Impurity assisted nanoscale localization of plasmonic excitations in graphene

The plasmon modes of pristine and impurity doped graphene are calculated, using a real-space theory which determines the non-local dielectric response within the random phase approximation. A full diagonalization of the polarization operator is performed, allowing the extraction of all its poles. It is demonstrated how impurities induce the formation of localized modes which are absent in pristine graphene. The dependence of the spatial modulations over few lattice sites and frequencies of the localized plasmons on the electronic filling and impurity strength is discussed. Furthermore, it is shown that the chemical potential and impurity strength can be tuned to control target features of the localized modes. These predictions can be tested by scanning tunneling microscopy experiments.Comment: 5 pages, 4 figure

Quantum Magnetic Properties in Perovskite with Anderson Localized Artificial Spin-1/2

Quantum magnetic properties in a geometrically frustrated lattice of spin-1/2 magnet, such as quantum spin liquid or solid and the associated spin fractionalization, are considered key in developing a new phase of matter. The feasibility of observing the quantum magnetic properties, usually found in geometrically frustrated lattice of spin-1/2 magnet, in a perovskite material with controlled disorder is demonstrated. It is found that the controlled chemical disorder, due to the chemical substitution of Ru ions by Co-ions, in a simple perovskite CaRuO3 creates a random prototype configuration of artificial spin-1/2 that forms dimer pairs between the nearest and further away ions. The localization of the Co impurity in the Ru matrix is analyzed using the Anderson localization formulation. The dimers of artificial spin-1/2, due to the localization of Co impurities, exhibit singlet-to-triplet excitation at low temperature without any ordered spin correlation. The localized gapped excitation evolves into a gapless quasi-continuum as dimer pairs break and create freely fluctuating fractionalized spins at high temperature. Together, these properties hint at a new quantum magnetic state with strong resemblance to the resonance valence bond system.Comment: 8 pages, 6 figure

Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir1−x_{1-x}Rux_{x})O3_{3}

Magnetic fluctuations in transition metal oxides are a subject of intensive research because of the key role they are expected to play in the transition from the Mott insulator to the unconventional metallic phase of these materials, and also as drivers of superconductivity. Despite much effort, a clear link between magnetic fluctuations and the insulator-to-metal transition has not yet been established. Here we report the discovery of a compelling link between magnetic fluctuations and the insulator-to-metal transition in Ca(Ir$_{1-x}$Ru$_{x}$)O$_{3}$ perovskites as a function of the doping coefficient x. We show that when the material turns from insulator to metal, at a critical value of x$\sim$ 0.3, magnetic fluctuations change their character from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant electron state with Hund's orbital coupling. These results are expected to have wide-ranging implications for our understanding of the unconventional properties of strongly correlated electrons systemsComment: 7 pages, 5 figure

Minimal physical requirements for crystal growth self-poisoning

Citation: Whitelam, S., Dahal, Y. R., & Schmit, J. D. (2016). Minimal physical requirements for crystal growth self-poisoning. Journal of Chemical Physics, 144(6), 7. doi:10.1063/1.4941457Self-poisoning is a kinetic trap that can impair or prevent crystal growth in a wide variety of physical settings. Here we use dynamic mean-field theory and computer simulation to argue that poisoning is ubiquitous because its emergence requires only the notion that a molecule can bind in two (or more) ways to a crystal; that those ways are not energetically equivalent; and that the associated binding events occur with sufficiently unequal probability. If these conditions are met then the steady-state growth rate is in general a non-monotonic function of the thermodynamic driving force for crystal growth, which is the characteristic of poisoning. Our results also indicate that relatively small changes of system parameters could be used to induce recovery from poisoning. (C) 2016 AIP Publishing LLC

Insights into Coupled Folding and Binding Mechanisms from Kinetic Studies.

Intrinsically disordered proteins (IDPs) are characterized by a lack of persistent structure. Since their identification more than a decade ago, many questions regarding their functional relevance and interaction mechanisms remain unanswered. Although most experiments have taken equilibrium and structural perspectives, fewer studies have investigated the kinetics of their interactions. Here we review and highlight the type of information that can be gained from kinetic studies. In particular, we show how kinetic studies of coupled folding and binding reactions, an important class of signaling event, are needed to determine mechanisms.This work was supported by the Wellcome Trust (WT 095195MA). M.D.C. is supported by a BBSRC studentship; L.D. by an EPSRC studentship B.I.M.W. by the Cambridge Trust. JC is a Senior Wellcome Trust Research Fellow.This is the final version of the article. It first appeared from the American Society for Biochemistry and Molecular Biology via https://doi.org/10.1074/jbc.R115.69271

On the Meissner Effect of the Odd-Frequency Superconductivity with Critical Spin Fluctuations: Possibility of Zero Field FFLO pairing

We investigate the influence of critical spin fluctuations on electromagnetic responses in the odd-frequency superconductivity. It is shown that the Meissner kernel of the odd-frequency superconductivity is strongly reduced by the critical spin fluctuation or the massless spin wave mode in the antiferromagnetic phase. These results imply that the superfluid density is reduced, and the London penetration depth is lengthened for the odd-frequency pairing. It is also shown that the zero field Flude-Ferrell-Larkin-Ovchinnikov pairing is spontaneously realized both for even- and odd-frequency in the case of sufficiently strong coupling with low lying spin-modes.Comment: 10 pages, 7 figure

Prevalence of antibiotic resistance Escherichia coli isolated from Bagmati River water of Kathmandu, Nepal

This study assessed the prevalence of antibiotic-resistant Escherichia coli in the Bagmati River, Kathmandu, Nepal. Water samples collected from multiple sites were analyzed for E. coli contamination and subjected to antibiotic susceptibility testing using the Kirby-Bauer disk diffusion method. The results revealed a high level of resistance to commonly used antibiotics such as Ampicillin and Erythromycin, with no zones of inhibition observed for most isolates. Conversely, newer antibiotics like Ciprofloxacin and Gentamicin demonstrated significant effectiveness, with inhibition zones ranging from 21–38 mm and 18–23 mm, respectively. Moderate susceptibility was observed for antibiotics such as Ceftriaxone, Chloramphenicol, and Nitrofurantoin, while resistance patterns for Tetracycline and Cotrimoxazole varied across samples. These findings underscore the alarming levels of antibiotic resistance in E. coli from the Bagmati River, highlighting significant public health risks and the urgent need for enhanced water quality management and antibiotic resistance monitoring in environmental reservoirs