Even-odd correlations in capacitance fluctuations of quantum dots

We investigate effects of short range interactions on the addition spectra of quantum dots using a disordered Hubbard model. A correlation function \cS(q) is defined on the inverse compressibility versus filling data, and computed numerically for small lattices. Two regimes of interaction strength are identified: the even/odd fluctuations regime typical of Fermi liquid ground states, and a regime of structureless \cS(q) at strong interactions. We propose to understand the latter regime in terms of magnetically correlated localized spins.Comment: 3 pages, Revtex, Without figure

Magnetic Ground State of Pr0.89_{0.89}LaCe0.11_{0.11}CuO4+α−δ_{4+\alpha-\delta} with Varied Oxygen Depletion Probed by Muon Spin Relaxation

The magnetic ground state of an electron-doped cuprate superconductor Pr$_{1-x}$LaCe$_x$CuO$_{4+\alpha-\delta}$ ($x=0.11, \alpha\simeq0.04$) has been studied by means of muon spin rotation/relaxation (\msr) over a wide variety of oxygen depletion, $0.03\le\delta\le0.12$. Appearance of weak random magnetism over entire crystal volume has been revealed by a slow exponential relaxation. The absence of $\delta$-dependence for the random magnetism and the multiplet pattern of muon Knight shift at higher fields strongly suggest that the random moments are associated with excited Pr$^{3+}$ ions under crystal electric field.Comment: 6 pages, 4 figures, submitted to J. Phys. Soc. Jp

Weak localization in InSb thin films heavily doped with lead

The paper reports on the investigations of the weak localization (WL) effects in 3D polycrystalline thin films of InSb. The films are closely compensated showing the electron concentration n>10^{16} cm^{-3} at the total concentration of the donor and acceptor type structural defects >10^{18} cm^{-3}. Unless Pb-doped, the InSb films do not show any measurable or show very small WL effect at 4.2 K. The Pb-doping to the concentration of the order of 10^{18} cm^{-3} leads to pronounced WL effects below 7 K. In particular, a clearly manifested SO scattering is observed. From the comparison of the experimental data on temperature dependence of the magnetoresistivity and sample resistance with the WL theory, the temperature dependence of the phase destroying time is determined. The determination is performed by fitting theoretical terms obtained from Kawabata's theory to experimental data on magnetoresistance. It is concluded that the dephasing process is connected to three separate interaction processes. The first is due to the SO scatterings and is characterized by temperature-independent relaxation time. The second is associated with the electron-phonon interaction. The third dephasing process is characterized by independent on temperature relaxation time tau_c. This relaxation time is tentatively ascribed to inelastic scattering at extended structural defects, like grain boundaries. The resulting time dephasing time shows saturation in its temperature dependence. The temperature dependence of the resistance of the InSb films can be explained by the electron-electron interaction for T2 K.Comment: 15 pages with 5 figure

Low-lying continuum structures in B8 and Li8 in a microscopic model

We search for low-lying resonances in the B8 and Li8 nuclei using a microscopic cluster model and a variational scattering method, which is analytically continued to complex energies. After fine-tuning the nucleon-nucleon interaction to get the known 1+ state of B8 at the right energy, we reproduce the known spectra of the studied nuclei. In addition, our model predicts a 1+ state at 1.3 MeV in B8, relative to the Be7+p threshold, whose corresponding pair is situated right at the Li7+n threshold in Li8. Lacking any experimental evidence for the existence of such states, it is presently uncertain whether these structures really exist or they are spurious resonances in our model. We demonstrate that the predicted state in B8, if it exists, would have important consequences for the understanding of the astrophysically important Be7(p,gamma)B8 reaction.Comment: 6 pages with 1 figure. The postscript file and more information are available at http://nova.elte.hu/~csot

Correlation energy of a two-dimensional electron gas from static and dynamic exchange-correlation kernels

We calculate the correlation energy of a two-dimensional homogeneous electron gas using several available approximations for the exchange-correlation kernel $f_{\rm xc}(q,\omega)$ entering the linear dielectric response of the system. As in the previous work of Lein {\it et al.} [Phys. Rev. B {\bf 67}, 13431 (2000)] on the three-dimensional electron gas, we give attention to the relative roles of the wave number and frequency dependence of the kernel and analyze the correlation energy in terms of contributions from the $(q, i\omega)$ plane. We find that consistency of the kernel with the electron-pair distribution function is important and in this case the nonlocality of the kernel in time is of minor importance, as far as the correlation energy is concerned. We also show that, and explain why, the popular Adiabatic Local Density Approximation performs much better in the two-dimensional case than in the three-dimensional one.Comment: 9 Pages, 4 Figure

Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation

The fully nonlinear response of a many-level tunneling system to a strong alternating field of high frequency $\omega$ is studied in terms of the Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent tunneling current $I(t)$ is calculated exactly and its resonance structure is elucidated. In particular, it is shown that under certain reasonable conditions on the physical parameters, the Fourier component $I_{n}$ is sharply peaked at $n=\frac {\Delta E} {\hbar \omega}$, where $\Delta E$ is the spacing between two levels. This frequency multiplication results from the highly nonlinear process of $n$ photon absorption (or emission) by the tunneling system. It is also conjectured that this effect (which so far is studied mainly in the context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from [email protected], submitted to Phys.Rev.

Quantum Point Contacts and Coherent Electron Focusing

I. Introduction II. Electrons at the Fermi level III. Conductance quantization of a quantum point contact IV. Optical analogue of the conductance quantization V. Classical electron focusing VI. Electron focusing as a transmission problem VII. Coherent electron focusing (Experiment, Skipping orbits and magnetic edge states, Mode-interference and coherent electron focusing) VIII. Other mode-interference phenomenaComment: #3 of a series of 4 legacy reviews on QPC'

Complete Genomic Structure of the Cultivated Rice Endophyte Azospirillum sp. B510

We determined the nucleotide sequence of the entire genome of a diazotrophic endophyte, Azospirillum sp. B510. Strain B510 is an endophytic bacterium isolated from stems of rice plants (Oryza sativa cv. Nipponbare). The genome of B510 consisted of a single chromosome (3 311 395 bp) and six plasmids, designated as pAB510a (1 455 109 bp), pAB510b (723 779 bp), pAB510c (681 723 bp), pAB510d (628 837 bp), pAB510e (537 299 bp), and pAB510f (261 596 bp). The chromosome bears 2893 potential protein-encoding genes, two sets of rRNA gene clusters (rrns), and 45 tRNA genes representing 37 tRNA species. The genomes of the six plasmids contained a total of 3416 protein-encoding genes, seven sets of rrns, and 34 tRNAs representing 19 tRNA species. Eight genes for plasmid-specific tRNA species are located on either pAB510a or pAB510d. Two out of eight genomic islands are inserted in the plasmids, pAB510b and pAB510e, and one of the islands is inserted into trnfM-CAU in the rrn located on pAB510e. Genes other than the nif gene cluster that are involved in N2 fixation and are homologues of Bradyrhizobium japonicum USDA110 include fixABCX, fixNOQP, fixHIS, fixG, and fixLJK. Three putative plant hormone-related genes encoding tryptophan 2-monooxytenase (iaaM) and indole-3-acetaldehyde hydrolase (iaaH), which are involved in IAA biosynthesis, and ACC deaminase (acdS), which reduces ethylene levels, were identified. Multiple gene-clusters for tripartite ATP-independent periplasmic-transport systems and a diverse set of malic enzymes were identified, suggesting that B510 utilizes C4-dicarboxylate during its symbiotic relationship with the host plant