Reconstruction of attosecond beating by interference of two-photon transitions in the bulk of solids

The reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) is one of the most widely used techniques for resolving ultrafast electronic dynamics in atomic and molecular systems. As it relies on the interference of photo-electrons in vacuum, similar interference has never been contemplated in the bulk of crystals. Using accurate numerical simulations in a realistic system, here we show that the interference of two-photon transitions can be recorded directly in the bulk of solids and read out with standard angle-resolved photo-emission spectroscopy. The phase of the RABBIT beating in the photoelectron spectra coming from the bulk of solids is sensitive to the relative phase of the Berry connection between bands and it experiences a shift of π as one of the quantum paths crosses a band. For resonant interband transitions, the amplitude of the RABBIT oscillation decays as the pump and probe pulses are separated in time due to electronic decoherence, providing a simple interferometric method to extract dephasing times.

An Engineered Biliverdin-Compatible Cyanobacteriochrome Enables a Unique Ultrafast Reversible Photoswitching Pathway

Cyanobacteriochromes (CBCRs) are promising optogenetic tools for their diverse absorption properties with a single compact cofactor-binding domain. We previously uncovered the ultrafast reversible photoswitching dynamics of a red/green photoreceptor AnPixJg2, which binds phycocyanobilin (PCB) that is unavailable in mammalian cells. Biliverdin (BV) is a mammalian cofactor with a similar structure to PCB but exhibits redder absorption. To improve the AnPixJg2 feasibility in mammalian applications, AnPixJg2_BV4 with only four mutations has been engineered to incorporate BV. Herein, we implemented femtosecond transient absorption (fs-TA) and ground state femtosecond stimulated Raman spectroscopy (GS-FSRS) to uncover transient electronic dynamics on molecular time scales and key structural motions responsible for the photoconversion of AnPixJg2_BV4 with PCB (Bpcb) and BV (Bbv) cofactors in comparison with the parent AnPixJg2 (Apcb). Bpcb adopts the same photoconversion scheme as Apcb, while BV4 mutations create a less bulky environment around the cofactor D ring that promotes a faster twist. The engineered Bbv employs a reversible clockwise/counterclockwise photoswitching that requires a two-step twist on ~5 and 35 picosecond (ps) time scales. The primary forward Pfr → Po transition displays equal amplitude weights between the two processes before reaching a conical intersection. In contrast, the primary reverse Po → Pfr transition shows a 2:1 weight ratio of the ~35 ps over 5 ps component, implying notable changes to the D-ring-twisting pathway. Moreover, we performed pre-resonance GS-FSRS and quantum calculations to identify the Bbv vibrational marker bands at ~659,797, and 1225 cm−1. These modes reveal a stronger H-bonding network around the BV cofactor A ring with BV4 mutations, corroborating the D-ring-dominant reversible photoswitching pathway in the excited state. Implementation of BV4 mutations in other PCB-binding GAF domains like AnPixJg4, AM1_1870g3, and NpF2164g5 could promote similar efficient reversible photoswitching for more directional bioimaging and optogenetic applications, and inspire other bioengineering advances.

Composition and Dimension Dependent Static and Dynamic Stabilities of Inorganic Mixed Halide Antimony Perovskites

Halide intermixing is an important approach to stabilise halide perovskite in the phase that gives the best optoelectronic properties, whereas replacing Pb is critical for eliminating the material toxicity to meet the requirements for domestic applications. Recently, all-inorganic lead-free Cs3Sb2I9 emerges as a promising lead-free absorber, with its optoelectronic properties being further controllable by manipulating its structural dimensionality (0D or 2D) via composition engineering. In particular, superior photoconversion efficiency (up to 5 %) under indoor illumination with high photostabilities have been demonstrated experimentally in 2D Cs3Sb2ClyI9-y}. To gain a more thorough understanding on how the properties of this family of materials are controlled by their chemistry and dimensionality, here, we employ density functional theory calculations to explore the phase stability, structural and electronic dynamics of Cs3Sb2X9 (X=Br and Cl) across 74 different combinations of composition/dimensionality. The results show that Cs3Sb2X9 solid solutions are predominantly stabilised by configurational entropy rather than enthalpy. In stark contrast to cubic inorganic lead/tin halides perovskites, Cs3Sb2X9 are dynamically more stable at 300 K, as reflected by their low vibrational anharmonicities, the values of which also exhibit weak compositional dependency. This consequentially reduces the strength of electron-phonon couplings, thus enhancing the photoexcited carrier lifetime in these materials, which further demonstrates their promising potential to be integrated into indoor photovoltaic devices.

Composition and Dimension Dependent Static and Dynamic Stabilities of Inorganic Mixed Halide Antimony Perovskites

Halide intermixing is an important approach to stabilise halide perovskite in the phase that gives the best optoelectronic properties, whereas replacing Pb is critical for eliminating the material toxicity to meet the requirements for domestic applications. Recently, all-inorganic lead-free Cs3Sb2I9 emerges as a promising lead-free absorber, with its optoelectronic properties being further controllable by manipulating its structural dimensionality (0D or 2D) via composition engineering. In particular, superior photoconversion efficiency (up to 5 %) under indoor illumination with high photostabilities have been demonstrated experimentally in 2D Cs3Sb2ClyI9-y}. To gain a more thorough understanding on how the properties of this family of materials are controlled by their chemistry and dimensionality, here, we employ density functional theory calculations to explore the phase stability, structural and electronic dynamics of Cs3Sb2X9 (X=Br and Cl) across 74 different combinations of composition/dimensionality. The results show that Cs3Sb2X9 solid solutions are predominantly stabilised by configurational entropy rather than enthalpy. In stark contrast to cubic inorganic lead/tin halides perovskites, Cs3Sb2X9 are dynamically more stable at 300 K, as reflected by their low vibrational anharmonicities, the values of which also exhibit weak compositional dependency. This consequentially reduces the strength of electron-phonon couplings, thus enhancing the photoexcited carrier lifetime in these materials, which further demonstrates their promising potential to be integrated into indoor photovoltaic devices.