Research Projects


Research in Symmetries at the University of Kentucky

  Project Mentor
1. Caustic Apertures for Measuring The Lifetime of the Neutron Christopher Crawford
2. Single Crystal Growth of Quantum Magnetic Materials  William Gannon
3. Digital Signal Processing for the Fermilab Muon g-2 Experiment Tim Gorringe
4. Geometrically Frustrated Magnetism Ribhu Kaul
5. Building a Scanning Tunneling Microscope with a 3D Printer Kwok-Wai Ng
6. Hands-on Experience with Nontrivial Atomic-Scale Heterostructures Ambrose Seo
7. Probing interfaces between two-dimensional van der Waals materials with scanning probe microscopy Douglas Strachan
8. Percolation Theory Joe Straley
9. RR Lyrae Variable Stars Ron Wilhelm

Pick any three!

1. Caustic Apertures for Measuring the Lifetime of the Neutron Mentor: Christopher Crawford 
Skills learned: Data analysis, finite impulse response (FIR) filters, least squares fitting

A high accuracy measurement of the decay lifetime of free neutrons could provide a test of the theory of Big Bang Nucleosynthesis. An experiment to do this is now being designed for the NIST nuclear reactor. It is essential to this measurement to know the absolute neutron flux and the precise rate of proton creation (through neutron decay) of a neutron beam as it passes through a known volume. The neutron detector involves a thin film of the Li-6 isotopes which react with some of the neutrons in the beam, producing alpha and triton particles, which are then captured in silicon detectors. One of the primary sources of error is the variation of detection efficiency across the surface of the detector due to varying distances from the silicon detectors. This project is to invent a novel 3-dimensional aperture for these detectors based on principles of the rainbow, which will have, in theory, 100% uniformity.

2. Single Crystal Growth of Quantum Magnetic Materials  Mentor: Wllliam Gannon
Skills learned: ...

A promising set of compounds that potentially host Quantum Spin Liquid phases in metals is R2T2X (R = rare earth, T  = transition metal, X = main group), where magnetic rare earth ions sit on the geometrically frustrated Shastry-Sutherland lattice.  These materials exhibit a rich variety of physics, including one dimensional quantum spin chains (Yb2Pt2Pb) and mixed valence (Yb2Si2Al) among many typical behaviors.  This project involves (a) initiating the growth of single crystals of these materials from molten flux, (b) evaluating the results using x-ray diffraction and scanning electron microscopy, and (c) using the results of (a) and (b) to refine the growth conditions and grow more, better quality crystals. Once suitable crystals are made, the student will characterize them by measuring specific heat and basic magnetic properties.  All of this will be undertaken under the supervision of graduate students in the Gannon lab on the most promising materials we are working on at the time.  The ultimate goal will be to use these crystals in a neutron scattering experiment at a national laboratory. The student will participate in beam time scheduled during the REU, or will go to Oak Ridge National Laboratory to visit with colleagues and see how these types of experiments work.

3. Nuclear Data Analysis Projects Mentor:  Tim Gorringe
Skills learned: Data analysis techniques

There are two possible projects:

The first project is related to the Fermilab muon g-2 experiment and the precision measurement of the muon's anomalous precession frequency. The precession frequency is extracted from a least squares fit to the time distribution of the electron  hits or the electron energy.   It involves an investigation of the correlations between the data points in how the electron hits of varying energy are distributed over time.   Simulated time distributions will be generated and fit to extract the anomalous frequency.  Data point correlations will be introduced, and a covariance matrix will be used, in order to study the handling of such effects. The simulation and fitting will be performed using python / ROOT programming languages and scientific / mathematical packages.

The second project is for a proposed pion decay experiment project.    Drivers for for a readout system based on PCI-express over optical fiber will be developed and tested. This will include the development of code for configuring and transfering of data from PCI-express end-point FPGAs.  The coding and benchmarking will be performed using the Linux operating system, C/C++ coding, and PCI-express libraries.

4. Geometrically Frustrated Magnetism.  Mentor: Ribhu Kaul

Skills Learned: Monte Carlo simulation, data analysis.

Many materials realize magnets on frustrated lattices in which simple antiferromagnetic interactions between the spins cannot all be satisfied even at the classical level. The interplay of energy mini- mization and entropic fluctuations then leads to surprising behaviors when the magnetic structure of these materials are measured in laboratories . In this project REU students will construct a model for such materials and then study the physical properties of the models through Monte Carlo simulations. We shall work specifically on models of spin ice in rare-earth pyrochlores

5. Building a Scanning Tunneling Microscope with a 3D Printer Mentor: Kwok-Wai Ng
Skills learned: 3D printing, scanning tunnelling microscopy.

A scanning tunneling microscope (STM) can provide very high-resolution images of flat conducting samples.  It makes use of the quantum tunneling of electrons from a sharp conducting tip to the sample surface.  Tunneling occurs when the electron wave functions at the tip and the sample overlap.  The challenge is to put the tip within angstrom of the surface without touching it.   The performance of a good STM is very sensitive to its design and construction.   3D printing promises to make design changes easier.    In this project, we will try using a 3D printer to make most of the parts of an STM, and compare the performance of this STM with the one made the usual way.

6. Hands-on experience in studying nontrivial atomic-scale heterostructures Mentor:  Ambrose Seo
Skills learned: Vacuum technology, Operation of laser, Crystal growth, Materials characterization

In simple theoretical models, the state of matter is governed by its atoms and how they are bonded to one another in crystal structures. However, the properties of materials can change at phase transitions as external conditions are varied, even though the atoms and structures remain the same. These phenomena lead to novel concepts such as the order parameter and spontaneous symmetry breaking. We are now witnessing another paradigm shift: The state of matter is also governed by topological invariants. This means that the state of matter depends on how quantum wavefunctions are tied in a knot. This REU project will study low dimensional systems such as thin-film heterostructures consisting of iridates and ruthenates whose physics is governed by coexisting strong electron correlation and the relativistic spin-orbit interaction. This project will strongly feature hands-on experience with state-of-the-art experimental techniques.

7. Probing interfaces between two-dimensional van der Waals materials with scanning probe microscopy Mentor:   Douglas Strachan
Skills learned:  Scanning probe technology; a bit about the physics of planar materials and their interfaces.

The field of highly-ordered interfaces comprising low-dimensional nano-materials has recently seen a rapid exciting growth due to discoveries of tunable correlated quantum phenomena. This phenomena, while of fundamental physical interest, also has the potential for a variety of future applications, including those involving quantum information and computation. Our group focuses on low-dimensional condensed matter interfaces consisting of, for example, two-dimensional (2-D) van der Waals materials, 1-D edges and tubes of such materials, and a variety of 0-D nano-particles.

Interfaces between 2-D vdW materials can generate Moiré lattices when the layers are slightly misaligned or mismatched. Moiré lattices are commonly observed on any scale when two screens or fine-meshed fences are layered on top of each other. On the nanometer scale these Moiré lattices can modify electronic states and the interactions amongst electrons, yielding new correlated quantum phenomena. The sensitivity of these electronic states to slight imperfections of the Moiré lattice requires protective overlapping layers which impede the exploration of the interfacial states of interest. In this project we will attempt to circumvent this difficulty by utilizing non-contact scanning probe techniques to investigate the interfacial states from a distance. The student will learn how to synthesize a Moiré lattice from atomically-thin sheets of vdW materials, perform scanning probe measurements on the interfaced materials, and to analyze the resulting data.

8. Percolation Theory Mentor: Joe Straley
Skills Learned: Computer programming, theory of continuous phase transitions

Percolation theory studies random networks – think of a city where streets have been blocked at random.   If there are many such blockages, it might be impossible to go across town at all!    There is a critical fraction of unblocked streets, called the percolation threshold, and only when this limit is exceeded is it likely that one can go a long distance.   This can be modeled as a resistor network, and a new question arises: how does the conductance of the network vary as the threshold is approached?  This has been studied in the past, but there is an open question how the conductance depends on shape and size of the network, and whether there is a model that makes it possible to understand what happens without having to solve a thousand simultaneous equations.   A significant part of the project will involve running computer programs, most of which exist but will be need to be modified for the study (modifying a program that already works is a fine way to learn how to write your own programs). 

9. RR Lyrae Variable Stars Mentor: Ron Wilhelm
Skills learned: Data analysis, spectrum and imaging simulation

RR Lyrae variable stars (RRL) are ancient, evolved, low-metallicity, helium-core burning stars that pulsate fundamentally in the radial mode. New technology and temporal surveys have revealed complex interactions, such as the effects of resonant frequencies and non-radial pulsation modes. It is becoming increasingly likely that classical, stable pulsating RRLs do not exist. One recognized RRL pulsation complexity is Stochastic Period-Fluctuating variables (SPF). The SPFs have rapid period changes that are not correlated to either external (orbital changes due to binarity) or internal effects (periodic Blazhko effect). Our project involves high-precision, photometry observations of SPF, coupled with analysis of ground base monitoring programs, such as the Kilo degree Little Telescope (KELT), and space-based observations such as the Transiting Exoplanet Survey Satellite (TESS). This project includes the following tasks: a) collection of observational data over the course of the REU project, using our on-campus, MacAdam Student Observatory, or remote observations using the Moore Observatory. b) Data reduction and analysis using the software package AstroImageJ to produce high-precision light curves for the individual SPF. c) Analysis of light curve data using the software Period04 to produce a Fourier spectrum, identify frequency peaks and produce frequency, amplitude and phase information for all significant Fourier structure. All data and results will become part of our ongoing monitoring program of SPFs.

 

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