July 10, 2009

LC12805BR

MOLECULES MADE OF ELECTRONS IN CARBON NANOTUBE
QUANTUM DOTS

The paradigm of few electrons trapped in quantum dots explains their
behavior as particles in a box. Obeying Fermi statistics, electrons
fill in the lowest-energy quantum states of the "box". This holds
also for carbon nanotube dots, where the box has only one dimension.
The authors suggest a different scenario, due to the unusually
strong Coulomb repulsion between electrons. They predict that a few
electrons in nanotubes behave like molecules, with the electrons
playing the role of nuclei, and the Coulomb repulsion acting as the
inter-nuclear interaction. The authors also claim this phenomenon
has already been observed in a recent experiment [Kuemmeth et al.,
Nature 452, 448 (2008)], which may be explained by this molecular
model ---alternative to the particle-in-a-box model. The localization
of electrons in space predicted by this model could help to achieve
control of the electron spin for future applications.

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LF12184

Novel method for detecting unusual superconducting state

This paper presents a method for experimentally detecting an unusual,
and so far unobserved, superconducting phase. This "FFLO" phase is
characterised by a density of superconducting carriers that oscillates
in space. It is central to theories of superconductivity in metals and
in particle physics, so its detection would be a major advance in our
understanding of these fields. Experiments on ultracold atomic gases
will soon be in a regime where the FFLO phase can form. However, one
major difficulty is detecting this phase: the oscillatory spatial
structure is below the resolution of current imaging technology. We
propose a method that directly probes this spatial structure. By
applying a spatially varying potential with a tunable wavelength,
theory shows that swaying motion of the entire atomic cloud (easily
resolved with current technology) is excited when the wavelength
matches that of the FFLO phase. Imagine a pendulum suspended from a
toothed wheel: moving a chain back and forth on this wheel causes the
pendulum to swing, but only when the spacing of the chain matches that
of the teeth. Just as the spacing of the teeth can be found by
determining what chain makes the pendulum swing, the presence and
properties of the FFLO phase can be seen by what wavelength of the
potential makes the cloud sway.


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BC11264

Plasmonic excitations in tight-binding nanostructures

Physicists have calculated what happens when light illuminates very small metal particles. They find that for the smallest metal particles the position of just one atom in the structure can completely alter how light is absorbed and scattered. This extreme sensitivity has been discovered using a quantum-mechanical non-local response theory that properly describes the motion of electrons in the atoms making up the metal. In particular, they identified the way in which electrons move together to form collective excitations that interact the strongest with light and how, by changing metal particle geometry by as little as just one atom, it is possible to switch a given response on or off. This opens up new ways to design nanotechnology devices that make direct use of quantum physics for their function.

Improving Phys. Rev. Letters

The American Physical Society (APS) is revamping publication standards to make Physical Review Letters (PRL) more selective and more efficient. PRL is already one of the world’s leading journals of physics, but the procedural changes that go into effect July 1, 2009 will produce PRL issues that include fewer, higher quality papers than have been typical of the journal in recent years . . .

Read more about it.

LE11884BJ

Voltage sensitivity of Curie temperature
of ultrathin metallic films

Imagine a material which can be either magnetic or non-magnetic
at room temperature depending on the applied voltage. This is what
the researches in the area of Spintronics have been seeking for
decades as such a material may substantially enhance the functionality
and performance of the future computational devices. Because of several
important technological issues (e.g., power consumption, fluctuations,
and cost in fabrication), the most attractive controllable ferromagnetism
is that of metals. However, due to their impenetrability by electric
field and thus the seeming uncontrollability of the metallic
magnetization (on lengths larger than the inter-atomic distance), metals
were excluded from the list of possible candidates. The search for the
controllable ferromagnetism has been focused solely on the semiconductor
ferromagnets. In our work, we proved that the desired goal can be achieved
in metallic ferromagnetic films. The possibility of the control arises
naturally near the ferromagnetic transition, at which the "charge" and
the "spin" degrees of freedom get separated on the spatial scale. As a
result, charging a surface affects the spin-alignment (and the existence
of the magnetization) across the entire film.