Misfit layer compounds (MLCs) are a versatile platform for exploring the electronic phase diagram of two-dimensional (2D) materials beyond the limits of conventional gating techniques. This work demonstrates the precise tunability of electron doping in monolayers through chemical alloying within the rocksalt layer of heterostructures. By combining first-principles density functional theory (DFT) calculations with angle-resolved photoemission spectroscopy (ARPES), we prove that the rocksalt unit acts as a universal electron donor. We show that varying the La/Pb ratio results in a rigid Fermi level shift, still preserving the electronic structure. Crucially, photon-energy-dependent ARPES confirms that the layers nearly maintain their intrinsic 2D character and orbital identity within the three-dimensional misfit. This study establishes MLCs as a reliable platform for engineering emergent states in 2D transition metal dichalcogenides through precise stoichiometric control.
Techniques to generate megabar (100 GPa) pressure are critical for the study of materials under extreme conditions. However, kJ-class lasers are typically needed to generate such extreme pressures. Here, we present a method to reach megabar pressure on a benchtop using only tens of mJ a few millijoules of laser pulse energy. The core of our method is the utilization of multiple laser rings of different diameters and time delays to additively excite a focusing shock wave. Using high-speed imaging and a streak camera, we measured the shock trajectory and inferred pressure, temperature and density using hydrocode simulation. Our shock compression efficiency, informed by hydrocode, has achieved 23 GPa/mJ. If scaled up, our method may enable high-energy-density experiments on a benchtop.
We present a tabletop method to investigate how tailored laser excitation can enhance shock wave generation in water. By delivering two spatiotemporally separated laser pulses focused into a confined liquid layer, we identify an optimized excitation condition that maximizes the resulting shock pressure. Remarkably, dual-pulse laser excitation leads to an overall shock pressure that far exceeds the sum of the shock pressures generated by the individual pulses. This nonlinear amplification reveals a previously unexploited laser-matter interaction regime that overcomes saturation limits in laser-driven shock generation.
An accurate estimation of the molecular abundances of isomers in the interstellar medium (ISM) is necessary to unravel the underlying chemistry and physics. After the recent detection of both isomers of formic acid (cis- and trans-HCOOH) in dense dark cold clouds, their accurate molecular line modeling became of interest. The conditions of these environments do not necessarily follow the local thermodynamic equilibrium, thus taking into account the competition between the radiative and collisional processes is required. This involves knowledge of the rotational excitation data for collisions with the most abundant interstellar species - He and H2. In this paper, the first potential energy surface (PES) for the interaction of formic acid with He atoms is computed using the explicitly correlated coupled-cluster theory [CCSD(T)-F12]. The obtained interaction potentials for the two rotamers demonstrate qualitative similarities and high anisotropy. The global minima are found with V = -53.0 cm-1 and V = -46.0 cm-1 for cis-HCOOH and trans-HCOOH, respectively. Collisional excitation cross sections calculated for total energies up to 100 cm-1 demonstrate similar propensity rules for both isomers. Quantitative differences between the cross sections associated with the two rotamers are also discussed.
Carbon hydrides play a crucial role in the formation of complex organic molecules in highly UV illuminated regions of the interstellar medium (ISM). The formation of CH+ is the first step in the reactions leading to the formation of various carbon hydrides. CH+ formation is relatively well understood with strong agreement between theoretical and experimental results. However, its destruction by collision with the H atom, at low temperatures of interest in the ISM, is in contrast still not well understood and there is a large discrepancy between theoretical and experimental data [R. Plasil et al., AstroPhys. J., 2011, 737, 1], which are almost an order of magnitude smaller than various classical and quantum mechanical calculations. In this work we have computed and fitted a new set of non-adiabatic potential energy surfaces (PES) for the title system, including the three lower adiabatic states. We then investigate three possible sources of disagreement with the experimental results: non-adiabatic effects from regions near the conical intersections, and rotational and vibrational excitation of the CH+ molecule. We conclude that vibrational excitation of the CH+ plays a major role in reducing the reactivity at low temperatures, and we raise the question of whether vibrational thermalization of the CH+ is not fully achieved in the experiment. Such non-thermalized conditions could explain the decrease of the measured reaction rate constant.
