Modeling a striped pseudogap state

We study the electronic structure within a system of phase-decoupled one-dimensional superconductors coexisting with stripe spin and charge density wave order. This system has a nodal Fermi surface (Fermi arc) in the form of a hole pocket and an antinodal pseudogap. The spectral function in the antinodes is approximately particle-hole symmetric contrary to the gapped regions just outside the pocket. We find that states at the Fermi energy are extended whereas states near the pseudogap energy have localization lengths as short as the inter-stripe spacing. We consider pairing which has either local d-wave or s-wave symmetry and find similar results in both cases, consistent with the pseudogap being an effect of local pair correlations. We suggest that this state is a stripe ordered caricature of the pseudogap phase in underdoped cuprates with coexisting spin-, charge-, and pair-density wave correlations. Lastly, we also model a superconducting state which 1) evolves smoothly from the pseudogap state, 2) has a signature subgap peak in the density of states, and 3) has the coherent pair density concentrated to the nodal region.Comment: 12 pages, 12 figures, extended discussion, added references; v3, added figure of antinodal spectra for normal/pseudo/sc state

Antiferromagnetic correlations and impurity broadening of NMR linewidths in cuprate superconductors

We study a model of a d-wave superconductor with strong potential scatterers in the presence of antiferromagnetic correlations and apply it to experimental nuclear magnetic resonance (NMR) results on Zn impurities in the superconducting state of YBCO. We then focus on the contribution of impurity-induced paramagnetic moments, with Hubbard correlations in the host system accounted for in Hartree approximation. We show that local magnetism around individual impurities broadens the line, but quasiparticle interference between impurity states plays an important role in smearing out impurity satellite peaks. The model, together with estimates of vortex lattice effects, provides a semi-quantitative description of the impurity concentration dependence of the NMR line shape in the superconducting state, and gives a qualitative description of the temperature dependence of the line asymmetry. We argue that impurity-induced paramagnetism and resonant local density of states effects are both necessary to explain existing experiments.Comment: 15 pages, 23 figures, submitted to Phys. Rev.

Spin-Driven Nematic Instability of the Multi-Orbital Hubbard Model: Application to Iron-Based Superconductors

Nematic order resulting from the partial melting of density-waves has been proposed as the mechanism to explain nematicity in iron-based superconductors. An outstanding question, however, is whether the microscopic electronic model for these systems -- the multi-orbital Hubbard model -- displays such an ordered state as its leading instability. In contrast to usual electronic instabilities, such as magnetic and charge order, this fluctuation-driven phenomenon cannot be captured by the standard RPA method. Here, by including fluctuations beyond RPA in the multi-orbital Hubbard model, we derive its nematic susceptibility and contrast it with its ferro-orbital order susceptibility, showing that its leading instability is the spin-driven nematic phase. Our results also demonstrate the primary role played by the $d_{xy}$ orbital in driving the nematic transition, and reveal that high-energy magnetic fluctuations are essential to stabilize nematic order in the absence of magnetic order.Comment: 8 pages, 6 figure

Relation between early life socioeconomic position and all cause mortality in two generations. A longitudinal study of Danish men born in 1953 and their parents

Objective: To examine (1) the relation between parental socioeconomic position and all cause mortality in two generations, (2) the relative importance of mother’s educational status and father’s occupational status on offspring mortality, and (3) the effect of factors in the family environment on these relations. Design: A longitudinal study with record linkage to the Civil Registration System. The data were analysed using Cox regression models. Setting: Copenhagen, Denmark. Subjects: 2890 men born in 1953, whose mothers were interviewed regarding family social background in 1968. The vital status of this population and their parents was ascertained from April 1968 to January 2002. Main outcome measures: All cause mortality in study participants, their mothers, and fathers. Results: A similar pattern of relations was found between parental social position and all cause mortality in adult life in the three triads of father, mother, and offspring constituted of the cohort of men born in 1953, their parents, and grandparents. The educational status of mothers showed no independent effect on total mortality when father’s occupational social class was included in the model in either of the triads. Low material wealth was the indicator that remained significantly associated with adult all cause mortality in a model also including parental social position and the intellectual climate of the family in 1968. In the men born in 1953 the influence of material wealth was strongest for deaths later in adult life. Conclusion: Father’s occupational social class is associated with adult mortality in all members of the mother-father-offspring triad. Material wealth seems to be an explanatory factor for this association

An integrated source of broadband quadrature squeezed light

An integrated silicon nitride resonator is proposed as an ultra-compact source of bright single-mode quadrature squeezed light at 850 nm. Optical properties of the device are investigated and tailored through numerical simulations, with particular attention paid to loss associated with interfacing the device. An asymmetric double layer stack waveguide geometry with inverse vertical tapers is proposed for efficient and robust fibre-chip coupling, yielding a simulated total loss of -0.75 dB/facet. We assess the feasibility of the device through a full quantum noise analysis and derive the output squeezing spectrum for intra-cavity pump self-phase modulation. Subject to standard material loss and detection efficiencies, we find that the device holds promises for generating substantial quantum noise squeezing over a bandwidth exceeding 1 GHz. In the low-propagation loss regime, approximately -7 dB squeezing is predicted for a pump power of only 50 mW.Comment: 23 pages, 12 figure

Robustness of the nodal d-wave spectrum to strongly fluctuating competing order

We resolve an existing controversy between, on the one hand, convincing evidence for the existence of competing order in underdoped cuprates, and, on the other hand, spectroscopic data consistent with a seemingly homogeneous d-wave superconductor in the very same compounds. Specifically, we show how short-range fluctuations of the competing order essentially restore the nodal d-wave spectrum from the qualitatively distinct folded dispersion resulting from homogeneous coexisting phases. The signatures of the fluctuating competing order can be found mainly in a splitting of the antinodal quasi-particles and, depending of the strength of the competing order, also in small induced nodal gaps as found in recent experiments on underdoped La{2-x}SrxCuO4.Comment: 5 pages, 4 figure

Changing the way we learn: towards agile learning and co-operation

This paper addresses the need for learning and competence development in industrial organizations. The people that enter professional organizations today are part of a gamer generation that have some or much experience with on-line games. Therefore they are more open to e-learning and in general more open to access anything on-line. At the same time industrial organizations experience a pressure on their ability to train employees faster due to the increase in complexity. We argue that games are not yet mature enough to support this training challenge as stand alone efforts. But games can support the training and competence development in a synchronized setup with other means

NICMOS2 hubble space telescope observations of the embedded cluster associated with Mon R2: Constraining the substellar initial mass function

We have analyzed Hubble Space Telescope NICMOS2 F110W-, F160W-, F165M-, and F207M-band images covering the central 1' × 1' region of the cluster associated with Mon R2 in order to constrain the initial mass function (IMF) down to 20M_J. The flux ratio between the F165M and F160W bands was used to measure the strength of the water-band absorption feature and select a sample of 12 out of the total sample of 181 objects that have effective temperatures between 2700 and 3300 K. These objects are placed in the H-R diagram together with sources observed by Carpenter et al. to estimate an age of ~1 Myr for the low-mass cluster population. By constructing extinction-limited samples, we are able to constrain the IMF and the fraction of stars with a circumstellar disk in a sample that is 90% complete for both high- and low-mass objects. For stars with estimated masses between 0.1 and 1.0 M_☉ for a 1 Myr population with A_V ≤ 19 mag, we find that 27% ± 9% have a near-infrared excess indicative of a circumstellar disk. The derived fraction is similar to or slightly lower than the fraction found in other star-forming regions of comparable age. We constrain the number of stars in the mass interval 0.08-1.0 M_☉ to the number of objects in the mass interval 0.02-0.08 M_☉ by forming the ratio R^(**) = N(0.08-1 M_☉)/N(0.02-0.08 M_☉) for objects in an extinction-limited sample complete for A_V ≤ 7 mag. The ratio is found to be R^(**) = 2.2 ± 1.3, assuming an age of 1 Myr, consistent with the similar ratio predicted by the system IMF proposed by Chabrier. The ratio is similar to the ratios observed toward the Orion Nebula Cluster and IC 348, as well as the ratio derived in the 28 deg^2 survey of Taurus by Guieu et al

Pinning of stripes by local structural distortions in cuprate high-Tc superconductors

We study the spin-density wave (stripe) instability in lattices with mixed low-temperature orthorhombic (LTO) and low-temperature tetragonal (LTT) crystal symmetry. Within an explicit mean-field model it is shown how local LTT regions act as pinning centers for static stripe formation. We calculate the modulations in the local density of states near these local stripe regions and find that mainly the coherence peaks and the van Hove singularity (VHS) are spatially modulated. Lastly, we use the real-space approach to simulate recent tunneling data in the overdoped regime where the VHS has been detected by utilizing local normal state regions.Comment: Conference proceedings for Stripes1