March Meeting 2025, Day 1

The APS Global Physics Summit is an intimate affair, with a mere 14,000 attendees, all apparently vying for lunch capacity for about 2,000 people.   The first day of the meeting was the usual controlled chaos of people trying to learn the layout of the convention center while looking for talks and hanging out having conversations.  On the plus side, the APS wifi seems to function well, and the projectors and slide upload system are finally technologically mature (though the pointers/clickers seem to have some issues).  Some brief highlights of sessions I attended:

• I spent the first block of time at this invited session about progress in understanding quantum spin liquids and quantum spin ice.  Spin ices are generally based on the pyrochlore structure, where atoms hosting local magnetic moments sit at the vertices of corner-sharing tetrahedra, as I had discussed here.  The idea is that the crystal environment and interactions between spins are such that the moments are favored to satisfy the ice rules, where in each tetrahedron two moments point inward toward the center and two point outward.  Classically there are a huge number of spin arrangements that all have about the same ground state energy.  In a quantum spin ice, the idea is that quantum fluctuations are large, so that the true ground state would be some enormous superposition of all possible ice-rule-satistfying configurations.  One consequence of this is that there are low energy excitations that look like an emergent form of electromagnetism, including a gapless phonon-like mode.  Bruce Gaulin spoke about one strong candidate quantum spin ice, Ce2Zr2O7, in a very pedagogical talk that covered all this.  A relevant recent review is this one.   There were two other talks in the session also about pyrochlores, an experimentally focused one by Sylvain Petit discussing Tb2Ti2O7 (see here), and a theory talk by Yong-Baek Kim focused again on the cerium zirconate.    Also in the session was an interesting talk by Jeff Rau about K2IrCl6, a material with a completely different structure that (above its ordering temperature of 3 K) acts like a "nodal line spin liquid".
• In part because I had students speaking there, I also attended a contributed session about nanomaterials (wires, tubes, dots, particles, liquids).  There were some neat talks.  The one that I found most surprising was from the Cha group at Cornell, where they were using a method developed by the Schroer group at Yale (see here and here) to fabricate nanowires of two difficult to grow, topologically interesting metals, CoIn3 and RhIn3.  The idea is to create a template with an array of tubular holes, and squeeze that template against a bulk crystal of the desired material at around 350C, so that the crystal is extruded into the holes to form wires.  Then the template can be etched away and the wires recovered for study.  I'm amazed that this works.
• In the afternoon, I went back and forth between the very crowded session on fractional quantum anomalous Hall physics in stacked van der Waals materials, and a contributed session about strange metals.  Interesting stuff for sure.

I'm still trying to figure out what to see tomorrow, but there will be another update in the evening.