DOE Experimental Condensed Matter Physics PI Meeting 2025 - Day 2

It was another very full day.   I had to pop in and out to attend to some things so I didn't get everything, but here are some physics items I learned:

• Dillon Fong introduced me to a technique I didn't know about before, x-ray photon correlation spectroscopy (see this paper).  You can look at time correlations of x-ray speckle near a particular Bragg spot and learn about dynamics and kinetics of transitions and materials growth.  Very cute.
• Charles Ahn presented work on high magnetic field superconductivity in Nd(1-x)Eu(x)NiO2, and I learned about the Jaccarino-Peter effect, in which an external magnetic field can counter the interaction between magnetic dopants and the conduction electrons.  This leads to "reentrant" superconductivity at high magnetic fields. 
• Danny Phelan showed that you can have two different crystal structures for La3Ni2O7, one that is stacked bilayers ("2222"), and one that is stacked monolayer/trilayer ("1313").  
• Ian Fisher talked about using the elastocaloric effect (rapidly and therefore adiabatically stretch or compress a material, leading to a change in its temperature) to identify phase transitions, since the effect is proportional to \( (\partial S/\partial \epsilon)_{T}\), the change in entropy with strain.
• Dan Dessau presented an interesting analysis of data in cuprates suggesting a form for the electronic self-energy that is called a power law liquid, and that this analysis implies that there is not a quantum critical point under the middle of the superconducting dome.
• Jak Chakhalian showed that epitaxially growing an iridate Weyl semimetal directly on top of insulating Dy2Ti2O7 spin ice leads to a dramatic anisotropic magnetoresistance at high in-plane fields that identifies interesting previously unknown physics.
• Daniel Rhodes showed some pretty work on superconductivity in T_d-MoTe2.  This material is extremely air-sensitive, and all of the device fabrication has to be done with great care in a glovebox.  This led to the following exchange.  Audience question: "It is notoriously difficult to make electrical contact to this material.  How did you do this?"  Answer: "Through tears and blood."  This was followed by a serious answer that concluded "The glovebox is always the problem."