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Woodstock and Superconductivity


Physicist lowers body temperature to achieve a superconducting state.
I came upon a child of god He was walking along the road And I asked him, where are you going And this he told me I’m going on down to Yasgur’s farm - Joni Mitchell

I never made it to Yasgur’s farm - I was just too young in 1969 to head to New York to catch all of the acts that I loved. Later that summer I did make it to the Atlantic City Pop Festival , which was a much-sanitized version. No rain, no mud slides, no babies born…and there was certainly no one making movies or disclaiming about the AC Pop Festival Generation.

Many years later I finally made amends for my serious cultural lapse in ‘69 and attended the next Woodstock - the Woodstock of Physics. This 1987 event was a wild affair as the news of high-temperature superconductivity was just breaking, along with promises of a Jetson-like future soon to be commonplace. There were thousands at the session in NYC, with most (including this author) watching the presentations via monitors in the corridors, straining to hear every word, to make out every blurred overhead with a hastily sketched graph, waiting to hear what would be the next latest (and higher) superconducting temperature…

          <em>We are stardust       We are golden       And we've got to get ourselves       Back to the garden       </em>             

A surprising fact about HTSC is that discovers Karl Müller and Johannes Bednorz received the Nobel Prize that same year -an amazingly short time for the Nobel committee to name an award winner. (They had first noticed the effect only a year earlier.) Typically it is many years between discovery and award, with other experimenters and theorists demonstrating that the original discovery was both true, and truly significant for physics. More amazing, there was no consensus on why HTSC occurs.

And theory has been pretty underwhelming since then.

Now, as the 20th-year anniversary of the HTSC Woodstock is celebrated, there may be a breakthrough. In a May 30th press release by CNRS (The Centre National de la Recherche Scientifique), an arm of France’s Ministry of Research, there is new experimental evidence that may lead to a true understanding of the HTSC phenomena. Note that the connection between understanding and modeling is explicitly stated in this passage:

Since the end of the 1980s (Nobel Prize in 1987), researchers have managed to obtain 'high temperature' superconducting materials: some of these compounds can be made superconducting simply by using liquid nitrogen (77 K, or -196 °C). The record critical temperature (the phase transition temperature below which superconductivity occurs) is today 138 K (-135 °C). This new class of superconductors, which are easier and cheaper to use, has given fresh impetus to the race to find ever higher critical temperatures, with the ultimate goal of obtaining materials which are superconducting at room temperature. However, until now, researchers have been held back by some fundamental questions. What causes superconductivity at microscopic scales? How do electrons behave in such materials? Researchers at the National Laboratory for Pulsed Magnetic Fields, working together with researchers at Sherbrooke, have observed 'quantum oscillations', thanks to their experience in working with intense magnetic fields. They subjected their samples to a magnetic field of as much as 62 teslas (a million times stronger than the Earth's magnetic field), at very low temperatures (between 1.5 K and 4.2 K). The magnetic field destroys the superconducting state, and the sample, now in a normal state, shows an oscillation of its electrical resistance as a function of the magnetic field. Such an oscillation is characteristic of metals: it means that, in the samples that were studied, the electrons behaved in the same way as in ordinary metals. The researchers will be able to use this discovery, which has been eagerly awaited for 20 years, to improve their understanding of critical high-temperature superconductivity, which until now had resisted all attempts at modeling it. The discovery has been effective in sorting out the many theories which had emerged to explain the phenomenon, and provides a firm foundation on which to build a new theory. It will make it possible to design more efficient materials, with critical temperatures closer to room temperature.

This experiment described here employs a fascinating, Zen-like approach to investigate a phenomena. High magnetic fields are used to TURN OFF the superconducting state. In effect, the behavior of electrons when the material is not super-conducting holds the key to what they do when the material is superconducting.

Absence makes the heart grow less conducting? What you don’t see is what you "get"? Let Joni make the call…

Then can I walk beside you I have come here to lose the smog And I feel to be a cog in something turning Well maybe it is just the time of year Or maybe its the time of man I don’t know who l am But you know life is for learning I should note that there have been other "breakthroughs" in modeling HTSC. e.g. in 2005, researchers at the University of Aberdeen announced work that showed the deep connection between lattice structure and superconductivity. Specifically, they found that the HTSC material had a negative thermal-expansion - a rare occurrence.