Events at Physics |
Events During the Week of September 13th through September 20th, 2026
Monday, September 14th, 2026
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Painleve property: from dynamical accessibility of phase-space holes and gravity cusps in 1D Vlasov-Poisson dynamics to stellarator optimization for quasisymmetry
- Time: 12:00 pm - 1:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Wrick Sengupta, Princeton University
- Abstract: We address the dynamical accessibility of a quasistationary state from the infinitely many formal equilibria of the Vlasov-Poisson system. We give a first-principles asymptotic selection theory for Bernstein-Greene-Kruskal (BGK) holes produced by two-stream relaxation and cold gravitational clumps produced by collisionless collapse based on two central ideas. First, repeated shell crossing leads to particle bunching and phase-space granulation through caustic formations. Nonlinear phase mixing erases the angle information but preserves the action dependence of the distribution function (DF). Following Berry and O'Dell's work on caustic whorls, and Jarzynski's least-biased information-theoretic interpretation, we show that the resulting coarse-grained DF is a circus-tent DF, made self-consistent for Vlasov-Poisson dynamics. Second, the selected potential is constrained by the Painleve property (PP) of Poisson's equation written in Sagdeev form. PP implies that the once-integrated Poisson equation must belong to an algebraic class reducible to Riccati or Weierstrass form up to suitable variable transformations, which must be determined by the underlying physical processes. The adiabatic theory describes the regular coherent self-organized state in both BGK and gravity. The excluded regions where action-angle variables fail: the O-point caustic sheet in gravity and the X-point separatrix sheet in BGK, require a phase-space-turbulence analysis, which we leave for subsequent work. Finally, we show that PP is also directly relevant to a very different area of plasma physics: the neoclassical optimization of stellarators. PP enables the construction of a reduced phase space for quasisymmetry where the well known quasisymmetric configurations such as the Landreman-Paul are constrained to live. Analytical predictions are thoroughly benchmarked against existing configurations such as those from the QUASR database.
- Theory Seminar (High Energy/Cosmology)
- Title to be announced
- Time: 1:00 pm - 2:30 pm
- Place: Chamberlin 5280
- Speaker: Yiming Chen, Stanford University
- Host: Jakob Moritz
Tuesday, September 15th, 2026
- No events scheduled
Wednesday, September 16th, 2026
- No events scheduled
Thursday, September 17th, 2026
- R. G. Herb Condensed Matter Seminar
- The Atomic Single Electron Transistor
- Time: 10:00 am - 11:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Dahlia Klein, University of Chicago
- Abstract: Electrons in solids owe their properties to the periodic potential landscapes they experience. The advent of moiré lattices has revolutionized our ability to engineer such landscapes on nanometer scales, leading to numerous groundbreaking discoveries. Despite this progress, direct imaging of these electrostatic potential landscapes remains elusive. Here, we introduce the Atomic Single Electron Transistor (SET), a novel scanning probe that uses a single atomic defect in a van der Waals (vdW) material as an ultrasensitive, high-resolution potential sensor. Built upon the quantum twisting microscope (QTM) platform, this probe leverages the QTM’s capability to form a pristine, scannable 2D interface between vdW heterostructures. Using the Atomic SET, we present the first direct images of the electrostatic potential in a canonical moiré interface: graphene aligned to hexagonal boron nitride. This potential exhibits an approximate C_6 symmetry, minimal dependence on carrier density, and a substantial magnitude of ~60 mV even in the absence of carriers. Theory indicates that this symmetry arises from a delicate interplay of physical mechanisms with competing symmetries. Intriguingly, the measured magnitude significantly exceeds theoretical predictions, suggesting that current understanding may be incomplete. With 1 nm spatial resolution and sensitivity to potentials generated by only a few millionths of an electron’s charge, the Atomic SET enables ultrasensitive imaging of charge order and thermodynamic properties across a wide range of quantum phenomena, including symmetry-broken phases, quantum crystals, vortex charges, and fractionalized quasiparticles.
- Host: Tiancheng Song
Friday, September 18th, 2026
- Physics Department Colloquium
- Title to be announced
- Time: 3:30 pm - 4:30 pm
- Place: Chamberlin 2241
- Speaker: Reshimi Mukherjee, Columbia/Barnard College
- Host: Ke Fang