Colloquium
The Fall 2020 Colloquia will be held over Zoom on Mondays at 4:45 PM, EST.
Fall Colloquium Chair, Nadia Fomin (nfomin@utk.edu)
August 24 |
Bob Dubois |
Getting Things Done |
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August 31 |
Kevin Dusling |
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September 7 |
No Colloquium |
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September 14 |
Elizabeth Brost |
Double the Fun: Searching for Higgs Pair Production at the LHC |
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September 21 |
Alan Robock |
Climatic and Humanitarian Impacts of Nuclear War |
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September 28 |
Meg Urry |
How Physics Can Get to Parity |
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October 5 |
Emily Smith |
Transforming Introductory Physics Labs to Engage Students in Experimentation |
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October 12 |
Deirdre Shoemaker |
Numerical Relativity in the Age of Gravitational Wave Observations |
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October 19 |
Jian Liu |
Toy-model Quantum Materials Artificially Built for Capturing Emergent Phenomena
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October 26 |
John Stockton |
Careers in Data Science |
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November 2 |
Norman Mannella |
A photoemission spectroscopy view of emergent complex magnetic ordering in Cr1/3NbS2 |
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November 9 |
Lisa Tran |
Shaping Particle Assemblies at the Interface of Liquid Crystals |
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November 16 |
Vesna Mitrovic |
Relativistic-quantum Magnets |
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November 23 |
Melina Avila |
Stellar Processes and the Role of Nuclear Physics |
Bob Dubois, UT Department of Psychology
Getting Things Done
(Missed it? Here's the recording)
A gorgeous planner for your year of dreams and joys. Excelling as a learner requires discipline and hard work. You can’t afford to procrastinate. Learn how you can use time management principles grounded in research to stay focused, organized, and productive.
Kevin Dusling, Editorial Staff, PRL
Physical Review Letters, The Inside Story
Physical Review Letters is the most cited journal in physics, with a Letter cited roughly every 80 seconds. Editors decide what to publish with extensive input from peer review and consultation with the PRL editorial board. This talk will provide an outline of how PRL manages the review of more than 10,000 annual submissions, less than 1/4 of which are published, while maintaining the breadth and exclusivity that is the hallmark of the journal.
We face many challenges as the publishing trends in some areas of physics shift to smaller, less comprehensive, or more interdisciplinary venues. I will discuss some of these challenges, and what PRL is doing, to maintain a competitive journal that best serves the physics community.
Elizabeth Brost, Brookhaven National Laboratory
Double the Fun: Searching for Higgs Pair Production at the LHC
Since the discovery of the Higgs boson at the Large Hadron Collider (LHC) in 2012, particle physicists have been hard at work studying its properties. While some properties of the Higgs boson, such as its mass and spin, have already been measured with great precision at the LHC and agree well with the Standard Model (SM), others remain unconstrained and could be a window into new physics.
The Higgs self-coupling can be directly measured in collisions resulting in pairs of Higgs bosons, and the measurement of this coupling will give insight into the conditions of the early universe. This is a challenging measurement, due to the incredibly small rate at which pairs of Higgs bosons are produced in the SM. At the same time, a wide range of beyond-the-SM models predict enhancements to the Higgs pair production rate, which motivates searching for this process even now. In this talk, I discuss current searches for Higgs pair production at the LHC, and a roadmap towards the eventual observation of this process and measurement of the Higgs self-coupling.
Alan Robock, Rutgers University Department of Environmental Sciences
Climatic and Humanitarian Impacts of Nuclear War
A nuclear war between any two nations, such as India and Pakistan, with each country using 50 Hiroshima-sized atom bombs as airbursts on urban areas, could inject 5 Tg of soot from the resulting fires into the stratosphere, so much smoke that the resulting climate change would be unprecedented in recorded human history. Our climate model simulations find that the smoke would absorb sunlight, making it dark, cold, and dry at Earth’s surface and produce global-scale ozone depletion, with enhanced ultraviolet radiation reaching the surface. The changes in temperature, precipitation, and sunlight from the climate model simulations, applied to crop models show that these perturbations would reduce global agricultural production of the major food crops for a decade. Since India and Pakistan now have more nuclear weapons with larger yields, and their cities are larger, even a war between them could produce emissions of 27 or even 47 Tg of soot.
My current research project, being conducted jointly with scientists from the University of Colorado, Columbia University, and the National Center for Atmospheric Research, is examining in detail, with city firestorm and global climate models, various possible scenarios of nuclear war and their impacts on agriculture and the world food supply. Using six crop models we have simulated the global impacts on the major cereals for the 5 Tg case. The impact of the nuclear war simulated here, using much less than 1% of the global nuclear arsenal, could sentence a billion people now living marginal existences to starvation. By year 5, maize and wheat availability would decrease by 13% globally and by more than 20% in 71 countries with a cumulative population of 1.3 billion people. In view of increasing instability in South Asia, this study shows that a regional conflict using less than 1 percent of the worldwide nuclear arsenal could have adverse consequences for global food security unmatched in modern history. The greatest nuclear threat still comes from the United States and Russia. Even the reduced arsenals that remain in 2020 due to the New START Treaty threaten the world with nuclear winter. The world as we know it could end any day as a result of an accidental nuclear war between the United States and Russia. With temperatures plunging below freezing, crops would die and massive starvation could kill most of humanity.
As a result of international negotiations pushed by civil society led by the International Campaign to Abolish Nuclear Weapons (ICAN), and referencing our work, the United Nations passed a Treaty to Ban Nuclear Weapons on July 7, 2017. On December 10, 2017, ICAN accepted the Nobel Peace Prize “for its work to draw attention to the catastrophic humanitarian consequences of any use of nuclear weapons and for its ground-breaking efforts to achieve a treaty-based prohibition of such weapons.” Will humanity now pressure the United States and the other eight nuclear nations to sign this treaty? The Physicists Coalition for Nuclear Threat Reduction is working to make that happen.
Megan Urry, Yale Center for Astronomy and Astrophysics
How Physics Can Get to Parity
Many decades after anti-discrimination laws were passed here and abroad, physicists still look very different than the general population. Women, people of color, members of the LGBTQ community, military veterans, and other “outsider” groups lag far behind, with large differences across sub-fields and countries indicating the role of culture and expectation. Demographic data and social science research confirm that ability is not the issue; rather, the driver is lower expectations and evaluations of outsiders as leaders, thinkers, do-ers. Sexual harassment is also a serious problem. After reviewing the data and obstacles, I offer some ideas about how to mitigate obstacles to equal participation, full utilization of available talent being critical to the health of STEM professions.
Emily Smith,Colorado School of Mines
Transforming Introductory Physics Labs to Engage Students in Experimentation
At Cornell University, we transformed the labs for the calculus-based introductory physics sequences to align with the Laboratory Guidelines by AAPT. Like other lab transformations at a variety of institutions, the learning outcomes focus on developing students' experimentation and critical thinking skills. We have found that labs designed to teach experimentation do not impact students’ knowledge of physics content, but engage students in expertlike experimentation practices, improve students’ attitudes about experimental physics, and inform students of their biases when engaging with data. In this talk, I will use results from physics education research to provide recommendations for turning existing lab activities into activities that productively engage students in experimentation and critical thinking.
Deirdre Shoemaker, Georgia Tech
Numerical Relativity in the Age of Gravitational Wave Observations
The advent of gravitational wave astronomy has created opportunities to probe strong-field gravity as black holes merge. Numerical relativity provides the means to confront the measurements with theoretical prediction from general relativity, allowing us to interpret the sources of gravitational waves and to test whether general relativity is the theory governing these events. In this talk, I’ll discuss the role numerical relativity plays in the observed black hole binaries by LIGO and Virgo and will play as the gravitational wave detectors mature.
Jian Liu, University of Tennessee
Toy-model Quantum Materials Artificially Built for Capturing Emergent Phenomena
The interplay of charge, spin, and orbital degrees of freedom of electrons in quantum materials has led to some of the most intriguing emergent phenomena in physics. A square lattice of spin-half electrons described by the Hubbard Hamiltonian is one of the key model systems and playgrounds for some of the most outstanding and challenging problems, such as metal-insulator transition and quantum magnetism. A profound example is the cuprates with the CuO2 plane that are also known as the high-Tc superconductor. Yet, it has been difficult to find other materials that host similar physics and are controllable. We have recently designed and constructed a variety of artificial layered structures that host a Hubbard-like square lattice based on the IrO2 plane from the perovskite iridate. Their analogy to the CuO2 plane is remarkable given the fact that the spin-orbit coupling (SOC) of Ir is much larger than Cu. It turns out that the hidden influence of the strong SOC leads to rich physics yet to be uncovered. By tuning the layer dimension and the quantum confinement structure, we are able to realize real systems preserving the SU(2) symmetry of the Hubbard Hamiltonian, which, more importantly, is a hidden symmetry due to SOC. It allows us to observe and control the fluctuations predicted decades ago by the Mermin-Wagner theorem for the first time as a giant magnetic response of the 2D antiferromagnetic order to a sub-Tesla external field. It also allows us to unveil the spin-charge fluctuations in the Slater-Mott crossover regime. These results illustrate the power of atomic layering in building toy-model quantum materials and capturing the emergent behavior beyond the conventional methods.
James Stockton, Altamira Technologies
Careers in Data Science
Data Science is and always has been a varied, interdisciplinary field. Broadly a combination of statistics, computing, and puzzle solving, data science as a career path can provide many opportunities for anyone with strong analytical, mathematical, and technical skills. A clear grasp of what data science is and isn’t along with an appreciation of the breadth of its subject matter is a necessary first step in understanding if it’s a good fit your goals. Join me for a quick tour of the field and a discussion of a few interesting projects presented against the backdrop of my winding path from a Math/Physics Bachelor’s degree to a PhD in Astronomy to Lead Data Scientist for the Chief Data Office of the United States Air Force (SAF/CO).
Norman Mannella, the University of Tennessee
A photoemission spectroscopy view of emergent complex magnetic ordering in Cr1/3NbS2
Condensed Matter Physics (CMP) usually receives media coverage for its technological applications, as exemplified in modern devices based on nanotechnology and spintronics. Popular media seldom present the intellectual beauty of CMP. In fact, CMP represents an incredible vast playground that hosts many interesting states of matter and allows the study of many paradigms that underline our understanding of nature. One prominent example is the manifestation of collective properties. These are often referred to as “emergent”, since they are not predicted by the laws governing the individual entities of the system. The intellectual challenge is to understand how collective behaviors arise from the basic laws governing the interactions among the constituents. In CMP, collective behaviors often stem from the interplay and competition between several degrees of freedom such as charge, lattice, and spin. In this Colloquium, I will discuss some of our work on the chiral helimagnet Cr1/3NbS2, a material that hosts a unique spin texture known as chiral soliton lattice. Our results provide an example of how Photoemission Spectroscopy can reveal the importance of microscopic length-scales, and the interplay between electronic and spin degrees of freedom underpinning the macroscopic magnetic and transport behavior of complex materials.
Lisa Tran, Columbia University/Utrecht University
Shaping Particle Assemblies at the Interface of Liquid Crystals
Liquid crystals are ubiquitous in modern society. These materials are the basis of the modern display industry because of their unique properties. They can be manipulated with electric fields, can alter light, and are elastic fluids --- all properties that allow for liquid crystals to be engineered into a pixel. Despite advances in their technological applications, the structures formed by liquid crystals are yet to be completely understood. Since liquid crystal molecules tend to order with one another, they can respond to geometrical confinement. Geometrical constraints can create patterns and defects – localized, ``melted" areas of disorder that reduce system distortion and can drive the assembly of inclusions. I will present recent work in which defects are controlled by using microfluidics to create liquid crystal double emulsion droplets – confining the liquid crystal into spherical shells. Molecular configurations are controlled by the topology and geometry of the system and by varying the concentration of surfactants. Defect structures are examined through experiments and simulations. I will present recent work where nanoparticles are used in place of traditional surfactants to pattern them at the liquid crystal-water interface. This work opens up fundamental questions about the roles of bulk elasticity, surface forces, and chemical interactions in interfacial assembly and has the potential to dynamically template nanomaterials for the enhancement of liquid crystal-based optical devices and sensors. I will end by discussing future work.
Vesna Mitrovic, Brown University
Relativistic-quantum Magnets
Study of the combined effects of strong electronic correlations with spin-orbit entanglement represents a central issue in quantum materials research. Predicting emergent properties represents a huge theoretical problem since the presence of spin-orbit coupling implies that the spin is not a good quantum number. Existing theories propose the emergence of a multitude of exotic quantum phases, distinguishable by either local point symmetry breaking or local spin expectation values, even in materials with simple cubic crystal structure. Experimental tests of these theories by local probes are highly sought for. In the talk I will present our work on harnessing local measurements designed to concurrently probe spin and orbital/lattice degrees of freedom that provide such tests [1]. Our results, to be presented, establish that multipolar spin interactions [2] are an essential ingredient of quantum theories of magnetism in materials with both strong correlations and spin-orbit entanglement, in general.
[1] L. Lu et al., Nature Communications, 8, 14407 (2017).
[2] G. Chen, R. Pereira, and L. Balents, Phys. Rev. B, 82, 174440 (2010).
Melina Avila, Argonne National Laboratory
Stellar Processes and the Role of Nuclear Physics
The study of stellar processes and the synthesis of the elements in the universe is central to nuclear astrophysics. In order to understand the mechanisms responsible for stellar evolution and the creation of the chemical elements, astrophysical models require knowledge of key nuclear reactions taking place at different stellar environments. Recreating these stellar conditions in the laboratory is challenging. This is due to the typically small cross sections of these reactions and the experimental difficulties associated with low-intensity radioactive beams needed to study them. As a consequence, many of the reaction rates relevant for nuclear astrophysics are still unknown. In this talk, I will go over some of the recent advances in the capabilities of radioactive ion beam facilities and experimental techniques that have opened up new possibilities for the study of these astrophysically important reactions.