Possible Observational Criteria for Distinguishing Brown Dwarfs from Planets

The difference in formation process between binary stars and planetary systems is reflected in their composition as well as their orbital architecture, particularly orbital eccentricity as a function of orbital period. It is suggested here that this difference can be used as an observational criterion to distinguish between brown dwarfs and planets. Application of the orbital criterion suggests that with three possible exceptions, all of the recently-discovered substellar companions discovered to date may be brown dwarfs and not planets. These criterion may be used as a guide for interpretation of the nature of sub-stellar mass companions to stars in the future.Comment: LaTeX, 11 pages including 2 figures, accepted for publication in the Astrophysical Journal Letter

Single-electron transistor effect in a two-terminal structure

A peculiarity of the single-electron transistor effect makes it possible to observe this effect even in structures lacking a gate electrode altogether. The proposed method can be useful for experimental study of charging effects in structures with an extremely small central island confined between tunnel barriers like a nanometer-sized quantum dot or a macromolecule probed with a tunneling microscope), where it is impossible to provide a gate electrode for control of the tunnel current.Comment: 5 pages, 2 figure

Proton-3^{3}He elastic scattering at low energies

We present new accurate measurements of the differential cross section $\sigma(\theta)$ and the proton analyzing power $A_{y}$ for proton-$^{3}$He elastic scattering at various energies. A supersonic gas jet target has been employed to obtain these low energy cross section measurements. The $\sigma(\theta)$ distributions have been measured at $E_{p}$ = 0.99, 1.59, 2.24, 3.11, and 4.02 MeV. Full angular distributions of $A_{y}$ have been measured at $E_{p}$ = 1.60, 2.25, 3.13, and 4.05 MeV. This set of high-precision data is compared to four-body variational calculations employing realistic nucleon-nucleon (NN) and three-nucleon (3N) interactions. For the unpolarized cross section the agreement between the theoretical calculation and data is good when a $3N$ potential is used. The comparison between the calculated and measured proton analyzing powers reveals discrepancies of approximately 50% at the maximum of each distribution. This is analogous to the existing ``$A_{y}$ Puzzle'' known for the past 20 years in nucleon-deuteron elastic scattering.Comment: 22 pages, 9 figures, to be published in Physical Review C, corrected reference 4

Parity Effect in Ground State Energies of Ultrasmall Superconducting Grains

We study the superconductivity in small grains in the regime when the quantum level spacing $\delta\varepsilon$ is comparable to the gap $\Delta$. As $\delta\varepsilon$ is increased, the system crosses over from superconducting to normal state. This crossover is studied by calculating the dependence of the ground state energy of a grain on the parity of the number of electrons. The states with odd numbers of particles carry an additional energy $\Delta_P$, which shows non-monotonic dependence on $\delta\varepsilon$. Our predictions can be tested experimentally by studying the parity-induced alternation of Coulomb blockade peak spacings in grains of different sizes.Comment: 4 pages, revtex, multicol.st

Gate-Voltage Studies of Discrete Electronic States in Al Nanoparticles

We have investigated the spectrum of discrete electronic states in single, nm-scale Al particles incorporated into new tunneling transistors, complete with a gate electrode. The addition of the gate has allowed (a) measurements of the electronic spectra for different numbers of electrons in the same particle, (b) greatly improved resolution and qualitatively new results for spectra within superconducting particles, and (c) detailed studies of the gate-voltage dependence of the resonance level widths, which have directly demonstrated the effects of non-equilibrium excitations.Comment: 4 pages, 7 figure

Effects of Spin-Orbit Interactions on Tunneling via Discrete Energy Levels in Metal Nanoparticles

The presence of spin-orbit scattering within an aluminum nanoparticle affects measurements of the discrete energy levels within the particle by (1) reducing the effective g-factor below the free-electron value of 2, (2) causing avoided crossings as a function of magnetic field between predominantly-spin-up and predominantly-spin-down levels, and (3) introducing magnetic-field-dependent changes in the amount of current transported by the tunneling resonances. All three effects can be understood in a unified fashion by considering a simple Hamiltonian. Spin-orbit scattering from 4% gold impurities in superconducting aluminum nanoparticles produces no dramatic effect on the superconducting gap at zero magnetic field, but we argue that it does modify the nature of the superconducting transition in a magnetic field.Comment: 10 pages, 5 figures. Submitted to Phys. Rev.

Mechanism for a next-to-lowest lying scalar meson nonet

Recent work suggests the existence of a non-conventional lowest-lying scalar nonet containing the a0(980). Then the a0(1450) and also the K0*(1430) are likely candidates to belong to a conventional p-wave $q \bar q$ nonet. However a comparison of their properties with those expected on this basis reveals a number of puzzling features. It is pointed out that these puzzles can be resolved in a natural and robust way by assuming a ``bare'' conventional p-wave scalar $q \bar q$ nonet to mix with a lighter four quark $qq \bar q \bar q$ scalar nonet to form new ``physical'' states. The essential mechanism is driven by the fact that the isospinor is lighter than the isovector in the unmixed $qq \bar q \bar q$ multiplet.Comment: 22 pages, 6 figure

Dephasing in Metals by Two-Level Systems in the 2-Channel-Kondo Regime

We point out a novel, non-universal contribution to the dephasing rate 1/\tau_\phi \equiv \gamma_\phi of conduction electrons in metallic systems: scattering off non-magnetic two-level systems (TLSs) having almost degenerate Kondo ground states. In the regime \Delta_{ren} < T < T_K (\Delta_{ren} = renormalized level splitting, T_K = Kondo temperature), such TLSs exhibit non-Fermi-liquid physics that can cause \gamma_\phi, which generally decreases with decreasing T, to seemingly saturate in a limited temperature range before vanishing for T \to 0. This could explain the saturation of dephasing recently observed in gold wires [Mohanty et al. Phys. Rev. Lett. 78, 3366 (1997)].Comment: Final published version, including minor improvements suggested by referees. 4 pages, Revtex, 1 figur

Precision Measurement of the n-3He Incoherent Scattering Length Using Neutron Interferometry

We report the first measurement of the low-energy neutron-$^3$He incoherent scattering length using neutron interferometry: $b_i' = (-2.512\pm 0.012{statistical}\pm0.014{systematic})$ fm. This is in good agreement with a recent calculation using the AV18+3N potential. The neutron-$^3$He scattering lengths are important for testing and developing nuclear potential models that include three nucleon forces, effective field theories for few-body nuclear systems, and neutron scattering measurements of quantum excitations in liquid helium. This work demonstrates the first use of a polarized nuclear target in a neutron interferometer.Comment: 4 figure

Exact correlation functions of the BCS model in the canonical ensemble

We evaluate correlation functions of the BCS model for finite number of particles. The integrability of the Hamiltonian relates it with the Gaudin algebra ${\cal G}[sl(2)]$. Therefore, a theorem that Sklyanin proved for the Gaudin model, can be applied. Several diagonal and off-diagonal correlators are calculated. The finite size scaling behavior of the pairing correlation function is studied.Comment: 4 pages revtex; 2 figures .eps. Revised version to be published in Phys. Rev. Let