LA13386
Using Einstein's general relativity, traditionally a theory of gravity, we
construct a model of a Josephson junction and find that it agrees with
results from condensed matter physics.
A Josephson junction is made by sandwiching a non-superconductor between
two superconductors. Superconducting electrons can 'tunnel' through the
non-superconducting barrier and produce a current. These junctions are
well-understood by condensed matter physics and have wide applications in
electronic circuits.
Recently, using tools from string theory, a gravity model of a
superconductor was found. It was created in hopes of understanding one of
the biggest puzzles in condensed matter: high temperature
superconductivity. We test this model by using it to build a Josephson
junction. We then calculate the behavior of the current across the
junction, and find that it matches the expectations from condensed matter
physics.
Wednesday, May 11, 2011
Surface plasmons can be imprinted on metal nanostructures for subsequent imaging
LA13268
- An unusual observation turned into a scientific breakthrough when researchers investigating the optical properties of nanomaterials discovered a new type of high resolution microscopy for imaging the electric fields of nanostructures.
Optical nanomaterials are mainly based on surface plasmon resonances – the property whereby, in metallic nanostructures, light can collectively excite surface electron waves. With the help of plasmons, light can be captured, modified and even stored in nanostructures. This emerging nanotechnology could find applications in curing cancer, biochemical sensing, solar cells, optical computing, negative refractive index materials, and even invisibility. The imaging of surface plasmons provides a direct way to map and understand the local electric fields that are responsible for the unusual electromagnetic properties of optical nanomaterials; the imaging of surface plasmons, however, is quite challenging. Generally speaking, while there are methods to image plasmons with high resolution, they come at a considerable increase in both cost and complexity.
Now, researchers have demonstrated that upon illuminating nanostructures made of nickel or palladium, the resulting surface plasmon pattern is imprinted on the structures themselves, allowing for subsequent imaging with standard surface probe techniques, such as scanning electron microscopy or atomic force microscopy. The imprinting method is quite unique, combining aspects of both imaging and writing techniques. The combination offers a resolution on plasmons that is, in principle, only limited by that of the atomically-sensitive surface probe techniques.
- An unusual observation turned into a scientific breakthrough when researchers investigating the optical properties of nanomaterials discovered a new type of high resolution microscopy for imaging the electric fields of nanostructures.
Optical nanomaterials are mainly based on surface plasmon resonances – the property whereby, in metallic nanostructures, light can collectively excite surface electron waves. With the help of plasmons, light can be captured, modified and even stored in nanostructures. This emerging nanotechnology could find applications in curing cancer, biochemical sensing, solar cells, optical computing, negative refractive index materials, and even invisibility. The imaging of surface plasmons provides a direct way to map and understand the local electric fields that are responsible for the unusual electromagnetic properties of optical nanomaterials; the imaging of surface plasmons, however, is quite challenging. Generally speaking, while there are methods to image plasmons with high resolution, they come at a considerable increase in both cost and complexity.
Now, researchers have demonstrated that upon illuminating nanostructures made of nickel or palladium, the resulting surface plasmon pattern is imprinted on the structures themselves, allowing for subsequent imaging with standard surface probe techniques, such as scanning electron microscopy or atomic force microscopy. The imprinting method is quite unique, combining aspects of both imaging and writing techniques. The combination offers a resolution on plasmons that is, in principle, only limited by that of the atomically-sensitive surface probe techniques.
Monday, May 9, 2011
New wireless devices based on current-induced torques
BA11499
- Current flowing through a magnetic material can alter its magnetization
by spin torque, whereby the spins of the electrons flowing in the
current exert a torque on the magnetization. This mechanism can induce
high-frequency precession of the magnetization. The effect can be used
to make high-frequency wireless devices for future mobile phones,
devices that are significantly smaller and consume less power than the
current state-of-art current technology based, for example, on standard
quartz crystal resonators. In this work, we demonstrate that a very
tiny magnetic tunnel junction device, in which two magnetic layers
(CoFeB) are separated by an oxide barrier (MgO) can emit strong
microwave signals with GHz frequencies. The novelty of our results is
that we are able to demonstrate microwave emission from both the top
magnetic layer, which is called free layer, and the bottom magnetic
layer which is called fixed layer. We show that the precession frequency
of the free layer changes linearly with bias voltage due to the linear
variation of perpendicular component of spin torque. In contrast, the
precession frequency of the fixed layer changes quadratically as a
result of heating effects. By changing the applied field magnitude it is
possible to control which layer is excited and hence to manipulate the
behavior of the frequency with bias voltage. Thus our work provides an
important step towards making next generation wireless devices.
- Current flowing through a magnetic material can alter its magnetization
by spin torque, whereby the spins of the electrons flowing in the
current exert a torque on the magnetization. This mechanism can induce
high-frequency precession of the magnetization. The effect can be used
to make high-frequency wireless devices for future mobile phones,
devices that are significantly smaller and consume less power than the
current state-of-art current technology based, for example, on standard
quartz crystal resonators. In this work, we demonstrate that a very
tiny magnetic tunnel junction device, in which two magnetic layers
(CoFeB) are separated by an oxide barrier (MgO) can emit strong
microwave signals with GHz frequencies. The novelty of our results is
that we are able to demonstrate microwave emission from both the top
magnetic layer, which is called free layer, and the bottom magnetic
layer which is called fixed layer. We show that the precession frequency
of the free layer changes linearly with bias voltage due to the linear
variation of perpendicular component of spin torque. In contrast, the
precession frequency of the fixed layer changes quadratically as a
result of heating effects. By changing the applied field magnitude it is
possible to control which layer is excited and hence to manipulate the
behavior of the frequency with bias voltage. Thus our work provides an
important step towards making next generation wireless devices.
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