It's that time of year again, when I get together with thousands of my closest condensed matter physics friends to hear and give talks, swap gossip, and swill overpriced coffee. This year the action is in Baltimore, where one of my main observations after the first day is that someone needs to label the correct room lighting setting so that the project images aren't really washed out.
Real life has intruded in a couple of ways on the meeting this year for me, so my posting will likely be more brief than in past years - sorry.
Yesterday I spent most of my time in the sessions on nickelates and vanadates. The nickelates are a very interesting system, of the form RNiO3, where R is a rare earth atom. These form a family of strongly correlated oxides, where electron-electron interactions can be extremely important in determining the properties. The key is the partially filled d band from the Ni atoms, each of which is octahedrally coordinated by oxygens. Depending on the rare earth ion, the Ni-O bond angles change, and there can be two inequivalent Ni sites. Simple band structure without interactions says these should be metals, and LaNiO3 is a (correlated) metal. However, other members of the family are more complex, such as NdNiO3, which has a metal insulator transition in the bulk at around 200K, between a high T paramagnetic metal and a low T antiferromagnetic insulator - some flavor of the Mott transition. I heard a very interesting talk by Greg Fiete from UT about the possibility that one can use interactions in these materials to create new topological insulators, ones where the energy gap that makes them insulating is an interaction-based gap (as opposed to ordinary TI materials, where they are boring band insulators).
The vanadate sessions were also pretty compelling. VO2 also has a metal-insulator transition, this one at 340K, where interactions and lattice distortions both play very important roles. There were many good talks, including one about some extremely pretty work to figure out the triple point of the phase transitions between rutile and two monoclinic phases. There were also multiple talks about manipulating the transition via chemical doping and field effect approaches. Fun stuff.
Other observations so far: lots of sessions on topological materials, lots of sessions on experimental approaches to quantum bits, and lots of worried discussion of the sequester.