SPRING 2023
PHYSICS Colloquium
March 23, 2023, Thursday, 3:30pm CST
Where: 110 Physical Sciences
Reception: PS 147, 3:00pm
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DR. MARK DEAN
Condensed Matter Physics and Materials Science Department
Brookhaven National Lab
X-RAY VISION OF ELECTRON BEHAVIOR IN QUANTUM MATERIALS
ABSTRACT: Many of the most remarkable properties of quantum materials come from the interplay of multiple charge, orbital, and spin degrees of freedom. Probing all of these with a single technique is consequently highly desirable. In this talk, I will describe the experimental technique of resonant inelastic x-ray scattering (RIXS) and its unique capabilities to probe all these degrees of freedom even in atomically thin samples or at ultrafast timescales. This will be illustrated by some of our work on iridium-based magnetic materials including the discovery of a novel “antiferromagnetic excitonic insulator” [1] and efforts to control magnetism via ultrafast laser excitation [2-3]. I will finish by outlining future research opportunities in this area.
[1] Antiferromagnetic excitonic insulator state in Sr3Ir2O7, D. G. Mazzone et al., Nature Communications 13, 913 (2022)
[2] Laser-induced transient magnons in Sr3Ir2O7 throughout the Brillouin zone
D. G. Mazzone, et al., Proceedings of the National Academy of Sciences 118, e2103696118 (2021)
[3] Ultrafast energy and momentum resolved dynamics of magnetic correlations in photo-doped Mott insulator Sr2IrO4, M. P. M. Dean et al., Nature Materials 15, 601–605 (2016)
PHYSICS Colloquium
February 28, 2023, Tuesday, 3:30pm CST
Where: 110 Physical Sciences
Reception: PS 147, 3:00pm
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DR. JULIUS DE ROJAS
Postdoctoral Research Associate
Durham University
Current(less) Trends in Spintronics: Magnetoionics & Magnonics for Energy Efficient Computing
ABSTRACT: The invention of the transistor 75 years ago kicked off a revolution in computing, and with it immense technological and societal progress. However, quickly approaching fundamental hurdles, including power constraints and manufacturing limitations, have left conventional computing hardware struggling to maintain energy efficiency as dimensions continue to shrink. To meet these challenges, hardware must move towards energy efficient approaches to data storage and processing. In this talk, I will overview the challenges facing conventional computing structures and discuss how emerging spintronic approaches such as magneto-ionics and magnonics provide a potential path forward. I will overview our work in magneto-ionics, an emerging subfield of spintronics in which material properties can be tuned by moving ions into and out of magnetic material under low-power, and I will discuss novel functionalities in oxygen-based and nitrogen-based systems. I will then conclude with my recent research in magnonics, in which spin-waves are used transport and process data and discuss our work on extending artificial spin ice systems to pseudo-3D structures.
PHYSICS Colloquium
February 23, 2023, Thursday, 3:30pm CST
Where: 110 Physical Sciences
Reception: PS 147, 3:00pm
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DR. JINSONG XU
Postdoctoral Fellow
Johns Hopkins University
DISCOVERY OF NEW SPIN CURRENT PHENOMENA IN QUANTUM MATERIALS
ABSTRACT: Spin, the basis of spintronic devices in information technology, provides new and effective ways to probe and control the state of quantum materials. A pure spin current has the advantage of delivering spin angular momentum with reduced energy dissipation and holding promise for the next generation devices. In this talk, I describe spin current phenomena and our discoveries in the following two areas: Vector spin Seebeck effect (SSE) and spin swapping effect in noncollinear antiferromagnets (AFs): With negligible stray field and high frequency dynamics, AFs hold promise for high-speed and high-density storage devices. Most studies to date have been conducted in collinear AF systems, which severely restrict the spintronic phenomena. I will describe our recent studies on noncollinear AF insulators LuFeO3 and LaFeO3 [1,2], and the discovery of vector SSE including both longitudinal and transverse SSE, where the latter is absent in collinear systems and never observed before. We identified spin swapping effect as the mechanism for transverse SSE, likely from the noncollinear spin structures. These noncollinear AF insulators expand new realms for exploring spin current phenomena and provide a new route to low-field AF spintronics and magnonics. Seebeck-contrast measurements for magnon Hall effect (MHE): MHE in topological magnon insulators with strong Berry curvature effects, the analogue of the well-known anomalous Hall effect (AHE) in ferromagnetic metals, was first discovered in Lu2V2O7 in 2010. To date, MHE could only be detected by the challenging thermal Hall conductivity measurements. We have recently demonstrated a new and simpler method of electrical detection of MHE [3]. Moreover, we established a protocol of Seebeck-contrast measurement to differentiate among MHE, SSE and anomalous Nernst effect (ANE), and found that there is spin current associated with MHE. The electrical method for MHE paved ways for exploring new topological magnon insulators and their applications for spintronics.
PHYSICS Colloquium
February 16, 2023, Thursday, 3:30pm CST
Where: 110 Physical Sciences
Reception: 3:00pm in PS 147
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DR. VEDRAN BRDAR
Senior Research Fellow
CERN
NEUTRINOS AT PRESENT AND NEAR FUTURE EXPERIMENTS: STANDARD MODEL AND BEYOND
ABSTRACT: Despite having already been awarded a Nobel Prize, the golden age of neutrino oscillation experiments is only just beginning. In addition to solving the remaining puzzles in the standard three-neutrino framework, neutrino experiments are also sensitive to new physics effects that could appear in the process of neutrino production, propagation and/or detection. In the first part of this talk, I will introduce a novel manifestation of physics beyond the Standard Model, testable already at present-day accelerator based experiments such as NOvA and T2K, which is based on the fact that neutrino mixing parameters at the scale of neutrino production and detection do not necessarily need to coincide. This will be shown in the context of a particular neutrino mass model within which large renormalization group effects occur. In the second part of the talk, I will address the anomalous findings of the MiniBooNE experiment, which have been touted as either a possible hint for new physics, or a reflection of our poor understanding of neutrino-nucleus interactions. I will address this anomaly by critically examining a number of theoretical uncertainties affecting the event rate prediction at MiniBooNE, focusing on charged current quasielastic events, single-photon events, and those from neutral pion decay. This will allow me to discuss the dependence of the statistical significance of the anomaly on such uncertainties. I will also critically examine new physics explanations of MiniBooNE anomaly, focusing on eV-scale sterile neutrinos. In the last part of the talk, I will discuss the potential of DUNE, the leading US-based neutrino experiment for the next decade, for probing light dark sectors, and will take axion-like particles (ALPs) as an example. At DUNE, the high-intensity proton beam impinging on a target will not only produce neutrinos, but will also yield copious amounts of photons, allowing for photophilic ALPs to be produced with high intensity. I will show that a wide range of ALP parameter space, including regions unconstrained by existing bounds, will be explored at DUNE.
PHYSICS Colloquium
February 14, 2023, Tuesday, 3:30pm CST
Where: 110 Physical Sciences
Reception: 3:00pm in PS 147
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DR. DOOJIN KIM
Physics & Astronomy
Texas A&M University
MAGIC CARPET RIDE TO A NEW PHYSICS WORLD
ABSTRACT: While the Standard Model is a successful description for mutual interactions and relationships of elementary particles, there are still issues and phenomena such as dark matter and non-zero mass of neutrinos that are unexplained by the Standard Model, hence motivating new physics beyond the Standard Model. Many theoretical considerations and experimental efforts thus far suggest that many of the related new particles are very weakly or feebly interacting with known particles and they may be sitting in "blind" spots that existing and near-future experiments across colliders, neutrino facilities, and cosmic-frontier experiments can be sensitive to. A possible way of exploring new physics scenarios in these experiments is to revisit familiar physics ideas and take a closer look at their overlooked physical implications. In this context, we will discuss three examples, energy peak, charged mesons, and superlight dark matter. For the energy peak, we will argue that energy, a Lorentz-variant quantity, has a subtle but hidden invariance property and discuss how it can be used in high energy physics experiments, especially at colliders. For the charged mesons, we will show that charged mesons can be great but overlooked sources of new physics particles and discuss their physics applications in various experiments including the beam-focused neutrino experiments and the complementarity among them. Finally, we will briefly discuss a new idea to detect superlight dark matter using a graphene Josephson Junction-based bolometer device that is sensitive to the sub-meV scale energy deposit, and related physics opportunities.
PHYSICS Colloquium
February 9, 2023, Thursday, 3:30pm CST
Where: 110 Physical Sciences
Reception: 3:00pm in PS 147
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DR. GILLY ELOR
Mainz Institute for Theoretical Physics
Johannes Gutenberg University
MESOGENESIS
ABSTRACT: What is the Universe made of? Why do complex structures such as ourselves exist? I will present a proposal for simultaneously solving both these outstanding mysteries of particle physics: Mesogenesis, which generates both the observed asymmetry of matter over antimatter in the early Universe, and the population of Dark Matter particles. Mechanisms of Mesogenesis generate an asymmetry through strongly coupled Standard Model particles known as mesons. Excitingly, this makes Mesogenesis highly testable and it can be searched for at the Large Hadron Collider, electron positron colliders, and even large volume neutrino experiments. Many experimental searches are currently underway to test Mesogenesis and I will present an overview of these exciting ongoing efforts.
PHYSICS Colloquium
February 7, 2023, Tuesday, 3:30pm CST
Where: 110 Physical Sciences
Reception: PS 147, 3:00pm
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DR. RAYMOND CO
University of Minnesota
AXION DYNAMICS PUTS A NEW SPIN ON SOLVING COSMOLOGICAL MYSTERIES
ABSTRACT: The QCD axion is a hypothetical particle proposed to solve the strong CP problem and thus explain why neutrons have a vanishing electric dipole moment. The axion has long been known to be an excellent candidate for dark matter, which must exist to explain the motion of stars and galaxies. We have discovered novel axion dynamics in the early universe, called axion rotations, which may naturally occur as a result of quantum gravity effects and cosmic inflation. This dynamic was overlooked in the extensive literature but has profound consequences. In this talk, I will discuss the example where axion rotations can simultaneously generate axion dark matter and the observed excess of matter over antimatter in the Universe. Remarkable, rich phenomenology automatically arises with sharp, distinct, and correlated predictions. These include specific axion properties, unique gravitational wave signals, and correlated mass scales of supersymmetry and neutrinos. Models with decaying heavy axions may be tested by neutrino experiments such as DUNE and long-lived particle searches at the LHC. Thus far, axion rotations have added fuel to experimental efforts and paved new theory research avenues, opening up resolutions to the deepest cosmological mysteries with discoverable signatures.
PHYSICS Colloquium
January 26, 2023, Thursday, 3:30pm CST
Where: 110 Physical Sciences
Reception: PS 147, 3:00pm
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DR. NICKOLAS SOLOMEY
Wichita State University
A POSSIBLE NEUTRINO AND DARK MATTER
EXPERIMENT IN SPACE
ABSTRACT: We are building a test detector capable of operating in space with the possibility to do improved studies of solar neutrinos and dark mater searches in space. This detector prototype is supported by NASA to fly a 3U CubeSat with a possible launch date of Summer 2024. If a detector capable of operating in space is sensitive to neutrinos that can be distinguished from the many different backgrounds in space, then it would allow a series of experiments in space such as going closer to the Sun where the neutrino flux increases 1,000x to 10,000x above that of earth, or going away from the Sun to search for Dark Matter where the solar neutrino background is five order of magnitude less. This technique is a double delayed coincidence from the conversion electron and excited start nuclear gamma decays with 2.5 microseconds. The aim of our CubeSat test flight is to test the detector concept idea in space operations and study real deep space backgrounds that can emulate the double delated coincidence signal.