Condensed matter physics includes the study of solids (solid state physics) as well as liquids. Nationally, condensed matter physics is the largest and most active area of physics research, comprising a wide range of topics. For example, the annual March meeting of the American Physical Society is the largest meeting of its kind with more than 5000 presentations reporting research activities primarily in condensed matter physics. The growth and size of this meeting each year reflects the growth of this area of physics. Condensed matter physics is a vitally important and growing field of physics. Students with advanced degrees in this area can find employment.

Faculty

Branton J. Campbell
Robert C. Davis
Gus Hart
Bret C. Hess
Harold T. Stokes
Richard Vanfleet

Supporting Courses

Physics 581: Solid State Physics
Physics 781,782: Modern Theory of Solids
Physics 731: Statistical Mechanics
Physics 618,619: Group Theory

Research at BYU

Optical measurements of spin lifetimes in semiconductors (Colton). Spin states of electrons in semiconductors have been proposed for use in prospective "quantum computers". In order to be a viable candidate for this type of quantum computer, the material has to have good spin properties -- specifically, the spins must not change states uncontrollably due to interactions with their environment, or at least the time scales of such state changes must be relatively long. This research has focused on experimental measurements of spin lifetimes in the semiconductor GaAs (gallium arsenide), its alloys, and in semiconductor nanostructures based on GaAs & alloys. Experimental techniques combine optical spectroscopies such as photoluminescence and reflectivity with magnetic resonance of the electron and nuclear spins. Experiments are done at very low temperatures (1.5 K) and large magnetic fields (1+ tesla).

Local and intermediate-range order in functional solid-state materials (Campbell). Systems of interest include fast-ion conductors, ferroelectric relaxors, magnetoresistive manganites, and microporous catalysts. Nanoscale structural features influence the macroscopic properties of many fascinating crystalline materials. These structures can be either static or dynamic, and consist of atomic displacements that spatially cooperate within regions as small as a nearest-neighbor bond (local order) or as large as a few tens of nanometers (intermediate-range order). Because atomic displacements are intimately coupled to other properties of interest, such as electronic and magnetic structure, vacancy or interstitial mobility, chemical reactivity, etc., structural defects or fluctuations modify local properties that, in many cases, also alter global properties.

We are developing new ways to "see" three-dimensional nanostructures in solid-state materials using advanced x-ray and neutron scattering tools, and to track them as a function of the properties that they influence. In addition to in-house diffraction experiments, we utilize state-of-the-art national and international scattering facilities, where we can probe subtle features that were previously inaccessible.

Nanoscale fabrication and imaging, experimental (Davis)

Biological Membrane Surface Imaging. The atomic force microscope is used to image soft biological structures in fluid with resolution down to the molecular level. Studies include membrane formation, protein incorporation and protein diffusion dynamics. In collaboration with David Busath (Physiology and Developmental Biology). Research supported by BYU mentoring funds.

Biomolecular electronics. Proteins and nucleic acids are candidate structures for self assembled molecular electronic materials. Conductivity measurements are performed on single horse spleen and bacterial ferritin molecules. In collaboration with Gary Watt (Chemistry and Biochemistry) and John Harb (Chemical Engineering). Research supported by NASA and BYU mentoring funds.

Nanoscale chemical patterning. Nanoscale chemical patterning of silicon and germanium surfaces has applications ranging from biomaterials to molecular electronics. An atomic force microscope probe is used to pattern surfaces with lines down to 20 nm across. In collaboration with Matthew Linford (Chemistry and Biochemistry). Research supported by NSF and BYU mentoring funds.

Nanotube mechanics. We are developing self-aligned processes for mechanical attachment of carbon nanotubes and perform atomic force microscope (AFM) based nanotube mechanics and adhesion and measurements. In collaboration with Matthew Linford (Chemistry and Biochemistry), David Tannenbaum (Pomona College), and Paul McEuen (Cornell University). Research supported by NSF.

Optical, transport and magnetic studies of nanostructured semiconductors (Hess). We study electron quantum mechanics in nanometer-scale semiconductors and molecular interconnects, by experiments with ultra-short pulse lasers, electron transport and magnetic resonance. This is part of a multidisciplinary collaboration of several faculty in physics and chemistry.

In our femtosecond laser laboratory, we use amplified ultra-short light pulses to track electron transitions between quantum states. Experiments include transient photo-induced absorption, up-conversion luminescence lifetime and other nonlinear optical spectroscopies with time resolution of less than 100 femtoseconds. Time-correlated-single-photon counting extends the dynamic range out to 50 microseconds. In addition, we use steady light sources for traditional spectroscopies and millisecond photomodulation studies.

Electron spin resonance allows us to detect unpaired spins, which are of particular importance at surfaces and interfaces, and in doped semiconductor nanocrystals.

We combine optical and transport studies to understand the localization of the electron states, alignment of levels in nanocrystals and interconnects, and the influence of excess charge in the nanocrystals.

This research has applications to new computing technologies, solar cells, nonlinear optical switches, and light emitting diodes for displays.

Phase transitions in solids, theoretical and computational (Stokes). When a solid changes its internal structure, interesting new physical properties may appear. Often these properties can be predicted and the material can be utilized for a particular purpose, for example, as superconductors, as ferroelectrics in copiers, as piezoelectrics in sensors, etc.

We apply principles of group theory to the study these transitions between different crystalline structures. This project has been ongoing since 1983. We have developed software that allows us to generalize our group-theoretical methods to a large number of possible cases that may be observed experimentally. Most recently, we have developed an web application, ISODISPLACE, with a user-friendly graphical interface as well as visualization tools.

Former Graduate Students

The following is a list of our students (most recent first) who have graduated with advanced degrees in condensed matter physics since 1990. We have included a description of their research, papers published in scientific journals, and talks presented at scientific meetings.

Jesse Z. Gunter, M.S., 2006. Advisor: Harold T. Stokes. Thesis: "Mechanisms of the Wurtzite to Rocksalt Phase Transition in Gallium Nitride." Jesse used the computer program COMSUBS to investigate possible atomic pathways in reconstructive phase transitions. He first helped us apply these methods to the zinc-blende to rocksalt transition in SiC. This worked resulted in a published article in Physical Review B, Vol. 71, p. 184109 (2005), and a contributed paper at the Meeting of the American Physical Society in Los Angeles (March 2005). He also applied these methods to the wurtzite to rocksalt transition in GaN, which was the topic of his thesis and which also resulted in a contributed paper at the Congress of the International Union of Crystallography in Florence, Italy (August 2005).

Thomas K. McKnight, M.S., 2005. Advisor: Branton J. Campbell. Thesis: "An Improved Flexible Neutron Detector for Powder Diffraction Experiments."

Ribeka Takahashi, M.S., 2004. Advisor: James P. Lewis. Thesis: "Molecular Electronics with Peptide Nanotubes: Calculation of Conventional and Complex Band Structure."

Jed Whittaker, M.S., 2004. Advisor: Robert C. Davis . Thesis: "Mechanical Attachment of Carbon Nanotubes to Atomic Force Microscopy Tips by Selective SiO₂ Deposition." Jed fabricated nanoscale three-dimensional structures using e-beam lithography and plasma etching. Nanotubes were deposited on these structures and mechanically probed by atomic force microscope (AFM). This work resulted in published articles in Applied Physics Letters, Vol. 83, p. 5307 (2003) and Nano Letters, Vol. 6, p. 953 (2006) and contributed talks at the American Vacuum Society International Symposia in 2002 and 2004.

Degao Xu, Ph.D., 2004. Advisor: Robert C. Davis . Dissertation: "Atomic Force Microscope Conductivity Measurements of Single Ferritin Molecules." Degao developed AFM methods for the measurement of electron conductivity of single proteins dispersed on gold surfaces. He applied this to a inorganic protein complex, ferritin. This work resulted in a published article in Nano Letters, Vol. 5, p. 571 (2005) and in contributed talks at the Four Corners Section Meeting of the American Physical Society in 2002 and 2003 and at the Gordon Research Conference on Electrochemistry in Ventura, California (Feb. 2005).

Chad Junkermeier, M.S., 2003. Advisor: James P. Lewis. Thesis: "Iteration Methods for Approximating the Lowest Order Energy Eigenstate of a Given Symmetry for One- and Two-Dimensional Systems." After graduating, he entered the PhD program at Brigham Young University.

Travis Hughes, M.S., 2003. Advisor: Robert C. Davis. Thesis: "Overcoming Inhibition of Supported Bilayer Formation for Influenza A M2 Single-Molecule AFM Studies." Travis used fluid atomic force microscopy to image individual flu virus proteins in lipid bilayers. This work resulted in a published article in Biophysics Journal, Vol. 87, p. 311 (2004) and in a contributed poster at the Biophysical Society Meeting in Baltimore, Maryland (Feb. 2004) and a contributed talk at the American Physical Society March Meeting in Montreal, Canada (March 2004).

Brent Wacaser, M.S., 2002. Advisor: Robert C. Davis. Thesis: "Chemo-mechanical Surface Patterning and Functionalization of Silicon Surfaces Using an Atomic Force Microscope". Brent developed a new approach to chemically patterning surfaces at the nanometer scale with the atomic force microscope. This work resulted in published articles in Langmuir, Vol. 19, p. 985 (2003), Applied Physics Letters, Vol. 82, p. 808 (2003), and Lab on a Chip, Vol. 4, p. 553 (2004) and in contributed presentations as the American Vacuum Society 49th International Symposium in Denver, Colorado (Nov. 2002) and the Four Corners Meeting of the American Physical Society in Tempe, Arizona (Oct. 2003)

Anthony Smith, M.S., 2001. Advisor: Harold T. Stokes. Thesis: "Nonlinear Dynamics in Systems of Discrete Symmetry." Nonlinear forces between atoms cause vibrational modes to interact with each other. If a particular mode is excited, the excitation can spread to other modes via this interaction. Using arguments of symmetry, we find that the excitation is confined to a finite number of modes, called a "bush" of modes, a concept pioneered by G. M. Chechin and V. P. Sakhnenko. Tony used computer software to search for the different types of bushes of modes which exist in crystalline solids. His search resulted in 17 classes of irreducible bushes and 8 classes of two-dimensional reducible bushes.

Rodion Tikhoplav, M.S., 1999. Advisor: Bret C. Hess. Thesis: "Effect of Pressure on Optical Properties of Pure and C₆₀-Doped MEH-PPV."

Xiaohua Yu, Ph.D., 1999. Advisor: Harold T. Stokes. Dissertation: "Investigation of a difficulty in the self-consistent atomic deformation method for first-principle energy calculations in crystalline solids." The self-consistent atomic deformation (SCAD) method was developed by Boyer, Mehl, and Stokes as an efficient density-functional calculation of the ground-state energy in crystalline solids. The results from SCAD are very poor for some crystals, though. Xiaohua investigated this problem and tried two different approaches to improve the performance of SCAD. He showed that neither approach worked very satisfactory.

Richard Hatt, Ph.D., 1998. Advisor: Dorian M. Hatch. Dissertation: "Order-parameter profiles across domain walls arising in ferroelastic phase transitions." He used group-theoretical methods to determine changes in crystalline structure near walls between two domains in a crystal. His results are general and can be applied to a large number of real crystals. The results of his work were presented at two meetings of the Utah Academy of Science (1995 and 1996), conferences in Montana and Kansas, and also at an international conference in Austria. His work resulted in two published articles: Ferroelectrics, Vol. 191, p. 29 (1997) and Vol. 226, p. 61 (1999).

Clark Snow, M.S., 1997. Advisor: Manuel Berrondo. Thesis: "Ab Initio calculations of the vibrational frequencies of oxidic free anions related to a crystal environment." He used the Hartree-Fock self-consistent field method to calculate by computer the vibrational frequencies of a number of free anions. These calculations are valuable for designing high-energy particle detectors.

Curtis Durfee, M.S., 1995. Advisor: H. Mark Nelson. Thesis: "Effect of pressure on cyanide reorientation in the low-temperature phases of potassium cyanide." He measured the dielectric loss in potassium cyanide at temperatures down to 77 K and at pressures up to 4 kbar. He extracted from the data the pressure dependence of the reorientation rate of the cyanide ions in the low-temperature ferroelastic phase.

Ke Huang, Ph.D., 1995. Advisor: Daniel L. Decker. Dissertation: "An EPR investigation of the tetragonal phase in BaTiO₃ along the tetragonal-cubic phase line." He obtained electron paramagnetic resonance (EPR) lines at temperatures ranging from -40 degrees C to 80 degrees C and at pressures up to 44 kbar. This is the first time anyone has ever observed EPR at such high pressures and low temperatures in any material. He showed from the data how the discontinuity in the transition from the tetragonal to the cubic phase gradually decreases as pressure is increased until the discontinuity disappears at a tricritical point and the transition becomes continuous. His work has resulted so far in one published article in Review of Scientific Instruments Vol. 68, p. 3877 (1997).

Jun Lu, Ph.D., 1995. Advisor: William E. Evenson. Dissertation: "Stochastic models of perturbed angular correlation due to diffusion of defects in materials." He developed several new families of stochastic models of perturbed angular correlation (PAC) due to diffusion of defects in materials. By fitting PAC data to the models, he can extract information about the structure and motion of these defects over a wide range of temperatures and dopant concentrations. Compared to models developed in the past, these models are more fully developed and are physically more meaningful. The results of his work were presented at an international conference in Belgium. Also, his work has resulted so far in two published articles in Hyperfine Interactions C Vol. 1, p. 392 (1996) and Hyperfine Interactions Vol. 120/121, p. 427 (1999).

Ping Hu, Ph.D., 1994. Advisor: Dorian M. Hatch. Dissertation: "Theoretical study on domain structure and domain walls in the phase transition of LaAg_xIn_1-x." He applied the Landau theory of phase transitions to the crystalline structure near walls between domains. This work was largely mathematical in nature, starting with a set of rather complex nonlinear partial differential equations, finding appropriate simplifications, and obtaining solutions that could be related to actual crystalline structures near domain walls in LaAg_xIn_1-x. The results of his work were presented at an international conference in Switzerland. Also, his work has resulted so far in one published article in Physical Review Letters, Vol. 76, p. 1288 (1996).

Hui Guan, Ph.D., 1994. Advisor: William E. Evenson. Dissertation: "Models of perturbed angular correlations in fluctuating electric field gradients." She calculated the effect of defect motions on PAC spectra and applied her results to the hopping of oxygen vacancies in ceria (CeO₂). The results of her work were presented at an international conference in Belgium. Also, her work has resulted so far in one published article in Hyperfine Interactions C Vol. 1, p. 392 (1996).

Eldon L. Decker, M.S., 1992. Advisor: J. Dean Barnett. Thesis: "High pressure electron paramagnetic resonance measurements on C₆₀(TDAE)_0.86." He used our EPR spectrometer to study the high-pressure properties of one of the compounds related to the new phase of carbon discovered in recent years.

Wei Chen, Ph.D., 1991. Advisor: Daniel L. Decker. Dissertation: "High precision measurement of electrical resistivity of nickel near the ferromagnetic phase transition at high pressure." This work was done in our large press. He was investigating the critical properties of nickel near its ferromagnetic phase transition. His work resulted in three published articles: Physical Review B, Vol. 46, p. 8237 (1992); Journal of Applied Physics, Vol. 71, 2624 (1992); High Temperatures-High Pressures, Vol. 24, p. 505 (1992). These last two articles were about techniques which he developed in order to attain the high precision necessary in the experimental measurements.

James D. Wells, M.S., 1990. Advisor: Harold T. Stokes. Thesis: "Computer generated basis functions of physically irreducible representations of crystallographic space groups." He developed computer algorithms and software that calculates atomic displacements and other distortions that occur in crystals during a phase transition. His work resulted in a published article in Physical Review B, Vol. 43, p. 11010 (1991).