Giant Fluctuations of Coulomb Drag in a Bilayer System

We have observed reproducible fluctuations of the Coulomb drag, both as a function of magnetic field and electron concentration, which are a manifestation of quantum interference of electrons in the layers. At low temperatures the fluctuations exceed the average drag, giving rise to random changes of the sign of the drag. The fluctuations are found to be much larger than previously expected, and we propose a model which explains their enhancement by considering fluctuations of local electron properties.Comment: 10 pages, 4 figure

Electron-electron interactions in the conductivity of graphene

The effect of electron-electron interaction on the low-temperature conductivity of graphene is investigated experimentally. Unlike in other two-dimensional systems, the electron-electron interaction correction in graphene is sensitive to the details of disorder. A new temperature regime of the interaction correction is observed where quantum interference is suppressed by intra-valley scattering. We determine the value of the interaction parameter, F_0 ~ -0.1, and show that its small value is due to the chiral nature of interacting electrons.Comment: 4 pages, 4 figures, 1 tabl

Constraints on warm dark matter from UV luminosity functions of high-z galaxies with Bayesian model comparison

The number density of small dark matter (DM) haloes hosting faint high-redshift galaxies is sensitive to the DM free-streaming properties. However, constraining these DM properties is complicated by degeneracies with the uncertain baryonic physics governing star formation. In this work, we use a flexible astrophysical model and a Bayesian inference framework to analyse ultraviolet (UV) luminosity functions (LFs) at z = 6-8. We vary the complexity of the astrophysical galaxy model (single versus double power law for the stellar-halo mass relation) as well as the matter power spectrum [cold DM versus thermal relic warm DM (WDM)], comparing their Bayesian evidences. Adopting a conservatively wide prior range for the WDM particle mass, we show that the UV LFs at z = 6-8 only weakly favour cold DM over WDM. We find that particle masses of ≤ 2 keV are rejected at a 95 per cent credible level in all models that have a WDM-like power spectrum cutoff. This bound should increase to ∼2.5 keV with the James Webb Space Telescope (JWST)