Theory of metal-intercalated phenacenes: Why molecular valence 3 is special

We develop a correlated-electron minimal model for the normal state of charged phenanthrene ions in the solid state, within the reduced space of the two lowest antibonding molecular orbitals of phenanthrene. Our model is general and can be easily extended to study the normal states of other polycyclic aromatic hydrocarbon superconductors. The main difference between our approach and previous correlated-electron theories of phenacenes is that our calculations are exact within the reduced basis space, albeit for finite clusters. The enhanced exchange of electron populations between these molecular orbitals, driven by Coulomb interactions over and above the bandwidth effects, gives a theoretical description of the phenanthrene trianions that is very different from previous predictions. Exact many-body finite cluster calculations show that while the systems with molecular charges of $-$1 and $-$2 are one- and two-band Mott-Hubbard semiconductors, respectively, molecular charge $-$3 gives two nearly $\frac{3}{4}$-filled bands, rather than a completely filled lower band and a $\frac{1}{2}$-filled upper band. The carrier density per active molecular orbital is thus nearly the same in the normal state of the superconducting aromatics and organic charge-transfer solids, and may be the key to understanding unconventional superconductivity in these molecular superconductors.Comment: Published in Phys. Rev. B. Title changed on editorial request. In all, 13 pages, 14 captioned figures, and 2 table

Opportunities for probing U(1)T3RU(1)_{T3R} with light mediators

We consider strategies for using new datasets to probe scenarios in which light right-handed SM fermions couple to a new gauge group, $U(1)_{T3R}$. This scenario provides a natural explanation for the light flavor sector scale, and a motivation for sub-GeV dark matter. There is parameter space which is currently allowed, but we find that much of it can be probed with future experiments. In particular, cosmological and astrophysical observations, neutrino experiments and experiments which search for displaced visible decay or invisible decay can all play a role. Still, there is a small region of parameter space which even these upcoming experiments will not be able to probe. This model can explain the observed 2.4-3$\sigma$ excess of events at the COHERENT experiment in the parameter space allowed by current laboratory experiments, but the ongoing/upcoming laboratory experiments will decisively probe this possibility.Comment: 19 pages, 7 figures, 2 table; manuscript is revised, results are unchanged, new figures, references added, matches the published versio

Distinct, ecotype-specific genome and proteome signatures in the marine cyanobacteria Prochlorococcus

The marine cyanobacterium Prochlorococcus marinus, having multiple ecotypes of distinct genotypic/ phenotypic traits and being the first documented example of genome shrinkage in free-living organisms, offers an ideal system for studying niche-driven molecular micro-diversity in closely related microbes. The present study,through an extensive comparative analysis of various genomic/proteomic features of 6 high light (HL) and 6 low light (LL) adapted strains, makes an attempt to identify molecular determinants associated with their vertical niche partitioning. Pronounced strand-specific asymmetry in synonymous codon usage is observed exclusively in LL strains. Distinct dinucleotide abundance profiles are exhibited by 2 LL strains with larger genomes and G+C-content ≈ 50% (group LLa), 4 LL strains having reduced genomes and G+C-content ≈ 35-37% (group LLb), and 6 HL strains. Taking into account the emergence of LLa, LLb and HL strains (based on 16S rRNA phylogeny), a gradual increase in average aromaticity, pI values and beta- & coil-forming propensities and a decrease in mean hydrophobicity, instability indices and helix-forming propensities of core proteins are observed. Greater variations in orthologous gene repertoire are found between LLa and LLb strains, while higher number of positively selected genes exist between LL and HL strains. Strains of different Prochlorococcus groups are characterized by distinct compositional, physicochemical and structural traits that are not mere remnants of a continuous genetic drift, but are potential outcomes of a grand scheme of niche-oriented stepwise diversification, that might have driven them chronologically towards greater stability/fidelity and invoked upon them a special ability to inhabit diverse oceanic environments

Reduction of Hysteresis for Carbon Nanotube Mobility Measurements Using Pulsed Characterization

We describe a pulsed measurement technique to suppress hysteresis for carbon nanotube (CNT) device measurements in air, vacuum, and over a wide temperature range (80-453 K). Varying the gate pulse width and duty cycle probes the relaxation times associated with charge trapping near the CNT, found to be up to the 0.1-10 s range. Longer off times between voltage pulses enable consistent, hysteresis-free measurements of CNT mobility. A tunneling front model for charge trapping and relaxation is also described, suggesting trap depths up to 4-8 nm for CNTs on SiO2. Pulsed measurements will also be applicable to other nanoscale devices such as graphene, nanowires, and molecular electronics, and could enable probing trap relaxation times in a variety of material system interfaces