These are the projects for the summer 2019 program. The projects for 2020 will be similar and posted prior to making offers.

New Classes of Fluid Instabilities in 3D Printing of Soft Matter Prof. Thomas Angelini
Electric field effect on the magnetism of La0.33Pr0.34Ca0.33MnO3 Prof. Amlan Biswas
Optically Pumped NMR in III-V Nanostructures Prof. Russ Bowers
High-pressure studies of unconventional superconductors Prof. James Hamlin
Computational Discovery and Design of 2D Materials for Electronic and Energy Applications Prof. Richard Hennig
Modeling electric field induced domain change in LPCMO nanostructures Prof. Selman Hershfield
Entanglement near impurity quantum phase transitions Prof. Kevin Ingersent
Design and Testing a Probe of Quantum Matter Prof. Dominique Laroche
Characterizing Self-Assembled Polymers Prof. Daniel Savin
Quantum phase transitions in low-dimensional antiferromagnets Prof. Yasu Takano
Preparing to measure vacuum birefringence Prof. David Tanner &
Prof. Guido Mueller &
Prof. Paul Fulda
Plasmonic Nanomaterials for Energy, Environment, and Biomedicine Prof. Wei David Wei
Modeling Spin-Lattice Coupling in Molecular Magnets Prof. Xiaoguang Zhang


New Classes of Fluid Instabilities in 3D Printing of Soft Matter, Prof. Thomas Angelini
        Technology for 3D printing with hard materials is in a very mature state; hobbyists can 3D print hard thermoplastics with high precision at low costs. Many important applications in medicine require the use of soft materials, like hydrogels and elastomers, which have the feel of Jell-O or soft rubber. The recent invention of a soft matter 3D printing technique at the University of Florida has opened the door to 3D printing precise objects made from soft matter. However, the new combinations of complex soft materials involved in this 3D printing technique have generated unanticipated fluid instabilities. The physical principles that control these instabilities have not yet been determined, limiting our ability to advance the technology.
        The REU student will 3D print simple platonic shapes like lines, spheres, cylinders, and planes and study their evolution under destabilizing forces. The shapes will be made from a viscous or viscoelastic liquid and suspended in 3D space without any support apart from an embedding continuum. The embedding material is a granular-gel based liquid-like solid which, as its name implies, is a solid from a technical thermodynamic perspective yet also possesses many of the properties of a liquid. The student will perform time-lapse microscopy and photography and learn digital image processing techniques for data analysis.

Electric field effect on the magnetism of La0.33Pr0.34Ca0.33MnO3, Prof. Amlan Biswas
        Ferromagnetic materials such as iron can be permanently magnetized using a magnetic field and are therefore used for data storage. In certain materials it is also possible to control the magnetism using an electric field which is of great interest both due to the underlying physics and possible device applications. In this project we will study a compound with chemical formula La0.33Pr0.34Ca0.33MnO3 (LPCMO), which is a ferromagnet and non-magnetic phases coexist forming a multiphase state in which ferromagnetic islands are formed in a non-magnetic matrix. While the material is a crystalline solid, the ferromagnetic phase can move like a fluid in the non-magnetic matrix. The main goal of this project is to use an electric field to reshape the fluid-like ferromagnetic phase and thus control the magnetic properties using an electric field.
        The REU student will characterize the properties of the thin film samples using scanning probe microscopy, transport, and magnetization measurements. Once the basic properties have been optimized, the student will study the effect of an electric field on the resistance and magnetization of LPCMO. The main techniques that the student will learn are scanning probe microscopy, low temperature resistance and magnetization measurements, and photolithography for fabricating micro/nanostructures of LPCMO.

Optically Pumped Nuclear Magnetic Resonance in Quantum-Confined GaAs Nanostructures, Prof. Russ Bowers
        Nuclear Magnetic Resonance (NMR) is a powerful form of radio frequency spectroscopy involving nuclear spin transitions in an applied magnetic field. In III-V semiconductors such as GaAs, nuclear spin polarization can be induced by pumping of optical interband transitions, resulting in milli-Kelvin nuclear spin temperatures. The NMR signal enhancement, which can exceed 4 orders of magnitude, facilitates NMR experiments on nuclei located in the small quantum confined volume in III-V semiconductor layers (e.g. GaAs) as thin as 4 nm. The optical pumping effect depends on many variables, including the electronic band structure, magnetic field, temperature, optical polarization, strain, electron-nuclear spin dynamics and nuclear spin diffusion. Potential applications include spin quantum computing.
        The REU student will attempt to observe OPNMR effects in types of inorganic semiconductors where it has never been observed before. Examples include wide-gap (e.g. GaN), mid-gap (GaP) and narrow-gap (InAsP) materials. The dilute magnetic semiconductor GaMnAs is also of interest. OPNMR experiments will be performed on thin film samples exposed to in-situ laser irradiation at high magnetic fields and low temperatures (down to ~1.5 K). Quantum confinement and strain effects which modify the electronic band structure may also be studied. The student involved in this project will gain experience in low-temperature NMR techniques, near infrared optical spectroscopy and laser systems,and semiconductor physics.

High-pressure studies of unconventional superconductors, Prof. James Hamlin
        Superconductivity is a phenomena with enormous applications potential. However, this promise has yet to be fully realized, in part because of our incomplete understanding of the conditions under which superconductivity develops in certain materials. The Hamlin group is utilizing applied high pressures both to understand the properties of known superconductors and to help discover new ones. Pressure is a powerful control parameter, capable of rapidly and continuously tuning a single sample between insulating, metallic, magnetic, or superconducting ground states.
        The REU student will participate in the synthesis of new materials, particularly in single crystalline form, and will learn about the characterization of these materials by x-ray diffraction, electrical transport, magnetic susceptibility, and specific heat measurements. The student will also gain experience in the use of diamond anvil cells, which allow the application of pressures spanning the range from kilobars (the pressure at the bottom of the ocean) to megabars (nearing the pressure at the center of the earth).

Computational Discovery and Design of 2D Materials for Electronic and Energy Applications, Prof. Richard Hennig
        The rapid rise of novel two dimensional (2D) materials, presents the exciting opportunity for materials science to explore an entirely new class of materials. This comes at the time when mature computational methods provide the predictive capability to enable the computational discovery, characterization, and design of 2D materials and provide the needed input and guidance to experimental studies. Materials informatics approaches such as data-mining and genetic algorithm can identify novel 2D materials with unexpected structures and unusual properties.
        In this project the REU student will learn how to use materials informatics tools and perform high-throughput simulations to discover new 2D materials. We will use density-functional theory to characterize these materials and determine their electronic and magnetic properties, and identify possible applications for these materials as photovoltaics, photocatalysis, transistors, spintronics, etc. The student will gain experience in solid-state physics, computer simulations, and materials informatics.

Modeling electric field induced domain change in LPCMO nanostructures, Prof. Selman Hershfield
        The magnetic domain structure of ferromagnetic materials is usually manipulated via an applied magnetic field; however, there are some materials for which an electric field can change the domain structure. One such material is La0.33Pr0.34Ca0.33MnO3 or LPCMO for short, which is being studied experimentally by Prof. Biswas (see above). Two phases coexist: a ferromagnetic metal and an nonmagnetic insulating phase. By applying an electric field, one can change the shape of the magnetic domains.
        The REU student will model this phenomena in the experiments of Prof. Biswas using two computer codes: one to determine the electric field for a set of magnetic domains and one to then modify the domains shape based on the electric field. These codes can be created by modify existing software in Prof. Hershfield's group, and the REU student should be able to understand them completely since they rely only on undergraduate electricity, magnetism, and statistical physics. The REU student will gain experience with mesoscale materials modelling, with some computational techniques used in physics, and with the physics of multiferroic materials.

Entanglement near impurity quantum phase transitions, Prof. Kevin Ingersent
        Entanglement entropy quantifies the extent to which two parts of a system are connected quantum-mechanically through wave-like superposition. Motivated by potential applications in quantum computing, there is much current interest in how entanglement entropy varies in the vicinity of a quantum phase transition taking place at the absolute zero of temperature between two qualitatively different ground states of a system (e.g., magnetically ordered and disordered states). Particularly intriguing is the possibility that quantum information storage is more stable close to a quantum phase transition than far away from the transition. This project will investigate this issue near quantum phase transitions found in theoretical models of magnetic impurities in metallic or semi-metallic host materials.
        The REU student will use a suite of pre-existing computer programs to calculate entanglement entropy near a quantum phase transition and will seek to relate the variation of this property to that of other key physical quantities, such as the magnetization. The student will acquire knowledge of solid-state physics and key concepts in strongly correlated systems, while gaining experience of running large-scale simulations in a Linux computing environment.

Design and Testing a Probe of Quantum Matter, Prof. Dominique Laroche
        By coupling different materials, e.g. superconductors and semiconductors, and by confining electrons to move in reduced dimensionality, new electronic states of matter can be created in the lab. Examples include the Luttinger liquid regime of the one dimensional electron gas, where the excitations of fermions (electrons) actually behave like bosons. Another example is the creation of a long sought excitation called a Majorana quasiparticle, which is the condensed matter analog of a particle which is its own antiparticle. To observe these phenomena Prof. Dominique Laroche uses nanoscale fabrication and low temperature physics measurement techniques.
        In this project the REU student will take part in the designing, building, and testing of a low temperature probe to be used in liquid Helium. The REU student will learn learn hands-on experimental techniques for building low temperature probes, wiring them, and performing low temperature electronic measurements. They will also learn about the exciting field of quantum matter.

Characterizing Self-Assembled Polymers, Prof. Daniel Savin
        Polymers are long molecules with a repeat unit cell that are essential for life and many everyday materials and applications. The Savin group studies the self-assembly of polymers and block copolymers. This has applications for use as remediation and delivery agents, oil dispersants, and energy-absorbing nanocomposites. The Savin lab both manufactures the polymer materials and characterizes them using a host of physics and chemistry techniques.
        The REU student will characterize self-assembled polymer samples using static and dynamic light scattering, as well as microscopy (transmission electron microscope, scanning electron microscope, and atomic force microscope). They will also have the opportunity to produce their own polymer samples. The REU student will learn about polymer physics and chemistry as well the experimental techniques used to study polymers.

Quantum phase transitions in low-dimensional antiferromagnets, Prof. Yasu Takano
        In some antiferromagnets, the dipole moments form a one- or two-dimensional array rather than a three-dimensional periodic structure. The quantum (or zero-absolute-temperature) phase transitions of such low-dimensional antiferromagnets are poorly understood and are presently the subjects of many experimental and theoretical studies.
        The REU student will measure the heat capacity of novel low-dimensional antiferromagnets at temperatures below 10 K to gain microscopic insights into the macroscopic properties near zero temperature. The student will become familiar with experimental techniques at low temperatures and use of computers in data acquisition and analysis, as well as various elements of modern magnetism and thermal physics. The student will participate in a five-day experiment at the National High Magnetic Field Laboratory in Tallahassee if magnet time is available.

Preparing to measure vacuum birefringence, Profs. David Tanner, Guido Mueller, and Paul Fulda
        When the index of refraction of a media depends on the light polarization direction, the material is said to be birefringent. One of the few predictions of quantum electro-dynamics that has not been experimentally confirmed is the birefringence of the vacuum in the presence of a large magnetic field. This prediction dates back to the 1930's. Profs. Fulda, Mueller, and Tanner are setting up a testbed to develop the experimental techniques necessary to measure vacuum birefringence later at the 200m linear magnetic field string at DESY in Hamburg, Germany.
        The REU student will help to set up the laser-optical testbed including optical cavities and interferometers and perform initial measurements of birefringence. The student will characterize the effects of the low thermal noise Khalili cavities used to generate the minuscule birefringence in our experiment. They will thus gain experience working with lasers and performing high precision optical measurements.

Plasmonic Nanomaterials for Energy, Environment, and Biomedicine, Prof. Wei David Wei
        The Wei group studies the electronic and optical properties of metallic and semiconductor nanomaterials and their applications in solar energy harvesting, conversion and storage; visible-light photocatalysis; chemical and biological sensing, and photothermal cancer therapeutics. As a specific example, using sunlight to facilitate and promote valuable chemical reactions is an ideal solution to the challenge of meeting future energy demands. Toward that end the Wei group aims to address fundamental questions concerning surface plasmon resonance (SPR)-mediated interfacial electron transfer (ET) and photothermal heating in order to develop new materials and strategies for efficiently converting solar energy to chemical energy. Specifically, they want to unambiguously reveal the mechanics of plasmon-mediated electron transfer (PMET) in Au/TiO2 heterostructures under visible light during in situ operation and directly probe the relaxation dynamics and energetics of the transferred "effective hot electrons" that participate in photocatalytic reactions. They are interested in exploring new strategies for manipulating "hot electrons" for the rational design and construction of a new class of multi-component solar photocatalysts for efficiently producing H2 from water.
        The REU student will work on the synthesis of multiple types of nanoparticles and then use their chemical and physical properties for photocatalysis. In the process they learn both the chemistry and physics of plasmonic nanomaterials.

Modeling Spin-Lattice Coupling in Molecular Magnets, Prof. Xiaoguang Zhang
        Single molecule magnets have magnetic atoms such as Mn which are coupled so as to behave like a single large magnetic moment. Potential applications of single molecule magnets include magnetic bits for data storage and qubits for quantum computers. Prof. Xiaoguang Zhang is studying the spin-lattice coupling in molecular magnets. When the magnetic moment in a molecular magnet changes its orientation, there is a deformation in the positions of the atoms in the molecule.
        The REU will apply computational materials techniques such as the semi-empirical quantum chemistry method to model spin-lattice coupling in molecular magnets. They will also have the opportunity to collaborate with others in his group using density functional theory and machine learning techniques. Some computational experience is preferable for this project. The REU student will learn some modern computational materials modeling techniques and the physics and chemistry of single molecule magnets.