronic devices.

The Key Role of Non-Local Screening in the Environment-Insensitive Exciton Fine Structures of Transition-Metal Dichalcogenide Monolayers.

In this work, we present a comprehensive theoretical and computational investigation of exciton fine structures of WSe2-monolayers, one of the best-known two-dimensional (2D) transition-metal dichalcogenides (TMDs), in various dielectric-layered environments by solving the first-principles-based Bethe-Salpeter equation. While the physical and electronic properties of atomically thin nanomaterials are normally sensitive to the variation of the surrounding environment, our studies reveal that the influence of the dielectric environment on the exciton fine structures of TMD-MLs is surprisingly limited. We point out that the non-locality of Coulomb screening plays a key role in suppressing the dielectric environment factor and drastically shrinking the fine structure splittings between bright exciton (BX) states and various dark-exciton (DX) states of TMD-MLs. The intriguing non-locality of screening in 2D materials can be manifested by the measurable non-linear correlation between the BX-DX splittings and exciton-binding energies by varying the surrounding dielectric environments. The revealed environment-insensitive exciton fine structures of TMD-ML suggest the robustness of prospective dark-exciton-based optoelectronics against the inevitable variation of the inhomogeneous dielectric environment.

Selective Photoexcitation of Finite-Momentum Excitons in Monolayer MoS2 by Twisted Light.

Twisted light carries a well-defined orbital angular momentum (OAM) of lℏ per photon. The quantum number l of its OAM can be arbitrarily set, making it an excellent light source to realize high-dimensional quantum entanglement and ultrawide bandwidth optical communication structures. In spite of its interesting properties, twisted light interaction with solid state materials, particularly two-dimensional materials, is yet to be extensively studied via experiments. In this work, photoluminescence (PL) spectroscopy studies of monolayer molybdenum disulfide (MoS2), a material with ultrastrong light-matter interaction due to reduced dimensionality, are carried out under photoexcitation of twisted light. It is observed that the measured spectral peak energy increases for every increment of l of the incident light. The nonlinear l-dependence of the spectral blue shifts is well accounted for by the analysis and computational simulation of this work. More excitingly, the twisted light excitation revealed the unusual lightlike exciton band dispersion of valley excitons in monolayer transition metal dichalcogenides. This linear exciton band dispersion is predicted by previous theoretical studies and evidenced via this work's experimental setup.