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Colloquium

Unless otherwise noted, the physics colloquia are held in Room 307 of the Science and Engineering Research Facility. Refreshments are served at 3:00 p.m. with the talk following at 3:30. Please note: beginning in Fall 2017 colloquia were not webcast or recorded. The department is evaluating new cost models and options.

The Spring 2017 colloquia are available here, with the archives from previous semesters available Webcast archives.

Spring 2018 Schedule
Date
Speaker
Title
Host

January 22

Gerardo Ortiz
Indiana University

The Majorana Mysteries

Cristian Batista

January 29

Alison Sweeney
University of Pennsylvania

Eye Patches: the Evolution of Novel Soft Matter

Max Lavrentovich

February 5

Gang Cao
University of Colorado

The Power of Strong Spin-Orbit Interactions:Challenges and Opportunities in Iridates

Haidong Zhou

February 12

Robert Pattie
Los Alamos National Laboratory

UCNtau: A Magneto-Gravitational Trap Measurement of the Free Neutron Lifetime

Yuri Kamyshkov

February 19

Steven Tomsovic
Washington State University

Quantum Chaos: Origins and Contemporary Research

Norman Mannella

February 26

Brian Nord
Fermilab

Implications and Challenges for the Application of Artificial Intelligence in Physics and in Society

Sowjanya Gollapinni

March 5

Susan Blessing
Florida State University

Prepare All Students for Success

Nadia Fomin

March 12

Spring Break

March 19

Wanli Yang
Lawrence Berkeley National Laboratory

A Soft X-ray Journey into Batteries: How Fundamental Spectroscopy Helps Out Practical Energy Storage Devices

Norman Mannella

March 26

Michelle Dolinski
Drexel University

Antimatter, Neutrinos, and the Search for Rare Events

Nadia Fomin

April 2

Nian Sun
Northeastern University

Integrated Ferroics for Frequency-Agile Sensing, Power, RF. Microwave and mm-Wave Electronics

Jian Liu

April 9

Leah Broussard
Oak Ridge National Laboratory

The Dark Side of the Neutron

Yuri Kamyshkov

April 16

Mark P.M. Dean
Brookhaven National Laboratory

X-ray Vision of Spins, Charges and Orbitals in Quantum Materials

Jian Liu

April 23

Physics Honors Day

Honoring Dr. Won Namkung (PhD, 1977) with the department's Distinguished Alumnus Award


Abstracts
January 22
Gerardo Ortiz, Indiana University

The Majorana Mysteries

On March 25th 1938 at the age of 32 years Ettore Majorana vanished, under mysterious circumstances, without leaving a trace. Only recently his name re-emerged as the Majorana fermion, a quasi-particle excitation that represents it own anti-quasi-particle, has been claimed to be detected by several experimental groups. Majorana fermions dance in a superfluid background. They have the potential to make quantum computers robust because of the special topological property of non-Abelian braiding, generated whenever Majorana fermions are transported around each other. But, what property distinguishes topologically trivial from non-trivial superfluids, supposedly hosting Majorana fermions? What is the meaning and fate of such excitations in closed, number conserving, interacting fermionic superfluids? I will attempt to answer these questions from both basic physics principles and concrete model perspectives. In particular, I will discuss a novel and realistic route to topological superfluidity realizable in repulsive ultracold alkaline-earth atomic systems, and will propose several novel experimental probes to unveil the topological superfluid state.


January 29
Alison Sweeney, University of Pennsylvania

Eye Patches: the Evolution of Novel Soft Matter

Life on Earth constitutes the most sophisticated iterations in the known universe of what physicists classify as soft matter. Research in my group focuses on learning the physical rules of soft matter self-assembly phenomena via the evolutionary processes by which they arose over Earth’s history. In this view of life as soft matter, evolution, with its own formal rules and algorithms, governs the appearance and diversification of novel forms of soft matter. The field of soft matter was until very recently restricted to analytical consideration of simpler systems like isotropically interacting colloids and cross-linked polymers such as rubber. Our approach allows us to understand soft materials in a nuanced manner that would be inaccessible from more top-down analytical approaches. In this colloquium, I will present the most detailed test case of this perspective to date: the evolutionary appearance of spherical, gradient-index lenses in squids. This complex optical material, first described in theory by Maxwell in 1854, emerges from 5-nm spheroidal proteins via patchy colloidal physics. The lens requires stable, transparent materials throughout the span of packing fractions (from near zero to near one); accordingly, the lens proteins exploit the entire patchy colloidal phase space, and our work is the first demonstration of many of these colloidal organizations in nature. The self-assembling squid proteins exhibit structural nuances that have also been predicted by self-assembly theories, such that the evolved system may provide helpful insight to engineers designing systems at similar lengthscales. Conceptually related projects such as the structure and function of quasi-ordered optics for camouflage of midwater squid eyes will also be discussed


February 5
Gang Cao, University of Colorado at Boulder

The Power of Strong Spin-Orbit Interactions: Challenges and Opportunities in Iridates

Effects of spin-orbit interactions in condensed matter are an important and rapidly evolving topic. Strong competition between spin-orbit, on-site Coulomb and crystalline electric field interactions in iridates drives exotic quantum states that are unique to this group of materials. This colloquium offers a brief review of current experimental studies of iridates [1] and emphasize discrepancies between experimental confirmation and theoretical proposals that address superconducting, topological and quantum spin liquid phases. It then reports our most recent study on electrical-current controlled behavior in iridates [2]. Electrical control of structural and physical properties is a long-sought, but elusive goal of contemporary science and technology. This work demonstrates that a combination of strong spin-orbit interactions and a canted antiferromagnetic Mott state is sufficient to attain that goal and points the way to novel possibilities for functional materials and devices.

References:
1. "The Challenge of Spin-Orbit-Tuned Ground-States in the Iridates: A Key Issues Review", Reports on Progress in Physics (forthcoming), Gang Cao and P. Schlottmann http://arxiv.org/abs/1704.06007
2. "Electrical Control of Structural and Physical Properties via Spin-Orbit Interactions in Sr2IrO4", G. Cao, J. Terzic, H. D. Zhao, H. Zheng, Peter Riseborough, L. E. DeLong, Phys. Rev. Lett. 120, 017201 (2018); DOI: https://doi.org/10.1103/PhysRevLett.120.017201; Editor’s Suggestion


February 12
Robert Pattie, Los Alamos National Laboratory

UCNtau: A Magneto-Gravitational Trap Measurement of the Free Neutron Lifetime

The neutron is the simplest nuclear system that can be used to probe the structure of the weak interaction and search for physics Beyond the Standard Model. Measurements of neutron β-decay observables are sensitive to scalar and tensor interactions in the weak force which are not present in the Standard Model. The lifetime of the neutron τn is an important parameter for Big-Bang Nucleo-synthesis models, solar fusion models, neutron star cooling, and absolute neutrino scattering cross-sections, and can be used to test the unitarity of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. Presently, the two typical methods used to measure the neutron lifetime, cold neutron beam measurements and stored ultracold neutron (UCN) measurements, disagree by roughly 4τ. This discrepancy motivates the need for new measurements with complementary systematic uncertainties to previous efforts.

The UCNτ experiment uses an asymmetric magneto-gravitational UCN trap with in situ counting of surviving neutrons to measure the neutron lifetime. Previous bottle experiments confined UCN in a material storage vessel creating a significant correction due to losses resulting from the material UCN interactions. The magnetic and gravitational confinement of the UCN minimizes losses due to material interactions. Additionally, UCNτ uses a detection system that is lowered into the storage volume which avoids emptying the surviving UCN into an external detector. This minimizes any possible transport related systematics. This in situ detector also enables counting at various heights in the vessel, which provides information on the trapped UCN energy spectrum, quasi-bound orbits, and possible phase space evolution. I will present the physics motivation for precision neutron physics, a description of the UCNτ experiment, the results of data collected during the 2016-2017 accelerator cycle which resulted in a value of τn=877.7±(0.7) stat (+0.3/−0.1) sys in agreement with previous material bottle UCN storage experiments, and the path toward a 0.1 s accuracy in measurement of τn.


February 19
Steve Tomsovic, Washington State University

Quantum Chaos: Origins and Contemporary Research

Einstein essentially pointed out in 1917, before Bohr's Correspondence principle and quantum mechanics actually arrived on the scene, that chaotic dynamics poses fundamental difficulties for understanding the relationship between classical and quantum mechanics. Research along these lines has come to be called colloquially, quantum chaos. Although various foundational work was being done beforehand, it’s origin is generally traced to Wigner’s introduction of random matrix theory for the purpose of understanding slow neutron resonances in heavy nuclei, which is a strongly interacting many-body system. Later Bohigas, Giannoni, and Schmit conjectured that even simple chaotic dynamical systems with positive Lyapunov exponents would have spectral and eigenstate properties given by random matrix theory.

The paradox that chaos is essentially absent from quantum mechanics, yet has to emerge according to the Correspondence principle is one of the main motivations of quantum chaos research. Most often, the research is focussed on either studying how chaos can emerge from quantum dynamics or perhaps more productively, what novel quantum mechanical phenomena exist whose origin can be traced to the fact that the classical counterpart is dynamically chaotic. The main theoretical methods of analysis are random matrix theory, semiclassical theory, and effective field theories of disordered systems. After discussing some history and context for quantum chaos, I will give a brief overview of two contemporary research projects in which I am involved, just to give a flavor of where the field is today. The first is an application in quantum information theory describing how much entanglement exists in bi-partite systems whose component subsystems are chaotic with tunable interaction strength. There is a universality in the transition from unentangled eigenstates to essentially fully entangled eigenstates as the strength increases. The second example is oriented toward ultracold atoms in optical lattices. It is shown that a semiclassical theory, which goes beyond the heavily used truncated Wigner approximation, accurately captures many-body interferences in the mean-field solutions of Bose-Hubbard systems.


February 26
Brian Nord, Fermilab

Implications and Challenges for the Application of Artificial Intelligence in Physics and in Society

The increased availability of large data sets and advancements in artificial intelligence (AI) algorithms have revolutionized the role of data in both commercial industries and academic research. Today, AI permeates multiple industries, from self-driving vehicles and entertainment choices to cancer-detection and criminal justice. Moreover, in the last few years, it has had substantial impacts in molecular chemistry, particle physics, and more recently astronomy. AI, and its subfields, like machine learning, are more than likely here to stay. But, what are these algorithms really doing, and are they ethically implemented?

We’ll discuss these topics, as well as the theory of deep learning, and its application to modern astronomical surveys, which are providing data sets that are unprecedented in size, precision, and complexity. Recent work with convolutional neural networks and strong gravitational lensing intimate the long-term potential for deep learning and its application to larger challenges in cosmology. However, AI is not without its own shortcomings. We’ll discuss the barriers to deep learning having its highest impact on science.


March 5
Susan Blessing, Florida State University

Prepare All Students for Success

The FSU undergraduate physics program was one of the case studies in the Joint Task Force on Undergraduate Physics Programs (J-TUPP) report. I will review the findings of the report and discuss the changes we have made to help students be more successful during their time at FSU and afterwards.


March 19
Wanli Yang, Lawrence Berkeley National Laboratory

A Soft X-ray Journey into Batteries: How Fundamental Spectroscopy Helps Out Practical Energy Storage Devices

Energy storage is a critical but weak link in the chain of modern sustainable energy applications. The pressing demand of improved energy storage systems, especially for electric vehicles and green-grid, calls for speedy strategies for developing materials based on advanced analytic tools. Synchrotron based soft x-ray core-level spectroscopy is one of such incisive tools that probes the key electronic states pertaining to the performance of batteries.

This colloquium starts with introductions on the challenges of batteries for various kind of energy storage requirements. Problems associated with critical electron states in the vicinity of the Fermi level will be emphasized. Soft X-ray core-level spectroscopy, including soft X-ray absorption, emission, and resonant inelastic X-ray scattering will then be introduced in line with the problem-oriented discussions. We will then discuss some recent achievements on using soft X-rays to reveal critical electronic structure information associated with materials for improving battery performance. We show that soft X-ray spectroscopy (i) reveals the key electron states that could trigger combined functionality of organic battery binder [1]; (ii) quantitatively determines the detrimental effect in battery cycling life time[2]; (iii) clarifies intriguing interstitial water effect of battery electrodes [3]; and (iv) reveals the novel reduction and oxidation reactions in battery electrodes in both transition-metals [4] and anions [5], which cannot be accessed by any other technique so far. Optionally, we will discuss some state-of-the-art soft x-ray in-situ/operando experiments of electrochemical devices [6], if there is time/interest.

This presentation itself will not focus on technical discussions for a specific scientific topic in battery materials, instead, the focus here is to showcase the soft X-ray spectroscopy for studying relevant electron states that are associated with a practical device, in hope that this could be taken as an example on core-level soft x-ray spectroscopy for material researches, and inspire further thoughts and other topics in material physics.

Selected References with direct DOI links:

  1. Liu et al., Adv. Mater. 2011 doi:10.1002/adma.201102421
  2. Qiao et al., Nano Energy 2015 doi:10.1016/j.nanoen.2015.06.024
  3. Liu et al., JACS (2012) doi:10.1021/ja303225e; Wu et al., JACS (2017) doi:10.1021/jacs.7b10460
  4. Firouzi et al., Nat. Comm. (2018) doi:10.1038/s41467-018-03257-1
  5. Gent et al., Nat. Comm. (2017) doi:10.1038/s41467-017-02041-x
  6. Liu et al., Nat. Comm. (2013) doi:10.1038/ncomms3568; Liu et al., Adv. Mater. (2014) doi:10.1002/adma.201304676

March 26
Michelle Dolinski, Drexel University

Antimatter, Neutrinos, and the Search for Rare Events

Tiny, weakly interacting neutrinos are difficult to study in the laboratory, but studying neutrinos can give us a better understanding of the origin and structure of the universe. In particular, the study of neutrino mass is a direct probe into new physics. It is an experimentally open question whether or not neutrinos have distinct antiparticles, and the answer is directly related to the origin of neutrino mass. The observation of neutrinoless double beta decay, a non-Standard Model version of a rare nuclear process, would prove that neutrinos are their own antiparticles. I will report on the status and recent results of the EXO-200 experiment, a liquid xenon time projection chamber that uses 100 kg of enriched xenon to search for neutrinoless double beta decay of Xe-136. I will also discuss research toward nEXO, a planned next generation neutrinoless double beta decay experiment.


April 2
Nian Sun, W.M. Keck Laboratory for Integrated Ferroics, & ECE Department, Northeastern University, Boston

Integrated Ferroics for Frequency-Agile Sensing, Power, RF. Microwave and mm-Wave Electronics

The coexistence of electric polarization and magnetization in multiferroic materials provides great opportunities for realizing magnetoelectric coupling, including electric field control of magnetism, or vice versa, through a strain mediated magnetoelectric coupling in layered magnetic/ferroelectric multiferroic heterostructures [1-9]. Strong magnetoelectric coupling has been the enabling factor for different multiferroic devices, which however has been elusive, particularly at RF/microwave frequencies. In this presentation, I will cover the most recent progress on new integrated magnetoelectric materials, magnetoelectric NEMS (nanoelectromechanical system) based sensors and antennas. Specifically, we will introduce magnetoelectric multiferroic materials, and their applications in different devices, including: (1) novel ultra-compact RF NEMS acoustic magnetoelectric antennas immune from ground plane effect with < λ0/100 in size, self-biased operation and potentially 1~2% voltage tunable operation frequency; (2) ultra-sensitive RF NEMS magnetoelectric magnetometers with ultra-low noise of ~1pT/Hz1/2 at 10 Hz for DC and AC magnetic fields sensing, which are the most sensitive room temperature nanoscale magnetometers, and (3) voltage tunable inductors, phase shifters, isolating bandpass filters, etc. These novel magnetoelectric devices show great promise for applications in compact, lightweight and power efficient sensors, antennas and tunable components for radars, communication systems, biomedical devices, IoT, etc.

Reference: 1. N.X. Sun and G. Srinivasan, SPIN, 02, 1240004 (2012); 2. J. Lou, et al., Advanced Materials, 21, 4711 (2009); 3. J. Lou, et al. Appl. Phys. Lett. 94, 112508 (2009); 4. M. Liu, et al. Advanced Functional Materials, 21, 2593 (2011); 5. T. Nan, et al. Scientific Reports, 3, 1985 (2013); 6. M. Liu, et al. Advanced Materials, 25, 1435 (2013); 7. M. Liu, et al. Advanced Functional Materials, 19, 1826 (2009); 8. Ziyao Zhou, et al. Nature Communications, 6, 6082 (2015). 9. T. Nan, et al. Nature Communications 8, 296 (2017).


April 9
Leah Broussard, ORNL

The Dark Side of the Neutron

The lifetime of the free neutron is a puzzle. Its decay should be described by our model of the electroweak interaction; however, the neutron apparently disappears at a faster rate (from "bottle" measurements) than expected given the rate of decay particles measured (from "beam" measurements). While this discrepancy might be explained by an experimental error, alternate channels for the neutron's disappearance could be responsible. I will discuss the possibility of a "dark decay" branch of the neutron, and recent experimental limits that constrain this possibility. I will also discuss the possibility of neutron oscillations into a dark, "mirror" neutron state and previous attempts to search for this transformation, including some controversial reported results. Finally, I will introduce a new proposed experiment at Oak Ridge which could give an unambiguous indication of mirror neutron oscillations.


April 16
Mark P.M. Dean, Brookhaven National Laboratory

X-ray Vision of Spins, Charges and Orbitals in Quantum Materials

The electrons in traditional metals and semiconductors tend to drift through the lattice as independent, non-interacting particles. Theories based on this behavior successfully explain many materials and form the bedrock of the transistor and computers. Quantum materials is a catch all term for systems in which strong interactions between the charge, spin and orbital degrees of freedom of the electrons cause these rules to break down yielding magnetism, superconductivity or other types of novel order. Probing how this happens is, however, often challenging. In this talk, I will describe a novel x-ray technique called resonant inelastic x-ray scattering (RIXS) and how it can be used to probe the behavior of electrons in quantum materials with outstanding sensitivity.

We will show how RIXS can observe the spontaneous ordering of the electrons in copper oxide superconductors [1], quantify the modification of electronic orbitals within heterostructures [2] and track changes in magnetism in ultra-fast transient states [3].

References

  • H. Miao et al., Proc. Natl. Acad. Sci. U.S.A 114, 12430–12435 (2017); H. Miao et al., H. Miao et al., Phys. Rev. X
  • G. Fabbris et al., Phys. Rev. Lett. 117, 147401 (2016); G. Fabbris et al., Phys. Rev. Lett. 118, 156402 (2017); L. Hao et al., Phys. Rev. Lett. 119, 027204 (2017)
  • M. P. M. Dean et al., Nature Materials 15, 601-605 (2016)

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