Solid State and Applied physics

When a large number of atoms condense into a fluid or solid, behaviors emerge that are only indirectly related to the physics of the individual atoms. Superconductivity is one such an emergent behavior, which could not be anticipated from even a detailed study of an isolated atom. The goal of Solid State and Applied Physics is not only to measure and explain such emergent phenomena, but also to manipulate these properties to produce the novel effects we desire. This allows us to both investigate fundamental physics and to develop commercially important applications.

A student in Solid State and Applied Physics must have a thorough understanding of both the microscopic quantum mechanics that underlies the system and the classical macroscopic theories of mechanics, electromagnetism, and statistical mechanics that describe its large scale behavior. This broad background enables students to go on to careers in academia, government labs, and industry.

The primary focus of our group is the study of highly confined electron systems in artificially structured semiconductors. We cover all aspects of these systems, from fundamental theory to device fabrication. This group operates as part of Center for Semiconductor Physics in Nanostructures (C-SPIN) one of the National Science Foundation's few Materials Research, Science and Engineering Centers. C-SPIN is a multi-million dollar, interdisciplinary research collaboration between scientists at the University of Oklahoma and the University of Arkansas. We have theoretical and experimental efforts in nano-scaled semiconductor devices, spin transport in semiconductors and high-speed transistors. In addition to semiconductor studies, the group also has research efforts in lithium ion conducting polymers. This work, performed in conjunction with researchers in the Department of Chemistry and Biochemistry, is directed towards the understanding and improvement of lithium batteries.

The majority of our experimental research takes place in the department's state-of-the-art laboratories. Our well equipped facilities include: a dual-chamber molecular beam epitaxy (MBE) system for the growth of III-V and IV-VI semiconductors; several scanning probe microscopes for high resolution imaging and pattering of atomic surfaces; a new optical lithography cleanroom for semiconductor processing; low temperature (<20mK) and high magnetic field (15T) facilities for optical and electrical studies; and picosecond pulsed laser systems for our polymer studies. Theoretical work is aided by a numerous workstations and an SP2 supercomputer. This work concentrates on electron-electron interaction effects, electronic band structure of the confined systems, and hot-electron transport and magneto-transport in confined electron systems.

The faculty in Solid State and Applied Physics share appointments in the Engineering Physics Program. The engineering physicist provides the link between the pure scientist and the engineer by applying fundamental scientific theories to the solution of technological problems. As the miniaturization of transistors, lasers, and memory elements continues, an understanding of their operation increasingly requires knowledge of the underlying physics. This trend will only continue in the foreseeable future.

For latest summary of research interests and recent publications, visit our web site at: http://www.nhn.ou.edu/ouresearch/solid.html.

Ryan E. Doezema
Professor
B.A. 1964 Calvin College
Ph.D. 1971 Maryland

My research interests center on the magneto-electronic properties of semiconductors. The work is focused on the lower-dimensional electron systems formed in synthetically created quantum wells and superlattices Photonic transitions between quantum levels in the wells, and between magnetic levels induced by strong external magnetic fields, are studied using both a far-infrared, optically-pumped laser system as well as a Fourier transform infrared spectrometer. Our goals include the determination of electron dispersion as well as relaxation processes

We are especially interested in novel properties of quantum-well systems caused by band structure effects such as mass-mismatch and extreme non-parabolicity. Our work is made possible by the flexibility for designing quantum-well systems with the MBE system as part of the Center for Semiconductor Physics in Nanostructures (C-SPIN). Our experiments concentrate on the narrow-gap system InSb which, as a quantum well material, shows much promise for infrared and laser devices. We have been able to determine the defining characteristics of the binding potentials for these quantum wells (gap mismatch and band offset). Especially exciting is our recent observation of spin resonance in this system and, in asymmetric wells, evidence of spin splitting in zero magnetic field because of strong spin-orbit coupling

N. Dai, F. Brown, R.E. Doezema, S.J. Chung, K.J. Goldammer, and M.B. Santos, ``Determination of the Concentration and Temperature Dependence of the Fundamental Energy Gap in $\rm Al_xIn_{1-x}Sb$,'' Appl. Phys. Lett., 73, 3132 (1998).

N. Dai, G.A. Khodaparast, F. Brown, R.E. Doezema, S.J. Chung, and M.B Santos, ``Band Offset Determination in the Strained-Layer $\rm InSb/Al_xIn_{1-x}Sb$ System," Appl. Phys. Lett. 76, 3905 (2000).

G.A. Khodaparast, S.J. Chung, R.E. Doezema, and M.B. Santos, ``Energy Probe of the Rashba Spin Splitting in Heterostructures," submitted for publication.

John E. Furneaux
Professor
B.S. 1969 U.S. Military Academy
Ph.D. 1979 Berkeley

My main research effort is in lithium ion conducting polymers in collaboration with Professor Frech in Chemistry. We are particularly interested in the interactions between the polymer and the ion conducting salt that can provide insight as to the mechanisms of Li ion diffusion. We are studying these properties by combining two newly available technologies, a state-of-the-art tunable pulsed laser system including an optical parametric oscillator (OPO), and a step-scan FTIR.

We are also studying ionic association and polymer configurations and coordinations as a function of salt concentration and temperature in order to understand the basic interactions in these systems. We have ongoing collaborations for novel polymer preparations with Dan Glatzhoffer in Chemistry, for modeling with Ralph Wheeler in Chemistry, and with researchers at the University of St. Andrews, Scotland, and Uppsala University, Sweden where I was on sabbatical in 1997-1998.

Sabina Abbrent, Jan Lindgren, J. E. Furneaux, Jorgen Tegenfeld, and C. Wendsj, ``A Comparative Study of Gel Electrolytes Containing Polar of Non-Polar Polymer Chains'', Solid State Ionics, in preparation.

J. E. Furneaux, S. V. Kravchenko, Whitney Mason, V. M. Pudalov and, M. D'Iorio, ``Scaling of a Metal/Insulator Transition in a 2D System at B=0'', Surface Science 361/362, 949 (1996).

Whitney Mason, S. V. Kravchenko, and J. E. Furneaux, ``Experimental Evidence of the Coulomb Gap in High-Mobility 2D Electron System in Silicon,'' Surface Science 361/362, 953 (1996).

Matthew B. Johnson
Associate Professor
B.Sc. 1979 Waterloo
Ph.D. 1989 Caltech

Semiconductor nanostructures such as quantum-wells, -wires, and -dots have led to the discovery and study of new physical processes, as well as to the fabrication of novel ``band-gap-engineered" devices. My research involves the use of scanning probe microscopy techniques (SPM) to study the growth, and the physical and electronic structure of molecular beam epitaxy (MBE) grown nanostructures with atomic resolution. To date, scanning tunneling microscopy (STM) on cross-sectionally cleaved III-V heterostructures is used to studied heterostructures with chemical, electronic and photonic sensitivity on the atomic scale. Similary, STMs attached to the MBE systems have been used to study growth surfaces with atomic resolution in situ.

Here at OU we have various types of STM instruments including one for cross-sectional studies and one attached to a multi-chamber MBE. My first goal is to use these instruments to further understand the growth of nanostructures on the atomic scale and correlate this information with the optical and electronic properties measured by more macroscopic techniques.

My second goal is to use the SPM instruments themselves to pattern semiconductors so as to fabricate nanostructures and to study the novel properties of these nanostructures. Such nanostructures are the prototypes of the switches that will be used in the next generation of integrated circuits.

K. J. Goldammer, W. K. Liu, G. A. Khodaparast, S. C. Lindstrom, M. B. Johnson, R. E. Doezema and M. B. Santos, ``Electrical Properties of InSb Quantum Wells Remotely-Doped with Si'', J. Vac. Sci. Technol. B16, 1367 (1998).

M. B. Johnson, P. M. Koenraad, W. C. van der Vleuten, H. M. W. Salemink and J. H. Wolter, ``Be $\delta$-doped layers in GaAs imaged with atomic resolution using scanning tunneling microscopy", Phys. Rev. Lett. 75, 1606 (1995).

M. Pfister, M. B. Johnson, S. F. Alvarado, H. W. M. Salemink, et al., ``Indium distribution in InGaAs quantum wires observed with the scanning tunneling microscope", Appl. Phys. Lett. 67, 1459 (1995).

Bruce A. Mason
Associate Professor
B.A. 1980 Oberlin College
Ph.D. 1985 Maryland

My research involves the theoretical study of the properties of electronic systems in semiconductors. This work uses extensive computer modeling of semiconductor structures to understand the electronic states of these systems, and their electron dynamics. This work includes the study of parabolic quantum wells, hetero-junctions, metal-oxide-semiconductor structures and semiconductor quantum wires. I am interested in the electronic transport, optical, and infrared properties of these systems including the effects of magnetic fields and disorder. The techniques used in these calculations include self-consistent local density simulations, many-body Green function techniques, Monte Carlo simulations, and path integrals. I am also interested in the device applications of novel quantum systems for transistors and detectors.

M. F. Khodr, P. J. McCann, and B. A. Mason, ``Effects of Band Nonparabolicity on the Gain and Current Density in EuSe-PbSeTe IV-VI Semiconductor Quantum Well Lasers'', I.E.E.E. Jour. Opt. Elect. 32, 236 (1996).

C. E. Hembree, B. A. Mason, J. T. Kwiatkowski, J. E. Furneaux, and J. Slinkman, ``Calculated Spin Effects in Wide Parabolic Quantum Wells'', Physical Review B 48, 9162 (1993).

B. A. Mason and K. Hess, ``Quantum Monte Carlo Calculations of Electron Dynamics in Dissipative Solid State Systems Using Real-Time Path Integrals'', Physical Review B 39, 5051 (1989).

Kieran Mullen
Associate Professor
B.S. 1982 Georgetown
Ph.D. 1989 Michigan

I am interested in the physics of novel effects in quantum systems. My work to date falls in three broad categories: mesoscopic electronic devices, submonolayer superfluid helium films, and the dynamics of correlated electrons in two dimensions.

``Mesoscopic" systems are those in between the regimes of classical and quantum physics, typically less than a micron across. Experimentalists can routinely fashion devices so small that the electrostatic energy of a single electron can control the flow of current, or in which electrons can travel coherently from one side of the device to the other. The theoretical challenges are to understand how the quantum mechanical effects in the microscopic device couple to macroscopic world of voltmeters and ammeters, and how to take advantage of the novel dynamics for new applications. Schrodinger's cat is no longer a cute puzzle in nanotechnology; it is a real issue with experimental consequences.

Superfluid helium is an archetype of a macroscopic system displaying quantum mechanical effects. Recent experiments have shown that helium can act as a superfluid even when there is less than a single atomic layer in the film. Such a two-dimensional Bose system is ideal for studying fundamental questions, such the effect of disorder, the dynamics of vortices, and the possible existence of superhexatics and supersolids. The helium system is so well understood experimentally, that it poses a challenging testbed for any theoretical technique.

My third area of interest is an overlap of the above two: the dynamics of electrons when they are confined to a two dimensional plane. This leads to a host of interesting topics including localization, behavior in a strong magnetic field, and the existence of electron ``bubbles" called skyrmions. These bubbles are comprised of a dozens of electrons whose spins are twisted into a stable pattern. The pattern is stable due to its topology. Such topological excitations provide a fascinating new way to study many-body systems in an elegant way.

``Thermodynamic Phase Diagram of the Quantum Hall Skyrmion System,'' K. Moon and K. Mullen, Phys. Rev. Lett. 84, 975 (2000).

Kieran Mullen, ``Geometrical defects in Josephson junction arrays,'' Phys. Rev. B 60, 4334 (1999).

K. Moon and K. Mullen, ``Anisotropic transport of quantum Hall meron-pair excitations", Physical Review B57, 1378 (1998).

H. T. C. Stoof, K. Mullen, M. Wallin, and S. M. Girvin, ``Hydrodynamics of Spatially Ordered Superfluids", Physical Review B53, 5670 (1996).

Sheena Murphy
Assistant Professor
B.S. 1984 MIT
Ph.D. 1991 Cornell

Over the last few years, my group has focused on the study of electrons in confined geometries. A two dimensional confinement is achieved when the electrons reside in a thin low bandgap semiconductor sandwiched between layers of a higher bandgap material. Further confinement results from processing the semiconductor sample into wires or dots using lithography techniques. As of late, it is in these reduced dimensional systems that some of the more significant developments in condensed matter physics have been found such as the integer and fractional quantum Hall effect, and quantized conductance in point contacts, to name a few.

At the University of Oklahoma, we have access to a particularly interesting semiconductor system, InSb. This material has an extremely low electron effective mass resulting in high mobility and a very large Lande g factor resulting in large spin effects. My group has been engaged in the study of the quantum Hall effect in this unique system. More recently we have started experiments to study spin injection and spin transport as well. We perform our experiments at low temperatures (from 10K to 0.01K) and in high magnetic fields (up to 15 Tesla). In addition to our low temperature/high field facilities, we also use the optical lithography facility of the Solid State group. In this facility we can fabricate devices with submicron sized features, package them for our experiments and perform room temperature inspection and characterization. In addition our affliliation with the OU/Arkansas Materials Center gives us access to a number of other magnetic, optical and electronic probes.

S.J. Chung, N. Dai, G.A. Khodaparast, J.L. Hicks, K.J. Goldammer, F. Brown, W.K. Liu, R.E. Doezema, S.Q. Murphy, and M.B. Santos, ``Electronic characterization of InSb quantum wells'', Physica E 7, 809 (2000).

S.Q. Murphy, J.L. Hicks, W.K. Liu, S.J. Chung, N. Dai, K.J. Goldammer, and M.B. Santos, ``Studies of the quantum Hall to quantum Hall insulator transition in InSb-based 2DESs'', Physica E 6, 293 (2000).

K.J. Goldammer, S.J. Chung, W.K. Liu, M.B. Santos, J.L. Hicks, S. Raymond and S.Q. Murphy, ``High-mobility electron systems in remotely-doped InSb quantum wells'', Journ. Cryst. Growth 201-202, 753 (1999).

S.Q. Murphy, J.P. Eisenstein, L.N. Pfeiffer and K.W. West, ``Lifetime of Two-Dimensional Electrons Measured by Tunneling Spectroscopy'', Phys. Rev. B, 52, 14825 (1995).

G.S. Boebinger, S.Q. Murphy, J.P. Eisenstein, L.N. Pfeiffer, K.W. West, and Song He, ``New collective quantum Hall states in double quantum wells'', Surf. Sci 305, 8 (1994).

S.Q. Murphy, J.P. Eisenstein, G.S. Boebinger, L.N. Pfeiffer and K.W. West, ``Many-Body Integer Quantum Hall Effect: Evidence for New Phase Transitions'', Phys. Rev. Lett., 72, 728 (1994).

Stewart Ryan
Associate Professor
B.S. 1964 Notre Dame
Ph.D. 1971 Michigan

My current work focuses on the use of video techniques to enhance physics instruction. Using 3-D computer animation, the Physics Video Project is producing a video series entitled Understanding Modern Technology to illustrate the application of the principals of physics to modern technology. Also in production is a companion series of Physics Video Clips designed to elucidate physical phenomena that evolve in time and thus are not readily illustrated in a static figure. The goal of the Physics Video Project is to enhance learning in introductory physics classes by illustrating the applications of physics and demonstrating concepts that students often have difficulty visualizing or understanding mathematically.

A continuing area of interest is the development of new techniques and instrumentation for use in such fields as materials characterization, non-destructive testing, and energy conservation. A differential, constant-resistance anemometer developed for energy conservation has application in both analytical chemistry and geophysics.

S. R. Ryan, Greg Parker, and Ron Kantowski, ``Understanding Modern Technology: The Audio Compact Disc", University of Oklahoma, 1998.

T. Xie, S. R. Ryan, and H. J. Fishbeck, ``Proton RBS Measurements of the Oxygen in Heavy-Metal Oxides'', Nuclear Instruments and Methods B 40/41, 766 (1989).

H. J. Fishbeck, D. J. Rogers, S. R. Ryan, and F. E. Swensen, ``Sourcing Ceramics in the Spiro Region: A Preliminary Study Using Proton Induced X-Ray (PIXE) Analysis'', Midcontinental Journal of Archaeology 14, 3 (1989).

Michael B. Santos
Associate Professor
B.S. 1986 Cornell
Ph.D. 1992 Princeton

My research interests focus on InSb-based heterostructures for electronic device applications. Since the bandgap of InSb is the smallest of all binary III-V compounds, two-dimensional electron systems (2DES) in InSb quantum wells have several extreme properties: a small effective mass, a large g-factor, a high intrinsic mobility, and a non-parabolic dispersion relation. Using the department's molecular beam epitaxy (MBE) system, my research group fabricates InSb quantum-well structures with $\rm Al_xIn_{1-x}Sb$ barrier layers. The room-temperature mobility in these structures is higher than in quantum wells made of any other semiconductor. We are exploring ways to exploit this feature in improved field-effect transistors and magnetic-field sensors. The behavior of our 2DES in the quantum Hall regime (low temperature and high applied magnetic field) is expected to differ from that observed in more commonly studied GaAs-based heterostructures. These fundamental studies are being pursued in collaboration with Professors Murphy and Doezema.

Since the operation of electronic devices depends on the material quality of the heterostructures, my group makes use of in situ surface analysis techniques (reflection high-energy electron diffraction, Auger electron spectroscopy, and x-ray photoelectron spectroscopy) and high-resolution x-ray diffraction. With the recent addition of a scanning probe microscope onto the MBE system, we are collaborating with Professor Johnson's group on nanostructure fabrication and studies of the MBE growth process.

S. J. Chung, N. Dai, G. A. Khodaparast, J. Hicks, K. J. Goldammer, F. Brown, W. K. Liu, R. E. Doezema, S. Q. Murphy, and M. B. Santos, ``Electronic Characterization of InSb Quantum Wells", Physica E7, 809 (2000).

S. J. Chung, K. J. Goldammer, S. C. Lindstrom, M. B. Johnson, and M. B. Santos, ``A study of factors limiting electron mobility in InSb quantum wells", Journal of Vacuum Science and Technology B17, 1151 (1999).

W. K. Liu, K. J. Goldammer, and M. B. Santos, ``Surface Segregation and Compensation of Si in $\delta$-doped InSb and $\rm Al_xIn_{1-x}Sb$ Grown by Molecular Beam Epitaxy", Journal of Applied Physics 84, 205 (1998).