The possibility to achieve entirely frictionless, i.e. superlubric, sliding between solids, holds enormous potential for the operation of mechanical devices. At small length scales, where mechanical contacts are well-defined, Aubry predicted a transition from a superlubric to a pinned state when the mechanical load is increased. Evidence for this intriguing Aubry transition (AT), which should occur in one dimension (1D) and at zero temperature, was recently obtained in few-atom chains. Here, we experimentally and theoretically demonstrate the occurrence of the AT in an extended two-dimensional (2D) system at room temperature using a colloidal monolayer on an optical lattice. Unlike the continuous nature of the AT in 1D, we observe a first-order transition in 2D leading to a coexistence regime of pinned and unpinned areas. Our data demonstrate that the original concept of Aubry does not only survive in 2D but is relevant for the design of nanoscopic machines and devices at ambient temperature.In the expanding fields of nanoscience, where the competition of length scales is of key
We experimentally study the motion of a colloidal monolayer which is driven across a commensurate substrate potential whose amplitude is periodically modulated in time. In addition to a significant reduction of the static friction force compared to an unmodulated substrate, we observe a Shapiro step structure in the force dependence of the mean particle velocity which is explained by the dynamical mode locking between the particle motion and the substrate modulation. In this regime, the entire crystal moves in a stick-slip fashion similar to what is observed when a single point contact is driven across a periodic surface. Contrary to numerical simulations, where typically a large number of Shapiro steps is found, only a single step is observed in our experiments. This is explained by the formation of kinks which weaken the synchronization between adjacent particles.
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Effects of electron scattering at metal-nonmetal interfaces on electron-phonon equilibration in gold filmsWe discuss the observation of a transient (000)-order attenuation in time-resolved transmission electron diffraction experiments. It is shown that this effect causes a decrease of the diffraction intensity of all higher diffraction orders. This effect is not unique to specific materials as it was observed in thin Au, Ag and Cu films.
Isolated impurity states in epitaxially grown semiconductor
systems
possess important radiative features such as distinct wavelength emission
with a very short radiative lifetime and low inhomogeneous broadening,
which make them promising for the generation of indistinguishable
single photons. In this study, we investigate chlorine-doped ZnSe/ZnMgSe
quantum well (QW) nanopillar (NP) structures as a highly efficient
solid-state single-photon source operating at cryogenic temperatures.
We show that single photons are generated due to the radiative recombination
of excitons bound to neutral Cl atoms in ZnSe QW and the energy of
the emitted photon can be tuned from about 2.85 down to 2.82 eV with
ZnSe well width increase from 2.7 to 4.7 nm. Following the developed
advanced technology, we fabricate NPs with a diameter of about 250
nm using a combination of dry and wet-chemical etching of epitaxially
grown ZnSe/ZnMgSe QW structures. The remaining resist mask serves
as a spherical- or cylindrical-shaped solid immersion lens on top
of NPs and leads to the emission intensity enhancement by up to an
order of magnitude in comparison to the pillars without any lenses.
NPs with spherical-shaped lenses show the highest emission intensity
values. The clear photon-antibunching effect is confirmed by the measured
value of the second-order correlation function at a zero time delay
of 0.14. The developed single-photon sources are suitable for integration
into scalable photonic circuits.
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