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: since Fall 2017 colloquia are not webcast or recorded. Videos from Spring 2017 colloquia are available here. Earlier semesters are available in the Webcast archives.
Quantum Oscillations of Electrical Resistivity in an Insulator
In metals, orbital motions of conduction electrons are quantized in magnetic fields, which is manifested by quantum oscillations in electrical resistivity. This Landau quantization is generally absent in insulators, in which all the electrons are localized. Here we report a notable exception in an insulator — ytterbium dodecaboride (YbB12). The resistivity of YbB12, despite much larger than that of usual metals, exhibits profound quantum oscillations under intense magnetic field. This unconventional oscillation is shown to arise from the insulating bulk, instead of conducting surface states. The large effective masses indicate strong correlation effects between electrons. Our result is the first discovery of quantum oscillations in the electrical resistivity of a strongly correlated insulator, and will bring crucial insight to the understanding of the ground state in gapped Kondo systems.
Update on Energy Choices and Consequences
With the world's population increasing from seven billion currently to approximately nine billion by the year 2040, achieving a healthy lifestyle for all people on earth will depend, in part, on the availability of affordable energy, especially electricity. This work considers the various choices, or options, for producing electricity and the consequences associated with each option. The options are fossil, renewables, and nuclear. The consequences associated with these three options are addressed in five different areas: economics, environmental effects, public health and safety, sustainability, and politics. All options are needed, but some options may be better than others when compared in the five areas. This presentation is a brief summary of the content in a short course entitled “Energy Choices and Consequences”, which was created by the author several years ago and is continually updated.
Soft Matter Physics of the Evolution of Multicellularity
The evolution of multicellularity set the stage for an incredible increase in the diversity and complexity of life on Earth. The increase in biological complexity associated with multicellularity required parallel innovation in the mechanical properties of multicellular bodies. Though a cursory review of any multicellular organism provides an appreciation of this intertwining of biological and mechanical complexity, little is known about how such mechanical properties may have evolved. We hypothesize that prior to the evolution of genetically-regulated development, physics played a key role in initiating simple multicellular development. Through a combination of experimental evolution (which allows us to observe the evolution of multicellularity in the lab, as it occurs), and the tools of soft matter (microscopy, mechanical testing, and more), we show that physics likely played a fundamental role in the evolution of complex multicellularity.
Probing Competing and Entangled Degrees of Freedom in Correlated Quantum Materials Using Resonant Inelastic X-Ray Scattering
Quantum materials hosting strongly correlated electrons are at the forefront of science and technology, with the potentially transformative applications across a diverse set of fields. Despite this potential, obtaining a complete understanding of these materials remains as one of the central unsolved problems of condensed matter physics. The primary difficulty arises from the fact that the electron's potential energy due to the Coulomb interaction is comparable to it kinetic energy. The competition between these two energy scales produces phases of matter that are governed by the collective motion of the particles, and where the electrons can become strongly entangled with the collective excitations associated with competing orders. As such, subtle factors and perturbing influences can often dictate a given material's functional properties. In this context, the challenge in understanding a given compound is to identify and unravel the action of the relevant degrees of freedom and incorporate this information into predictive models. Over the past decade, resonant inelastic x-ray scattering (RIXS) has emerged as a powerful probe of quantum materials, owing to its ability to simultaneously access charge, spin, orbital, and lattice degrees of freedom in a single experiment. In this talk, I will present an overview of RIXS as an experimental probe and discuss several case studies where we have used this technique to understand and disentangle the physics of correlated materials. I will also conclude with a brief perspective on future directions for the method with the development of next-generation light sources.
Life and Death of the Free Neutron
Modern neutron sources provide extraordinary opportunities to study a wide variety of physics topics, including the physical system of the neutron itself. One of the processes under the microscope, neutron beta decay, is an archetype for all semi-leptonic charged-current weak processes. Precise measurements of the correlation parameters in neutron beta decay as well as the neutron lifetime itself are required for tests of the Standard Model and for searches of new physics. The state of the field will be presented and a program of current and future experiments and potential impacts explored.
Colloids and Gels with Order
Colloids and gels are ubiquitous soft matter systems of our everyday life, ranging from milk to personal care products. I will discuss unexpected self-assembly of highly anisotropic rod-like and disc-like nanoparticles within such soft matter systems [1,2]. This self-assembly allows for the realization of polar fluids predicted by Max Born over a century ago and optically biaxial liquid crystals, often referred to as “Higgs bosons of condensed matter”, that were intensively searched for about five decades. I will show how this fascinating physical behavior of colloids and gels with order may enable applications ranging from thermally super-insulating windows [3] to extraterrestrial habitats.
1. H. Mundoor, S. Park, B. Senyuk, H. Wensink and I. I. Smalyukh. Science 360, 768-771 (2018).
2. Q. Liu, P.J. Ackerman, T. C. Lubensky and I. I. Smalyukh. Proc. Natl. Acad. Sci. U.S.A. 113, 10479–10484 (2016).
3. Q. Liu, A. W. Frazier, X. Zhang, J. De La Cruz, R. Yang, A. Hess and I. I. Smalyukh. Nano Energy 48, 266–274 (2018).
Illuminating a Dark World: Gravitational Wave Astrophysics with Binary Black Holes
Three years ago, gravitational waves from a pair of coalescing black holes were detected, confirming Einstein's prediction and opening a new window on the universe. Since then, LIGO and Virgo's ongoing observing has identified several new binary black holes; more will be reported soon, and hundreds more per year are expected over the decade to come. In this talk, I survey the rich and rapidly-developing field of gravitational wave astronomy with binary black holes. I describe what we learn from individual gravitational wave measurements, and how these measurements are being used to draw insights into the lives and deaths of massive stars, the star formation rate and expansion history of the universe, and processes that cause black holes to form in binaries. I summarize the immediate challenges faced during the next few years, in a quest to fully exploit the abundant binary black hole population which GW observatories have unveiled.
Ultrafast Dynamics and Control in Complex Materials
The past decade has seen enormous advances in materials and ultrafast optical spectroscopy spanning from classical to quantum physics. On the classical front, metamaterials are artificial composites with unique electromagnetic properties that derive from their sub-wavelength structure. Metamaterials enable new ways to control light with negative refractive index and cloaking as two examples of continuing interest. Further, it is possible to use metamaterials to localize and enhance incident electromagnetic fields well below the diffraction limit. Moving to the quantum realm, correlated electron materials exhibit fascinating phenomena ranging from superconductivity to metal-insulator transitions. Many of these materials exhibit colossal changes to small perturbations, which includes electromagnetic excitation. This opens up exciting possibilities such as photoinduced phase transitions with the goal to create and control novel states with unique properties. To illustrate the richness of this still emerging field, I will present examples from our work such as terahertz induced field-emission and carrier acceleration from metamaterial split ring resonators, nonlinear plasmonics, optically induced metastable insulator-to-metal phase transitions, and very recent work on photoinduced phenomena in superconductors.
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, magnetic anisotropies, as well as symmetric and antisymmetric exchange interactions [3]. Due to their topology magnetic skyrmions can be stable with quasi-particle like behavior, where they can be manipulated with very low electric currents. This makes them interesting for extreme low-power information technologies, where it is envisioned that data will be encoded in topological charges, instead of electronic charges as in conventional semiconducting devices. Towards the realization of this goal we demonstrated magnetic skyrmions in magnetic heterostructures stable at room temperature, which can be manipulated using spin Hall effects [4]. Furthermore, using inhomogeneous electric charge currents allows the generation of skyrmions in a process that is remarkably similar to the droplet formation in surface-tension driven fluid flows. However, detailed micromagnetic simulations show that depending on the electric current magnitude there are at least two regimes with different skyrmion formation mechanisms [5]. Lastly, we demonstrated that the topological charge gives rise to a transverse motion on the skyrmions, i.e., the skyrmion Hall effect, which is in analogy to the ordinary Hall effect originating from the motion of electrically charged particles in the presence of a magnetic field [6].
This work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division. Lithographic patterning was carried out at the Center for Nanoscale Materials, which is supported by DOE, Office of Science, BES (#DE-AC02-06CH11357).
References
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2. A. Hoffmann and H. Schultheiß, Curr. Opin. Solid State Mater. Sci. 19, 253 (2015)
3. W. Jiang, et al., Phys. Rep. 704, 1 (2017).
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6. W. Jiang, et al., Nature Phys. 13, 162 (2017).
Multum in Parvo
On Thanksgiving Day, 1931, there was discovered the first isotope whose observable properties were predicted in advance by first-principles quantum theory. It was found by a combination of atomic spectroscopy and low temperature physics. At birth a minor satellite line in the Balmer spectrum of atomic hydrogen, it became a Nobel namesake at the age of three, and revolutionized chemistry; as a teenager it caused bloody fights in World War II; and coming of age, at 21 it fueled the first manmade thermonuclear chain reaction. It - deuterium - remains a workhorse today of astronomy, biology, chemistry, geology and physics.
New Results on the Search for the Elusive
with the KOTO DetectorThe KOTO experiment was designed to observe and study the decay. The Standard Model (SM) prediction for the mode is 2.4 x 1011 with a small theoretical uncertainty [1]. An experimental upper limit of 2.6 x 10-8 was set by the KEK E391a collaboration [2]. The rare "golden" decay is ideal for probing for physics beyond the standard model. A comparison of experimentally obtained results with SM calculations permits a test of the quark flavor region and provides a means to search for new physics.
The signature of the decay is a pair of photons from the π0 decay and no other detected particles. For the measurement of the energies and positions of the photons, KOTO uses a Cesium Iodide (CSI) electromagnetic calorimeter as the main detector, and hermetic veto counters to guarantee that there are no other detected particles.
KOTO’s initial data was collected in 2013 and achieved a similar sensitivity as E391a result [3]. Since then, we completed significant hardware upgrades and had additional physics runs in 2015 at beam powers of roughly 24-40 kW. This presentation will present new results from KOTO and its search of detecting .
[1] C. Bobeth, A. J. Buras, A. Celis, and M. Jung, J. High Energy Phys. 04, 079 (2017).
[2] J. K. Ahn et al., Phys. Rev. D 81, 072004 (2010).
[3] J. K. Ahn et al., Prog. Theor. Phys. 021C01 (2017).
See the World! With Neutrinos: Current and Future Accelerator Based Neutrino Experiments
One of the most promising investigations of beyond-the-Standard-Model physics has been the study of neutrino oscillation, that is, the conversion of neutrinos from one flavor to another as they propagate. While neutrino oscillation is studied in a wide variety of experiments, accelerator based experiments, use a muon neutrino or antineutrino beam as a probe, of energies of order 1 GeV. The most recent analysis of data from the Tokai-to-Kamioka experiment in Japan hint at differences between neutrino and antineutrino oscillation, indicative of possible CP violation with neutrinos and maximal mixing between tau and muon flavors. This talk will discuss what we aim to learn from current and future experiments, how those experiments operate, and the future challenges of accelerator based programs.
Gravitational Quantum States of Neutrons, Atoms and Anti-atoms
Quantum gravitational spectroscopy with ultracold systems [1] is an emerging field based on recent experimental and theoretical advances. Gravitational spectroscopy profits from exceptional sensitivity due to the extreme weakness of gravitation compared to other fundamental interactions; thus, it provides an access to the precision frontier in particle physics and other domains. Quantum gravitational spectroscopy is its ultimate limit addressing the most fragile and sensitive quantum states of ultracold particles and systems. Ultracold particles – neutrons, atoms, and antiatoms – with sufficiently high phase-space density are the condition for providing observable phenomena with gravitational quantum states. Some of such studies, like those with ultracold neutrons, have become reality [2-4]; others with ultracold atoms [5] and antiatoms [6-8] are in preparation. GRANIT [9] is one of follow-up projects pushing forward the precision and sensitivity of quantum gravitational spectroscopy with ultracold neutrons. Quantum states of antihydrogen atoms in GBAR [6-8] are the key for pushing the precision of measurements of gravitational properties of antimatter. Precision measurements of gravitational quantum states of atoms [5] and neutron whispering-gallery states [10] are promissing methods for improving constraints for fundamental short-range forces [11].
[1] V.V. Nesvizhevsky, and A.Yu. Voronin, Surprising Quantum Bounces (Imperial College Press, London, UK, 2015).
[2] V.V. Nesvizhevsky, H.G. Boerner, A.K. Petukhov et al., Quantum states of neutrons in the Earth’s gravitational field, Nature 415, 297 (2002).
[3] T. Jenke, P. Geltenbort, H. Lemmel et al., Realization of a gravity-resonance-spectroscopy technique, Nature Phys. 7, 468 (2011).
[4] G. Ichikawa, S. Komamiya, Y. Kamiya et al., Observation of the spatial distribution of gravitationally bound quantum states of ultracold neutrons and its derivation using the Wigner function, Phys. Rev. Lett. 112, 071101 (2014).
[5] S. Vasiliev, J. Ahokas, V.V. Nesvizhevsky et al., Gravitational and matter-wave spectroscopy of atomic hydrogen at ultra-low energies, submitted to Hyperfine Interactions (2018).
[6] P. Perez, Y. Sacquin, The GBAR experiment: gravitational behaviour of antihydrogen at rest, Class. Quant. Grav. 29, 184008 (2012).
[7] P. Perez, D. Banerijee, F. Biraben et al., The GBAR antimatter gravity experiment, Hyper. Inter. 233, 21 (2015).
[8] A.Yu. Voronin, P. Froelich, V.V. Nesvizhevsky, Gravitational quantum states of antihydrogen, Phys. Rev. A 83, 032903 (2011).
[9] D. Roulier, F. Vezzu, S. Baessler et al., Status of the GRANIT facility, Adv. High En. Phys. 730437 (2015).
[10] V.V. Nesvizhevsky, A.Yu. Voronin, R. Cubitt et al., Neutron whispering gallery, Nature Phys. 6, 114 (2010).
[11] I. Antoniadis, S. Baessler, V.V. Nesvizhevsky, and G. Pignol, Quantum gravitational spectroscopy, Adv. High En. Phys. 467409 (2015).
The IceCube Neutrino Observatory and the Beginning of Neutrino Astrophysics
The IceCube Neutrino Observatory is the world’s largest neutrino detector, instrumenting a cubic kilometer of ice at the geographic South Pole. IceCube was designed to detect high-energy astrophysical neutrinos from potential cosmic ray acceleration sites such as active galactic nuclei, gamma ray bursts and supernova remnants. IceCube announced the detection of a diffuse flux of astrophysical neutrinos in 2013, including the highest energy neutrinos ever detected. In September 2018, IceCube observed a neutrino in coincidence with a flaring blazar. I will discuss the latest results from IceCube and discuss prospects for future upgrades and expansions of the detector.