Coupled superconductors and beyond

This paper describes the events leading to the discovery of coupled superconductors, the author's move in the 1970s to a perspective where mind plays a role comparable to matter, and the remarkable hostility sometimes encountered by those who venture into unconventional areas.Comment: Invited paper for special issue of Low Temperature Physics/Fizika Nizkikh Temperatur devoted to "Quantum Coherent Effects in Superconductors and New Materials". 6pp. v5: open-access published versio

The Effectiveness of Post-Katrina Disaster Aid: The Influence of SBA Loans on Small Businesses in Mississippi

Following Hurricane Katrina, the United States government provided $45 billion in loans and rebuilding funds to individuals and businesses for the purpose of repairing the damage caused by the hurricane. However, it is not yet clear what impact this assistance had on small businesses in affected areas. In particular, the role of Small Business Administration (SBA) loans has yet to be fully examined. Though few doubt the benefits of short-term and immediate disaster relief, there is some debate on the benefits of SBA loans. Evidence suggests that receiving business loans may do more harm than good if the loan ultimately increases debt load. In this study we contribute to the disaster relief literature through completing the first analysis regarding the receipt of SBA loans after Hurricane Katrina. We find that there are several characteristics which increase the probability of application for a loan, but there is a set of different characteristics which determine the amount ultimately received. Further, results indicate that targeting programs for certain groups were unsuccessful in directing loans to these groups

Oscillatory decay of a two-component Bose-Einstein condensate

We study the decay of a two-component Bose-Einstein condensate with negative effective interaction energy. With a decreasing atom number due to losses, the atom-atom interaction becomes less important and the system undergoes a transition from a bistable Josephson regime to the monostable Rabi regime, displaying oscillations in phase and number. We study the equations of motion and derive an analytical expression for the oscillation amplitude. A quantum trajectory simulation reveals that the classical description fails for low emission rates, as expected from analytical considerations. Observation of the proposed effect will provide evidence for negative effective interaction.Comment: 4 pages, 3 figue

Probing Pseudogap by Josephson Tunneling

We propose here an experiment aimed to determine whether there are superconducting pairing fluctuations in the pseudogap regime of the high-$T_c$ materials. In the experimental setup, two samples above $T_c$ are brought into contact at a single point and the differential AC conductivity in the presence of a constant applied bias voltage between the samples, $V$, should be measured. We argue the the pairing fluctuations will produce randomly fluctuating Josephson current with zero mean, however the current-current correlator will have a characteristic frequency given by Josephson frequency $\omega_J = 2 e V /\hbar$. We predict that the differential AC conductivity should have a peak at the Josephson frequency with the width determined by the phase fluctuations time.Comment: 4 pages, 2 eps figure

Phase Modulated Thermal Conductance of Josephson Weak Links

We present a theory for quasiparticle heat transport through superconducting weak links. The thermal conductance depends on the phase difference ($\phi$) of the superconducting leads. Branch conversion processes, low-energy Andreev bound states near the contact and the suppression of the local density of states near the gap edge are related to phase-sensitive transport processes. Theoretical results for the influence of junction transparency, temperature and disorder, on the phase modulation of the conductance are reported. For high-transmission weak links, $D\to 1$, the formation of an Andreev bound state at $\epsilon_{\text{\tiny b}}=\Delta\cos(\phi/2)$ leads to suppression of the density of states for the continuum excitations that transport heat, and thus, to a reduction in the conductance for $\phi\simeq\pi$. For low-transmission ($D\ll 1$) barriers resonant scattering at energies $\epsilon\simeq(1+D/2)\Delta$ leads to an increase in the thermal conductance as $T$ drops below $T_c$ (for phase differences near $\phi=\pi$).Comment: 4 pages, 3 figures Expanded discussion of boundary conditions for Ricatti amplitude

Puzzlement about thermal redshift

Discussed is the classical theoretical description of the experimentally established thermal redshift of spectral lines. Straightforward calculation of the observable spectrum from a canonical ensamble of monochromatic radiators yileds overall blueshift rather than redshift. It is concluded that the customary explanation of the thermal redshift as a second order Doppler effect does not bear closer examination, and that in fact, the phenomenon ''thermal redshift'' is not yet fully uderstood in classical terms.Comment: 4 pages RevTeX, 1 postscript figur

Effect of psychosocial factors on low back pain in industrial workers

Aim: To test the hypothesis that workplace psychosocial factors such as demand, control, support, job satisfaction and job appreciation can predict the future onset of disabling low back pain (LBP). Methods: The present study involved a prospective cohort of 4500 Iranian industrial workers. Data were gathered by means of a self-reported questionnaire about LBP, as well as working life exposure, lifestyle factors, social exposures, co-morbidity, life events and psychosomatic complaints in 2004. All new episodes of disabling LBP resulting in medically certified sick leave during the 1-year follow-up registered by occupational health clinic inside the factory. Results: The participation rate was good (85). A total of 744 subjects reported current LBP (point prevalence cases). A total of 52 (<2) new episodes of disabling LBP were observed during the 1-year follow-up (incident cases). Male employees reported higher demands, lower control and lower support than female employees. Employees with high demands, low control, job strain, low job satisfaction and low job appreciation showed increased odds ratios, and these results were statistically significant. Conclusions: Few prospective studies in this field have been published, but all of them are related to industrialized countries. This prospective study suggests the aetiological role of job strain for LBP. The findings of this study indicate a substantial potential for disease prevention and health promotion at the workplace. © The Author 2008. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved

Microscopic model of critical current noise in Josephson-junction qubits: Subgap resonances and Andreev bound states

We propose a microscopic model of critical current noise in Josephson-junctions based on individual trapping-centers in the tunnel barrier hybridized with electrons in the superconducting leads. We calculate the noise exactly in the limit of no on-site Coulomb repulsion. Our result reveals a noise spectrum that is dramatically different from the usual Lorentzian assumed in simple models. We show that the noise is dominated by sharp subgap resonances associated to the formation of pairs of Andreev bound states, thus providing a possible explanation for the spurious two-level systems (microresonators) observed in Josephson junction qubits [R.W. Simmonds et al., Phys. Rev. Lett. 93, 077003 (2004)]. Another implication of our model is that each trapping-center will contribute a sharp dielectric resonance only in the superconducting phase, providing an effective way to validate our results experimentally. We derive an effective Hamiltonian for a qubit interacting with Andreev bound states, establishing a direct connection between phenomenological models and the microscopic parameters of a Fermionic bath.Comment: 11 pages, 8 figure

Superconducting Plasma Excitation at Microwave Frequencies in Parallel Magnetic Fields in Bi2Sr2CaCu2O8+δ\mathrm{\mathbf{Bi_2Sr_2CaCu_2O_{8+\delta}}}

Josephson plasma resonance has been studied in a wide microwave frequency range between 10 and 52 GHz in a magnetic field parallel to the $ab$-plane in under-doped \BI. Above about 30 GHz two resonance modes were observed: one (LT mode) appears at low temperatures and another (HT mode) at higher temperatures, leaving a temperature gap between two regions. These two resonance modes exhibit a sharp contrast each other both on temperture and magnetic field dependences and show distinct characters different entirely from the c-axis Josephson plasma resonance. From temperature and field scan experiments at various frequencies it is suggested that the LT mode can be attributed to the coupled Josephson plasma mode with Josephson vortices, while the HT mode is a new plasma mode associated possibly with the periodic array of Josephson vortices.Comment: submitted to Physica C (Prceedings of Plasma2000, Sendai

Critical fluctuations in superconductors and the magnetic field penetration depth

The superconducting transition is studied within the one-loop renormalization group in fixed dimension $D=3$ and at the critical point. A tricritical behavior is found, and for $\kappa > \kappa_c$, an attractive charged fixed point, distinct from that of a neutral superfluid. The critical exponents of the continuous transition are evaluated, and it is shown that the anomalous dimension of the gauge field equals unity. This implies the proportionality of the magnetic field penetration depth and the superconducting correlation length below the transition. The penetration depth exponent is nonclassical. We argue that it can not be extracted from the dual theory in a straightforward manner since it is not renormalized by fluctuations of the dual field.Comment: 12 pages, LaTex, two figures available upon reques