Pump-Probe Analysis of a Phase Transition: A Case Study Using the Ising Model
Keely Ralf
A liquid-liquid phase transition (LLPT) has been proposed to occur in supercooled water, in which high-density and low-density liquid phases become distinct below a critical temperature located in the supercooled region of the water phase diagram. The LLPT is challenging to detect because it must be observed in the metastable supercooled liquid in the brief time window (< 10μs) prior to crystal formation. Recent pump-probe experiments provide evidence of the LLPT by heating thin-film amorphous ice samples with a IR laser pulse to conditions close to the LLPT, and then probing the response using x-ray laser pulses. To provide guidance for interpreting the x-ray scaPering results from these experiments, we conduct simulations of the Ising model which mimic the sample and pump-probe methodology of the experiment. We model 2D thin- film Ising systems having fixed boundary conditions along one direction. Starting from a homogeneous spin- up phase, we apply an external field and a temperature gradient and monitor the system properties as a function of time. Our results clarify how the evolution of the system’s structure is influenced by non-uniform boundary conditions and a temperature gradient. We quantify how a temperature gradient across the sample, believed to be present in the experiments on water, affects the structural evolution of the system.
Detection of Cosmic Ray Muons with Teachspin and Cosmic Watch Muon Detectors
Max McNeil
Muons, fundamental particles within the Standard Model of Particle Physics, are produced when cosmic rays interact with the Earth’s upper atmosphere. These particles are constantly striking the Earth’s surface and can be detected using scintillator-based detectors. In this project, two different detectors were used to preform muon flux experiments. The first, the Teachspin Muon Detector, was calibrated based on the well-established value for muon lifetime. The second detector, the Cosmic Watch Muon Detector, was specifically constructed for this project. Through this investigation, we hope to gain a greater understanding of how these detectors functionality and to set up experiments to further explore muon behavior.
