Physics Department Colloquia
Fall 2011 - Spring 2012
Colloquia are held on Fridays, beginning at 2:30 p.m. in Robeson 210
Refreshments are served at 2:15 p.m. (unless otherwise indicated)

< S2011 | September | October | November | December || January | February | March | April | May | F2012 >

August 2011
August 26

(poster)

Faculty Meeting

September 2011
September 2

(poster)

Prof. Eric Sharpe (Dept. of Physics, Virginia Tech)

Mirror symmetry and the renormalization group in string theory

September 9

(poster)

Prof. Patrick Huber (Dept. of Physics, Virginia Tech)

Submarine neutrino communication

The research presented in this colloquium draws on a number of disciplines: naval engineering, oceanography, geographic information systems, information theory, particle physics and history of the Cold War.

I will discuss the possibility to use a high energy neutrino beam from a muon storage ring to provide one way communication with a submerged submarine. Neutrino interactions produce muons which can be detected either, directly when they pass through the submarine or by their emission of Cerenkov light in sea water, which, in turn, can be exploited with sensitive photo detectors. Due to the very high neutrino flux from a muon storage ring, it is sufficient to mount either detection system directly onto the hull of the submersible. The achievable data transfer rates compare favorable with existing technologies and do allow for a communication at the usual speed and depth of submarines.

September 16

(poster)

Prof. Enrique del Barco (University of Central Florida)

Spintronics at the single-molecule level

Electrical transport properties of individual molecules have received considerable attention over the last several years due to the introduction of single-electron transistor (SET) devices. The potential of single-electron transport spectroscopy for the understanding of the fundamental physics and chemistry of individual molecules has been recently demonstrated by various breakthrough experimental discoveries. For example, transport excitations associated with fundamental vibrational modes of an individual C60 molecule in a SET have been reported. More recently, groups at Cornell and Harvard have observed the Kondo effect in individual paramagnetic molecules. Along this line, single-molecule magnets (SMMs) will provide a unique venue for probing novel aspects of the interplay between conduction electrons and molecular spin levels. I will discuss some of the phenomena expected to be observed in the conductance through a SMM-based SET. I will also describe the fabrication procedure and characterization of three terminal single-electron transistor devices utilizing Al/Al2O3 gate electrodes developed for these studies. The devices were patterned via multiple layers of optical and electron beam lithography. Electromigration induced breaking of the nanowires reliably produces 1-3 nm gaps between which the SMM can be situated. Preliminary results of the conductance through a Mn4 SMM displaying the coulomb blockade effect with several excitations that bend with the magnetic field have already been obtained.

Hosted by: Kyungwha Park

September 23

(poster)

Prof. Anna Hasenfratz (University of Colorado-Boulder)

Strongly coupled systems for theories beyond the Standard Model

The Standard Model of particle physics is an amazingly good description of electroweak phenomena, yet one of its fundamental ingredients, the Higgs boson, has resisted discovery for over 30 years. New data from LHC limit the Higgs mass to a fairly narrow window, but even more important are the limits experimental data are putting on beyond-Standard Model physics. A popular class of BSM models rely on coupled fermion-gauge systems and describe the Higgs boson as a composite particle. Since these models are usually strongly coupled, non-perturbative methods are needed to investigate them. In this talk I will give a brief overview of some of these models and describe how lattice QCD techniques are used to study them.

Hosted by: Uwe Täuber

September 30

10:00AM-11:00AM
in 304 Robeson

(poster)

Special Physics Education Seminar

Prof. Gerd Kortemeyer (Michigan State University)

The Assessment Continuum - Before, In, and After Lecture

The talk will discuss strategies for formative and summative assessment using LON-CAPA (http://www.lon-capa.org/). It will cover the implementation of pre-lecture questions that are embedded in the online reading materials (including Just-In-Time teaching strategies), LON-CAPA-graded clicker questions during lecture (using i>clicker and i>clicker2), online homework problems after lecture, practice exams, and exams as summative assessment (including online retakes for partial credit). For each of these elements of the assessment cycle, experiences, proven implementation mechanisms, and research results, gathered over the last 10 years, will be shared. It will also discuss the mechanisms for sharing assessment content across disciplines and institutions.

Hosted by: Tatsu Takeuchi

September 30

(poster)

Prof. Gerd Kortemeyer (Michigan State University)

The History of Modern Physics: A Study Abroad Course Following the Footsteps of Einstein, Heisenberg, Planck, Schrödinger, Pauli, Bohr, and the Rest of the Gang

We twice organized and led a European Study Abroad course to explore the early history of relativity and quantum theory. The course led us to Munich, Bern, Berlin, Zurich, Copenhagen, and Göttingen. The talk describes the sites, impressions, experiences, academics, logistics, and learning outcomes of our courses. It also addresses how some of the aspects of the history of physics can and should be used in teaching regular physics courses.

Hosted by: Tatsu Takeuchi

October 2011
October 7

(poster)

Fall Break

October 14

(poster)

Prof. Jean Heremans (Dept. of Physics, Virginia Tech)

Spin and quantum interference in nanostructures

Solid-state geometries of a length scale sufficiently small that quantum phase coherence and spin coherence are observable, enable experiments to explore, verify, and quantify quantum and semiclassical phenomena. We discuss experiments where antilocalization, a result of quantum interference of time-reversed paths, is used to determine the electron spin- and phase coherence lengths in strongly spin-orbit coupled semiconductors and semimetals. We experimentally conclude that the spin coherence lengths tend to increase under dimensional confinement, with consequences for various applications. Using the sensitivity of antilocalization to the electron spin-flip time, we have also studied the magnetic interactions between surface electrons and local magnetic moments from rare earth ions. We discuss the results, as well as the broader applicability of the experiments. Further, in ring geometries we observe coexistent Aharonov-Bohm oscillations due to quantum interference between both spatial paths and time-reversed paths. A transport formalism describing quantum coherent networks allows a comparison of the electron spin- and phase coherence lengths extracted for such spatial- and temporal-loop quantum phenomena. Finally, we discuss how we can draw on the results of the above experiments in a search for new quantum states of matter where magnetoelectric phenomena play an important role.

October 21

(poster)

78th Annual Meeting of the Southeastern Section of the American Physical Society

October 28

(poster)

Prof. Seongshik Oh (Rutgers University)

Do we really have topological insulators yet?

Over the past few years, topological insulators (TIs) have emerged as a new platform for coherent spin-polarized electronics and quantum computations. They are predicted to have an insulating bulk state and spin-momentum-locked metallic surface states. This spin-momentum-locking mechanism and their band structure topology are predicted to prevent the surface metallic states from being localized due to backscattering. However, in spite of many reports supporting the existence of TI surface states, their bulk state has always turned out to be metallic, instead of insulating. In other words, current-generation TIs are not truly topological insulators, but rather topological metals. These metallic bulk states not only shunt the surface state conduction, thus making extraction of the surface contribution difficult, but also degrade the surface states by providing scattering channels that are forbidden in true TIs. In this talk, I will discuss these challenges and our efforts to implement true topological insulators through thin film engineering schemes.

Hosted by: Kyungwha Park

November 2011
November 4

(poster)

Prof. Jeff Gore (MIT)

Cooperation, cheating, and collapse in laboratory populations

Natural populations can suffer catastrophic collapse in response to small changes in environmental conditions, and recovery after such a collapse can be exceedingly difficult. We have used laboratory yeast populations to study proposed early warning signals of impending extinction. Yeast cooperatively breakdown the sugar sucrose, meaning that there is a minimum number of cells required to sustain the population. We have demonstrated experimentally that the fluctuations in the population size increase in magnitude and become slower as the population approaches collapse. The cooperative nature of yeast growth on sucrose suggests that the population may be susceptible to cheater cells, which do not contribute to the public good and instead merely take advantage of the cooperative cells. We have confirmed this possibility experimentally, but recent results argue that competition between species may stabilize cooperation within a species.

Hosted by: Uwe Täuber

November 11

(poster)

Prof. Michael Bachmann (University of Georgia)

Challenges in Structural Computational Biology

For the first time after a long period of diversification, the natural sciences currently reunify in a joint ambition of unraveling the nature of molecular structures and their function in complex systems such as the biological cell - the highest level of emergence in cooperative interactions among molecular constituents. In this talk, the interplay of geometric structure and biological function will be discussed for representative molecular machines. A highly powerful methodology that, although still in the beginnings, will finally allow for a deeper, systematic understanding of micromolecular aspects of biological processes is high-performance computing. Developments are reviewed and also discussed in the light of generic, intrinsic driving forces of these highly specialized and functionalized macromolecules.

Hosted by: Royce Zia

November 18

(poster)

Prof. Austen Lamacraft (University of Virginia)

Statistical mechanics and dynamics of multicomponent quantum gases

Condensed matter physicists crave new states of matter beyond the humdrum trio of solid, liquid, and gas. The lure of creating new phases, whose existence depends upon the quantum mechanical behavior of their constituent atoms, explains the excitement surrounding ultracold atomic physics, and the remarkable scientific progress achieved over the past decade.

In this talk I'll try and convey some of this excitement by showing how multicomponent gases give rise to new problems in statistical mechanics and dynamics.

Hosted by: Djordje Minic

November 25

(poster)

Thanksgiving Break

December 2011
December 2

(poster)

Prof. Diana Vaman (University of Virginia)

A hologram of strings

In this talk I will review the holographic duality which relates strings in d+1-dimensions to quantum field theories in d-dimensions. In broad terms, the duality states that the information contained in a 5-dimensional theory of gravity (which asymptotes to a space of constant negative curvature called anti de-Sitter or AdS) is mapped holographically onto the boundary of this space, in terms of a 4-dimensional QCD-like gauge theory.

I will sketch the holographic description of "quarks" and of bound states like "mesons" and "baryons". I will conclude with a description of the duality at finite temperature, and describe some of its implications for the behavior of the field theory strongly coupled plasma.

Hosted by: Djordje Minic

December 9

(poster)

Final Exams Begin

December 16

(poster)

Fall Commencement

December 23

(poster)

Winter Break

December 30

(poster)

Winter Break

January 2012
January 6

(poster)

Winter Break

January 13

(poster)

Winter Break

January 20

(poster)

Faculty Meeting

January 27

(poster)

Prof. Dick Furnstahl (The Ohio State University)

Atomic Nuclei at Low Resolution

For digital televisions and cameras, higher resolution is considered better. Progress in particle physics usually requires higher resolution (shorter wavelengths) using higher-energy accelerators. But for many-body problems, such as the microscopic description of nuclei, lowering the resolution can be a big advantage. Evolving Hamiltonians to low resolution involves only basic principles of quantum mechanics, but with less familiar features such as nonlocality and many-body forces, which can run counter to intuition about potentials and wave-function correlations. I will illustrate the machinery and consequences of lowering the resolution and outline the benefits for major nuclear theory initiatives such as a project to develop a Universal Nuclear Energy Density Functional (UNEDF).

Hosted by: Uwe Täuber

February 2012
February 3 (Friday)

(poster)

Astronomy/Astrophysics Colloquium

Dr. Robert Gibson (University of Washington)

Accumulating Knowledge: A Multi-Survey View of Active Galactic Nuclei

Astronomical surveys are mapping the sky with ever-increasing breadth and depth. Each new survey also multiplies the value of accumulated data from previous missions, effectively providing a temporal, multi-wavelength view of the sky. However, the analysis of such large, combined data sets quickly becomes a detailed engineering problem. I will demonstrate how heterogeneous and multi-epoch data are advancing our understanding of the emission, outflows, and environments of active galactic nuclei (AGN), including their evolution over shorter, human time scales (decades). I will also briefly describe some of the serious challenges -- and opportunities -- that such large-scale analyses are facing as the supply of data rapidly grows.

February 6 (Monday)
3:00PM-4:00PM
304 Robeson

(poster)

Special Astronomy/Astrophysics Colloquium

Dr. Duncan Farrah (University of Sussex)

The Assembly History of Galaxies: Star Formation and Black Hole Accretion Across Cosmic Time

Over the last 13 billion years, galaxies such as our own have assembled several hundred billion stars and a central black hole weighing at least a few hundred million solar masses. Understanding how, when and why galaxies assemble their stars and central black holes is a fundamental goal of modern astrophysics. In this talk I will present recent results from several ongoing projects within which I am playing a leading role. First, I will show that the clustering of galaxies on the sky can be used as an efficient tracer of the underlying dark matter distribution across wide ranges in redshift.

Second, I will demonstrate that an actively accreting central black hole can bring star formation in the host galaxy to a resounding halt, which provides an observational resolution to a problem that has plagued galaxy evolution models for over a decade. Finally, I will present preliminary results from a large-scale far-infrared spectroscopic survey of star-forming galaxies, highlighting the use of both fine-structure ionic lines and molecular absorption and emission features in diagnosing the physical conditions within the galaxies interstellar medium.

February 8 (Wednesday)
2:30PM-3:30PM
304 Robeson

(poster)

Special Astronomy/Astrophysics Colloquium

Dr. Lisa Winter (CASA, University of Colorado at Boulder)

Multi-wavelength Study of Winds Driven by Supermassive Black Holes

While powerful winds driven by accretion around central supermassive black holes likely affect host galaxy evolution in the distant universe, we can not directly observe these processes at work. We can, however, easily observe the host galaxy and active galactic nuclei (AGN) properties of nearby sources. Previous surveys of outflows in local AGN relied on biased samples of the UV/soft X-ray brightest sources, making their results also biased. To understand the true outflow properties in a local sample of AGN, I present results from optical, UV, and X-ray spectroscopic follow-ups of a sample of Seyfert 1s detected in the very hard X-rays (14-195 keV) with NASA's Swift Burst Alert Telescope. Due to the high energy selection, this survey is largely unbiased to the gas and dust which obscures softer X-ray bands. We find that outflows are detected in a majority of the sample and may be present in all local Seyfert 1s. This implies a covering fraction of the outflows much larger than previous results. This work is timely in presenting the basis for studies of the evolution of black holes and their host galaxies at the closest distances, while several upcoming NASA/ESA missions will soon provide new samples of more distant obscured active galaxies.

February 10 (Friday)

(poster)

Neutrino Physics Colloquium

Dr. Žarko Pavlović (Los Alamos National Laboratory)

Searching for sterile neutrinos

When Pauli first introduced the neutrino in 1930, it was assumed it would never be observed experimentally. Since then we have made a tremendous progress and actually observed all three Standard Model neutrinos. Furthermore, we have experimentally confirmed that neutrinos can change from one species to the other. This phenomenon of neutrino oscillations allows us to precisely measure the mass difference between neutrino species. The oscillation experiments with atmospheric, solar, reactor and accelerator neutrinos revealed two mass splittings between the three neutrinos. However, the excess of events observed with LSND experiment could be pointing to oscillations with a third distinct mass splitting. If the LSND signal is due to neutrino oscillations it would imply Physics Beyond the Standard Model such as the existence of sterile neutrinos. I will discuss the results from the MiniBooNE, an experiment designed to test whether the excess observed with the LSND experiment is due to neutrino oscillations, as well as the results from other neutrino experiments sensitive to the same parameter space.

February 13 (Monday)
2:30PM-3:30PM
304 Robeson

(poster)

Special Neutrino Physics Colloquium

Prof. Lisa Kaufman (CEEM, Indiana University)

Weighing the Neutrino: Early Results from EXO-200

Neutrinos are all around us, yet many of their properties remain a mystery. The study of neutrinoless double beta decay can shed light on the properties of neutrino mass and whether or not the neutrino is its own anti-particle. In addition, because neutrinoless double beta decay violates lepton number conservation, its discovery would lead the way to physics beyond the standard model. The Enriched Xenon Observatory (EXO) program is aimed at searching for this decay in Xe-136. I will discuss the recent results from EXO-200 which has observed the two-neutrino double beta decay process for the first time in Xe-136 - the slowest directly-measured nuclear process to date!

February 15 (Wednesday)
2:30PM-3:30PM
304 Robeson

(poster)

Special Astronomy/Astrophysics Colloquium

Dr. Jifeng Liu (Harvard University)

Black holes in the Milky Way and nearby galaxies

Black holes are the inevitable prediction of Einstein's gravitational theory, and are expected in the astrophysical settings. Astronomical observations have already revealed, by studying their companions, stellar black holes of a few (tens of) solar masses as end products of massive stars and supermassive massive black holes above several millions of solar masses in the centers of galaxies. In this talk, I will first describe some studies on stellar black holes, including measuring the distorted space-time around the black holes through their spin, and my newly assembled project to find stellar black holes in quiescence combining the power of GALEX, SDSS and China's LAMOST sky surveys. I will then describe the efforts, including my own, to study ultraluminous X-ray sources in search of intermediate mass black holes of a few thousands of solar masses, the "missing" link between the stellar black holes and the supermassive black holes.

February 16 (Thursday)
2:00PM-3:00PM
304 Robeson

(poster)

Special Neutrino Physics Colloquium

Dr. Matthew Green (University of North Carolina at Chapel Hill)

Neutrinoless Double Beta Decay and the Nature of the Neutrino

Neutrinos have been intriguing subjects of study since they were first postulated over 80 years ago. Their exceptionally low - but nonzero - masses, combined with the fact that they interact only Weakly, have made them notoriously difficult to probe experimentally, yet their high abundances in the early universe have given them the opportunity to strongly influence cosmological evolution. In particular, the neutral charge of the neutrino allows for the possibility that neutrinos are their own anti-particles ie. are Majorana in nature, and their non-zero mass allows for this to be expressed through neutrinoless double beta decay, an as yet undetected process that would demonstrate lepton-number violation, probe of the absolute mass of the neutrino, and accomodate CP-violation in the lepton sector, a potential contributor to the matter/anti-matter asymmetry in the universe. I will discuss the physics of Majorana neutrinos and neutrinoless double beta decay, give a overview of current experimental efforts, and the Majorana Collaboration's efforts to detect neutrinoless double beta decay and dark matter in an ultra-low background array of high-purity germanium detectors.

February 17 (Friday)

(poster)

Astronomy/Astrophysics Colloquium

Dr. Katrien Steenbrugge (Universidad Católica del Norte)

Winds and jets from active galactic nuclei in the nearby universe

I will present the X-ray data obtained during a 3 month observational campaign of the Seyfert 1 galaxy Mrk 509, using 5 different satellites, and obtained with the goal to determine the mass, kinematic luminosity and feedback on the host galaxy of this outflow. The excellent statistics allow us to study in detail the ionization structure and relative abundances of this gas. The ionization structure spans 3 orders of magnitude and is discrete and the abundance ratios are consistent with solar ratios. We detect absorption from an AGN wind which is located at distances between 5 and 400 pc. In the other part of the talk I will talk about the emission and impact of the current and relic jets observed in the Cygnus A. Cygnus A is the nearest powerful classical double radio galaxy. I will show that the jet precesses, allowing us to determine an upper limit to the velocity of the kpc-scale jet. In the 200 ks Chandra X-ray image we detect emission from a relic counterjet structure. This emission comes from ∼103 Lorentz factor electrons inverse-Compton scattering of the cosmic microwave background. A re-energised relic counterlobe is detected in the low frequency 151 MHz image, and weak X-ray emission from the relic lobe is detected up to ∼100 kpc from the nucleus.

February 20 (Monday)
2:30PM-3:30PM
304 Robeson

(poster)

Special Astronomy/Astrophysics Colloquium

Prof. Sukanya Chakrabarti (Florida Atlantic University)

A New Probe of the Distribution of Dark Matter in Galaxies

The cold dark matter (CDM) paradigm of structure formation is successful at recovering the basic skeletal structure of the universe - the large-scale distribution of galaxies. However, the agreement between theory and observation is less secure when this model is applied to galactic (and sub-galactic) scales. The "missing satellites problem" refers to the excess of predicted CDM sub-structure relative to observed Local Group dwarf galaxies. Recent discoveries of dark-matter dominated dwarf galaxies, some fainter than some star clusters, makes one wonder whether there may be a population of faint dwarf galaxies, lurking just beyond our reach. The extended atomic hydrogen disks of galaxies provide an unique probe of galaxy evolution. They are ideal tracers of tidal interactions with satellites and the galactic gravitational potential well. We have recently developed a method whereby one can infer the mass, and relative position (in radius and azimuth) of satellites from analysis of the observed disturbances in outer gas disks, without requiring knowledge of their optical light. I will present the proof of principle of this method by applying it to galaxies with known optical companions. I will also present our earlier prediction for a dim companion of the Milky Way. I will end by presenting an extension of this method to characterize the density profile of the dark matter halo in spiral galaxies, and discuss future prospects for understanding galaxy evolution by studying the interplay of dark matter and baryons in galaxies.

February 21 (Tuesday)
2:00PM-3:00PM
304 Robeson

(poster)

Special Neutrino Physics Colloquium

Dr. Camillio Mariani (Columbia University)

Double Chooz first results

In this talk I will present the first results from 100 days of running of the Double Chooz detector. This experiment searches for the last unmeasured mixing angle, θ13, in the three-neutrino mixing matrix, via the disappearance of anti-νe produced by the dual 4.27 GWth Chooz B Reactors. We demonstrate that the detector is running well. With this data set, we fit total interaction rate and energy dependence to extract the mixing parameter at Δm231=2.4×10-3 eV2. We find sin213 = 0.086 ± 0.051. This is an important first step in our multi-year program to establish the magnitude of θ13 and a valuable input to today's global fits to the three-neutrino oscillation model.

February 24 (Friday)

(poster)

Neutrino Physics Colloquium

Dr. Alex Sousa (Harvard University)

Unraveling the Neutrino Mysteries with Long-Baseline Experiments

Neutrinos remain the least understood of the fundamental building blocks of matter. During the past decade, accelerator-based neutrino experiments played a fundamental role in confirming neutrino flavor change and in measuring neutrino oscillation parameters with high precision. The MINOS experiment, based at Fermilab and at the Soudan Undergound Laboratory, is playing a leading role in these measurements. The NOvA next generation experiment, currently under construction at Fermilab and Ash River, Minnesota, will begin probing the existence of CP violation in the leptonic sector and possibly open a unique window on physics at the grand unified scale. After reviewing the phenomenology of neutrino oscillations, I will present the latest results from the MINOS experiment, and discuss the surprising possibility that neutrinos may be superluminal particles. We will then go over the status and physics reach of the NOvA project, and conclude with a look into future prospects for US-based long-baseline neutrino experiments and how they can address the very challenging open questions in neutrino physics.

March 2012
March 2

(poster)

APS March Meeting

March 8 (Thursday)
11:00 A.M.
4069 Derring Hall

(poster)

Special Physics Colloquium

Vinh Quang Nguyen (University of California- Santa Barbara)

New insights into the picosecond dynamics of water and solvated proteins

According to computer simulations, the slowest, largest-scale harmonic motions of solvated biomolecules and the relaxation times of water occur on the picosecond regime. Experimental methods for the characterization of these collective vibrational modes, however, have been severely lacking. In response, I have developed the world's highest precision, highest sensitivity and highest frequency dielectric spectrometer. Operating over the frequency range from 65 GHz up to 1 THz, this spectrometer provides an unparalleled ability to probe the dynamics of water and aqueous proteins over the 100 fs to 10 ps timescale. Using this spectrometer to characterize the collective dynamics of solvated lysozyme I find that the collective vibrational modes of this protein are characterized by a hitherto unrecognized cutoff at 250 GHz (corresponding to 0.6 ps) arising due to the finite size of the molecule. Employing an effective medium approximation to describe the complex dielectric response of the protein in solution I find that each molecule is surrounded by a tightly held layer of 164 ± 5 water molecules that behave as if they are an integral part of the protein. Following studies of the spectra of water and of aqueous salt solutions I identify three Debye relaxations with the characteristic times of 8.56, 1.1 ps and 179 fs (at 25°C). Of note, while the relative strengths of these relaxation modes depend in a systematic way on solute concentration, their relaxation times do not. My observation sheds new light on the femtosecond to picosecond collective dynamics of water and solvated biomolecules.
[1]. N. Q. Vinh, et al., JACS 113, 8942 (2011)

March 9

(poster)

Spring Break

March 13 (Tuesday)
2:00 P.M.
Fralin Auditorium

(poster)

Special Physics Colloquium

Dr. Cary L. Pint (Intel Corporation)

Electron and Photon Manipulation Using Nanocarbon Scaffolds

A key challenge facing future applications of nanomaterials in diverse areas such as energy, electronics, and health, is the ability to extrapolate the fascinating nanoscale properties of these materials into macroscopic applications. In this spirit, my talk will discuss how the nanoscale structure of nanocarbon materials can be utilized as a tool to manipulate electrical and optical properties, spanning from fundamental transport and absorption processes to energy storage and conversion applications. I will first focus on techniques to fabricate nanocarbon scaffolds, primarily composed of single-walled carbon nanotubes (SWNT), where synthetic processes lend bottom-up control on the SWNT material characteristics necessary for efficient applications. Next, I will focus on studies of the anisotropic optical properties of this material on different length scales ranging from the visible to terahertz frequencies, giving rise to the broader application of these materials as ideal terahertz optical components. I will then discuss how the bottom-up controlled structure of these materials, when combined with atomic layer deposition (ALD) processes, can be an effective tool to manipulate electrons and photons in devices. This includes the development of high-power solid-state capacitive energy storage systems and structure-controlled nanocarbon/semiconductor templates designed to decouple light absorption and carrier collection processes to yield high efficiency solar conversion devices.

March 16

(poster)

Prof. Phillip Kim (Columbia University)

Spin and Pseudo-Spin in Graphene

Graphene, a single atomic layer of graphite, has been provided physicists opportunities to explore an interesting analogy to the relativistic quantum mechanics. The unique electronic band structure of graphene lattice yields a linear energy dispersion relation where the Fermi velocity replaces the role of the speed of light and pseudo spin degree of freedom for the orbital wavefunction replaces the role of real spin in usual Dirac Fermion spectrum. The exotic quantum transport behavior discovered in these materials, such as unusual half-integer quantum Hall effect and Klein tunneling effect, are a direct consequence of the pseudo-spin rotation in graphene. Interacting systems with internal symmetries will tend to break those symmetries in order to lower their energy. In graphene, the strong Coulomb interactions and approximate spin-pseudo spin symmetry are predicted to lead to a variety of quantum Hall ferromagnetic ground states and excitations which manifest as integer quantum Hall plateaus appearing within a graphene. In this presentation I will discuss various experimental evidence support the importance of spin and pseudo-spin structures in graphene at the strong quantum limit.

March 20 (Tuesday)
2:00 P.M.
Fralin Auditorium

(poster)

Special Physics Colloquium

Dr. Ryan Barnett (University of Maryland)

Multi-Component Ultracold Quantum Gases: Themes from Condensed Matter Physics and Beyond

Ultracold atomic gases have recently proven to be enormously rich systems from the perspective of a condensed matter theorist. With the advent of optical lattices, such systems can now realize idealized model Hamiltonians used to study complex materials. Conversely, ultracold atomic gases can exhibit quantum phases and dynamics with no counterpart in the solid state due to their extra degrees of freedom and unique environments virtually free of dissipation. In this talk, I will discuss examples of such behavior arising from spinor degrees of freedom on which my recent research has focused. Examples will include bosons with artificially induced spin-orbit coupling and the non-equilibrium dynamics of spinor condensates.

March 22 (Thur)
7:30 P.M.
Alumni Assembly Hall

(poster)

Special Public Lecture
Sponsored by the College of Science Institute of Advanced Study

Sir Anthony James Leggett (University of Illinois at Urbana-Champaign, Nobel Laureate 2003)



Why Can't Time Run Backwards?

We can all tell when a movie of some everyday event, such as a kettle boiling or a glass shattering, is run backwards. Similarly, we all feel that we can remember the past and affect the future, not vice versa. So there is a very clear ‘arrow’ (direction) of time built into the interpretation of our everyday experience. Yet the fundamental microscopic laws of physics, be they classical or quantum-mechanical, look exactly the same if the direction of time is reversed. So what is the origin of the ‘arrow’ of time? This is one of the deepest questions in physics; I will review some relevant considerations, but do not pretend to give a complete answer.

March 23
Hahn Hall- North Wing 130

(poster)

Sir Anthony James Leggett (University of Illinois at Urbana-Champaign , Nobel Laureate 2003)

Testing the limits of quantum mechanics: motivation, state of play, prospects

I present the motivation for experiments which attempt to generate, and verify the existence of, quantum superpositions of two or more states which are by some reasonable criterion ‘macroscopically’ distinct, and show that various a priori objections to this programme made in the literature are flawed. I review the extent to which such experiments currently exist in the areas of free-space molecular diffraction, magnetic biomolecules, quantum optics and Josephson devices, and sketch possible future lines of development of the programme.

March 29 (Thur)
7:30PM-8:30PM
GLC Auditorium

(poster)

Special Public Lecture
Graduate Education Week Featured Event / Women's Month 2012 Calendar Event
Sponsored by the Department of Physics, the College of Science, the Graduate School,
and Women in Leadership and Philanthropy.

Dr. Evalyn Gates (CEO, Cleveland Museum of Natural History)

 
Author photo by Dan Dry © W. W. Norton

Einstein's Telescope: The Hunt for Dark Matter and Dark Energy

Abstract: Data from a wealth of cosmological observations insist that normal baryonic matter makes up less than 5% of the Universe - dark matter accounts for 23%, while the remaining 72% is not matter of any kind but some strange new substance, dubbed dark energy, about which we know very little. Gravitational lensing - dismissed by Einstein in 1936 as a “most curious effect” that had little chance of ever being observed - is currently one of the most powerful techniques for exploring this dark universe. Using the warps and dimples in spacetime described by Einstein's theory of General Relativity as “cosmic lenses,” gravitational lensing allows us to search for black holes and planets within our own Galaxy; to map out the dark matter in distant galaxies, clusters and the cosmic web; and to detect the subtle influence of dark energy on the evolution and formation of structure in the Universe.

About the Speaker: Dr. Evalyn Gates is the Executive Director and CEO of the Cleveland Museum of Natural History. Before coming to the Museum in May, 2010, she was the Assistant Director of the Kavli Institute for Cosmological Physics and a Senior Research Associate in the Department of Astronomy and Astrophysics at the University of Chicago.
  Her research focuses on various aspects of cosmology and particle astrophysics, from neutrinos to the cosmic microwave background. Most recently she has been working on various aspects of dark matter, and searching for ancient stellar fossils in the form of the oldest white dwarfs. After receiving her Ph.D. in theoretical physics from Case Western Reserve University in 1990, Gates held postdoctoral fellowships at Yale University and the University of Chicago, and was a member of the theoretical astrophysics research group at Fermi National Accelerator Laboratory. She spent seven years at the Adler Planetarium and Astronomy Museum, initially as Director of Astronomy and then as Vice President for Science and Education.
  Dr. Gates has a strong interest in addressing the under-representation of women and minorities in the physical sciences and has written several articles on the topic of women in physics. She is also committed to inviting individuals of all ages and backgrounds to explore the ideas and discoveries of current scientific research. Her first book, Einstein's Telescope: The Hunt for Dark Matter and Dark Energy in the Universe, was published by W.W. Norton in February 2009.

Her lecture will be preceded by a book signing event starting from 7:00PM.

Hosted by: Tatsu Takeuchi

March 30
11:15 A.M.
104A Surge Building

(poster)

Special Center for Neutrino Physics Seminar

Dr. Thomas E. Shea (TomSheaNuclear Consulting Services)

Challenges and Opportunities: Proliferation, Existing Nuclear Arsenals & Nuclear Terrorism

Nuclear weapons, dirty bombs and sabotage of nuclear installations pose extraordinary threats to the security of nations, mass casualties and economic peril. The presentation will review contemporary threats and the national and international measures in place to limit the risks, noting that our luck has held since 1945 but there are no guarantees for today or tomorrow. The presentation includes consideration of the technological means to prevent, deter, detect and interdict actions that may raise significant threats, and possible careers in the areas of nuclear security.

April 2012
April 5 (Thursday)
2:00 P.M.
Fralin Auditorium

(poster)

Special Physics Colloquium

Dr. William Mather (University of California at San Diego)

Synthetic Biology: Clocks, Queues, and Crowds

Engineered biological circuits expressed in living cells are becoming increasingly attractive as a technology, but the rational design of biological circuits has been hindered by a relative scarcity of robust design principles. Synthetic biology offers one solution to this problem by testing design principles in smaller circuits with known components.

In this talk, I outline the exploration of design principles in three separate synthetic settings (oscillators, queueing systems, and multicellular environments) where the origin of dynamic behavior has been linked to simple but sometimes ignored interactions.

April 6

(poster)

Prof. Alysia Marino (University of Colorado-Boulder)

Beaming Neutrinos Across Japan with T2K

Neutrinos are one of the basic building blocks of the Universe, but many questions remain about their fundamental properties. Over the past 15 years, we have gathered strong evidence that neutrinos change from one type to another. This talk will outline the major remaining questions about neutrino masses and flavor mixing and will focus on the questions that can be addressed with neutrino beams. As an example of an experiment that uses an accelerator-generated neutrino beam, much of the talk will concentrate on the Tokai-2-Kamioka (T2K) experiment, which sends a beam of muon neutrinos 295 km across Japan. T2K began taking data in 2009, and this talk will present some of the initial results from the first 2 years of T2K data, which provide hints for a new type of neutrino oscillation.

April 13

(poster)

Awards Ceremony

April 20

(poster)

Dr. William Louis (Los Alamos National Laboratory)

Searching for Sterile Neutrinos at the SNS

Although neutrinos and photons are the two most numerous particles in the universe, there is still much that we do not know about neutrinos. In particular, we do not know the absolute neutrino masses nor the number of neutrino types. The number of active neutrinos that interact by the weak interaction has been measured to be three by the LEP experiments at CERN; however, additional "sterile" neutrinos that do not interact by the weak interaction may exist and may explain various anomalies from short-baseline neutrino experiments. These anomalous neutrino results will be discussed as well as a proposed neutrino oscillation experiment, OscSNS, that could be performed at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory and that would have the capability of proving the existence of sterile neutrinos.

April 27

(poster)

Prof. Karen Leighly (U. of Oklahoma)

Broad Absorption Line Quasars: New Results in the High-column Regime

Outflows are believed to be ubiquitous and fundamentally important in active galaxies and quasars. Despite their importance, key physical properties of outflows remain poorly unconstrained. It is especially difficult to constrain the column density, i.e., the amount of gas observed in the line of sight that is accelerated out of central engine. I will discuss new results that constrain the properties of outflows using metastable helium and four-times ionized phosphorus in broad absorption line quasars.

May 2012
May 4

(poster)

Final Exams Begin

   
Virginia Polytechnic Institute & State University 
Department of Physics MC 0435, 910 Drillfield Drive, Blacksburg, VA 24061 
Phone: (540) 231-6544; Fax: (540) 231-7511