Today was the first day of the 2007 International Conference on Strongly Correlated Electron Systems (SCES), hosted this year in Houston jointly by Rice and UH. It's a pretty big meeting, typically with between 600 and 700 participants. Traditionally the meeting has had a very strong European and Asian participation, with a focus on heavy fermion compounds and high-Tc superconductivity. This year, there's an increased inclusion of strongly correlated physics in mesoscopic systems (quantum dots, nanotubes, graphene, single-molecule devices), as well as discussion of model correlated systems based on ultracold trapped atoms and molecules.
Because I'm on an internal search committee for a dean, my semester still hasn't really ended, which means that I'm going to miss a fair bit of the meeting. However, I'll still try to blog a couple of highlights daily. Here are two neat, new (and as yet unpublished) results that I saw this morning.
First, Louis Taillefer spoke about new measurements done in extremely high quality hole-doped YBCO at high magnetic fields (pulsed up to 60 Tesla). This work has been focused on trying to suppress superconductivity with a field in this, the grand-daddy of the high-Tc compounds, and to understand the ground state and possible quantum phase transitions (as a function of doping) of the normal phase. The exciting new result is that Taillefer and collaborators have been able to see Shubnikov-deHaas oscillations in this material for the first time. This is a big deal. First, it tells you that there are some sort of excitations in the normal state that can execute closed cyclotron orbits in the presence of a magnetic field. Since the validity of weakly interacting quasiparticles in the normal state is in significant doubt, this is interesting. Second, the frequency of the oscillations in 1/B reveals the area enclosed by those orbits in k-space - essentially it tells you how big the hole pockets are in the Brillouin zone, and therefore how many mobile holes there are per copper atom. Third, the temperature dependence of the S-deH oscillations lets you infer an effective mass (in this case, about 1.9 free electron masses) for whatever's doing the cyclotron motion. Very neat!
Second, Abhay Pasupathy from Ali Yazdani's group at Princeton showed some beautiful new STM data on BSCCO. The neat thing here is that their superfancy STM is absurdly stable over a big temperature range for days. That means that they can map out the tunneling density of states of the material on the atomic scale as a function of temperature, from deep within the superconducting state to well above the resistively detected Tc. They see that the gap in the density of states indicative of pair formation vanishes nonuniformly over the surface, with local bits persisting to well above the average Tc. They also show that the temperature dependence of the gap as a function of gap size is very different than that in low-Tc materials.