Moiré Engineering of Spin-Orbit Coupling in Twisted Platinum Diselenide

We study the electronic structure and correlated phases of twisted bilayers of platinum diselenide using large-scale ab initio simulations combined with the functional renormalization group. PtSe2 is a group-X transition metal dichalcogenide, which hosts emergent flat bands at small twist angles in the twisted bilayer. Remarkably, we find that moiré engineering can be used to tune the strength of Rashba spin-orbit interactions, altering the electronic behavior in a novel manner. We reveal that an effective triangular lattice with a twist-controlled ratio between kinetic and spin-orbit coupling scales can be realized. Even dominant spin-orbit coupling can be accessed in this way and we discuss consequences for the interaction driven phase diagram, which features pronounced exotic superconducting and entangled spin-charge density waves.

Sodium Diffusion and Dynamics in Na2Ti3O7: Neutron Scattering and Ab-initio Simulations

We have performed quasielastic and inelastic neutron scattering (QENS and INS) measurements from 300 K to 1173 K to investigate the Na-diffusion and underlying host dynamics in Na2Ti3O7. The QENS...

Stochastic Low-frequency Variability in Three-dimensional Radiation Hydrodynamical Models of Massive Star Envelopes

Increasing main-sequence stellar luminosity with stellar mass leads to the eventual dominance of radiation pressure in stellar-envelope hydrostatic balance. As the luminosity approaches the Eddington limit, additional instabilities (beyond conventional convection) can occur. These instabilities readily manifest in the outer envelopes of OB stars, where the opacity increase associated with iron yields density and gas-pressure inversions in 1D models. Additionally, recent photometric surveys (e.g., TESS) have detected excess broadband low-frequency variability in power spectra of OB star lightcurves, called stochastic low-frequency variability (SLFV). This motivates our novel 3D Athena++ radiation hydrodynamical (RHD) simulations of two 35 M ⊙ star envelopes (the outer ≈15% of the stellar radial extent), one on the zero-age main sequence and the other in the middle of the main sequence. Both models exhibit turbulent motion far above and below the conventional iron-opacity peak convection zone (FeCZ), obliterating any “quiet” part of the near-surface region and leading to velocities at the photosphere of 10–100 km s−1, directly agreeing with spectroscopic data. Surface turbulence also produces SLFV in model lightcurves with amplitudes and power-law slopes that are strikingly similar to those of observed stars. The characteristic frequencies associated with SLFV in our models are comparable to the thermal time in the FeCZ (≈3–7 day−1). These ab initio simulations are directly validated by observations and, though more models are needed, we remain optimistic that 3D RHD models of main-sequence O-star envelopes exhibit SLFV originating from the FeCZ.

Tracing the reactivity of single atom alloys for ethanol dehydrogenation using ab initio simulations

An ab initio micro-kinetic model (MKM) is constructed to understand the reactivity trend of single atom alloys (SAAs) of Cu and Au for non-oxidative dehydrogenation (NODH) of ethanol to produce...

A new iron-phosphate compound (Fe7P11O38) obtained by pyrophosphate stoichiometric glass devitrification

Iron phosphates are a wide group of compounds that possess versatile applications. Their properties are strongly dependent on the role and position of iron in their structure. Iron, because of its chemical character, is able to easily change its redox state and accommodate different chemical surroundings. Thus, iron-phosphate crystallography is relatively complex. In addition, the compounds possess intriguing magnetic and electric properties. In this paper, we present crystal structure properties of a newly developed iron-phosphate compound that was obtained by devitrification from iron-phosphate glass of pyrophosphate stoichiometry. Based on X-ray diffraction (XRD) studies, the new compound (Fe7P11O38) was shown to adopt the hexagonal space group P63 (No. 173) in which iron is present as Fe3+ in two inequivalent octahedral and one tetrahedral positions. The results were confirmed by Raman and Mössbauer spectroscopies, and appropriate band positions, as well as hyperfine interaction parameters, are assigned and discussed. The magnetic and electric properties of the compound were predicted by ab initio simulations. It was observed that iron magnetic moments are coupled antiferromagnetically and that the total magnetic moment of the unit cell has an integer value of 2 µB. Electronic band structure calculations showed that the material has half-metallic properties.

Y2O3:Eu and the Mössbauer isomer shift coefficient of Eu compounds from ab-initio simulations

We report on a full potential density functional theory characterization of Y2O3 upon Eu doping on the two inequivalent crystallographic sites 24d and 8b. We analyze local structural relaxation,electronic properties and the relative stability of the two sites. The simulations are used to extract the contact charge density at the Eu nucleus. Then we construct the experimental isomer shift versus contact charge density calibration curve, by considering an ample set of Eu compounds : EuF3, EuO,EuF2, EuS, EuSe, EuTe, EuPd3 and the Eu metal. The, expected, linear dependence has a slope of α= 0.054 mm/s/Å3, which corresponds to nuclear expansion parameter ∆R/R= 6.0·10−5.αallows to obtain an unbiased and accurate estimation of the isomer shift for any Eu compound. We test this approach on two mixed-valence compounds Eu3S4 and Eu2SiN3, and use it to predict theY2O3:Eu isomer shift with the result +1.04 mm/s at the 24d site and +1.00 mm/s at the 8b site.