396 research outputs found
Fluidity Onset in Graphene
Viscous electron fluids have emerged recently as a new paradigm of
strongly-correlated electron transport in solids. Here we report on a direct
observation of the transition to this long-sought-for state of matter in a
high-mobility electron system in graphene. Unexpectedly, the electron flow is
found to be interaction-dominated but non-hydrodynamic (quasiballistic) in a
wide temperature range, showing signatures of viscous flows only at relatively
high temperatures. The transition between the two regimes is characterized by a
sharp maximum of negative resistance, probed in proximity to the current
injector. The resistance decreases as the system goes deeper into the
hydrodynamic regime. In a perfect darkness-before-daybreak manner, the
interaction-dominated negative response is strongest at the transition to the
quasiballistic regime. Our work provides the first demonstration of how the
viscous fluid behavior emerges in an interacting electron system.Comment: 8pgs, 4fg
Spectropolarimetric observations of cool DQ white dwarfs
Following our recent discovery of a new magnetic DQ white dwarf (WD) with CH molecular features, we report the results for the rest of the DQ WDs from our survey. We use high signal-to-noise spectropolarimetric data to search for magnetic fields in a sample of 11 objects. One object in our sample, WD1235+422, shows the signs of continuum circular polarization that is similar to some peculiar DQs with unidentified molecular absorption bands, but the low S/N and spectral resolution of these data make more observations necessary to reveal the true nature of this object
Evidence of phi --> pi0 pi0 gamma and phi --> pi0 eta gamma decays in SND experiment at VEPP-2M
Preliminary results on the study of e+e- --> phi(1020) --> pi0 pi0 gamma, eta
pi0 gamma processes from SND experiment at VEPP-2M collider in Novosibirsk are
presented. Branching ratios of rare radiative phi --> pi0 pi0 gamma and phi -->
pi0 eta gamma decays are measured:
B(phi --> pi0 pi0 gamma ) = (1.1 +- 0.2) * 10^-4
(invariant mass (pi0 pi0) < 800 MeV),
B(phi --> eta pi0 gamma ) = (1.3 +- 0.5) * 10^-4.Comment: Talk at the HADRON97 conference, BNL, Aug 24-30 1997; LaTeX, 4 pages,
4 eps figure
Giant oscillations in a triangular network of one-dimensional states in marginally twisted graphene
The electronic properties of graphene superlattices have attracted intense
interest that was further stimulated by the recent observation of novel
many-body states at "magic" angles in twisted bilayer graphene (BLG). For very
small ("marginal") twist angles of 0.1 deg, BLG has been shown to exhibit a
strain-accompanied reconstruction that results in submicron-size triangular
domains with the Bernal stacking. If the interlayer bias is applied to open an
energy gap inside the domain regions making them insulating, marginally-twisted
BLG is predicted to remain conductive due to a triangular network of chiral
one-dimensional (1D) states hosted by domain boundaries. Here we study electron
transport through this network and report giant Aharonov-Bohm oscillations
persisting to temperatures above 100 K. At liquid helium temperatures, the
network resistivity exhibits another kind of oscillations that appear as a
function of carrier density and are accompanied by a sign-changing Hall effect.
The latter are attributed to consecutive population of the flat minibands
formed by the 2D network of 1D states inside the gap. Our work shows that
marginally twisted BLG is markedly distinct from other 2D electronic systems,
including BLG at larger twist angles, and offers a fascinating venue for
further research.Comment: 11 pages, 8 figure
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