gg-factor engineering with InAsSb alloys toward zero band gap limit

Band gap is known as an effective parameter for tuning the Lande $g$-factor in semiconductors and can be manipulated in a wide range through the bowing effect in ternary alloys. In this work, using the recently developed virtual substrate technique, high-quality InAsSb alloys throughout the whole Sb composition range are fabricated and a large $g$-factor of $g\approx -90$ at the minimum band gap of $\sim 0.1$ eV, which is almost twice that in bulk InSb is found. Further analysis to the zero gap limit reveals a possible gigantic $g$-factor of $g\approx -200$ with a peculiar relativistic Zeeman effect that disperses as the square root of magnetic field. Such a $g$-factor enhancement toward the narrow gap limit cannot be quantitatively described by the conventional Roth formula, as the orbital interaction effect between the nearly triply degenerated bands becomes the dominant source for the Zeeman splitting. These results may provide new insights into realizing large $g$-factors and spin polarized states in semiconductors and topological materials

Transcriptional regulation of NAD metabolism in bacteria: genomic reconstruction of NiaR (YrxA) regulon

A comparative genomic approach was used to reconstruct transcriptional regulation of NAD biosynthesis in bacteria containing orthologs of Bacillus subtilis gene yrxA, a previously identified niacin-responsive repressor of NAD de novo synthesis. Members of YrxA family (re-named here NiaR) are broadly conserved in the Bacillus/Clostridium group and in the deeply branching Fusobacteria and Thermotogales lineages. We analyzed upstream regions of genes associated with NAD biosynthesis to identify candidate NiaR-binding DNA motifs and assess the NiaR regulon content in these species. Representatives of the two distinct types of candidate NiaR-binding sites, characteristic of the Firmicutes and Thermotogales, were verified by an electrophoretic mobility shift assay. In addition to transcriptional control of the nadABC genes, the NiaR regulon in some species extends to niacin salvage (the pncAB genes) and includes uncharacterized membrane proteins possibly involved in niacin transport. The involvement in niacin uptake proposed for one of these proteins (re-named NiaP), encoded by the B. subtilis gene yceI, was experimentally verified. In addition to bacteria, members of the NiaP family are conserved in multicellular eukaryotes, including human, pointing to possible NaiP involvement in niacin utilization in these organisms. Overall, the analysis of the NiaR and NrtR regulons (described in the accompanying paper) revealed mechanisms of transcriptional regulation of NAD metabolism in nearly a hundred diverse bacteria

Estimating the Expediency of Investing in the Development of a Regional Electrical Grid

AbstractThree situations associated with making decisions on investing in the development of a regional electrical grid are considered, and a game-theoretic approach to establishing the expediency of the investment in the grid and to finding optimal investment strategies for both the government and private investors in these situations is outlined. The implementation of this approach is associated with formulating and solving particular games on polyhedral sets of player strategies that are presented and discussed

Engineering Dirac Materials: Metamorphic InAs_1–<i>x</i>Sb_<i>x</i>/InAs_1–<i>y</i>Sb_<i>y</i> Superlattices with Ultralow Bandgap

Quasiparticles with Dirac-type dispersion can be observed in nearly gapless bulk semiconductors alloys in which the bandgap is controlled through the material composition. We demonstrate that the Dirac dispersion can be realized in short-period InAs_1–<i>x</i>Sb_<i>x</i>/InAs_1–<i>y</i>Sb_<i>y</i> metamorphic superlattices with the bandgap tuned to zero by adjusting the superlattice period and layer strain. The new material has anisotropic carrier dispersion: the carrier energy associated with the in-plane motion is proportional to the wave vector and characterized by the Fermi velocity <i>v</i>_F, and the dispersion corresponding to the motion in the growth direction is quadratic. Experimental estimate of the Fermi velocity gives <i>v</i>_F = 6.7 × 10⁵ m/s. Remarkably, the Fermi velocity in this system can be controlled by varying the overlap between electron and hole states in the superlattice. Extreme design flexibility makes the short-period metamorphic InAs_1–<i>x</i>Sb_<i>x</i>/InAs_1–<i>y</i>Sb_<i>y</i> superlattice a new prospective platform for studying the effects of charge-carrier chirality and topologically nontrivial states in structures with the inverted bandgaps