Physics and Astronomy Colloquium

semester, 2017

Thursday, January 19th 2017
3:35 pm:
There will be no colloquium this week.

Thursday, January 26th 2017
3:35 pm:
Speaker: Mary K. Gaillard, University of California, Berkeley
Subject:  A Singularly Unfeminine Profession
Refreshments to be served outside Smith 100 after the colloquium.

I will recount some of my experiences as a woman in a very male dominated field, while tracing the development of the Standard Model as I witnessed it and participated in it.

Faculty Host: Tony Gherghetta

Thursday, February 2nd 2017
3:35 pm:
Speaker: John Bowers, UCSB
Subject: Heterogeneous Photonic Integration on Silicon
Refreshments to be served outside Smith 100 after the colloquium.

We review recent advances in heterogeneous silicon photonic integration technology and components and describe progress in silicon photonic integrated circuits. Techniques for laser integration and the impact of active silicon photonic integrated circuits could have on interconnects, telecommunications and silicon electronics are reviewed. A variety of materials are being heterogeneously integrated, including arsenides for short wavelength lasers, phosphides for infrared lasers, LiNbO3 for nonlinear applications and YIG for isolators and circulators. One application that has been recently demonstrated is a 2.56 Tbit/s optical network on a chip that involved integrating over 400 optical elements, including DFB lasers, EAMs, photodetectors, and AWGs to make 64 transceivers operating at 40 Gbit/s.

John E. Bowers holds the Fred Kavli Chair in Nanotechnology, and is the Director of the Institute for Energy Efficiency and a Professor in the Departments of Materials and Electrical and Computer Engineering at UCSB. He is a cofounder of Aurrion, Aerius Photonics and Calient Networks. Dr. Bowers received his M.S. and Ph.D. degrees from Stanford University and worked for AT&T Bell Laboratories and Honeywell before joining UC Santa Barbara. Dr. Bowers is a member of the National Academy of Engineering and the National Academy of Inventors. He is a fellow of the IEEE, OSA and the American Physical Society, and a recipient of the IEEE Photonics Award, OSA Tyndal Award, the OSA Holonyak Prize, the IEEE LEOS William Streifer Award and the South Coast Business and Technology Entrepreneur of the Year Award. He has published eight book chapters, 600 journal papers, 900 conference papers and has received 54 patents. He and coworkers received the EE Times Annual Creativity in Electronics (ACE) Award for Most Promising Technology for the hybrid silicon laser in 2007.

Faculty Host: Marvin Marshak

Thursday, February 9th 2017
3:35 pm:
Speaker: Yongzhong Qian
Subject: Did a Low-Mass Supernova Trigger the Formation of the Solar System? Clues from Stable Isotopes and Be-10
Refreshments to be served outside Smith 100 after the colloquium.

About 4.6 billion years ago, some event disturbed a cloud of gas and dust, triggering the gravitational collapse that led to the formation of the solar system. A core-collapse supernova, whose shock wave is capable of compressing such a cloud, is an obvious candidate for the initiating event. This hypothesis can be tested because supernovae also produce telltale patterns of short-lived radionuclides, which would be preserved today as isotopic anomalies. Previous studies of the forensic evidence have been inconclusive, finding a pattern of isotopes differing from that produced in conventional supernova models. Here we argue that these difficulties either do not arise or are mitigated if the initiating supernova was a special type, low in mass and explosion energy. Key to our conclusion is the demonstration that short-lived Be-10 can be readily synthesized in such supernovae by neutrino interactions, while anomalies in stable isotopes are suppressed.

Thursday, February 16th 2017
3:35 pm:
Speaker: Alberto Nicolis, Columbia University
Subject: String theory in the bathtub
Refreshments to be served outside Smith 100 after the colloquium.

I will describe the peculiar mechanical properties of certain string-like objects that can exist in ordinary fluids and superfluids: vortex lines and vortex rings. I will then show how these properties follow straightforwardly from the principles of effective field theory applied to strings living in a medium.

Faculty Host: Tony Gherghetta

Thursday, February 23rd 2017
3:35 pm:
Speaker: Daniel Baker, University of Colorado
Subject: Economic and Societal Impacts of Severe Space Weather
Refreshments to be served outside Smith 100 after the colloquium.

This presentation describes extreme space weather impacts and their economic and societal costs. Modern technological society is characterized by a complex set of interdependencies among its critical infrastructures. These are vulnerable to the effects of intense geomagnetic storms and solar storms. Strong currents flowing in the ionosphere can disrupt and damage Earth-based electric power grids and contribute to the accelerated corrosion of oil and gas pipelines. Magnetic storm-driven ionospheric disturbances interfere with high-frequency radio communications and navigation signals from Global Positioning System (GPS) satellites. Exposure of spacecraft to solar particles and radiation belt enhancements can cause temporary operational anomalies, damage critical electronics, degrade solar arrays, and blind optical systems such as imagers and star trackers. Moreover, intense solar particle events present a significant radiation hazard for astronauts during the high-latitude segment of the International Space Station (ISS) orbit as well as for future human explorers of the Moon and Mars. In addition to such direct effects as spacecraft anomalies or power grid outages, a thorough assessment of the impact of space weather events on present-day society must include the collateral effects of space-weather-driven technology failures. For example, polar cap absorption events due to solar particles can degrade – and, during severe events, completely black out – radio communications along transpolar aviation routes. A complete picture of the socioeconomic impact of space weather must include both direct, as well as collateral, effects of space-weather-driven technology failures on dependent infrastructures and services. It is also imperative that we—as a technological society—develop a truly operational space weather observing and modeling system in which the benefits of accurate forecasts are clearly established.

Faculty Host: Roberta Humphreys

Thursday, March 2nd 2017
3:35 pm:
Speaker: Francis Halzen, University of Wisconsin-Madison
Subject: IceCube: Cosmic Neutrinos and More
Refreshments to be served outside Smith 100 after the colloquium.

The IceCube project has transformed one cubic kilometer of natural Antarctic ice into a neutrino detector. The instrument detects more than 100,000 neutrinos per year in the GeV to PeV energy range. Among those, we have isolated a flux of high-energy cosmic neutrinos. I will discuss the instrument, the analysis of the data, and the significance of the discovery of cosmic neutrinos. The observed cosmic neutrino flux implies that accelerated protons, and not just electrons, generate a significant fraction of the energy in the non-thermal universe. I will also discuss the study of the neutrinos themselves in the wide energy range revealed by IceCube.

Faculty Host: Clement Pryke

Thursday, March 9th 2017
3:35 pm:
Speaker: Anthony Leggett, University of Illinois at Urbana-Champaign
Subject: Superfluidity, phase coherence and the new Bose-condensed alkali gases
Refreshments to be served outside Smith 100 after the colloquium.

The phenomenon of superfluidity was discovered in liquid helium nearly sixty years ago, and ever since, following the almost immediate suggestion of Fritz London, it has been the almost universal belief in the condensed-matter community that it is due to the onset of the phenomenon of Bose-Einstein condensation which is theoretically predicted to occur in that system at sufficiently low temperature. However, for various practical reasons, it is extremely difficult even to establish unambiguously that BEC is occurring in 4-He, let alone to test directly some of the ideas which connect it to superfluidity. The recent attainment of BEC in dilute atomic alkali gases opens a new arena in this respect, allowing us to do many experiments which we would have loved to do in 4-He, but which are in practice unfeasible in that system. In this talk, I first review briefly the fundamental ideas developed in the helium context, then give a general introduction to the physics of the BEC alkali gases, and finally discuss some of the novel possibilities they open up, both already realized and still on the drawing-board.

Faculty Host: Martin Greven

Thursday, March 16th 2017
3:35 pm:
There will be no colloquium this week due to Spring Break

Thursday, March 23rd 2017
3:35 pm:
Speaker: Nandini Trivedi, Ohio State University
Subject: New Paradigms for Superconductivity
Refreshments to be served outside Smith 100 after the colloquium.

A superconductor is a perfect conductor and a perfect diamagnet in which currents flow with zero resistance and screen external magnetic fields. This emergent state of electrons has been described successfully by the Bardeen-Cooper-Schrieffer (BCS) paradigm. Within this standard paradigm, superconductivity arises when the Fermi surface in a normal metal becomes unstable to pairing. What happens when this paradigm breaks down, for example, in systems with very small Fermi surfaces, or in the absence of a Fermi surface altogether, as in a band insulator? In this talk I will provide some answers and also show how exciting new directions for superconductivity and superfluidity research are opening up in quantum materials and ultra-cold atomic gases.

Faculty Host: Fiona Burnell

Thursday, March 30th 2017
3:35 pm:
Speaker: Alex Koulakov, Cold Spring Harbor Laboratory
Subject: Mechanism of Olfaction
Refreshments to be served outside Smith 100 after the colloquium.

Olfaction is the final frontier of our senses - the one that is still almost completely mysterious to us. Despite extensive genetic and perceptual data, and a strong push to solve the neural coding problem, fundamental questions about the sense of smell remain unresolved. Unlike vision and hearing, where relatively straightforward relationships between stimulus features and neural responses have been foundational to our understanding sensory processing, it has been difficult to quantify the properties of odorant molecules that lead to olfactory percepts. In a sense, we do not have olfactory analogs of ``red, ``green and ``blue''. The seminal work of Linda Buck and Richard Axel identified a diverse family of about 1000 receptor molecules that serve as odorant sensors in the nose. However, the properties of smells that these receptors detect remain a mystery. I will review our current understanding of the molecular properties important to the olfactory system. I will also describe a theory that explains how odorant identity can be preserved despite substantial changes in the odorant concentration.

Faculty Host: Boris Shklovskii

Thursday, April 6th 2017
3:35 pm:
Speaker: Asimina Arvanitaki, Perimeter Institute
Subject: Particle Physics Beyond Colliders
Refreshments to be served outside Smith 100 after the colloquium.

When we think about Particle physics the first thing that comes to mind is colliders and high energies. Recently there have been several proposals of low-energy precision experiments that can also look for new particles, new forces, and the Dark Matter of the Universe in a way that is complementary to collider searches. In this talk, I propose two different experiments that search for a type of Dark Matter naturally arising in String Theory. In String Theory fundamental constants, such as the electron mass or charge, are determined by fields known as moduli. When these fields are the Dark Matter of our Universe, they cause the fundamental constants to oscillate with a frequency set by the Dark Matter mass. For frequencies smaller than 1 Hz atomic clocks with their unprecedented sensitivity can pick up these oscillations. For higher frequencies above 1 kHz, Dark Matter can excite acoustic modes in resonant mass detectors originally designed to detect gravitational radiation from astrophysical sources. Both techniques extend searches for this type of Dark Matter by several orders of magnitude in the near future.

Faculty Host: Tony Gherghetta

Thursday, April 13th 2017
3:35 pm:
Speaker: Mansour Shayegan, Princeton
Subject: Measurements of Composite Fermion Geometric Resonance
Refreshments to be served outside Smith 100 after the colloquium.

There has been a surge of recent interest in the physics of interacting, two-dimensional (2D) electrons in a large perpendicular magnetic field when they occupy a half-filled Landau level. The long ago proposed composite fermion (CF) picture, in which two magnetic flux quanta are bound to each electron to form a CF, explains many properties of the system. These include the compressible (metallic) behavior of the 2D system at filling factor ν = ½, the existence of a Fermi contour with a well-defined Fermi wave vector, and the presence of fractional quantum Hall states as the filling deviates from ν = ½. In this talk, I will highlight the results of several recent experiments that probe the presence and properties of CFs via measuring the geometric resonance of CFs’ cyclotron orbit diameter with the period of an imposed, unidirectional density modulation. The data reveal several important aspects: (1) An unexpected asymmetry of the CFs’ Fermi wave vector for filling factors smaller and larger than ν = ½, suggesting a subtle breaking of particle-hole symmetry. (2) Anisotropic Fermi contours for CFs that can be tuned by applying in-plane magnetic field or in-plane strain. The strain results are particularly intriguing as they imply that the CFs inherit a Fermi contour anisotropy from their (parent) zero-field particles through a simple relation. (3) I will also discuss a bilayer experiment where the geometric resonance of CFs in one layer is used to probe an electron Wigner solid in the other layer.

Faculty Host: Michael Zudov

Wednesday, April 19th 2017
3:35 pm:
Special Physics and Astronomy Colloquium in Moos Health Science Tower 2-650
Speaker: Arthur McDonald, Queen's University and Sudbury Neutrino Observatory
Subject: Neutrino and Dark Matter Experiments at SNOLAB
Note change of day and location this week only for Van Vleck Lecture -- Refreshments to be served after the colloquium.

The Sudbury Neutrino Observatory (SNO) was a 1,000 tonne heavy-water-based neutrino detector created 2 km underground in an active nickel mine near Sudbury, Canada. SNO studied neutrinos from 8B decay in the Sun by observing one neutrino reaction sensitive only to solar electron neutrinos and others sensitive to all active neutrino flavors. It found clear evidence for neutrino flavor change. This requires modification of the Standard Model for Elementary Particles and confirms solar model calculations with great accuracy. Future measurements at the expanded SNOLAB facility will search for Dark Matter particles thought to make up 26% of our Universe and neutrino-less double beta decay, a rare form of radioactivity that can tell us further fundamental properties of neutrinos. The lecture will provide a brief description of the science of SNO and the status and science to be addressed by SNOLAB experiments.

Thursday, April 27th 2017
3:35 pm:
Speaker: Adriano Fontana, National Institute for Astrophysics (Italy)
Subject: The Large Binocular Telescope from first stars to exoplanets: challenges and results.
Refreshments to be served outside Smith 100 after the colloquium.

Modern-day astrophysics is facing many outstanding scientific questions.
They include the nature of the first stars and galaxies, the physics of the assembly and evolution of massive galaxies, the constraints to dark matter and cosmological model, the demographics of exoplanets and the physics of planet formation.

Progress in these fields is often driven by technological developments. Thanks to a wealth of new instrumentation that will become available in the very next years, we expect to be able to address or to make substantial advances toward the solution of most of these problems.

Crucially, key new technologies in the optical domain involve the use of adaptive optics for ground based telescopes, of which the Large Binocular Telescope is a world-leader.

In my talk I will briefly illustrate some of the “big” scientific questions that are on the table - at least in my personal and biased view - and then present the new technologies and instrumentation -mostly of which developed at LBT - that promise to revolutionize the field in a decade, including some early results from LBT.

Faculty Host: Roberta Humphreys

Thursday, May 4th 2017
3:35 pm:
Speaker: Henry Sobel, University of California, Irvine
Subject: The Study of Neutrinos and Nucleon Decay in Japan
Student Awards will be presented at the start of Colloquium. Refreshments to be served outside Smith 100 after the colloquium.

The study of neutrinos and nucleon decay has along history in Japan beginning with the Kamiokande experiment in the 1980’s and continuing today with Super-Kamiokande and the T2K long baseline experiment. I will describe the sequence of experiments, their major results, and the current planning for the next stage of experiments with Super-Kamiokande-Gd, Hyper-Kamiokande and T2K-II.

Faculty Host: Yong-Zhong Qian

Thursday, September 7th 2017
3:35 pm:
There will be no colloquium this week.

Thursday, September 14th 2017
3:35 pm:
Speaker: Jeremy Mans, University of Minnesota
Subject: A Look at LHC Physics beyond the Higgs Discovery

The LHC collider and its detectors have been a generational effort to design, construct, and commission, with the primary mission to understand the nature of electroweak symmetry-breaking and the origin of rest-mass for fundamental particles. The discovery of the Higgs boson in 2012 marked a major achievement for particle physics, but this discovery has brought a number of long-standing puzzles into sharper focus. I will discuss several of these questions and how the University of Minnesota CMS group is addressing them. These questions include neutrino mass and left-right symmetry in particle interactions, the internal consistency of the Standard Model, and the nature of cosmological dark matter.

Thursday, September 21st 2017
3:35 pm:
Speaker: Yan Song, University of Minnesota
Subject: Formation of Alfvenic Electromagnetic Plasma Structures and Auroral Particle Acceleration: -- Exploring Theory of High Energy Plasma Physics

The acceleration of charged particles to high energy and the associated emission of electromagnetic (EM) radiation produced by the accelerated electrons and ions, occur throughout space and cosmic plasmas. During these processes, a large part of stored free magnetic energy can rapidly and efficiently convert into the kinetic energy of charged particles producing non-thermal high energy particles and EM radiation. To find the mechanism of such high energy particle acceleration is one of the most important unsolved problems in space and cosmic plasmas.

In general, applying parallel electrostatic electric fields associated with charge separation is the simplest and powerful method to directly accelerate particles to high energy. However, once the electric fields are produced, they will quickly short themselves out by the motion of free charges. Thus, a central question in auroral physics is to find the mechanism by which long-lasting parallel electrostatic electric fields can be generated.

I will present the theory of the generation of parallel electrostatic electric fields (Song and Lysak, 2001, 2006), and point out that the generation of parallel electric fields is favored by a low plasma density and high magnetic shear. In the auroral current system, nonlinear Alfvenic interactions between Alfven wave packets can produce EM plasma structures, such as Alfvenic Double Layers. The Alfvenic Double Layer consists of localized long-lasting electrostatic electric fields, which are embedded in low density cavities and surrounded by enhanced magnetic stresses. These structures are dynamical in nature, where the Poynting flux carried by Alfven waves continuously supplies energy to the Alfvenic Double Layers to maintain strong electrostatic electric fields for a fairly long time. These structures become a new fundamental dynamical state in cosmic plasmas, which constitute powerful high energy particle accelerators.

It has been broadly considered that the magnetic reconnection is a fundamental physical process which is responsible for almost all high energy plasma processes in space and cosmic plasmas. Magnetic reconnection is described as a process occurring when oppositely directed magnetic field lines in a plasma are cut and rejoined. I will show that the crucial components of magnetic reconnection lack support from fundamental physical theory, and suggest that we should use the fundamental physical laws and principles to study “reconnection” related processes.

Thursday, September 28th 2017
3:35 pm:
Speaker: Wendy Freedman, University of Chicago
Subject: A New Calibration of the Hubble Constant
Fall 2017 Misel Lecturer

The accuracy with which we can measure the Hubble
constant, Ho has been steadily increasing over the past
decade. The direct and traditional means to measure Ho
is based on measurement of distances and velocities to
galaxies in the local universe; for example, using Cepheid
variables and Type Ia supernovae. A model-dependent
Ho can be inferred from applying a cosmological model
to measurements of anisotropies in the cosmic microwave
background. Recently, these two precise techniques have
yielded values of Ho that disagree at more than 3-sigma.
This disagreement may be signaling errors in one or both
techniques. Alternatively, it could be signaling new physics
not currently included in the standard model of cosmology.
The Chicago-Carnegie Hubble Program is undertaking a
completely independent calibration of the Hubble constant
using red giant stars in the nearby universe. These stars
are proving to be both more precise and more accurate
than the traditional Cepheid variables. Moreover, with
the imminent launch of the James Webb Space Telescope
and new geometric parallaxes measured by Gaia, they will
provide a means of extending the distance scale beyond
the realm of Cepheids, and for measuring Ho to both a
precision and accuracy of 1%.

Thursday, October 5th 2017
3:35 pm:
Speaker: David Kaiser, MIT
Subject: Testing Bell’s Inequality with Astrophysical Observations

Albert Einstein once dubbed quantum entanglement "spooky action at a distance," and the concept remains one of the starkest examples of how quantum theory differs from our usual intutions about space, time, and matter. Physicists have tested Bell’s inequality experimentally for over four decades, and have always found results consistent with quantum theory; today entanglement is at the heart of next-generation devices like quantum computers and quantum encryption. Yet every experimental test to date has been subject to one or more "loopholes," which could possibly account for the results even in the absence of genuine quantum entanglement. This talk describes the latest experimental tests of quantum entanglement, including a new series of experiments that uses some of the oldest light in the universe to address the last major loophole and pave the way for a genuinely loophole-free test of Bell’s inequality.

Faculty Host: Michel Janssen

Thursday, October 12th 2017
3:35 pm:
Speaker: Clem Pryke, University of Minnesota
Subject: Studying the Beginning of the Universe from the Bottom of the World

The theory of Cosmic Inflation postulates that our entire observable universe
was spawned from a quantum fluctuation in an incredibly brief burst of hyper
expansion. Some believe that the evidence for Inflation is already
overwhelming (especially now that the results from the Planck space mission
are in). However, there are determined skeptics, and such extraordinary claims
require extraordinary evidence. Fortunately there is a chance that we can
obtain this! During the exponential inflationary expansion perturbations of
all kinds will have been injected into the fabric of spacetime, including a
background of gravitational waves. It turns out that our best hope to detect
these is to look for their imprint in the polarization pattern of the cosmic
microwave background (CMB). The BICEP/Keck telescopes, located at the South
Pole in Antarctica are currently the world leaders in this endeavor. In this
talk, I will describe the instruments, the results, and the continuing hunt
for inflationary gravitational waves.

Thursday, October 19th 2017
3:35 pm:
Speaker: Paula Heron, University of Washington
Subject: Preparing Physics Students for 21st Century Careers: The PHYS21 Report

With support from the NSF IUSE program, the AAPT and APS formed a Joint Task Force on Undergraduate Physics Programs (JTUPP). The task force reviewed employment data, surveys of employers, and reports generated by other disciplines. We also met with physicists in selected industries to get their views on the strengths and weaknesses of physics graduates, commissioned a series of interviews with recent physics graduates employed in the private sector, and identified exemplary programs that ensure that all of their students are well prepared to pursue a wide range of career paths. The resulting report “PHYS21: Preparing Physics Students for 21st Century Careers” describes the skills and knowledge that undergraduate physics degree holders should possess to be well prepared for a diverse set of careers and makes recommendations intended to help departments and professional associations support student career preparation.

Paula R.L. Heron is a Professor of Physics at the University of Washington. She holds a B.Sc. and an M.Sc. in physics from the University of Ottawa and a Ph.D. in theoretical physics from Western University. She joined the Physics Department at the University of Washington in 1995. Dr. Heron’s research focuses primarily on student ability to apply what they have learned about the dynamics of point particles in more advanced contexts involving elastic media, rigid bodies, etc. She has given numerous invited talks on her research at national and international meetings and in university science departments. Dr. Heron is co-Founder and co-Chair of the biannual “Foundations and Frontiers in Physics Education Research” conference series, the premier venue for physics education researchers in North America. She has served on the Executive Committee of the Forum on Education of the American Physical Society (APS), the Executive Committee of the Topical Group on Physics Education Research of the APS, the Committee on Research in Physics Education of the American Association of Physics Teachers (AAPT) and on the ad hoc National Research Council committee on the status and outlook for undergraduate physics education. She co-chaired the Joint Task Force on Undergraduate Physics Programs of the APS and AAPT, which produced the report Phys21: Preparing Physics Students for 21st Century Careers. She also serves as Associate Editor of Physical Review – PER. She was elected Fellow of the APS In 2007 and in 2008 she shared the APS Education award with colleagues Peter Shaffer and Lillian McDermott. Dr. Heron is a co-author on the upcoming 2nd Edition of Tutorials in Introductory Physics, a set of instructional materials that has been used in over 200 institutions in the US and that has been translated into German and Spanish.

Faculty Host: Kenneth Heller

Thursday, October 26th 2017
3:35 pm:
Speaker: Cindy Regal, University of Colorado-Boulder
Subject: Interferometry in a Strong Light

Optical interferometry is at the heart of many precise measurements from gravitational wave searches to microscopy. Generally one improves interferometer precision by increasing the light intensity, as well as by calming the many technical sources of noise that can perturb the mirrors or optical path. However, at extreme levels of light strength where radiation forces are significant, a new and interesting disturbance should appear – the quantum shaking associated with random arrival of individual photons at a mirror of the interferometer. This quantum backaction of light has been long foreseen and played a formative role in quantum optics theory. In this talk I will discuss an experiment in which we used a particularly compliant micro-scale drum to observe backaction in an interferometer, and demonstrate how quantum correlations can improve measurement in the presence of backaction. In this strong-light limit, interferometer mirrors can also be used as a nonlinear medium to manipulate light – for example to make squeezed light.

Faculty Host: Clement Pryke

Thursday, November 2nd 2017
3:35 pm:
Speaker: Shivaji Sondhi, Princeton University
Subject: Statistical Mechanics, Localization and Periodically Driven Quantum Systems

The statistical mechanics of equilibrium systems is characterized by two fundamental ideas: that closed systems approach a late time thermal state and that of phase structure wherein such late time states exhibit singular changes as various parameters characterizing the system are changed. Recent progress has established generalizations of these ideas which apply to periodically driven, or Floquet, closed quantum systems. I will describe this progress, which centrally uses other recent advances in our understanding of many body localization. I will describe how it has resulted in the discovery of entirely new phases such as the Pi-spin glass/Floquet time crystal which exist only in driven quantum system

Faculty Host: Fiona Burnell

Thursday, November 9th 2017
3:35 pm:
Speaker: Stan Brodsky, SLAC
Subject: Physics on the Light Front: A Novel Approach to Quark Confinement and QCD Phenomena

I will survey a number of exciting new developments in hadron and nuclear physics which can be derived from the underlying conformal properties of quantum chromodynamics and the application of Dirac's boost-invariant light-front quantization. These include new insights into the origin of the QCD mass scale and the physics of quark confinement, as well as surprising supersymmetric relations between the masses of mesons, baryons, and tetraquarks. I also will discuss a number of novel features of QCD, such as color transparency, hidden color, intrinsic heavy quark phenomena, and factorization-breaking lensing effects.

Faculty Host: Keith Olive

Thursday, November 16th 2017
3:35 pm:
Speaker: Cory Dean, Columbia University
Subject: From 3D to 2D and Back Again
Note the room change for this week only

Graphene , a single layer of carbon atoms arranged in a hexagonal lattice, is probably the best known, and most extensively characterized two-dimensional material. However, this represents just one of a larger class of van der Waals materials, in which atomic monolayers can be mechanically isolated from the bulk. By integrating these materials with one another, an exciting new opportunity has emerged in which layered heterostuctures can be fabricated with properties beyond those of the constituent materials. In this talk I will present some of our recent efforts where, by tuning the geometry of these heterostructures at the nanoscale, we are able to realize yet a new level of control over their electronic properties.

Faculty Host: Boris Shklovskii

Thursday, November 23rd 2017
3:35 pm:
Speaker: There will be no colloquium this week due to Thanksgiving

Thursday, November 30th 2017
3:35 pm:
Speaker: Philip Kim, Harvard University
Subject: Unusual quasiparticle correlation in graphene
Fall 2017 Van Vleck Lecturer

Interactions between particles in quantum many-body systems can lead to a collective behavior. In a condensed matter system consisting of weakly interacting particles, a propagating particle interacting with its surroundings can be viewed as a ‘dressed’ quasiparticle with renormalized mass and other dynamic properties. The lack of screening enables strong Coulomb interactions between charged particles, leading to new collective dynamics. In this talk, I will discuss three examples concerning strongly interacting quasiparticles in graphene. In the first example, it will be shown that the thermally populated electrons and holes to realize Dirac fluid, where a huge violation of Wiedemann-Franz law is observed. The second example is realizing magnetoexcitons to correlated the quasiparticles in quantized Landau levels to form magnetoexcitons, which can condense into Bose-Einstein condensation. Finally, we will also discuss another way of correlated quasi-particles in graphene using superconducting proximity effect. Here, we employ the crossed Andreev reflection across thin type II superconducting electrodes to correlated spatially separated quasiparticles. Under strong magnetic fields, the quantum Hall edge states can carry these quasiparticles.

Thursday, December 7th 2017
3:35 pm:
Speaker: Mark Bowick, KITP Santa Barbara
Subject: Fragile Objects: The Hard Science of Soft Matter

The natural and synthetic world has an extremely rich variety of states of matter. Many of these are fragile structures that are both flexible and complex and they range from atomic in scale to the very large. I will present four vignettes from the world of fragile objects (soft matter) that illustrate their counter-intuitive behavior and the intellectual challenge they present. I will demonstrate how the concept “state of matter” is often not as simple as one might think and show how fluctuations can lead to rather surprising behavior.

Faculty Host: Boris Shklovskii

Thursday, December 14th 2017
3:35 pm:
There will be no colloquium this week.

Thursday, December 28th 2017
3:35 pm:
There will be no colloquium this week.

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