O.M. Stewart Colloquium

Every Monday, at 4 PM the department of Physics and Astronomy hosts the O. M. Stewart Colloquium, in rm 120, Physics Bldg. Refreshments are served starting at 3:30 PM in the Physics Library (rm 223, second floor).

Spring 2016
Date Speaker/Title/Abstract
02/15/2016 Wei Zhang – Argonne National Laboratory
Spin-orbitronics as a promising route towards future energy-efficient electronics
New concepts for low-power, high-capability electronic devices are urgently required due to the rapid-reaching fundamental limits of conventional charge-based electronic devices. Spin-orbitronics, aiming at harnessing spin-orbit coupling in condensed matter for electronic computing, is a promising approach towards future energy-efficient electronics. The spin-Hall effect, existing in most d-orbital metals, is one of the most important enabling phenomena in spin-orbitronics, which have attracted increasing research interests in both fundamental and application aspects. I will first introduce the fundamentals of spin-Hall effect, followed by the various experimental approaches that allow for precise quantification of such an effect. I will then move a bit towards materials science perspective and talk about how such an effect can be influenced by introducing magnetic ordering by studying a series antiferromagnetic materials. Finally, I will use examples to demonstrate how such an effect can become a useful technology to enable many unique functions, such as driving insulating nanomagnets, for enabling future electronic devices. This work was supported by DOE-BES Materials Science and Engineering Division. References: Wei Zhang et al, PRL 113, 196602 (2014); PRB 91, 115316 (2015); PRB 92, 144405 (2015).
02/17/2016 Sergei Kopeikin, Dept. of Physics and Astronomy, MU
Special O.M. Stewart Colloquium - Gravitational Waves
The existence of gravitational waves - propagating miniscule distortions of space-time predicted by Einstein's theory of general relativity 100 years ago- was announced by LIGO (Laser Interferometer Gravitational-Wave Observatory) scientists on February 11, 2016. This has been hailed by some notable scientists as the discovery of the century! Prof. Sergei Kopeikin of MU’s Dept. of Physics and Astronomy will present a colloquium discussing the principles of generation, propagation and detection of gravitational waves, and their significant impact on our understanding of the universe. This talk is meant for faculty, graduate, and undergraduate students alike from all disciplines. Take a break from your daily stress; come enjoy a mind-blowing talk on the “ripples” in the fabric of space-time.  Venue: Rm 120 Physics Bldg.
02/22/2016 John Nichol – Harvard University
Quantum control and sensing with electron spins in semiconductors
Confined spins in semiconductors are a versatile platform for exploring quantum information processing and condensed matter physics. Individual spins can have coherence times exceeding seconds in some cases, making them promising quantum bits, or qubits, and also highly sensitive probes of their local electric and magnetic environments. I will discuss recent work exploiting the joint spin-state of two electrons in a GaAs double quantum dot as a “singlet-triplet” qubit. We perform high-fidelity single- and two-qubit gates with this architecture. We also use the qubit as a sensor to precisely measure its magnetic environment, which results from the statistically fluctuating nuclear spins in the semiconductor crystal. Using these measurement techniques, we extend the qubit coherence time by more than two orders of magnitude through adaptive control, and we uncover the surprisingly strong effect of spin-orbit coupling on electron-nuclear dynamics in GaAs.
03/07/2016 Peter Lu, Bowling Green State University
Single-molecule protein conformational dynamics in enzymatic reactions and cell signaling
Enzymatic reactions are traditionally studied at the ensemble level, despite significant static and dynamic inhomogeneities.  Subtle conformational changes play a crucial role in protein functions, and these protein conformations are highly dynamic rather than being static. We applied single-molecule spectroscopy to study the mechanisms and dynamics of enzymatic reactions involved with kinase and lysozyme proteins.  Enzymatic reaction turnovers and the associated structure changes of individual protein molecules were observed simultaneously in real-time by single-molecule FRET detections.  We obtained the rates for single-molecule conformational active-site open-close fluctuation and correlated enzymatic reactions.  Our new approach is applicable to a wide range of single-molecule FRET measurements for protein conformational changes under enzymatic reactions and protein-protein interactions in cell signaling.  Using this approach, we analyzed enzyme-substrate complex formation dynamics to reveal (1) multiple intermediate conformational states, (2) conformational motions involving in active complex formation and product releasing from the enzymatic active site, and (3) conformational memory effects in the chemical reaction process. Furthermore, we have applied AFM-enhanced single-molecule spectroscopy to study the mechanisms and dynamics of enzymatic reactions.  We obtained the rates for single-molecule conformational active-site open-close fluctuation and correlated enzymatic reactions.  We have demonstrated a specific statistical analysis to reveal single-molecule FRET anti-correlated fluctuations from a high background of fluorescence correlated thermal fluctuations.  Our new approach is applicable to a wide range of single-molecule AFM-FRET measurements for protein conformational changes under enzymatic reactions, including AFM-FRET control of enzymatic reactivity by mechanical-force manipulating protein conformations.  
03/14/2016 APS March Meeting
04/04/2016 Herb Fertig, Indiana University
Time Dependence, Topology, and Transport in Two Dimensions
In some two-dimensional systems, electrons have topological properties which endow them with surprising transport properties.  While nature provides us with a few such materials, their topology is limited by the materials which can actually be synthesized.  In this talk I will review recent work in which such topology is induced by time-dependent potentials, allowing in principle a broad set of possibilities for topological bands to be created. These "Floquet Topological Insulators" support surprising fundamental behaviors,  including a quantized Hall effect with no magnetic field, and in some cases transport enhancement by disorder.   I this talk I will discuss how these possibilities play out for electrons in graphene, showing how a time-dependent electric field yields a rich set of topological phases, and how they support phenomena which cannot be realized in a static setting.  
05/02/2016 Prof. Shubhra Gangopadhyay, ECE - MU
Super-resolution Imaging of Silver Nanostructures on Plasmonic Grating
Advanced super-resolution (SR) techniques rely on expensive, sophisticated, and demanding approaches, such as confocal laser scanning microscopy (CLSM), Airyscanning and ground state depletion (GSD) microscopy. On the other hand, the grating-based surface plasmon resonance (SPR) method can overcome the limit of optical resolution through enhancing and propagating electromagnetic field. In this work, silver nanoparticles (NPs) were imaged utilizing inexpensive silver plasmonic grating platform, fabricated by nanoimprint lithography, with different SR approaches including 3D GSD, Airyscanning and blinking localization microscopy with an epi-fluorescence microscope. The NP shape (triangle) from the bright field images were identified in an epi-fluorescence mode via SPR based enhancement. In addition, the enhanced fluorescence signal from dye molecules provided a unique ability to observe single-molecule (SM) blinking from 10 nM to 1 fM and lower dye concentrations, as well as, to study the localized effects such as temperature fluctuations, nanoparticle mobility, chemical reactions, bio self-assembly in nanoscale.
01/25/2016 Guang Bian, Princeton University
Exploring Fundamental Physics in Topological Phases of Condensed Matter
Ever since the experimental discovery of graphene and topological insulators, there have been intense research activities in searching and identifying new topological phases of condensed matter. Low energy properties of these crystalline solids have deep connections to fundamental topics in high-energy physics such as Weyl fermions, Majorana fermions, the chiral anomaly and supersymmetry. Thanks to the on-going efforts in synthesizing high quality bulk crystals and epitaxial thin films of these materials and in improving the capabilities of state-of-the-art spectroscopy methods, ample opportunities have emerged for exploring new fundamental physics in solid materials. In the first part of the talk, I will review recent experimental progress in direct spectroscopic detection of topological order in epitaxial Sb films and Berry phase in graphene, which give rise to the robust surface modes and a remarkably high electron mobility in these systems. In the second part, I will discuss the novel properties of Weyl semimetals and topological nodal-line semimetals. The observed Fermi arcs, drumhead surface states and transport chiral anomaly suggest potential applications of these materials in electronic and spintronic devices.
Fall 2015
Date Speaker/Title/Abstract
08/24/2015 No colloquium
First Day of Classes
09/07/2015 Jeffrey Kuhn, University of Hawaii
Justin Memorial Huang Lecture: A future for human exploration in the Universe – Finding life beyond the solar system
09/14/2015 Lisa Young, New Mexico Tech.
09/28/2015 Bjorn Lussem, Kent State University
Flexible organic electronics – challenges and prospects
10/05/2015 Eugene Mamontov, ORNL
Quasielastic neutron scattering to study interfacial water near biomolecules
10/19/2015 Gordon Stacey, Cornell University
Cerro Chajnantor Atacama telescope
10/26/2015 Michael Woodside, University of Alberta
Protein dynamics
11/02/2015 Baowen Li, University of Colorado
Phononics and thermal metamaterials
11/09/2015 Bin Hu, University of Tennessee
Perovskite photovoltaics
11/16/2015 Branislav Nikolic, University of Delaware
What can topological insulators do for spintronics?
11/30/2015 Hans-Peter Wagner, U. Cincinnati
Controlling Light-Matter Interaction in Plasmonic Waveguides and in Semiconductor/Metal Core-Shell Nanowires
12/07/2015 Charles Telesco, University of Florida


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