Category Archives: APS March Meeting 2007

Been there…got the t-shirt

I actually didn’t buy an APS t-shirt — or a bumper sticker, slinky or travel mug — but I’m still glad I came to Denver.

Here’s some miscellany I learned today.

• There are no guns allowed in the Colorado Convention Center — but nowhere to “check ‘em at the door”.

• Top basketball coaches at US universities earn in excess of one million dollars a year. Not sure how much a top physicist earns…

• APS editor in chief Gene Sprouse told me that the funny symbol that appears next to articles of interest in Physical Review Letters is a colophon that appeared on the cover of the first issue of PRL.

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A little bang at SLAC

What’s the best way to determine the structure of a molecule that cannot be integrated within a periodic lattice?

Blow the heck out of it using x-ray pulses from the Linac Coherent Light Source (LCLS) — at least according to SLACs Philip Bucksbaum.

The LCLS will open next year at SLAC in California and will be much brighter than existing x-ray sources and will be capable of producing very short x-ray pulses.

It takes about 200 fs for the molecule to explode and the trick is to collect the diffraction data in the first 10-20 fs — when the molecule is still intact. By blowing up 100,000s of the same molecules, Bucksbaum claims that a 3d image of the molecule can be reconstructed. This technique has already been proven at an x-ray facility in Germany.

In his talk “Ultrafast X-ray Science at SLAC and LCLS” (U19 1), Bucksbaum described several other ways of harnessing the violent reaction between the X-ray pulses and sample.

For example, the pulses could be slammed into a solid such as iron. This would heat the sample and drive structural phase transitions that would propagate through the iron as “shock waves”. Real-time images of this process could be generated from the diffracted x-rays. This could give physicists valuable information about how lattice defects and other material properties affect the dynamics of phase transitions.

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The great pages debate

IOP Publishing’s reception was a big hit last night, judging by the fact that the buffet had to be replenished several times — you can work up a huge appetite running back and forth between sessions for nearly 10 hours a day.

I spent most of my time talking to IOP referees and journal board members as well as the competition — two editors from Physical Review B (not sure how they got in!).

It seems that paper length — or the lack thereof — is a growing concern in the journals community. Authors are apparently under lots of pressure to summarize their work in four pages (I wonder where that comes from?).

One IOP referee told me that he often asks authors to add clarifying paragraphs to their papers, but the authors are reluctant to do so because they believe that publishers favour shorter papers. The referee was concerned that highly truncated papers are of little pedagogic use to newcomers to a field, and that brief papers are so focused on results that the purpose of the research and the underlying physics is sometimes lost.

On the other hand, longer papers are much more difficult to write and referee — with some folks expressing concerns that quality could slip if papers were longer.

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Brrr…it’s cold in there

Some of the most interesting condensed matter physics occurs at very low temperatures and physicists need accurate ways of knowing just how cold their samples are. Traditionally, this has meant spending hours building, calibrating and troubleshooting temperature measurement and control systems — instead of actually doing the experiments.

Those days are over in many labs — at least according to Shane Hritz of Lake Shore Cryotronics. Hritz was in town to talk to physicists about the company’s cryogenic sensors, temperature control systems and magnetic measurement systems. He believes that physicists are hesitant to commit valuable resources to building and maintaining laboratory equipment. Instead, they want off-the-shelf kit that works the first time.

The company has just launched a new ruthenium oxide temperature sensor that is said to be the first commercial system calibrated down to 20mK — its last sensor was calibrated down to 50mK. “This doesn’t sound like much,” said Hritz, “but at these temperatures heat transfer through the leads becomes a big problem — any small bit of energy that gets into the sample can affect its temperature.”

Hritz say the company is now working on a sensor that is calibrated down to 10mK.

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On to the exhibition

I was having so much fun with the physicists that I nearly forgot to check out the exhibition before it closed for good this afternoon.

First stop was the IOP Publishing stand where I had a chat with Sharice Collins, who is our senior marketing manager for the Americas. Sharice is based in our Philly office and has organized a proper knees-up tonight for the IOP Journals community (Sharice prefers to call it a reception). I will of course be reporting on the reception in a future entry.

It seems that my initial concerns about the remote location of the exhibition were unfounded. Sharice reported a steady stream of traffic through the IOP stand. She said that delegates were very pleased to hear about our community website strategy — and the IOP flashing badges were a big hit.

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Living surfaces self-organize

Here’s a new recipe from Jeffrey Brinker of the University of New Mexico (P42 1)

Mix together water, alcohol, detergent, silica and a good dollop of single-cell organisms.

Dip in a substrate of your choice.

Remove and let dry.

While you do the washing up, the silica, detergent and cells will be busy organizing themselves on the substrate surface to create a highly ordered solid film. The amazing thing about this film is that cells survive the assembly process — and they remain alive for up to one month by eating the detergent.

Such films become even more interesting if they are made with organisms that act as biosensors — organisms that react to changes in light or the presence of certain chemicals.

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‘Buckets of BEC with inter-bucket tunnelling’

What? Not Mott?
Pots not dots, lots per pot
…and hot!

You can only get away with describing your experiment with a poem if you have a Nobel Prize — and JILA’s Eric Cornell has one of them.

The pots are the wells within a two-dimensional optical lattice and they were filled with lots of atoms in the Bose-Einstein condensate state. Atoms can tunnel between wells, so you can also think of this as an array of Josephson junctions (still with me?).

“Buckets of BEC with inter-bucket tunnelling”, is how Cornell described it.

Cornell and his team were looking for a Kosterlitz-Thouless transition in the lattice. This occurs when vortices form in the array above a certain temperature.

The lattice is made up of little triangles that look like this (the “O”s are the wells):

O O
O

Atoms moving clockwise (or counter-clockwise) from well to well around the triangle create a vortex.

And that’s exactly what they saw.

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Visible invisibility cloak?

Purdue University’s Vladimir Shalaev is giving the following paper tomorrow :

“Negative-Index Metamaterials in the Visible Range” (W38 1).

Could this be the first invisibility cloak for visible light?

Shalaev has already worked out a way to make metamaterials that respond magnetically to visible light, and has come tantalizingly close to creating negative index materials in the visible range.

I asked Shalaev if he would be unveiling an invisibility cloak on Thursday — but he just grinned, said “come to my talk”, and then he vanished into thin air!

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Facts and opinion about graphene

Graphene guru Pablo Jarillo-Herrero of Columbia University set me straight on the miraculous flakes of carbon.

-There were 180 papers published on graphene in the last year, but less than 10% were experimental.

-If it’s five or more atomic layers thick, then it’s just plain old graphite.

-If it’s 1-2 layers thick, the electrons think they are confined to two dimensions and the fun begins.

-Graphene is compatible with silicon fabrication processes and transistors can be made from graphene.

-Graphene has high electon mobility and is a superb heat conductor, which could allow graphene transistors to operate at vey high frequencies.

- A paper presented here at the APS has claimed that graphene grown on SiC has an electron energy gap of ~250 meV, which Jarillo-Herrero says is enough to make room temperature transistors.

-Graphene is not flat and its undulating surface affects its electronic properties

-The undulations could be a way of damping out thermal vibrations and therefore graphene could become flat below a certain temperature

-Graphene provides a laboratory for studying a range of fascinating phenomena including the quantum Hall effect, Berry’s phase and Dirac fermions

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Commercial high-Tc applications

In my entry on “Rock star physicists” I said that there are no commercially viable applications of high Tc superconductors. I have just discovered that this could be wrong — at least according to Alexis Malozemoff of American Superconductor Corporation.

In his talk “Transforming the Grid with Superconductivity” (L1 5), Malozemoff said that the company had sold two “synchronous condensers” to the Tennessee Valley Authority. These are electric motor-like devices that act as “shock absorbers” in an electricity grid and help keep voltage levels steady. The devices are wound with high Tc superconductor wire.

The company is also working on giant electric motors to power US Navy warships, and Malozemoff said that the company is still in the running for a contract to supply motors for next-generation destroyers.

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