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Physics Colloquium


Spring 2016 Colloquium Schedule

Date Speaker Title Host
January 25 Mu-Chun Chen
UC Irvine
Neutrinos and Physics beyond the Standard Model Yuri Kamyshkov
February 1 Jeremy C. Smith
UT, BCMB Department
Protein Physics and Drugs Jaan Mannik
February 8 Peter J. Hirschfeld
University of Florida
Disorder and Quasiparticle Interference in High-Tc Superconductors Steve Johnston
February 15 Ruxandra I. Dima
University of Cincinnati Department of Chemistry
Multi-scale Modeling of the Nanomechanics of Biomolecular Shells Jaan Mannik
February 22 Sergei Urazhdin
Emory University
Active Magnetic Nanostructures Driven by Spin Currents Jian Liu
February 29 John F. Mitchell Argonne National Lab TBD Haidong Zhou
March 7 James C. Weisshaar
U. Wisconsin-Madison
TBD Jaan Mannik
March 14 Spring Break NA NA
March 21 Matteo Rimi
Physical Review Focus

Norman Mannella
March 28 Zhigang Jiang
Georgia Tech
TBD Haidong Zhou
April 4 David Hsieh
TBD Jian Liu
April 11 Brent VanDevender
Pacific Northwest National Lab
TBD Nadia Fomin
April 18 Dean J. Lee
North Carolina State University
TBD Lucas Platter
April 25 TBD TBD TBD


January 25, 2016

Neutrinos and Physics beyond the Standard Model
Mu-Chun Chen
University of California, Irvine

Neutrino, having several Nobel Prizes in Physics directly under its belt, including this year's Prize for the discovery of neutrino mass by the Super-Kamiokande and Sudbury Neutrino Observatory Collaborations, is the most elusive and, besides photon, the most abundant particle in the Universe. On the other hand, there are still many outstanding questions about the neutrino that are yet to be answered. While we now know that the Higgs particle gives masses to all charged elementary fermions, we still have no clue what generates the neutrino masses. Furthermore, we don't know at the fundamental level what causes neutrinos to morph from one type to another while traveling through space, and whether the time reversal symmetry is broken in neutrino oscillation. Neutrinos also play a very important role in cosmology. While the Cosmic Microwave Background takes us all the way back to 380,000 years after the Big Bang, the standard Cosmic Neutrino Background, if ever observed, will take us all the way back to the very first second after the Big Bang! In addition, neutrinos may be responsible for the generation of the matter-antimatter asymmetry in the Universe.

In this talk, I will briefly review the current state of neutrino physics. I will discuss possible new physics, based on symmetry principle, that can naturally give rise to small neutrino masses and their oscillation pattern. Because of the symmetry, there exist predictions that allow for the theory to be tested at current and upcoming experiments. I will present a novel mechanism for the violation of time reversal symmetry, which is one of the necessary conditions for generating dynamically the matter-antimatter asymmetry in the Universe. Finally, I will elucidate a tantalizing possibility of the existence of a non-standard Cosmic Neutrino Background, enabled if neutrinos are Dirac fermions, that would provide a novel window into the very early Universe.

February 1, 2016

Protein Physics and Drugs
Jeremy C. Smith
Governor’s Chair, University of Tennessee and Director
Center for Molecular Biophysics, Oak Ridge National Laboratory

Proteins are nature’s most finely-tuned materials, and the source of great mysteries. Energy landscapes for functionally-important internal protein motions are highly complex, with effective dynamical relaxation times existing over many decades in time, from ps up to ~100 s. Our recent work using massive supercomputer simulations has shown that motions in single protein molecules are non-ergodic, non-equilibrium and exhibit ageing, properties arising from the fractal nature of the topology and geometry of the energy landscape explored. However, although motions in proteins are complex, dynamic concepts can accelerate drug discovery, and we give practical examples of this in the discovery of lead compounds for several diseases.

February 8, 2016

Disorder and Quasiparticle Interference in High-Tc Superconductors
Peter Hirschfeld
Department of Physics, University of Florida

New superconductors are discovered every year, but why the electrons form Cooper pairs is still a mystery in many cases. Often understanding the symmetry and structure of the pair wave function provides important clues to the answer, but direct probes are difficult to implement. In recent years, creative use has been made of the information available from scanning tunneling microscopy experiments (STM) on superconducting surfaces to determine the electronic energy bands of the materials and the momentum dependence of the pair wave function. Crucial to this so-called "quasiparticle interference" (QPI) experiment is the understanding of the role of disorder, which creates ripples in the Fermi sea. I will discuss the theory of QPI, give some examples where experiments have proven crucial, and propose some new methods to tighten the interplay of experiment and theory, working toward the solution of the high-Tc problem.

February 15, 2016

Multi-scale Modeling of the Nanomechanics of Biomolecular Shells
Ruxandra I. Dima
Department of Chemistry, University of Cincinnati

Large-size biomolecular systems that assemble, disassemble, and self-repair by controlled inputs play fundamental roles in biology. Microtubules are important in cytoskeletal support and cell motility. Physical properties of capsids of plant and animal viruses are important factors in capsid self-assembly, survival of viruses in the extracellular environment, and their cell infectivity. We focus on deciphering the microscopic origin of the physico-chemical properties of such biological assemblies and the molecular mechanisms of their response to controlled mechanical inputs. Because assemblies have modular architecture and strong interand intra-molecular coupling that modulate their properties, any approach has to model them on multiple spatial scales. We developed a multi-scale approach, combining coarsegraining1,2,3 with atomic details3,4, implemented on Graphics Processing Units (GPUs) for computational acceleration, to map out the mechanical properties of large size biological systems on experimental timescales. I will present our results for the micromechanics of microtubules4,5,6,7, related to the mechanism of microtubule disassembly, and our findings regarding the link between discrete microscopic transitions and the continuous mechanical response of the Cowpea Chlorotic Mottle Virus capsid at the macroscopic level8, in direct correspondence with AFM indentation experiments.

February 22, 2016

Active Magnetic Nanostructures Driven by Spin Currents
Sergei Urazhdin
Department of Physics, Emory University

21st century has witnessed a dramatic transformation of magnetism research from passive structures to electronically driven magnetic (spintronic) nanostructures that can find applications in memory and microwave technologies. It has been predicted that such devices are most efficient when operated by pure spin currents – spin flows not associated with charge currents. I will describe our recent demonstrations of two types of spin current-driven active nanodevices, one based on the spin Hall effect, and another based on nonlocal spin injection. I will show that the operation of these nanodevices generally relies on the nonlinear effects that result in the transformation of the dynamical spectrum of the magnetic system under the influence of spin current. The most interesting and potentially useful behaviors occur when one dynamical mode becomes singled out from the spectrum. I will describe two experimentally observed scenarios: one can be qualitatively understood in terms of the quasi-equilibrium statistics of Bose particles and is similar to the Bose-Einstein condensation, another can be understood in terms of the nonlinear Schrödinger equation and is similar to the energy quantization for a particle in a box.

Spin-current oscillators can be utilized, among other applications, as local sources in magnonic circuits – circuits that utilize spin-waves (magnons) as the information carrier. If time permits, I will describe a novel approach to the integration of spin-current nano-oscillators with magnonic waveguides based on the effects of the dipolar fields in magnetic nano-patterns. The approach enables good spectral matching between the localized oscillation and the magnonic waveguide, and efficient directional transmission of spin waves excited by the spin current. These results facilitate the development of electronically controllable magnetic nanocircuits that integrate information storage, transmission, and manipulation.

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