A Theoretical Analysis of Coherent Cross-Peaks in Polarization Selective 2DIR for Detection of Cross-α Fibrils

The coupled amide-I vibrational modes in peptide systems such as fibrillar aggregates can often provide a wealth of structural information, though the associated spectra can be difficult to interpret. Using exciton scattering calculations, we characterized the polarization selective 2DIR peak patterns for cross-α peptide fibrils, a challenging system given the similarity between the monomeric and fibrillar structures, and interpret the results in light of recently collected 2D data on the cross-α peptide PSMα3. We find that stacking of α-helices into fibrils couples the bright modes across helical subunits, generating three new Bloch-like extended excitonic states that we designate A⏊, E∥, and E⏊. Coherent superpositions of these states in broad-band 2DIR simulations lead to characteristic signals that are sensitive to fibril length, and match the experimental 2DIR spectra.

Giant enhancement of exciton diffusivity in two-dimensional semiconductors

Two-dimensional (2D) semiconductors bear great promise for application in optoelectronic devices, but the low diffusivity of excitons stands as a notable challenge for device development. Here, we demonstrate that the diffusivity of excitons in monolayer MoS2 can be improved from 1.5 ± 0.5 to 22.5 ± 2.5 square centimeters per second with the presence of trapped charges. This is manifested by a spatial expansion of photoluminescence when the incident power reaches a threshold value to enable the onset of exciton Mott transition. The trapped charges are estimated to be in a scale of 1010 per square centimeter and do not affect the emission features and recombination dynamics of the excitons. The result indicates that trapped charges provide an attractive strategy to screen exciton scattering with phonons and impurities/defects. Pointing towards a new pathway to control exciton transport and many-body interactions in 2D semiconductors.

Nonadiabatic exciton-phonon coupling in Raman spectroscopy of layered materials

We present an ab initio computational approach for the calculation of resonant Raman intensities, including both excitonic and nonadiabatic effects. Our diagrammatic approach, which we apply to two prototype, semiconducting layered materials, allows a detailed analysis of the impact of phonon-mediated exciton-exciton scattering on the intensities. In the case of bulk hexagonal boron nitride, this scattering leads to strong quantum interference between different excitonic resonances, strongly redistributing oscillator strength with respect to optical absorption spectra. In the case of MoS2, we observe that quantum interference effects are suppressed by the spin-orbit splitting of the excitons.

Exciton scattering via algebraic topology

This paper introduces an intersection theory problem for maps into a smooth manifold equipped with a stratification. We investigate the problem in the special case when the target is the unitary group [Formula: see text] and the domain is a circle. The first main result is an index theorem that equates a global intersection index with a finite sum of locally defined intersection indices. The local indices are integers arising from the geometry of the stratification. The result is used to study a well-known problem in chemical physics, namely, the problem of enumerating the electronic excitations (excitons) of a molecule equipped with scattering data.

Подавление электронно-дырочного обменного взаимодействия в резервуаре неизлучающих экситонов

Mechanisms of the suppression of the electron-hole exchange interaction in nonradiative excitons with a large in-plane wave vector in high-quality heterostructures with quantum wells are analyzed theoretically. It is shown that the dominant suppression mechanism is exciton-exciton scattering accompanied by the mutual spin flips of like carriers (either two electrons or two holes), comprising the excitons. As a result, the electron spin polarization in nonradiative excitons may be retained for a long time. The analysis of experimental data shows that this relaxation time can exceed one nanosecond. This long-term and optically controllable spin memory in an exciton reservoir may be of interest for future information technologies.

Unveiling lasing mechanism in CsPbBr3 microsphere cavities

The mechanism of single-mode lasing in CsPbBr3 microsphere shifts from exciton–exciton scattering to exciton–phonon scattering with the increase in temperature from 77 to 300 K, and two different phonon modes were involved in the exciton–phonon scattering process.