At The Edge of Strange

Back to the Future

Who steals this treasure must contend with its flame
Where only the strange remain
Yea, only the strange remain
~ Mickey Hart – “Only The Strange Remain” on the Mystery Box

Science fascinates me though I’m not a scientific genius. I am in awe of the edge of possibility, of that fearlessness of scientists to go where no man has gone before, to push the envelope into the unknown and risk what isn’t known about what is discovered.

So recently my attention was attracted to an article in the Aug 23, 2014 issue of Science News by Andrew Grant titled “Weird materials find a practical use”. Finding out that the practical was based in something called “topological insulators” I thought first to learn more about them. So I went to Wikipedia – not the most respected scientific journal but something accessible to the common person who lacks specialized understandings.

The first thing I learned about these materials is that they have a time reversal symmetry. Time, now that is another aspect of life that fascinates me. Reversing time ? Symmetry ? Need to learn more !! James Clark Maxwell described a thought experiment that has been dubbed Maxwell’s Demon. So it is described this way – “a microscopic demon guards a gate between two halves of a room. It only lets slow molecules into one half, only fast ones into the other. By eventually making one side of the room cooler than before and the other hotter, it seems to reduce the entropy of the room, and reverse the arrow of time”.

Back to topological insulators – these materials behave like an insulator in their interiors but electrons are able to move on the surface. The surface states of topological insulators are special because they are symmetry protected by the conservation of their particle number and due to time reversal symmetry. What is really important to the “latest ideas for practical usage” is that electrons moving along the surface have their spin locked at a right-angle to their momentum (spin-momentum locking).

Silver colored surface is a superconducting quantum interference device which detects magnetic fields (red) created by an edge current (blue) in a topological insulator.

Time-reversal symmetry protected edge states were predicted to occur in quantum wells (very thin layers) of mercury telluride sandwiched between cadmium telluride in 1986 by Pankratov and observed in 2007. And in 2007, they were predicted to occur in three-dimensional bulk solids of binary compounds involving bismuth. Penn State condensed matter physicist Nitin Samarth wanted to do something useful with them and was inspired by the work of Dan Ralph another condensed matter physicist at Cornell University who wants to speed up the processes that currently limit speed and capacity in computer RAM and hard drives.

There are several components within a computer that help make it faster and more powerful. A computer with more memory (RAM) will be capable of storing more programs that are currently running in memory. If your computer runs out of memory, the computer must swap unused data stored in memory to your hard disk drive until it is needed again. This makes each task more complex by adding another extra step and because the hard drive is the slowest type of memory in the computer it will decrease the speed even more.

Most current hard drives store data as 1 and 0 based on magnetic orientation. Generating those magnetic fields is a relatively inefficient process. Ralph’s team built devices in which electrons brush past compass needles and because of their spin provide a subtle torque. The key to maximizing torque is generating currents of electrons with the same spin. Joining together the work of both Samarth and Ralph, they tested a theory that electrons racing across the surface of a topological insulator could manipulate a magnetic material by their spin. To do this, they layered a nickle-iron wafer atop the topological insulator bismuth selenide and sent an alternating current of electrons through the device. Each electron in the bismuth selenide exerted about 10 times as much torque as electrons in any other material tested so far. That torque would be sufficient for utilization in a memory device.

Shifting my focus now to be closer to home. At some point more than a decade ago we decided to test our home for radon with a little mail order kit. We were shocked to discover that our home had unacceptably high levels of radon. This is not good news because radon is a radioactive gas that can cause cancer. And what’s unsettling about this lethal invader is that you can’t see, taste or smell it’s presence. Radon is the second leading cause of lung cancer in the United States today and if you smoke tobacco and your home has high radon levels, then you’re at high risk for developing lung cancer.

We don’t smoke but we still don’t like knowing radon is here in our home. So, we installed a little fan in one window of our basement and opened up the little window at the opposite side. It’s the best we can do for now. We began a construction project which the lethargic economy has put on indefinite hold but you can believe that we have taken a proactive stance against even the possibility of radon ever being an issue in our construction planning.

The atomic radius of Radon is 1.34 angstroms and it is the heaviest known gas, nine times denser than air. Because it is a single atom gas (unlike oxygen, O2, which is comprised of two atoms) it easily penetrates many common materials like paper, leather, low density plastic, most paints, and building materials like gypsum board and sheetrock, concrete block, mortar, sheathing and tar paper, wood paneling, and most insulation materials.

Molecular Cage perfectly sized to trap a gas atom.

So imagine the possibilities being explored by materials chemist, Andrew Cooper of the University of Liverpool in England. It was one of those unintended consequences that happen frequently in science. Cooper and his colleagues had set out to create a polymer. Instead, they produced a 3-D “cage”. This was accomplished by reacting 4 aldehyde molecules with 6 nitrogen-containing ones. The cages clumped together to form a multichambered atomic jail as reported in an article “Molecular cage traps rare gases” in the same Aug 23, 2014 issue of Science News by Beth Mole.

In their research, the scientists estimate that radon could only slip out 3% of the time, once it slipped in. While one of the applications could strip out xenon so valuable it sells for $5,000 a kilogram (and this is useful for it has applications in lighting, medical imaging and anesthesia), Cooper and his colleagues think the molecular traps could detect radon in homes. I think even further out, could this technology eventually “trap” radon to make our homes safer someday ?

~ Information Resources

Lyrics “Only The Strange Remain” by Mickey Hart on the Mystery Box cd – https://www.mickeyhart.net/music/lyrics/only-strange-remain

“Weird materials could make faster computers” by Andrew Grant posted 07/23/14 at Science News – https://www.sciencenews.org/article/weird-materials-could-make-faster-computers

“Topological Insulator” at Wikipedia – http://en.wikipedia.org/wiki/Topological_insulator

“T-symmetry” (the theoretical symmetry of physical laws under a time reversal transformation) at Wikipedia – http://en.wikipedia.org/wiki/T-symmetry

“What makes a computer fast and powerful ?” posted at Computer Hope – http://www.computerhope.com/issues/ch001380.htm

“Radon Fact Sheet” – http://www.radon.com/radon/radon_facts.html

“Molecular cage traps rare gases” posted by Beth Mole on 07/23/14 at Science News – https://www.sciencenews.org/article/molecular-cage-traps-rare-gases

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Blog author ~ Deborah Hart Yemm is co-founder of
Yemm & Hart, a green materials producer

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