There is increasing interest in thermoelectric materials motivated in part by recent progress and in part by the potential of these materials in various energy technologies. Thermoelectric performance is a multiply contra-indicated property of matter. For example, it requires (1) high thermopower and high electrical conductivity, (2) high electrical conductivity and low thermal conductivity and (3) low thermal conductivity and high melting point. The keys to progress are finding an optimal balance and finding ways of using complex electronic and phononic structures to avoid the counter-indications mentioned above. In this talk, I discuss some of the issues involved in the context of recent results. One key aspect is optimization of the doping level in a given thermoelectric material. While this has long been understood in terms of standard semiconductor parabolic band models, we find surprisingly different results for many thermoelectric materials when the actual first principles band structures are used. This has led to prediction of a number of useful thermoelectrics, some that are new, and surprisingly some that are old. This work was done in collaboration with David Parker, Xin Chen, Olivier Delaire and Mao-Hua Du and was supported by the Department of Energy through the S3TEC Energy Frontier Research Center.

In addition to providing vital clues as to the formation and evolution of black holes, the spin of black holes may be an important energy source in the Universe. Over the past couple of years, tremendous progress has been made in the realm of observational measurements of spin. I will describe these efforts with particular focus on the use of X-ray spectroscopy to probe the spin of supermassive black holes in active galactic nuclei (AGN). For the first time, we are obtaining hints about the distribution of spins across the population of supermassive black holes with some interesting and unexpected consequences. After discussing spin, I will also address questions related to the driving of relativistic jets from AGN and the jet-disk connection. I shall conclude by discussing future prospects enabled by Astro-H (to be launched in 2015) and LOFT/ATHENA+ (currently under consideration by ESA).

A permanent electric dipole moment (EDM) of a particle or system would arise due to breaking of time-reversal (T), or equivalently charge-conjugation/parity (CP) symmetry. Over the past five decades, a number of experiments on the neutron, atoms and molecules have only set upper limits on EDMs, and the search continues, motivated in large part by the expectation that beyond Standard-Model physics CP violation is required to explain the baryon asymmetry of the universe. In addition, new techniques and access to systems in which the effects of CP violation would be greatly enhanced are driving the field forward. Systems that may be favorable for significant advances include the isotopes 225Ra and 221/223Rn, where the combination of significant octupole collectivity and relatively closely spaced opposite parity levels would increase the nuclear Schiff moment by orders of magnitude compared to other diamagnetic atoms, i.e. 199Hg. A number of technical and nuclear-structure issues must be addressed in order to assess the prospects for an experiment of significant impact. Among the technical challenges for the Radon-EDM program are developing an on-line EDM experiment at an isotope-production facility that will collect and make measurements on the short-lived species (half lives are approximately 25 min). We have developed and tested a system for high-efficiency collection and spin-exchange polarization of noble-gas isotopes that has been tested at the TRIUMF ISAC facility (experiment S929). Radon polarization techniques were studied at ISOLDE and Stony Brook, and spin-precession detection techniques are under development. Nuclear-structure issues include determining the octupole collectivity as well as the spacing of opposite parity levels. A series of experiments at ISOLDE (IS475 and IS552) have recently directly measured octupole collectivity in 220Rn and 224Ra leading to strengthened confidence in conclusions about the octupole enhancements. Experiments are also underway at NSCL at Michigan State University TRIUMF/ISAC to study the nuclear structure of isotopes in this mass region. I will report on progress on all these fronts and discuss recent developments in our studies of how we learn about the basic physical parameters of CP violation from the suite of EDM measurements. Refreshments will be served in CP 179 at 3:15 PM

Refreshements at 3:15pm in CP179.

The first evidence for dark matter dates back to observations of the Coma cluster made by Fritz
Zwicky in 1933. Since that time, astrophysicists and astronomers have produced compelling evidence for the existence of dark matter and determined that it constitutes the bulk of the matter in the Universe. Despite this fact, the composition of the dark matter remains unknown. One compelling candidate for particle dark matter is the Weakly Interacting Massive Particle (WIMP). Working in a low-background environment in the Soudan Mine, located in northern Minnesota, the SuperCDMS experiment is designed to directly detect interactions between WIMPs and nuclei in its target Ge crystals. In this talk I will present the latest results from the SuperCDMS experiment. I will also discuss the current status of the SuperCDMS at Soudan experiment and plans for a future 200-kg scale experiment which is slated for operation in SNOLAB.

Ferromagnetic (FM) thin films patterned into periodic lattices of nanoscale holes or dots are candidated for UHD data storage media, an drelated wire network patterns are of fundamental interest as examples of controlled phase transitions in "artificial spin ice". Our recent Physical Review Letter reported an experimental study of the static and dynamic magnetic properties of FM permalloy thin films patterned as Penrose P2 (quasicrystal) tilings that exhibit long-range order, but aperiodic translational symmetry. Our DC magnetization and ferromagnetic resonance data constitute, we believe, the first experimental study of th espin wave dynamics of an artificial FM quasicrystalline thin film. Ground-breaking efforts were required to both pattern and deposit the sample film materials, and to execute large-scale numerical simulations of their static and dynamic behavior. This work demonstrates a new method for controlling the evolution of FM domain walls and spin wave spectra in magnetic media, in spite of a lack of periodic symmetry in an artificial quasicrystalline pattern. Simulations reveal a remarkably controlled sequence of reversals of individual film segments located on sublattices of the quasicrystal pattern, which may signal the occurence of true metamagnetic phase transitions in larger-area samples. These results directly imply FM films patterned as Penrose P2 tilings constitute a novel class of magnonic crystals whose magnon frequency dispersion and physical properties were heretofore unknown.

Within each of Nature's crystals is an exotic quantum world of electrons weaving to and fro. Each crystal has its own unique tapestry, as varied as the crystals themselves. In some crystals the electrons weave an orderly quilt. Within others the electrons are seemingly entwined in an entangled web of quantum motion. In thi stalk I will describe the ongoing efforts to disentangle even Nature's most intricate quantum embroidery. Cutting-edge quantum many-body simulations together with recent ideas from quantum information theory, such as entangelment entropy, are enabling a coherent picture to emerge. Refreshments will be served in CP 179 at 3:15 PM

The problem of understanding how gravity fits together with other fundamental interactions of matter has been at the forefront of theoretical research for many decades, leading to the rich framework of string theory and M-theory. In this framework, many fundamental questions are being resolved, but many remain quite mysterious, suggesting that some novel concepts may be needed. I review the recent concept of multicritical gravity with Lifshitz-type anisotropic scaling, and its applications in areas ranging from particle phenomenology beyond the standard model to non-relativistic versions of the AdS/CFT correspondence.

I will summarize our current understanding of the formation and evolution of galaxies and supermassive black holes, and emphasize the underlying relationship between these two populations. I will pose several of the most fundamental shortcomings of our current models and then examine how they may be addressed by what we have learned from observations in the local universe of the effects that massive stars and supermassive black holes have on their surroundings. I will do my best to give a "physicist-friendly" talk that minimizes jargon and stresses the basic underlying physical processes.

Refreshments will be served in CP 179 at 3:15 PM

Organic semiconductors are becoming increasingly attractive given their solution processability, which allows for low-cost production on flexible media like paper, plastic, or textiles. But in spite of these advantages, the complexity of film formation resulting from solution growth processes makes it challenging to control the device performance in a reliable way. In this talk I will discuss the growth, structure, and electronic properties of functionalized pentacene and anthradithiophene organic thin-film transistors deposited by scalable solution deposition methods, such as spray deposition or vibration-assisted crystrallization. The results will be compared with those obtained in single crystal devices and several approaches to improve film quality and device performance will be presented. The effect of processing parameters on charge carrier mobilities, on/off ratios and interfacial trap densities will be detailed. Transitioning from mono-mulecular crystals to multi-component materials, such as the organic charge transfer complexes, which are combinations of charge donating (D) and charge accepting (A), I will show examples on how novel functionalities can emerge from D/A intermolecular interactions.
 

Refreshments will be served in CP 179 at 3:15 PM