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Michael Banks: March 2008 Archives

One of the most sought after theories in condensed matter physics is that of high temperature superconductivity. It is hard to walk into these kind of talks and understand what is going on. If it is theory, it’s next to impossible as the first slide almost jumps into a large Hamiltonian, and as I guess these Hamiltonian’s have been discussed ad nauseum by now, people have started to not even describe any of the terms.

In a talk given by Doug Scalapino from the University of California at Santa Barbara, he discussed the question of a pairing ‘glue’ in high temperature superconductors. From what I understand this goes back to last year when Phil Anderson wrote a perspectives in science with the point that if “we have a mammoth and an elephant in our refrigerator - do we care much if there is also a mouse?”

Here the mammoth and the elephant are U, the on site repulsion and J, the exchange interaction in the Hubbard model which describes the transition between conducting and insulating systems. So Anderson says as these interactions are so large why do we need a mouse or a much smaller interaction that is the ‘glue’ that pairs electrons. In ordinary superconducting metals, like lead or Tin, these exchanged particles are phonons (lattice vibrations) that act like a bosonic “glue” to hold the electron pairs together. But what is the ‘glue’ for high temperature superconductors, like the cuprates? Anderson contends that the pairing interaction is coming from J which is instantaneous, attractive and large, so why do we need a smaller interaction to describe the bosonic glue?

Well, the glue that Scalapino was describing was not very clear to me, and it seems that was also the case with some audience members. Indeed, one person did ask at the end of the talk what is the glue and Scalapino’s answer was, well, spin fluctuations. But as Anderson points out these are just a natural consequence of the exchange interaction, J.

I think the jury is still out.

Comparisons

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Being at the APS meeting last year in Denver, I can’t help but think about some comparisons. Although I was at the march meeting last year in a different capacity (as a researcher, giving my 10+2 minute talk), It seems to me that the scale of this year’s event is much smaller compared to last year.

Although people from the APS say this year more than 7000 participants are registered, having chatted to a few people in the exhibition area, where most of the companies selling their equipment are based, they say business is much less than last year, and indeed the number of people just walking around and in sessions, to me at least, seems much less.

Most people who I have talked to seem to think along the same lines. Of course one can come up with their own conclusions about this, but maybe physics departments and institutions are tightening their belts as a result of funding tightening both in the UK and US.

I don’t have any figures to back up my claim about any possible decrease in participant figures, but possibly Bush’s last US science budget request for the financial year 2009 will promise more money for physicists and a return turnout for the APS march meeting 2009.

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Now for a topic that is close to the heart for many inhabitants of New Orleans - hurricanes. The devastation caused by the events in 2005 by hurricane Katrina led to most of the inhabitants of New Orleans to be displaced and caused news and debate around the world for months - still today, nearly two years on from the events many inhabitants are still homeless.
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A hurricane can be modeled as a vortex, with a depth of only around 50 - 100 ft, but being miles across. Katrina was a Category 5 hurricane which brought water levels to around 30 ft at the coastal lines and was the sixth strongest Atlantic hurricane ever recorded.

Greg Holland from the National Center for Atmospheric Research, Boulder, Colorado, talked about understanding extreme hurricanes. Hurricane activity has increased substantially since the 1970’s, Holland pointed out that in his simulations just a 5 m/s increase in wind speeds can lead to a 100% increase in category 5 hurricanes - which he says seems to correlate well with observed behavior.

Of course the economic costs can be great of the devastation brought from a hurricane such as Katrina, which has now cost around $140 per household in the US. A following talk from Harold Brooks from National Severe Storms Laboratory, in Norman Oklahoma, showed another aspect of climate change - large hail stones. He showed that the frequency of large hail fall (i.e that the size of a baseball - still going on the baseball theme) is increasing by about 6% a year, and the ‘favorable severe environment’ for such weather conditions is increasing by 0.8 % per year. Both exploding just after the 1980’s.

Town planning was also a subject under scrutiny, with Holland pointing out the lemming like way we are build more and more communities next to the coast on some of the dangerous places like on marsh land.

However, it was noted during the session that Katrina is likely a few hundred year event, but this, however, now remains to be seen.

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How much do drugs affect the performance of athletes and more interestingly how can we quantify such enhanced performance? That was the question that Roger Tobin, a condensed matter physicist from Tufts University, posed in his talk on ‘Sox and Drugs: Baseball, steroids and physics’. Quantifying enhancement is an interesting question, if someone takes drugs and it increases their performance to, say, score one more goal per season or hit a golf ball a few centimetres farther is it really worth it to make a fuss?

The sport in question in Tobin’s talk was of course baseball. In other sports such as weight lifting, taking steroids can have an obvious effect. But what about other sports where strength is an advantage, but cannot easily correlate with results.

He characterized two eras, namely before and after steroid use became well documented (which he put as around 1990s onwards). If one looks at the record home runs in a single season, this explodes in the late 1990s when Sosa hits 66 and Bonds hits 73 home runs in a single season. This increased effect for baseball is around 20% (from the previous efforts of Ruth). Imagine a 20% increase in the 100 m sprint, this would mean a sprinter taking around 8 seconds to run it. If steroid use is the culprit, how can steroid use affect baseball so much but not other sports?

Tobin says that the only advantage of using steroids in baseball comes in the bat speed. It’s pretty straight forward — steroids build muscles, or increase muscle cross section, which allows the player to exert more force on the ball, which then gives the ball more speed. He calculates that steroid use could increase the ball speed by about 3%. Which if one thinks about it is not a lot…

However, here comes the catch. If I took steroids (don’t worry I am not planning to do the experiment) and started playing baseball, it wouldn’t automatically mean that I am going to beat Babe Ruth’s previous home run record, but as Tobin says the player must already “be pretty special.” So what happens? Well, if you look at the hit distribution of a top player, he may hit 10% of all shots as home runs in a season, but he will hit many that are near home runs, in fact the distribution will have a peak at the place which are nearly home runs. What Tobin says is that steroid use shifts this peak so that all those previous near home runs, now become, well, home runs, so this shift alone increases a players 10% home runs to around 15% in a season — all with the help of a few more percent in ball speed…and some steroids.

Seems like condensed matter physicists are spreading their wings, he also plans to extend his work to other sports, so footballer and golfers beware…

Annealing at 1K

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My first session was on supersolid He-4, up bright and early for the 8am start. The paper under discussion for the first talk appeared in Nature last year by Xi Lin and colleagues from Penn State University. They looked at the heat capacity of He-4 at low temperature (T < 0.5 K), and reported a peak centered around T = 0.08K.

It also became apparent the difficulties of making accurate measurement at such temperatures, they reported that they constructed 20 low temperature cells for the measurement, and only one of them was heat leak proof.

A large question in the area of supersolid He-4 is what the role of He-3 impurities are, in the final talk of the session given by Philip Anderson this question seems to have even got the better of the Nobel prize winner himself, when he openly admitted to not knowing the answer.

The supersolid peak is independent on the amount of He-3 impurities with Lin presenting samples with 0.3 ppm (parts per million) and 1ppb (parts per billion) of He-3 impurity. But the peak did slightly decrease in temperature when the samples was annealed for longer, so it seemed to depend on how the sample is made. A comment was later made that the supersolid peak could be intimately linked with disorder.

Unfortunately the session did break up a little when the second speaker didn’t show up - which was supposedly a knock on effect from the storm that was over the east coast at the weekend.

Arrived and ready

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The 21 hour door-to-door trip is past us now as we focus on the start of the conference tomorrow. We arrived at the hotel early on Sunday morning after a quick connection in Chicago. The whole trip from Heathrow to New Orleans went quite smoothly, except for the need to change planes in Chicago after we were all seated and ready to go - apparently there was a problem with the braking system, so I wasn’t complaining to change planes. It was also on the flight from Chicago that it became apparent that there were possibly many physicists on-board, most of them armed and ready with poster tubes.

Today, we had our first chance to see some of New Orleans. We had a brief walk around the French Quarter and along the Mississippi river where most of the hotels are situated near to the convention center. Though it was not immediately clear from these areas the devastation that was inflicted by hurricane Katrina in 2005.

I popped into the convention center itself, and already saw a mass of physicists queuing up to register. Coming to the center is the first time the scale of the APS March meeting hits you - containing massive halls where the exhibitions are held. Some people already have their hands on the thick conference book, meticulously studying it, though no doubt looking for the location of colleague’s talks.

After a few too many shrimps this afternoon, we are ready for the conference tomorrow and look forward to keeping you updated on all the in’s and out’s of the 2008 APS March meeting.