Tag Archives: LCN

Freezing transient events (frozen magnetic monopoles)

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A Jan. 20, 2014 news item on Nanowerk highlights a new phase in laboratory physics (Note: A link has been removed),

Many of the most interesting things in nature – from spectacular lightning strikes to the subtlety of life itself – are transient, or far-from-equilibrium. To discover the secrets of far from equilibrium states, physicists need simple yet appealing laboratory systems. Now a researcher at the London Centre for Nanotechnology [UK] has collaborated with workers in Grenoble (France), Cardiff [Wales], Oxford [UK] and Kitakyushu (Japan), to create just such a system in the magnetic material known as “spin ice” (“Far-from-equilibrium monopole dynamics in spin ice”).

The Jan. 19 (?), 2014 (?) London Centre for Nanotechnology (LCN) research brief by Steve Bramwell, which originated the news item. explains ‘spin ice’ in greater detail and the trickery employed by the scientists’,

Spin ice is an unusual magnetic material in that it contains the magnetic equivalent of electrical charges – so called magnetic monopoles. It has attracted great interest on account of the currents of these charges forming a magnetic equivalent of electricity or “magnetricity”.

The number of magnetic monopoles in spin ice diminishes as the temperature goes down in much the same way as does the number of electrical charge carriers in semiconducting materials such as silicon – the basis of the electronics industry. The monopoles or charges disappear at low temperatures by positive and negative charges annihilating each other.

The researchers found a trick that used magnetic fields to create a hot “gas” of magnetic monopoles in very cold surroundings. The surroundings then sucked the heat out of the magnetic monopole gas, resulting in many magnetic monopoles trapped at a fraction of a degree above the absolute zero. The frozen monopoles no longer annihilated each other but instead could be made to flow by applying magnetic fields.

“Our low temperature experiments will tell us a lot about how magnetic monopoles move, as well as about the physics of far-from equilibrium systems in general” explains Prof. Steve Bramwell.

The researchers have provided this artist’s illustration of their work,

Figure: Artist’s impression of a hot gas of magnetic monopoles in very cold surroundings. Eventually the surroundings suck the heat out of the monopole gas leaving it frozen at low temperature. [downloaded from http://www.london-nano.com/research-and-facilities/highlight/frozen-magnetic-monopoles-create-new-laboratory-physics]

Figure: Artist’s impression of a hot gas of magnetic monopoles in very cold surroundings. Eventually the surroundings suck the heat out of the monopole gas leaving it frozen at low temperature. [downloaded from http://www.london-nano.com/research-and-facilities/highlight/frozen-magnetic-monopoles-create-new-laboratory-physics]

Here’s a link to and a citation for the paper,

Far-from-equilibrium monopole dynamics in spin ice by C. Paulsen, M. J. Jackson, E. Lhotel, B. Canals, D. Prabhakaran, K. Matsuhira, S. R. Giblin, & S. T. Bramwell. Nature Physics (2014) doi:10.1038/nphys2847 Published online 19 January 2014

This paper is behind a paywall with several payment options.

Only for the truly obsessed: a movie featuring gold nanocrystal vibrations

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Folks at the London Centre for Nanotechnology (at the University College of London) have released a film made with a pioneering 3D imaging technique that shows how gold nanocrystals vibrate. From the May 23, 2013 news release on EurekAlert,

A billon-frames-per-second film has captured the vibrations of gold nanocrystals in stunning detail for the first time.

The film, which was made using 3D imaging pioneered at the London Centre for Nanotechnology (LCN) at UCL [University College of London], reveals important information about the composition of gold. The findings are published in the journal Science.

Jesse Clark, from the LCN and lead author of the paper said: “Just as the sound quality of a musical instrument can provide great detail about its construction, so too can the vibrations seen in materials provide important information about their composition and functions.”

“It is absolutely amazing that we are able to capture snapshots of these nanoscale motions and create movies of these processes. This information is crucial to understanding the response of materials after perturbation. “

Caption: The acoustic phonons can be visualized on the surface as regions of contraction (blue) and expansion (red). Also shown are two-dimensional images comparing the experimental results with theory and molecular dynamics simulation. The scale bar is 100 nanometers. Credit: Jesse Clark/UCL

Caption: The acoustic phonons can be visualized on the surface as regions of contraction (blue) and expansion (red). Also shown are two-dimensional images comparing the experimental results with theory and molecular dynamics simulation. The scale bar is 100 nanometers. Credit: Jesse Clark/UCL

Here are more details from the news release,

Scientists found that the vibrations were unusual because they start off at exactly the same moment everywhere inside the crystal. It was previously expected that the effects of the excitation would travel across the gold nanocrystal at the speed of sound, but they were found to be much faster, i.e., supersonic.

The new images support theoretical models for light interaction with metals, where energy is first transferred to electrons, which are able to short-circuit the much slower motion of the atoms.

The team carried out the experiments at the SLAC National Accelerator Laboratory using a revolutionary X-ray laser called the “Linac Coherent Light Source”. The pulses of X-rays are extremely short (measured in femtoseconds, or quadrillionths of a second), meaning they are able to freeze all motion of the atoms in any sample, leaving only the electrons still moving.

However, the X-ray pulses are intense enough that the team was able to take single snapshots of the vibrations of the gold nanocrystals they were examining. The vibration was started with a short pulse of infrared light.

The real keeners can watch the movie if they click on the link to the May 23, 2013 news release on EurekAlert.

The team developing this movie was international in scope (from the news release),

The research team included contributors from UCL, University of Oxford, SLAC, Argonne National Laboratory [US] and LaTrobe University, Australia.