Effect of paramagnetic fluctuations on a Fermi-surface topological transition in two dimensions

We study the Fermi-surface topological transition of the pocket-opening type in a two-dimensional Fermi liquid. We find that the paramagnetic fluctuations in an interacting Fermi liquid typically drive the transition first order at zero temperature. We first gain insight from a calculation using second-order perturbation theory in the self-energy. This is valid for weak interaction and far from instabilities. We then extend the results to stronger interaction, using the self-consistent fluctuation approximation. Experimental signatures are given in light of our results

Phase diagram of two interacting helical states

We consider two coupled time-reversal-invariant helical edge modes of the same helicity, such as would occur on two stacked quantum spin Hall insulators. In the presence of interaction, the low-energy physics is described by two collective modes, one corresponding to the total current flowing around the edge and the other one describing relative fluctuations between the two edges.We find that quite generically, the relative mode becomes gapped at low temperatures, but only when tunneling between the two helical modes is nonzero. There are two distinct possibilities for the gapped state depending on the relative size of different interactions. If the intraedge interaction is stronger than the interedge interaction, the state is characterized as a spin-nematic phase. However, in the opposite limit, when the interaction between the helical edge modes is strong compared to the interaction within each mode, a spin-density wave forms, with emergent topological properties. First, the gap protects the conducting phase against localization by weak nonmagnetic impurities; second, the protected phase hosts localized zero modes on the ends of the edge that may be created by sufficiently strong nonmagnetic impurities

Weakly interacting one-dimensional topological insulators: a bosonization approach

We investigate the topological properties of one-dimensional weakly interacting topological insu- lators using bosonization. To do that we study the topological edge states that emerge at the edges of a model realized by a strong impurity or at the boundary between topologically distinct phases. In the bosonic model, the edge states are manifested as degenerate bosonic kinks at the boundaries. We first illustrate this idea on the example of the interacting Su-Schrieffer-Heeger (SSH) chain. We compute the localization length of the edge states as the width of an edge soliton that occurs in the SSH model in the presence of a strong impurity. Next, we examine models of two capacitively coupled SSH chains that can be either identical or in distinct topological phases. We find that weak Hubbard interaction reduces the ground state degeneracy in the topological phase of identical chains. We then prove that similarly to the non-interacting model, the degeneracy of the edge states in the interacting case is protected by chiral symmetry. We then study topological insulators built from two SSH chains with inter-chain hopping, that represent models of different chiral symmetric universality classes. We demonstrate in bosonic language that the topological index of a weakly coupled model is determined by the type of inter-chain coupling, invariant under one of two possible chiral symmetry operators. Finally, we show that a general one-dimensional model in a phase with topological index ν is equivalent at low energies to a theory of at least ν SSH chains. We illustrate this idea on the example of an SSH model with longer-range hopping

Carbon Nanotubes as Nanoelectromechanical Systems

We theoretically study the interplay between electrical and mechanical properties of suspended, doubly clamped carbon nanotubes in which charging effects dominate. In this geometry, the capacitance between the nanotube and the gate(s) depends on the distance between them. This dependence modifies the usual Coulomb models and we show that it needs to be incorporated to capture the physics of the problem correctly. We find that the tube position changes in discrete steps every time an electron tunnels onto it. Edges of Coulomb diamonds acquire a (small) curvature. We also show that bistability in the tube position occurs and that tunneling of an electron onto the tube drastically modifies the quantized eigenmodes of the tube. Experimental verification of these predictions is possible in suspended tubes of sub-micron length.Comment: 8 pages, 5 eps figures included. Major changes; new material adde

Insulin-Like Growth Factor Levels During Pregnancy in the Cow are Affected by Protein Supplementation in the Maternal Diet

To determine if dietary protein supplementation in early pregnancy alters total circulating insulinlike growth factor (IGF) levels, genetically similar heifers were fed diets containing different levels of protein in the first and second trimesters of gestation. The groups were: low/low (L/L), fed a diet containing 7% crude protein (CP) per kg/DM (low protein) in the first and second trimesters; high/high (H/H), fed a diet containing 14% CP per kg/DM (high protein) in the first and second trimesters; low/high (L/H), fed low protein in the first trimester and high in the second trimester and vice versa for the high/low (H/L) group. At day 62 of gestation, there was a significant difference (

Thermodynamics of Dipolar Chain Systems

The thermodynamics of a quantum system of layers containing perpendicularly oriented dipolar molecules is studied within an oscillator approximation for both bosonic and fermionic species. The system is assumed to be built from chains with one molecule in each layer. We consider the effects of the intralayer repulsion and quantum statistical requirements in systems with more than one chain. Specifically, we consider the case of two chains and solve the problem analytically within the harmonic Hamiltonian approach which is accurate for large dipole moments. The case of three chains is calculated numerically. Our findings indicate that thermodynamic observables, such as the heat capacity, can be used to probe the signatures of the intralayer interaction between chains. This should be relevant for near future experiments on polar molecules with strong dipole moments.Comment: 15 pages, 5 figures, final versio

Low temperature electronic properties of Sr_2RuO_4 II: Superconductivity

The body centered tetragonal structure of Sr_2RuO_4 gives rise to umklapp scattering enhanced inter-plane pair correlations in the d_{yz} and d_{zx} orbitals. Based on symmetry arguments, Hund's rule coupling, and a bosonized description of the in-plane electron correlations the superconducting order parameter is found to be a orbital-singlet spin-triplet with two spatial components. The spatial anisotropy is 7%. The different components of the order parameter give rise to two-dimensional gapless fluctuations. The phase transition is of third order. The temperature dependence of the pair density, specific heat, NQR, Knight shift, and susceptibility are in agreement with experimental results.Comment: 20 pages REVTEX, 3 figure

Tryptophan-like and humic-like fluorophores are extracellular in groundwater: implications as real-time faecal indicators

Fluorescent natural organic matter at tryptophan-like (TLF) and humic-like fluorescence (HLF) peaks is associated with the presence and enumeration of faecal indicator bacteria in groundwater. We hypothesise, however, that it is predominantly extracellular material that fluoresces at these wavelengths, not bacterial cells. We quantified total (unfiltered) and extracellular (filtered at < 0.22 µm) TLF and HLF in 140 groundwater sources across a range of urban population densities in Kenya, Malawi, Senegal, and Uganda. Where changes in fluorescence occurred following filtration they were correlated with potential controlling variables. A significant reduction in TLF following filtration (ΔTLF) was observed across the entire dataset, although the majority of the signal remained and thus considered extracellular (median 96.9%). ΔTLF was only significant in more urbanised study areas where TLF was greatest. Beneath Dakar, Senegal, ΔTLF was significantly correlated to total bacterial cells (ρs 0.51). No significant change in HLF following filtration across all data indicates these fluorophores are extracellular. Our results suggest that TLF and HLF are more mobile than faecal indicator bacteria and larger pathogens in groundwater, as the predominantly extracellular fluorophores are less prone to straining. Consequently, TLF/HLF are more precautionary indicators of microbial risks than faecal indicator bacteria in groundwater-derived drinking water

Layers of Cold Dipolar Molecules in the Harmonic Approximation

We consider the N-body problem in a layered geometry containing cold polar molecules with dipole moments that are polarized perpendicular to the layers. A harmonic approximation is used to simplify the hamiltonian and bound state properties of the two-body inter-layer dipolar potential are used to adjust this effective interaction. To model the intra-layer repulsion of the polar molecules, we introduce a repulsive inter-molecule potential that can be parametrically varied. Single chains containing one molecule in each layer, as well as multi-chain structures in many layers are discussed and their energies and radii determined. We extract the normal modes of the various systems as measures of their volatility and eventually of instability, and compare our findings to the excitations in crystals. We find modes that can be classified as either chains vibrating in phase or as layers vibrating against each other. The former correspond to acoustic and the latter to optical phonons. Instabilities can occur for large intra-layer repulsion and produce diverging amplitudes of molecules in the outer layers. Lastly, we consider experimentally relevant regimes to observe the structures.Comment: 17 pages, 20 figures, accepted versio

Physical activity but not sedentary activity is reduced in primary Sjögren’s syndrome

The aim of the study was to evaluate the levels of physical activity in individuals with primary Sjögren’s syndrome (PSS) and its relationship to the clinical features of PSS. To this cross-sectional study, self-reported levels of physical activity from 273 PSS patients were measured using the International Physical Activity Questionnaire-short form (IPAQ-SF) and were compared with healthy controls matched for age, sex and body mass index. Fatigue and other clinical aspects of PSS including disease status, dryness, daytime sleepiness, dysautonomia, anxiety and depression were assessed using validated tools. Individuals with PSS had significantly reduced levels of physical activity [median (interquartile range, IQR) 1572 (594–3158) versus 3708 (1732–8255) metabolic equivalent of task (MET) × min/week, p < 0.001], but similar levels of sedentary activity [median (IQR) min 300 (135–375) versus 343 (223–433) (MET) × min/week, p = 0.532] compared to healthy individuals. Differences in physical activity between PSS and controls increased at moderate [median (IQR) 0 (0–480) versus 1560 (570–3900) MET × min/week, p < 0.001] and vigorous intensities [median (IQR) 0 (0–480) versus 480 (0–1920) MET × min/week, p < 0.001]. Correlation analysis revealed a significant association between physical activity and fatigue, orthostatic intolerance, depressive symptoms and quality of life. Sedentary activity did not correlate with fatigue. Stepwise linear regression analysis identified symptoms of depression and daytime sleepiness as independent predictors of levels of physical activity. Physical activity is reduced in people with PSS and is associated with symptoms of depression and daytime sleepiness. Sedentary activity is not increased in PSS. Clinical care teams should explore the clinical utility of targeting low levels of physical activity in PSS