Events at Physics |
Events on Thursday, September 25th, 2025
- R. G. Herb Condensed Matter Seminar
- Manipulating Valley Degree of Freedom via Nano-gating and Twist
- Time: 10:00 am - 6:00 pm
- Place: 5310 Chamberlin
- Speaker: Ke Wang, UMN
- Abstract: Within condensed matter physics, the study of two-dimensional (2D) systems is a diverse and active field of interest with a rich history. High-quality two-dimensional electron gases (2DEG) in GaAs/AlGaAs heterostructures have enabled the discovery of rich quantum Hall physics. With the help of electron-beam-defined nano gates, system dimensions can be further reduced to be mesoscopic and comparable to the electron wavelength. In such gate-defined nanostructures, novel quantum phases can be locally defined and coherently manipulated to realize quantum bits and quantum interferometers, providing versatile experimental platforms to answer many key questions in condensed matter physics.
Since the discovery of graphene via mechanical exfoliation, it has been shown that the electronic properties of solids can undergo dramatic changes when the material thickness is reduced to the atomic limit. Moreover, the properties of the 2D materials can be further tailored by stacking them with relative twist angles. Combining this designer material platform with the gate-defined nanostructures, the highly tunable local Hamiltonian allows a local probe to the rich underlying physics and a platform to study new mesoscopic quantum phenomena. In this talk, I will discuss our recent experiments in tuning valley-specific Berry curvature and band topology in bilayer graphene via gate-defined nanostructures and twist, towards investigating novel mesoscopic quantum physics and demonstrating new quantum device concepts.
- Host: TIANCHENG SONG
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Recent Advances in Modeling Cosmic Ray Observations and New Developments in Telescope Array Data Analysis
- Time: 2:30 pm - 3:30 pm
- Place: Chamberlin 5280
- Speaker: Anatoli Fedynitch, Academia Sinica, Taiwan
- Abstract: Understanding the cosmic ray flux is essential across astroparticle physics. The observed spectrum and mass composition provide critical inputs for modeling atmospheric muons and neutrinos, dominant backgrounds in neutrino observatories, and for applied fields such as muon tomography. In 2017, we introduced the Global Spline Fit (GSF), an agnostic framework designed to let data guide the modeling with minimal assumptions. Nearly a decade later, new results from space-based observatories (AMS, DAMPE, CALET) and dedicated measurements near the knee (GRAPES, LHAASO) enable a substantial update. I will present the next-generation GSF2025 and discuss its implications for our global view of cosmic rays from GeV to EeV. In the second part of the talk, I will highlight our group’s ongoing effort to reinvent the analysis chain of the Telescope Array surface detectors. Leveraging deep neural network–based reconstruction, we address systematic uncertainties that stem from the unknown mass composition, achieving significant improvements in energy and angular resolution. This approach also opens new possibilities for inferring primary mass and Xmax in future iterations. To rigorously propagate uncertainties, we have developed a Bayesian forward-folding framework that naturally incorporates both intrinsic and external constraints into the measurement’s error bands.
- Host: Lu Lu