16 research outputs found
Neutron dark-field imaging of hydrogen-fatigued pressure vessel steel
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Microscopic Polarization in Bilayer Graphene
Bilayer graphene has drawn significant attention due to the opening of a band
gap in its low energy electronic spectrum, which offers a promising route to
electronic applications. The gap can be either tunable through an external
electric field or spontaneously formed through an interaction-induced symmetry
breaking. Our scanning tunneling measurements reveal the microscopic nature of
the bilayer gap to be very different from what is observed in previous
macroscopic measurements or expected from current theoretical models. The
potential difference between the layers, which is proportional to charge
imbalance and determines the gap value, shows strong dependence on the disorder
potential, varying spatially in both magnitude and sign on a microscopic level.
Furthermore, the gap does not vanish at small charge densities. Additional
interaction-induced effects are observed in a magnetic field with the opening
of a subgap when the zero orbital Landau level is placed at the Fermi energy
Whispering gallery modes in photoluminescence and Raman spectra of a spherical microcavity with CdTe quantum dots: anti-Stokes emission and interference effects
We have studied the photoluminescence and Raman spectra of a system consisting of a polystyrene latex microsphere coated by CdTe colloidal quantum dots. The cavity-induced enhancement of the Raman scattering allows the observation of Raman spectra from only a monolayer of CdTe quantum dots. Periodic structure with very narrow peaks in the photoluminescence spectra of a single microsphere was detected both in the Stokes and anti-Stokes spectral regions, arising from the coupling between the emission of quantum dots and spherical cavity modes
Evolution of Microscopic Localization in Graphene in a Magnetic Field from Scattering Resonances to Quantum Dots
Graphene is a unique two-dimensional material with rich new physics and great
promise for applications in electronic devices. Physical phenomena such as the
half-integer quantum Hall effect and high carrier mobility are critically
dependent on interactions with impurities/substrates and localization of Dirac
fermions in realistic devices. We microscopically study these interactions
using scanning tunneling spectroscopy (STS) of exfoliated graphene on a SiO2
substrate in an applied magnetic field. The magnetic field strongly affects the
electronic behavior of the graphene; the states condense into welldefined
Landau levels with a dramatic change in the character of localization. In zero
magnetic field, we detect weakly localized states created by the substrate
induced disorder potential. In strong magnetic field, the two-dimensional
electron gas breaks into a network of interacting quantum dots formed at the
potential hills and valleys of the disorder potential. Our results demonstrate
how graphene properties are perturbed by the disorder potential; a finding that
is essential for both the physics and applications of graphene.Comment: to be published in Nature Physic