Relativistic Ring-Diagram Nuclear Matter Calculations

A relativistic extension of the particle-particle hole-hole ring-diagram many-body formalism is developed by using the Dirac equation for single-particle motion in the medium. Applying this new formalism, calculations are performed for nuclear matter. The results show that the saturation density is improved and the equation of state becomes softer as compared to corresponding Dirac-Brueckner-Hartree-Fock calculations. Using the Bonn A potential, nuclear matter is predicted to saturate at an energy per nucleon of --15.30 MeV and a density equivalent to a Fermi momentum of 1.38 fm$^{-1}$, in excellent agreement with empirical information. The compression modulus is 152 MeV at the saturation point.Comment: 23 pages text (LaTex) and 2 figures (paper, will be faxed upon request), UI-NTH-92-0

Can surface flux transport account for the weak polar field in cycle 23?

To reproduce the weak magnetic field on the polar caps of the Sun observed during the declining phase of cycle 23 poses a challenge to surface flux transport models since this cycle has not been particularly weak. We use a well-calibrated model to evaluate the parameter changes required to obtain simulated polar fields and open flux that are consistent with the observations. We find that the low polar field of cycle 23 could be reproduced by an increase of the meridional flow by 55% in the last cycle. Alternatively, a decrease of the mean tilt angle of sunspot groups by 28% would also lead to a similarly low polar field, but cause a delay of the polar field reversals by 1.5 years in comparison to the observations.Comment: 9 pages, 8 figures, Space Science Reviews, accepte

Extended Analysis of Gravitomagnetic Fields in Rotating Superconductors and Superfluids

Applying the Ginzburg-Landau theory including frame dragging effects to the case of a rotating superconductor, we were able to express the absolute value of the gravitomagnetic field involved to explain the Cooper pair mass anomaly previously reported by Tate. Although our analysis predicts large gravitomagnetic fields originated by superconductive gyroscopes, those should not affect the measurement of the Earth gravitomagnetic field by the Gravity Probe-B satellite. However, the hypothesis might be well suited to explain a mechanical momentum exchange phenomena reported for superfluid helium. As a possible explanation for those abnormally large gravitomagnetic fields in quantum materials, the reduced speed of light (and gravity) that was found in the case of Bose-Einstein condensates is analysed

Sensitivity of deexcitation energies of superdeformed secondary minima to the density dependence of symmetry energy with the relativistic mean-field theory

The relationship between deexcitation energies of superdeformed secondary minima relative to ground states and the density dependence of the symmetry energy is investigated for heavy nuclei using the relativistic mean field (RMF) model. It is shown that the deexcitation energies of superdeformed secondary minima are sensitive to differences in the symmetry energy that are mimicked by the isoscalar-isovector coupling included in the model. With deliberate investigations on a few Hg isotopes that have data of deexcitation energies, we find that the description for the deexcitation energies can be improved due to the softening of the symmetry energy. Further, we have investigated deexcitation energies of odd-odd heavy nuclei that are nearly independent of pairing correlations, and have discussed the possible extraction of the constraint on the density dependence of the symmetry energy with the measurement of deexcitation energies of these nuclei.Comment: 14 pages, 3 figure

Interaction of an electron gas with photoexcited electron-hole pairs in modulation-doped GaAs and CdTe quantum wells

The nature of the correlated electron gas and its response to photo-injected electron-hole pairs in nominally undoped and modulation-doped multiple quantum-well (MQW) structures was studied by experiment and theory, revealing a new type of optically-active excitation, magnetoplasmons bound to a mobile valence hole. These excitations are blue-shifted from the corresponding transition of the isolated charged magnetoexciton X-. The observed blue-shift of X- is larger than that of two-electron negative donor D-, in agreement with theoretical predictions.Comment: 4 pages, 3 figures, EP2DS-14 manuscript, to be published in Physica

Investigation of bonded hydrogen defects in nanocrystalline diamond films grown with nitrogen/methane/hydrogen plasma at high power conditions

In this work, we investigate the influence of some growth parameters such as high microwave power ranging from 3.0 to 4.0 kW and N2 additive on the incorporation of bonded hydrogen defects in nanocrystalline diamond (NCD) films grown through a small amount of pure N2 addition into conventional 4% CH4/H2 plasma using a 5 kW microwave plasma CVD system. Incorporation form and content of hydrogen point defects in the NCD films produced with pure N2 addition was analyzed by employing Fourier-transform infrared (FTIR) spectroscopy for the first time. A large amount of hydrogen related defects was detected in all the produced NCD films with N2 additive ranging from 29 to 87 µm thick with grain size from 47 nm to 31 nm. Furthermore, a specific new H related sharp absorption peak appears in all the NCD films grown with pure N2/CH4/H2 plasma at high powers and becomes stronger at powers higher than 3.0 kW and is even stronger than the 2920 cm−1 peak, which is commonly found in CVD diamond films. Based on these experimental findings, the role of high power and pure nitrogen addition on the growth of NCD films including hydrogen defect formation is analyzed and discussed

Influence of Supercurrents on Low-Temperature Thermopower in Mesoscopic N/S Structures

The thermopower of mesoscopic normal metal/superconductor structures has been measured at low temperatures. Effect of supercurrent present in normal part of the structure was studied in two cases: when it was created by applied external magnetic field and when it was applied directly using extra superconducting electrodes. Temperature and magnetic field dependencies of thermopower are compared to the numerical simulations based on the quasiclassical theory of the superconducting proximity effect.Comment: 21 pages, 12 figures. To be published in the proceedings of the ULTI conference organized in Lammi, Finland (2006

Dirac Hartree-Fock for Finite Nuclei Employing realistic Forces

We discuss two different approximation schemes for the self-consistent solution of the {\it relativistic} Brueckner-Hartree-Fock equation for finite nuclei. In the first scheme, the Dirac effects are deduced from corresponding nuclear matter calculations, whereas in the second approach the local-density approximation is used to account for the effects of correlations. The results obtained by the two methods are very similar. Employing a realistic one-boson-exchange potential (Bonn~A), the predictions for energies and radii of $^{16}$O and $^{40}$Ca come out in substantially better agreement with experiment as compared to non-relativistic approaches. As a by-product of our study, it turns out that the Fock exchange-terms, ignored in a previous investigation, are not negligible.Comment:

Sulfuric acid and hydrogen peroxide surface passivation effects on AlGaN/GaN high electron mobility transistors

In this work, we have compared SiNx passivation, hydrogen peroxide, and sulfuric acid treatment on AlGaN/GaN HEMTs surface after full device fabrication on Si substrate. Both the chemical treatments resulted in the suppression of device pinch-off gate leakage current below 1 μA/mm, which is much lower than that for SiNx passivation. The greatest suppression over the range of devices is observed with the sulfuric acid treatment. The device on/off current ratio is improved (from 104–105 to 107) and a reduction in the device sub-threshold (S.S.) slope (from ∼215 to 90 mV/decade) is achieved. The sulfuric acid is believed to work by oxidizing the surface which has a strong passivating effect on the gate leakage current. The interface trap charge density (Dit ) is reduced (from 4.86 to 0.90 × 1012 cm−2 eV−1), calculated from the change in the device S.S. The gate surface leakage current mechanism is explained by combined Mott hopping conduction and Poole Frenkel models for both untreated and sulfuric acid treated devices. Combining the sulfuric acid treatment underneath the gate with the SiNx passivation after full device fabrication results in the reduction of Dit and improves the surface related current collapse