## Tuesday, March 15, 2016

### APS March Meeting, day 2

Another eclectic bunch of talks today:

• There was a very interesting session this morning about coupling superconductors to semiconductors - this is a topic that has a long history and has enjoyed a huge resurgence as people have figured out ways to create composite systems with wild properties, like Majorana fermions.  Amir Yacoby gave a talk about what happens when a superconductor (Al) is coupled to a strong spin-orbit semiconductor, a HgCdTe quantum well.  The superconducting order parameter leaks into the semiconductor (the proximity effect), and more interestingly, it oscillates in space between $s$-wave pairing (the electrons in each Cooper pair form an antisymmetric spin configuration,  $(1/\sqrt{2})(| \uparrow \downarrow\rangle - |\downarrow \uparrow \rangle)$, that flips sign if you swap the electrons ) and $p$-wave pairing (the electrons forming a symmetric spin configuration, like $(1/\sqrt{2})(|\uparrow \uparrow\rangle + |\downarrow \downarrow \rangle)$.  From current data as a function of in-plane magnetic field and out-of-plane magnetic field, plus some disorder in the contact region, you can explain almost everything.  The next talk, by Dale van Harlingen, discussed superconductors coupled to the 2d surface of a 3d topological insulator, Bi2Se3, making Josephson junctions.  These things end up playing host to Majorana fermions, and can be used to push them around in interesting ways.
• Later, after seeing some contributed talks, chatting with folks, and visiting the trade show to get literature from a bunch of vendors, I stood through a talk about trying to detect evidence of dark energy with a (comparatively) "tabletop" atomic physics experiment.   A very cool topic, but the room was so claustrophobic I couldn't stay for the talk about the gravity-decoherence paper I'd mentioned here.
• After learning about "Advanced undergraduate labs:  why bother?", I went to the extremely dense session about spintronic devices beyond spin-transfer torque.   The metal spin device toolkit is now very extensive, and it will be interesting to see if the materials issues can be worked out well enough to produce devices that will really revolutionize information storage and processing.  Power dissipation remains a big issue.  Here is a recent review article on this stuff (sorry - I didn't want to direct-link to someone's private copy of the pdf).  I should write a separate post on this stuff.
More tomorrow....