Physics Research Projects 2024

Anvita Deshpande, Lily Muehlenhard & Can Somer

Advisor: David Schaffner

Studying the influence of magnetic obstacles on plasma magnetic fields and wave fluctuations

Plasma is a superheated gas where thermal energy is so intense that it has torn atoms apart, stripping electrons from them and thus creating an ionized gas that is that is influenced by both electric and magnetic fields. Although there is an electromagnetic field that permeates through these locally charged ions and electrons, plasmas are mostly quasi-neutral, as is the plasma generated by the BMX lab. Plasmas make up the majority of the visible universe and are a subject of great interest and importance as we strive to better understand our world. Plasma, for the most part, exhibits chaos in its behavior—turbulence, in actual terms. The exact nature of such turmoil is yet to be discovered, and BMX seeks to observe plasma behavior when an obstruction is placed initsway. Thisobstruction,ofwhichtheeffectsareobserved,inthecaseofBMX,is specifically a magnetic obstruction induced by a current-carrying wire, as there is less direct observability of the kinetic turbulence of the plasma but more of a magnetic turbulence, the effects of which can be observed. The best case for plasma’s overwhelming importance in our lives can be seen by looking at our very own sun. The sun is a massive sphere of plasma that continuously ejects some of this plasma into the surrounding solar system, in a process known as the solar wind. Some planets, like Earth, have a magnetic field which interferes with the solar wind’s original path, forcing most of its particles to travel around the planet. Earth’s magnetosphere protects us from solar winds by altering the flow of its plasma. In our laboratory, we will utilize the BMX Plasma Gun to simulate the interaction between the solar wind and planetary magnetic fields. More specifically, in this experiment we will model this by placing a 1/8 inch diameter copper rod surrounded by ceramic downstream of the BMX Plasma Gun. By pulsing varying amounts of current through the rod, it allows it to act as a magnetic obstacle, so that we can study how the obstacle’s magnetic field interacts with the turbulent plasma. We predict a decrease in a measured magnetic field downstream of the magnetic obstacle and are in search of wave fluctuations within the plasma due to its interaction with the copper rod’s magnetic field.

Yiling Hou

Advisor: Xuemei Cheng

Micromagnetic simulations of field-driven antiferromagnetically coupled skyrmions pairs

Antiferromagnetically (AF) coupled skyrmions, characterized by antiparallel spin alignment between the skyrmion pairs, offer significant advantages for spintronic applications, including smaller skyrmions sizes, reduced skyrmions Hall effect, and increased data storage density. Our group has experimentally investigated the field-driven AF-coupled skyrmion pairs in [Co/Gd/Pt]10 multilayers by photoemission electron microscopy (PEEM) imaging and further performed micromagnetic simulation with the vertical periodic boundary conditions. While the application of vertical periodic boundary conditions can increase the computation efficiency, its validity remains to be examined.

In this summer research, I will perform micromagnetic simulations of AF-coupled skyrmion pairs in [Co/Gd/Pt]10multilayers using Mumax3 without vertical periodic boundary conditions. The 30-layer system will be modeled with parameters extracted from magnetometry measurements. The effect of the application of pulsed magnetic field with varied magnitudes and tilt angles will be simulated. The simulation results are expected to provide insights into the underlying mechanism of the field-driven skyrmion evolution revealed by the PEEM imaging.

Jessica Johnson

Advisor: Xuemei Cheng

Experimental study of sputtering yield and sputtering rate for thin film deposition

Thin films are layers of material with a thickness significantly smaller than their length and width, often possessing unique properties different from their bulk counterparts due to the finite size effect. They have wide applications in many fields, including nanotechnology and data storage. Sputtering, a commonly used physical deposition technique for growing thin films, is of great significance not only in research labs but also in industry. Sputtering yield, the number of atoms ejected per incident ion, is an important parameter for the sputtering process, and the sputtering rate is hypothesized to be proportional to it. However, the relationship between the sputtering yield and the sputtering rate has yet to be examined more carefully by experiments.

In this summer's research, I will collaborate with graduate students in the Cheng group to grow various metal films (Cr, Cu, Ti, and Au) by DC magnetron sputtering and SiO2 insulating films by RF sputtering. The thickness of the grown films will be characterized by measuring the small-angle X-ray reflectivity (XRR) of the samples. Furthermore, the sputtering rate and the sputtering yield of these sputtering deposition processes will be investigated. Our results are expected to clarify the relationship between the sputtering yield and the sputtering rate, providing guidance for the thin film sputtering process.

Sophie Lewis

Advisor: Michael Schulz

One-Dimensional Random-Field Ising Model

This project investigates the one-dimensional random-field Ising model of a magnet. The main goals of this project are to investigate how to compute and generalize the “on-spike” entropy at integer values of 2J/h as well as reproduce the result of “o􏰀-spike” entropy. The random-field Ising model consists of a lattice of spins, each of which can point up or down along the z-axis. At each site, there is a neighbor-neighbor interaction of strength J and an external magnetic field, h, (the sign of which is chosen randomly at each site). The energy of this system is lowest when each spin is aligned with the external magnetic field and when neighboring spins are aligned. However, at integer values of the ratio 2J/h, it is possible for chains of several spins to flip without changing the energy, resulting in a much greater entropy at these values (“on-spike” entropy) as compared to nearby values (“o􏰀- spike” entropy). Statistical mechanics, the Metropolis Monte Carlo method, and other mathematical techniques will be used to analyze this system. Magnets are imperative to contemporary society and understanding their empirical and theoretical properties can help in technological advancements.

Yingxiao (Thea) Liao

Advisor: Xuemei Cheng

X-ray Magnetic Circular Dichroism (XMCD) Study of Induced Pt Magnetic Moment in Co/Gd/Pt Multilayers

The magnetic proximity effect (MPE) describes the tendency for a heavy metal (HM) to be magnetized when placed near a magnetic material. This phenomenon of the induced magnetic moment of MPE has been intensively studied to understand the underlying fundamental physics and explore potential applications in spintronics. However, among the MPE-related studies, HM/ rare earth structures have been largely overlooked.

Our group has applied X-ray Magnetic Circular Dichroism (XMCD) to investigate the induced magnetic moment in HM Pt from rare earth element Gd in a specially designed [Co (0.5 nm)/Gd (1 nm)/Pt (1 nm)]10 multilayers. XMCD spectra, the difference of X-ray Absorption Spectra (XAS) excited by left and right circularly polarized X-rays, can provide quantitative information on the atomic spin and orbital magnetic moments. Additionally, XMCD is an element-specific technique, powerful for studying the magnetic properties of materials at the atomic level.

In this summer’s research, I will analyze the XMCD spectra of [Co(0.5)/Gd(1)/Pt(1)]10 multilayers measured at the Pt L2,3 edges, Co L2,3 edges, and Gd M4,5 edges as a function of temperature. By applying the sum rules, the spin and orbit magnetic moments of Co, Gd, and Pt atoms will be calculated. These results are expected to shed light on the induced magnetism in Pt from rare earth elements, such as Gd.

Madeline Rehwinkel

Advisor: Michael Schulz

Equivalence of Instanton and WKB Methods in Quantum Mechanics

Quantum mechanics is applied in technology that we use everyday, including LED lights and smartphones. In quantum mechanics and quantum field theory, few systems can be solved explicitly via the Schrödinger equation. So, approximation methods are important. To calculate propagators, or probability amplitudes, across potential energy barriers, two approximation methods that are commonly used are the WKB approximation and instanton techniques (path integrals). Despite equivalent end results, the computations involved in both methods are so dissimilar that it is difficult to see at a technical level why both methods would agree. Two students in the 2021 SSR program sought insight from a simple, exactly soluble model, but I will take the complementary approach of proving the formal equivalence of both methods for any system. I will attempt to relate intermediate results from both methods to the Morette-Pauli-van Vleck functional determinant to formally prove that the propagators across a potential energy barrier calculated by the WKB and instanton methods are equivalent

Elinor Rivera

Advisor: Asja Radja

Flow Fields Created by Gorgonian Coral Polyp Tentacles

Coral reefs are integral to marine ecosystems, and rising ocean temperatures resulting from global warming are contributing to coral bleaching and disrupting these systems. Some Gorgonian corals, phylogenetic cousins to the more well-known hard corals, have been shown to be resilient to climate change, and although the mechanism by which they adapt to these changes isn’t definitively known, it is hypothesized that it may be related to their plastic morphologies and the way they interact with flow fields in their environments. This summer, I will be imaging the water flow through the tentacles of gorgonian coral polyps by building a tabletop flow tank and using particle image velocimetry (PIV). PIV is an optical measurement technique in which neutrally buoyant tracer particles are used to image the flow and velocity field of a moving fluid. Image recordings are converted to vector maps of the flow fields with a python-based open-access software to help us understand how water moves around gorgonians on the scale of individual polyps. This will, in turn, inform gorgonian polyp feeding abilities and give us clues to how they may combat warming ocean environments and survive.

Jordyn Strunk & Tina Zhao

Advisor: Michael Noel

Measuring ultracold Rydberg atom density using 2-body and 3-body dipole-dipole interactions

Determining the density of Rydberg atoms in a sample is crucial for advancing current studies and can contribute significantly to quantum computing and simulations. Rubidium-85 atoms in a magneto-optical trap can be excited into Rydberg states, which are energy levels with a high principal quantum number. We will measure and model 2-body and 3-body energy interactions to determine the density of Rydberg atom samples. This technique will be compared with other methods of measuring the density to corroborate the results.

Grace Trembath

Advisor: Asja Radja

Effects of simulated marine heat wave on polyp morphology in the gorgonian octocoral Eunicea flexuosa. 

As ocean temperatures rise due to anthropogenic-induced climate change, the health of coral reefs is put at risk. Corals rely on a complex microbiome to remain healthy, and extreme temperature fluctuations are detrimental to the delicate balance of organisms involved. Particularly, their ability to maintain homeostasis is threatened, as high temperatures lead to the breakdown of their photosystem, resulting in a condition called bleaching. Coral are host to a symbiotic algae called zooxanthellae, which share nutrients with the coral host. When a coral bleaches, it expels its zooxanthellae and is no longer able to photosynthesize. Longterm, the bleached coral colony is not able to obtain enough nutrients and is at risk of dying. One group of corals within the Subclass Octocorallia, gorgonians, have been shown to be resistant to bleaching. One hypothesis for this is that gorgonians are more adept at filter feeding, which allows them to compensate for a decrease in photosynthesis. In this study I will be measuring the tentacle length and body wall volume of the gorgonian Eunicea flexuosa during a simulated heat wave, to see if they may adjust the morphology of their polyps to increase their filter feeding capabilities in elevated temperatures.