Colloquium
Fall 2023 Colloquia will be held in Room 307 of the Science and Engineering Research Facility (unless slated as virtual in the schedule below) on Mondays at 3:30 PM, EST.
August 28 |
Travis Humble |
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September 4 |
LABOR DAY HOLIDAY |
NO Colloquium |
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September 11 |
Miguel Madurga |
Tipping the Nuclear Scale: Beta-Decay Spectroscopy of (Very) Neutron Rich Nuclei |
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September 18 |
Lucas Platter |
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September 25 |
Takeshi Egami |
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October 2 |
Sam McKenzie |
From Scientist to Politician: Connecting Skills in Science and Politics |
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October 9 |
FALL BREAK |
NO Colloquium |
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October 16 |
Kevin Pitts |
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October 23 |
Rob Appleby |
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October 30 |
James A. Sauls |
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November 6 |
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November 13 |
Fan Zhang |
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November 20 |
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November 27 |
Stephen Taylor |
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December 4 |
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Discovery and Innovation in Quantum Science and Technology
The Quantum Science Center is a National Quantum Information Science Research Center headquartered at Oak Ridge National Laboratory. The purpose of the center is to discover and innovate in the field of quantum information science (QIS) to ensure American scientific leadership, economic competitiveness, and national security. QSC addresses this mandate by targeting three major scientific challenges 1) quantum simulation platforms for scientific discovery applications, 2) quantum sensing for real-world applications, and 3) topological quantum materials for new quantum devices. This talk will give an overview of the center's scientific goals as well as highlights of recent scientific impacts and their outcomes in each of these areas.
Tipping the Nuclear Scale: Beta-Decay Spectroscopy of (Very) Neutron Rich Nuclei
The continuing development of production and separation techniques allowing for the study of nuclei far away from the line of stability has spurred the low energy nuclear field for the past three decades. Large proton-neutron imbalances drive emerging exotic phenomena such as shape coexistence or halo distributions of nuclear matter, which in turn have helped refine our understanding of the nuclear interaction in the nuclear medium. In this talk I will discuss our experimental efforts using beta-delayed gamma and neutron spectroscopy to characterize the nuclear structure of neutron rich nuclei around doubly magic 132Sn. In particular I will concentrate in the role nucleon excitations across shell closures play in all three regions, driving both increasingly smaller decay-half lives and larger neutron branching ratios.
Effective Field Theories in Nuclear Physics
In the simplest electroweak nuclear reaction, the proton-proton fusion process, two protons combine into a deuteron while emitting a positron and a neutrino. It is the starting point of the chain of fusion reactions that generate the sun's energy. Only effective field theory can provide a high precision, first principles description of this process needed for modern stellar models. Such a calculation requires not only the nuclear interaction but also electroweak one- and two-body currents derived in a consistent effective field theory framework. I will review the effective field formalisms used to describe this process. I will explain how it depends on fundamental electroweak two-nucleon properties, and how these can be measured in complementary experiments. I will also discuss how the same tools as in proton-proton fusion can be used to describe electroweak processes involving so-called halo nuclei consisting of a tightly bound core and weakly bound valence nucleons.
Figuring Out Dynamic Correlation in Disordered Systems: Glass Transition and High-Temperature Superconductivity
Particle interactions create static and dynamic correlations even in seemingly disordered systems, and such correlations determine the properties, for instance through the fluctuation-dissipation theorem. Thus, figuring out such correlations is the key to understanding dynamic aperiodic matter (DAM), such as liquid, glass and itinerant electrons (Fermi liquid). However, correlations are often concealed and hard to detect by experiments, making the studies difficult, but interesting. I discuss two recent breakthrough examples by my research group, one on the glass transition and the other on the high-temperature superconductivity (HTSC). These two appear totally disconnected, but actually similar experimental approaches to dynamic correlation, the dynamic pair-distribution function determined by neutron/x-ray scattering or by simulation, brought us to the goal. In the case of the glass transition the discovery of density wave instability in liquid was the key [1], and for the HTSC the crucial step was the recognition that the electron dynamics affects electron correlation and the Bose-Einstein condensation [2].
1. T. Egami and C. W. Ryu, Frontiers in Materials, 9, 874191 (2022); J. Phys: Condens. Matter, 35, 174002 (2023).
2. T. Egami, Physica C, 613, 1354345 (2023).
From Scientist to Politician: Connecting Skills in Science and Politics
Plato is quoted as saying "If you do not take an interest in the affairs of your government, then you are doomed to live under the rule of fools." Scientists have long been underrepresented in seats of political power. The 117th Congress had only one physicist, one chemist, and one geologist. In my talk I will discuss what it is like transitioning from being a scientist managing maintenance on the Spallation Neutron Source at the Oak Ridge National Laboratory to a career in local and state politics, and how my scientific training has aided my decision making.
The Upgrade of the Large Hadron Collider, What the UK is Doing, and How We Are Telling People About It
The Large Hadron Collider at CERN is a two-beam proton synchrotron with a design energy per proton beam of 7 Tera-electron volts. It has been operating at CERN since 2010, with the high-profile success of finding the Higgs boson in 2012, thus completing the standard model of particle physics. The collider has been running since, and now preparations are being made to upgrade the collision rate (luminosity) of the proton collisions through the HL-LHC project. This upgrade will permit high precision measurements and more sensitive particle searches and involves considerable accelerator upgrade. This talk will review the LHC accelerator, the luminosity upgrade and present some of the UK's contributions to this project. Following this, several public engagement projects linked to the LHC are presented, which attempt to communicate the science of the LHC to a range of diverse audiences, using a range of diverse methods.
The Left Hand of the Electron
Sixty plus years ago parity violation by the weak force was demonstrated in experiments led by Chien-Shiung Wu on the asymmetry of electron currents emitted in the beta decay of polarized 60Co. The asymmetry reflects two broken symmetries - mirror reflection and time-reversal, the latter imposed by an external magnetic field. The same year Bardeen, Cooper and Schrieffer published the celebrated BCS theory of superconductivity, and soon thereafter P. W. Anderson and P. Morel proposed that the ground-state of liquid 3He (the light isotope of Helium) was possibly a BCS superfluid exhibiting spontaneously broken mirror reflection and time-reversal symmetries. Indeed superfluid 3He-A, discovered in 1972, is the realization of a quantum state of matter that violates both parity and time-reversal symmetry. Definitive proof of broken mirror symmetry in 3He-A came 41 years later from the observation of asymmetry in the motion of electrons in superfluid 3He-A.1 I discuss these and related discoveries, as well as the physics underlying anomalous electron transport in such quantum systems with broken mirror and time-reversal symmetries.2,3
- H. Ikegami, Y. Tsutsumi, & K. Kono, Chiral Symmetry in Superfluid 3He-A, Science, 341,59–62, 2013.
- O. Shevtsov & J. A. Sauls, Electrons & Weyl Fermions in Superfluid 3He-A, Phys. Rev. B, 94, 064511, 2016.
- V. Ngampruetikorn & J. A. Sauls, Anomalous Thermal Hall Effect in Chiral Superconductors, PRL 124, 157002 (2020). † Research supported by NSF grant DMR-1508730.