Contact resistance and shot noise in graphene transistors

Potential steps naturally develop in graphene near metallic contacts. We investigate the influence of these steps on the transport in graphene Field Effect Transistors. We give simple expressions to estimate the voltage-dependent contribution of the contacts to the total resistance and noise in the diffusive and ballistic regimes.Comment: 6 pages, 4 figures; Figs 3 and 4 completed and appendix adde

Bose-Einstein Correlations for Mixed Neutral Mesons

Correlations are shown to arise in nonidentical mixed-particle pairs like $K^o \bar K^o$ when observed in identical decay modes like $K_S K_S$ in multiparticle final states containing many partial waves. No enhancement is found in any single partial wave and all partial wave analyses of the s-wave threshold resonance $a_o$ and $f_o$ should give the same results for all decay modes. In CP violation experiments where $B^o - \bar B^o$ pairs are inclusively produced and correlated decays into $\psi K_S$ and leptonic modes are observed, the CP-violating lepton asymmetry is enhanced by a factor of two in the kinematic region where Bose enhancement occurs.Comment: 11 page

Effect of Hadron Dynamics on the Proton Lifetime

A detailed, quantitative re-examination of the effect of hadron dynamics on baryon decay, modeled in terms of Skyrme-field tunneling, indicates that any hadronic suppression should be quite mild. This appears to be another illustration of the `Cheshire-cat' phenomenon, that variation of the apportionment between description of the nucleon as a bag of quarks and description as a Skyrme field configuration has little influence on many nucleon properties. Perhaps the largest remaining uncertainty in evaluating the decay rate has to do with the overlap between a specified quark-antiquark configuration and a final meson state.Comment: minor corrections, 19 pages, 9 figure

Absence of strong localization at low conductivity in the topological surface state of low disorder Sb2Te3

We present low-temperature transport measurements of a gate-tunable thin film topological insulator system that features high mobility and low carrier density. Upon gate tuning to a regime around the charge neutrality point, we infer an absence of strong localization even at conductivities well below $e^2/h$, where two dimensional electron systems should conventionally scale to an insulating state. Oddly, in this regime the localization coherence peak lacks conventional temperature broadening, though its tails do change dramatically with temperature. Using a model with electron-impurity scattering, we extract values for the disorder potential and the hybridization of the top and bottom surface states.Comment: 6 pages, 4 figures, with 11 pages of supplementary informatio

Charge-monopole versus Gravitational Scattering at Planckian Energies

The amplitude for the scattering of a point magnetic monopole and a point charge, at centre-of-mass energies much larger than the masses of the particles, and in the limit of low momentum transfer, is shown to be proportional to the (integer-valued) monopole strength, assuming the Dirac quantization condition for the monopole-charge system. It is demonstrated that, for small momentum transfer, charge-monopole electromagnetic effects remain comparable to those due to the gravitational interaction between the particles even at Planckian centre-of-mass energies.Comment: 9 pages, revtex, IMSc/93-4

Singlet-triplet transition in a single-electron transistor at zero magnetic field

We report sharp peaks in the differential conductance of a single-electron transistor (SET) at low temperature, for gate voltages at which charge fluctuations are suppressed. For odd numbers of electrons we observe the expected Kondo peak at zero bias. For even numbers of electrons we generally observe Kondo-like features corresponding to excited states. For the latter, the excitation energy often decreases with gate voltage until a new zero-bias Kondo peak results. We ascribe this behavior to a singlet-triplet transition in zero magnetic field driven by the change of shape of the potential that confines the electrons in the SET.Comment: 4 p., 4 fig., 5 new ref. Rewrote 1st paragr. on p. 4. Revised author list. More detailed fit results on page 3. A plotting error in the horizontal axis of Fig. 1b and 3 was corrected, and so were the numbers in the text read from those fig. Fig. 4 was modified with a better temperature calibration (changes are a few percent). The inset of this fig. was removed as it is unnecessary here. Added remarks in the conclusion. Typos are correcte

Transport Properties of Carbon Nanotube C60_{60} Peapods

We measure the conductance of carbon nanotube peapods from room temperature down to 250mK. Our devices show both metallic and semiconducting behavior at room temperature. At the lowest temperatures, we observe single electron effects. Our results suggest that the encapsulated C$_{60}$ molecules do not introduce substantial backscattering for electrons near the Fermi level. This is remarkable given that previous tunneling spectroscopy measurements show that encapsulated C$_{60}$ strongly modifies the electronic structure of a nanotube away from the Fermi level.Comment: 9 pages, 4 figures. This is one of two manuscripts replacing the one orginally submitted as arXiv:cond-mat/0606258. The other one is arXiv:0704.3641 [cond-mat

Confinement, Crossing Symmetry, and Glueballs

We suggest that the quark-confining force is related by crossing symmetry to a color-singlet glueball ${\cal G}$ which is well described as a loop of one quantum of color magnetic flux. Electron pair annihilation as high as $\approx 2 GeV$ above the $\Upsilon$ mass could produce $\Upsilon \rightarrow \ell^+\ell^-$ accompanied by ${\cal G}$ or one of its excited states.Comment: LaTeX, 12 pages, no figures, Los Alamos preprint LA-UR-94-263