Brief items - Static electricity, quantum geometry, Hubbard model, + news

It's been a busy time that has cut into my blogging, but I wanted to point out some links from the past couple of weeks.

• 
  Physics Today has a cover article this past issue about what is colloquially known as static electricity, but what is more technically described as triboelectricity, the transfer of charge between materials by rubbing.  I just wrote about this six months ago, and the detailed mechanisms remain poorly understood.  Large surface charge densities (like \(10^{12}\) electronic charges per square cm) can be created this way on insulators, leading to potential differences large enough to jump a spark from your finger to the door handle.  This can also lead to static electric fields near surfaces that are not small and can reveal local variations in material properties.
  
• That leads right into this paper (which I learned about from here) about the extreme shapes of the heads of a family of insects called treehoppers.  These little crawlies have head and body shapes that often have cuspy, pointy bits that stick out - spines, horns, etc.  As we learn early on about electrostatics, elongated and pointy shapes tend to lead to large local electric fields and field gradients.  The argument of this paper is that the spiky body and cranial morphology can help these insects better sense electric field distributions, and this makes it easier for them to find their way and avoid predators. 
• This manuscript on the arXiv this week is a particularly nice, pedagogical review article (formatted for Rev Mod Phys) about quantum geometry and Berry curvature in condensed matter systems.  I haven't had the chance to read it through, but I think this will end up being very impactful and a true resource for students to learn about these topics.
• Another very pretty recent preprint is this one, which examines the electronic phase diagram of twisted bilayers of WSe2, with a relative twist angle of 4.6°.  Much attention has been paid to the idea that moiré lattices can be in a regime seemingly well described by a Hubbard-like model, with an on-site Coulomb repulsion energy \(U\) and an electronic bandwidth \(W\).  This paper shows an exceptionally clean example of this, where disorder seems to be very weak, electron temperatures are quite cold, and phase diagrams are revealed that look remarkably like the phenomena seen in the cuprate superconductors (superconducting "domes" as a function of charge density adjacent to antiferromagnetic insulating states, and with "strange metal" linear-in-\(T\) resistance in the normal state near the superconducting charge density).  Results like this make me more optimistic about overcoming some of the major challenges in using twisted van der Waals materials as simulators of hard-to-solve hamilitonians.

I was all set to post this earlier today, with no awful news for once about science in the US that I felt compelled to discuss, but I got sidetracked by real work.  Then, late this afternoon, this executive order about federal grants was released.  

I can't sugar coat it - it's awful.  Ignoring a large volume of inflammatory rhetoric, it contains this gem, for instance:  "The grant review process itself also undermines the interests of American taxpayers."   It essentially tries to bar any new calls for proposals until a new (and problematic) process is put in place at every agency (see Sect. 3(c)).  Also, it says "All else being equal, preference for discretionary awards should be given to institutions with lower indirect cost rates."  Now, indirect cost rates are set by negotiations between institutions and the government.   Places that only do very small volumes of research have low rates, so get ready for MIT to get fewer grants and Slippery Rock University to get more.  The only certainty is that the nation's lawyers are going to have a field day with all the suits that will come out of this.