College of Arts and Sciences

Michelson Postdoc Prize Lecture 3 
 

2D electron-phonon physics from first-principles

Reduced dimensionality has consequences for phonons and electron-phonon interactions. So does the use of gates to dope the layer within the typical field-effect setups used in experiments. In this second lecture, I will describe density-functional perturbation approaches developed to explore those consequences. First-principles results will be supported by analytical models and intuitive explanation of the mechanisms at play. I will first present the general physics of polar-optical phonons, relevant for any semiconductor with more than one element. The energetics and electron-phonon interactions associated with those modes strongly depends on dimensionality and the environment.

Continue reading… Thibault Sohier (CNRS, Montpelier)

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Extraterrestrial Life: Are We the Sharpest Cookies in the Jar?
 

The search for extraterrestrial life is one of the most exciting frontiers in Astronomy. First tentative clues were identified  close to Earth in the form of the weird interstellar object `Oumuamua. Our civilization will mature once we find out who resides on our cosmic street by searching with our best telescopes for unusual electromagnetic flashes, industrial pollution of planetary atmospheres, artificial light or heat, 

Continue reading… Avi Loeb (Harvard)

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Helping students develop a growth mindset

Instructors often focus on content and pedagogical approaches to improve student engagement and learning in physics courses. However, students’ motivational characteristics can also play an important role in their engagement and success in physics. For example, students’ views about whether intelligence in physics is “fixed” or “malleable,” their sense of belonging in a physics class, and their self-efficacy can affect engagement and learning. I will discuss prior research studies that show how different types of interventions (e.g., social belonging and growth mindset) have improved the motivation and learning of all students,

Continue reading… Emily Marshman (Community College of Allegheny County)

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Electrons in 2D moiré superlattices

 
When two van der Waals materials of slightly different orientations or lattice constants are overlaid, a moiré pattern emerges. The moiré pattern introduces a new length scale, many times the lattice constant of the original materials, for Bragg scattering of Bloch electrons in each layer.  This gives rise to moiré minibands and rich emergent phenomena. In this talk I will discuss recent experiments on angle-aligned semiconductor heterobilayers, which exhibit remarkable correlated insulating states. I will also discuss the prospect of using moiré superlattices as a Hubbard model quantum simulator.  

Continue reading… Jie Shan (Cornell)

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Cellular mechanobiology: from screening to disease biophysics

Cells are materials and the physical properties of cells are critical for many physiological functions including how cells deform to circulate through the body and how cells resist mechanical stresses.  A major goal of the Rowat lab is to understand how cells maintain their physical properties and regulate them in response to external cues. To achieve this goal, we developed a high throughput platform to quantify cell deformability using knowledge of the physics of fluid flow through porous media. We recently conducted a screen of 1280 small molecules and discovered compounds that make cancer cells stiffer and less invasive. 

Continue reading… Amy Rowat (UCLA Integrative Biology)

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Interpretable Machine Learning of Quantum Emergence

Decades of efforts in improving computing power and experimental instrumentation were driven by our desire to better understand the complex problem of quantum emergence. However, the increasing volume and variety of data made available to us today present new challenges. I will discuss how these challenges can be embraced and turned into opportunities by employing machine learning. The rigorous framework for scientific understanding physicists enjoy through our celebrated tradition requires the interpretability of any machine learning essential. I will discuss our recent results using machine learning approaches designed to be interpretable from the outset.

Continue reading… Eun-Ah Kim (Cornell)

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Quantum Magic in Moiré Lattices

 
The remarkable properties of electrons moving through crystalline lattices, which brought us the semiconductor electronics revolution, continue to surprise us. Recently, electrons in artificial Moiré lattices have emerged as an extraordinary new platform. The simplest such moire material consists of a pair of graphene sheets twisted relative to one another. At a  “magic” angle of about 1 degree, a variety of phenomena, including strong-coupling superconductivity, is observed. In this talk, I will review this rapidly moving field and describe our theoretical ideas that invoke the geometry of quantum states and topological textures like skyrmions.

Continue reading… Ashvin Vishwanath (Harvard University)

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El Niño as a Topological Insulator: A Surprising Connection Between Climate, and Quantum, Physics

Symmetries and topology play central roles in our understanding of physics. Topology, for instance, explains the precise quantization of the Hall effect and the protection of surface states in topological insulators against scattering from disorder or bumps. However discrete symmetries and topology have up until now played little role in our thinking about the fluid dynamics of oceans and atmospheres. In this talk I show that, as a consequence of the rotation of the Earth that breaks time reversal symmetry,

Continue reading… Brad Marston (Brown University)

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Old and recent puzzles in flavour physics

Abstract: The origin of the hierarchical spectrum of quark and lepton masses observed in Nature is one of the long-standing open questions in particle physics. The recent hints of non-standard phenomena in low-energy flavour-changing processes have opened new directions in model building which might address this issue, and possibly connect it to the more general search for physics beyond the Standard Model. In this talk I will critically review these hints and highlight some of the new research directions they might suggest.

Continue reading… Gino Isidori (University of Zurich)

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Co-sponsored by the Program in Cell Biology and Department of Physics at CWRU

Kurt Hinterbichler (Physics) on the Nobel Prize in Physics; Ron Conlon (Department of Genetics and Genome Sciences) on the Prize in Chemistry; and Donald Anthony (Department of Medicine) on the Prize in Physiology or Medicine. 

The 2020 Nobel Prize in Physics was awarded half to Roger Penrose “for the discovery that black hole formation is a robust prediction of the general theory of relativity,” and half to Reinhard Genzel and Andrea Ghez “for the discovery of a supermassive compact object at the centre of our galaxy.” 

Continue reading… The 2020 Nobel Prizes in Science

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Zoom ID:  943 5186 3408, Passcode:  627107

https://cwru.zoom.us/j/94351863408

Theory of quantum anomalous Hall and axion insulators

Topological insulators are insulating crystals in which the electronic wave functions are topologically twisted in a certain sense. In recent years, a bewildering variety of types of topological insulators have been proposed. In this talk I will focus on two. First, I will introduce 2D quantum anomalous Hall insulators, which exhibit a quantum Hall effect without any external electric field. I will briefly discuss some computational efforts to identify new,

Continue reading… David Vanderbilt (Rutgers University)

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Reducing Nuclear Weapons and the Risk of Nuclear War

The Cold War ended 30 years, but nuclear weapons and the threat of nuclear war are still with us. Nine countries together deploy about 10,000 nuclear weapons, most with a destructive potential an order of magnitude greater than the bomb that destroyed Hiroshima. The United States and Russia, which together account for 90 percent of global stockpiles, each maintain about 1000 nuclear weapons on constant alert, ready to be launched in a few minutes. Arms control agreements that have constrained US and Russian arsenals and provided stability are on the brink of collapse,

Continue reading… Steve Fetter (School of Public Policy, University of Maryland)

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From cat skin to submarines – new materials that are a bit of a stretch.

Liquid crystals are self-organising fluids that are perhaps best known for their use in displays (LCDs) and much of the research in the area over the past 30 years or so has been focused on achieving faster switching and more complex images in flat panel TVs. However, such technology is now mature and for some time now new, exciting properties of liquid crystals that might lead to rather futuristic applications have been emerging.  

Continue reading… Helen Gleeson (University of Leeds)

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Traveling Waves in Brains

What we know about brain function has tracked technology.  The discovery of weak electrical signals from the surface of the scalp by Hans Berger in 1924 hinted at complex oscillatory activity.  Recordings from single neurons in the cerebral cortex by David Hubel and Torsten Wiesel in 1960 made possible by the tungsten microelectrode showed that each neuron in the visual cortex responds selectively to
visual stimuli.  The development of microelectrode arrays in the 21st century has revealed a mesoscopic
surprise:  The oscillations in the cortex are not synchronous,

Continue reading… Terry Sejnowski (Salk Institute)

Light Does Not Always Travel On The Light Cone

Despite the massless character of their associated particles, electromagnetic and gravitational radiation do not travel strictly on the null cone in curved spacetimes. This ‘tail’ phenomenon was first uncovered by the mathematician Jacques Hadamard in his study of partial differential equations; and introduced to physicists by Robert Brehme and Bryce DeWitt — they pointed out that there is a novel self-force on electromagnetically charged systems arising from this inside-the-light-cone signal. The gravitational counterpart of this self-force (derived by Mino, Misao Sasaki, Tanaka; and also by Quinn and Wald) is of relevance to understanding gravitational waves generated by compact bodies orbiting near supermassive black holes,

Continue reading… Yi-Zen Chu (National Central University, Taiwan)

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Electronic Transport in Strain-Engineered Graphene 

There is wide interest in using strain-engineering to modify the physical properties of 2D materials, for both basic science and applications. Deformations of graphene, for example, can lead to the opening of band gaps, as well as the generation of pseudo-magnetic fields and novel electronic states. We demonstrate how controllable, device-compatible strain patterns in graphene can be engineered by depositing graphene on corrugated substrates. We discuss several techniques for creating corrugated substrates, focusing on periodic spherical curvature patterns in the form of closely packed nanospheres.

Continue reading… Nadya Mason (University of Illinois, Urbana-Champaign)

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Modeling Mechanical Actuation in Liquid Crystal Polymers

Liquid crystal polymer networks undergo reversible shape change in response to any stimulus that affects their nematic order, allowing them to flex like artificial muscles. These soft actuators can be fabricated as thin films, surface coatings, or 4D printed solids and have potential applications in soft robotics, biomedical devices, microfluidics, and sensors. Trajectories for shape change are “programmed” by patterning the nematic director when the polymer is cross-linked. Actuation is induced when the strength of nematic order is modulated by stimuli such as a change of temperature,

Continue reading… Robin Selinger (Advanced Materials and Liquid Crystal Institute, Kent State Univ)

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The Information Paradox in the Age of Holographic Entanglement Entropy

The black hole information paradox — whether information escapes an evaporating black hole or not —  remains one of the greatest unsolved mysteries of theoretical physics. The apparent conflict between validity of semiclassical gravity at low energies and unitarity of quantum mechanics has long been expected to find its resolution in the deep quantum gravity regime. Recent developments in the holographic dictionary and in particular its application to entanglement, however, have shown that a semiclassical analysis of gravitational physics has a hallmark feature of unitary evolution.

Continue reading… Netta Engelhardt (MIT)

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Data Science in Art: Discerning the Painter’s Hand

Ken Singer, Ambrose Swasey Professor of Physics

with

Michael Hinczewski, Warren E. Rupp Associate Professor of Physics

Ina Martin, Senior Research Associate (Physics), Adjunct Faculty in the Department of Materials Science and Engineering

Betsy Bolman, Elsie B. Smith Professor in the Liberal Arts and Chair, Department of Art History and Art 

The Departments of Art History and Art, Physics, Materials Science and Engineering,

Continue reading… Ken Singer et al (CWRU Physics and Art History)

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Challenging the Standard Model With High-Energy Neutrinos

Particle physicists are living in interesting times. We are faced with the paradox of a highly predictive theory –the Standard Model — that is filled with patterns that are hard to explain. We are also faced with “known unknowns,” like dark matter. Right now, neutrinos are the only particles exhibiting beyond Standard Model behavior, seen in the flavor transitions called neutrino oscillations, which are due to neutrino mass. This is an important clue towards a larger theory. Building on this, I am interested in what other types of flavor transitions neutrinos may have due to new particles,

Continue reading… Carlos Arguelles Delgado (Harvard University)

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Topological Quasiparticles: Magnetic Skyrmions

The field of spintronics, or magnetic electronics, is maturing and giving rise to new subfields [1].  An important ingredient to the vitality of magnetism research in general is the large complexity due to competitions between interactions crossing many lengthscales and the interplay of magnetic degrees of freedom with charge (electric currents), phonon (heat), and photons (light) [2].  One perfect example, of the surprising new concepts being generated in magnetism research is the recent discovery of magnetic skyrmions.  Magnetic skyrmions are topologically distinct spin textures that are stabilized by the interplay between applied magnetic fields,

Continue reading… Axel Hoffmann (University of Illinois, Urbana-Champaign)

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Decoding Primordial Fluctuations
 
All the information we will ever obtain from the primordial universe is imprinted in the spatial correlations of fluctuations at the hot Big Bang. I will explain how an influx of ideas from various areas of fundamental physics is providing us with new conceptual and practical tools to decode the physics of these primordial fluctuations. A thorough understanding of the fluctuations will give us insight into particle physics at the highest energies and may provide a window into the nature of spacetime itself.

Continue reading… Guilherme Pimentel (Amsterdam, Leiden)