physics & astronomy

Controlled Magnetic Reversal and Emergent Metamagnetism in Permalloy Films Patterned into Artificial Quasicrystals

Dr. Lance Delong University of Kentucky

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.

 

 

Quantum Tapestries

Dr. Matthew Fisher University of California, Santa Barbara

Quantum Tapestries 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.

Quantum Gravity with Anisotropic Scaling and the Multicritical Universe

 

 

Dr. Petr Horava University of California, Berkeley

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.

 

 

A Random Walk from the Laboratory to the Boardroom

After receiving a graduate degree at UK, Bill Roark successfully worked in the aerospace industry for many years, and started his own company, Torch Technologies. He will discuss his work experience and how his science background has helped and affected his career path.

Date: 
Thursday, October 10, 2013 - 4:00pm to 5:00pm
Location: 
CP 155

The Co-Evolution of Galaxies and Black Holes: A Local Perspective

 

 

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.

 

 

Colloquium: Charge Transport in Organic Materials and Devices

Dr. Oana Jurchescu 
Wake Forest University


Charge Transport in Organic Materials and Devices 

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. 

 

 

 

 

Colloquium: Cosmological Implications of Recent Low-noise, High-resolution Measurements of the Cosmic Microwave Background

Dr. Lloyd Knox University of California, Davis

Observing the sky in the microwave region of the spectrum allows us to directly image the universe when it was just a few hundred thousand years old. The universe was much simpler then, simple enough that its expected statistical properties, given a model, can be calculated with high accuracy. Recent improvements in measurement resolution and sensitivity, most notably from the Planck satellite, but also from the South Pole Telescope, have provided precision tests of the standard cosmological model. In this colloquium I will introduce the cosmic microwave background (CMB) and the standard cosmological model. I will explain the nature of these precision tests and what we are learning about the origin of all structure in the universe, and about the background of neutrinos thermally produced in the big bang. I will also cover how the improvements in resolution and sensitivity are opening up a new window on the dark universe, via gravitational lensing of the CMB.

A&S Inducts Alumni and Emeritus Faculty Into Hall of Fame

A&S will induct new members into its Hall of Fame Oct. 11, 2013, to join the ranks of the current 32 alumni and 8 emeritus faculty A&S Hall of Fame members.

Colloquium: Quantum Critical Spin Systems

 

 

Close to the absolute zero of temperature, when pushed to the edge between two phases of matter, simple lattice Hamiltonians of spins can display the incredibly rich phenomena of "quantum criticality". Quantum critical ground states are described by the most complex wavefunctions known to physicists, yet they can be categorized by "universality classes" that are independent of the details of the Hamiltonians that realize them. In this colloquium I will show how such quantum critical spin systems can arise in real-world materials, and explain our successes in developing quantum many-body simulations of a new universality class of deconfined quantum critical points.

Close to the absolute zero of temperature, when pushed to the edge between two phases of matter, simple lattice Hamiltonians of spins can display the incredibly rich phenomena of "quantum criticality". Quantum critical ground states are described by the most complex wavefunctions known to physicists, yet they can be categorized by "universality classes" that are independent of the details of the Hamiltonians that realize them. In this colloquium I will show how such quantum critical spin systems can arise in real-world materials, and explain our successes in developing quantum many-body simulations of a new universality class of deconfined quantum critical points.

Dr. Ribhu Kaul University of Kentucky

 

 

William Cottrell

William Cottrell presenting at Great Lakes String 2013

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