Events List for the Academic Year

Event Time: Thursday, April 22, 2021 | 10:00 am - 11:00 am
Event Location:
Zoom link in description
Add to Calendar 2021-04-22T10:00:00 2021-04-22T11:00:00 CM Seminar - ZnO: Ultrafast generation and decay of a surface metal Event Information: https://ubc.zoom.us/j/64183011430?pwd=U2lFNXEwSmlBRWVBdTR5OG1ZdlVSZz09 Meeting ID: 641 8301 1430 Passcode: 113399 Speaker: Julia Stähler (Department of Chemistry, Humboldt-Universiät zu Berlin and Fritz Haber Institute of the Max Planck Society) Title: ZnO: Ultrafast generation and decay of a surface metal L. Gierster1,2, S. Vempati1,3, and J. Stähler1,2   1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abt. Physikalische Chemie, Faradayweg 4-6, 14195 Berlin, Germany 2Humbolt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str. 2, 12489 Berlin, Germany 3Present address: Department of Physics, Indian Institute of Technology Bhilai, Raipur-492015, India   Band bending (BB) at semiconductor surfaces or interfaces plays a pivotal role in technology, ranging from field effect transistors to nanoscale devices for quantum technologies. The control of BB via chemical doping or electric fields can create metallic surfaces with properties not found in the bulk, such as high electron mobility, magnetism or superconductivity. Optical generation of metallic surfaces via BB on ultrafast timescales would facilitate a drastic manipulation of the conduction, magnetic and optical properties of semiconductors for novel high-speed electronics. We demonstrate the ultrafast (20 fs) generation of a metal at the (10‑10) surface of ZnO upon photoexcitation. This semiconductor is widely used in optoelectronics due to its transparency for visible light and its ease of nanostructuring. Compared to hitherto known ultrafast photoinduced semiconductor-to-metal transitions (SMTs) that occur in the bulk of inorganic semiconductors, the SMT at the ZnO surface is launched by 3-4 orders of magnitude lower photon fluxes; also, the back-transition to the semiconducting state is at least one order of magnitude faster than in previous studies of other materials. Using time- and angle-resolved photoelectron spectroscopy, we show that the SMT is caused by the photoexcitation of deep surface defects. The resulting positive surface charges lead to downward BB toward the surface. Above a critical excitation density, a metallic band below the equilibrium Fermi level is formed. This process is in analogy to chemical doping of semiconductor surfaces. Hence, it is not material-specific and presents a general route for controlling metallicity confined to semiconductor interfaces on ultrafast timescales. [1] L. Gierster et al. Nat. Commun. 12 978 (2021) Event Location: Zoom link in description
Event Time: Tuesday, April 20, 2021 | 2:00 pm - 4:00 pm
Event Location:
via Zoom
Add to Calendar 2021-04-20T14:00:00 2021-04-20T16:00:00 Departmental Doctoral Oral Examination (Thesis Title: “Atomic modification of graphene on silicon carbide: adsorption and intercalation”) Event Information: Abstract: Graphene, the first truly 2D material to be isolated, is host to a wealth of remarkable properties. It can be modified in a variety of ways—strained, twisted, stacked, placed on a substrate, decorated with adatoms, etc.—to further enhance these properties or introduce new ones. In this thesis, we use a number of complementary surface characterization techniques to study two methods of modifying epitaxial graphene on a silicon carbide (SiC) substrate via the addition of other atoms. In the first method, we induce the Kekulé distortion—a periodic distortion of the carbon-carbon bonds in graphene—using a small number of lithium atoms adsorbed on the graphene surface. Mediated by the graphene, the adatoms interact over large distances, leading to symmetry breaking between graphene unit cells and a (√3×√3) R30° superstructure. Using angle-resolved photoemission spectroscopy (ARPES), we observe the formation of the superstructure in the appearance of a new Dirac cone in the centre of the Brillouin zone due to band folding. The same superstructure was confirmed by the appearance of new spots in low-energy electron diffraction (LEED) experiments. ARPES data also reveals a gap opening 2Δ = (238±3) meV at the Dirac point. Using a Monte Carlo toy model, we study the importance of deposition parameters in the formation of the Kekulé phase. Finally, we show that this phase is generic to other graphene systems, regardless of charge carrier type or density. In the second method, we intercalate a layer of copper atoms between the graphene and the SiC substrate by contacting it with copper paste and annealing in vacuum. Using scanning tunnelling microscopy (STM), we observe the formation of 2.2 Å tall islands under the graphene, which exhibit a modification of the observed graphene/SiC superstructure from SiC (6×6) to SiC (6√3×6√3) R30°. The same periodicity is observed in LEED, and the intercalation of copper is further confirmed by the appearance of additional bands in ARPES. This presents a simple method of producing metal-intercalated graphene, without the need for deposition by evaporation. Event Location: via Zoom
Event Time: Monday, April 19, 2021 | 3:00 pm - 4:00 pm
Event Location:
Connect via zoom
Add to Calendar 2021-04-19T15:00:00 2021-04-19T16:00:00 The Southern Stellar Stream Spectroscopic Survey: Overview and Latest Science Results Event Information: The Southern Stellar Stream Spectroscopic Survey (S5) is an ongoing spectroscopic program that maps the newly discovered stellar streams with the fiber-fed AAOmega spectrograph on the Anglo-Australian Telescope (AAT). S5 is the first systematic program pursuing a complete census of known streams in the Southern Hemisphere, providing a uniquely powerful sample for understanding the building blocks of the Milky Way's stellar halo, the progenitors and formation of stellar streams, the mass and shape of the Milky Way's halo, and ultimately the nature of dark matter. The survey started in Summer 2018 and has mapped ~20 streams with over 50 nights on AAT. In this talk, I will give a brief overview of the current status of the program, highlighting the latest science results from the survey, and end the talk with the public data release plan. Event Location: Connect via zoom
Event Time: Thursday, April 15, 2021 | 4:00 pm - 5:00 pm
Event Location:
Connect via zoom
Add to Calendar 2021-04-15T16:00:00 2021-04-15T17:00:00 First Results from the Fermilab Muon g-2 Experiment! Event Information: One of the most promising ways of searching for evidence of physics beyond the standard model is through precision measurements of the so-called "g-factor" of the muon. Twenty years ago, the Brookhaven experiment that measured the muon’s anomalous magnetic moment aμ = (g-2)/2 completed its data-taking campaign.  When the final analyses were published a few years later, the result differed by more than 2 standard deviations (σ) from the concurrent standard model (SM) prediction.  Alas, this felt like a rotten situation to be in, one that had to be resolved one way or the other.   A number of us formed a new collaboration to design and build an experiment capable of higher precision.  In the intervening years, the international theory community involved in predicting aμ formed the Muon g-2 Theory Initiative, with the similar aim to reduce theoretical uncertainties.   Last year, following a Workshop held here at the INT, the theorists published a comprehensive Physics Report with a consensus value for aμ. When compared to experiment, the difference swelled to 3.7 σ, an exciting yet still not definitive result.   Over the past 10 years, our new experiment has been built and we are steadily acquiring data. The University of Washington and CENPA have been central to the design, construction, commissioning, running, and analysis of this experiment since Day 1.  It is therefore my great pleasure and honor to represent our group and announce in this Colloquium the first results from our 2018 run. Event Location: Connect via zoom
Event Time: Thursday, April 15, 2021 | 10:00 am - 11:00 am
Event Location:
Zoom link in description
Add to Calendar 2021-04-15T10:00:00 2021-04-15T11:00:00 CM Seminar - Pressure Control of Competing Orders in Superconductors Event Information: Abstract: External control of electronic phases in correlated-electron materials is a long-standing challenge of condensed-matter research. In the recent years it has been realized that the underlying crystal lattice was more than a mere spectator and could be used as an insightful tuning knob. In this talk, I will show how the combination of pressure (hydrostatic or uniaxial) tuning and x-ray spectroscopy has been used in the course of the last decade to gain fresh insights on the interplay between coexisting, competing or intertwined electronic phases in conventional and unconventional superconductors. I will in particular report on recent studies of the lattice dynamics under pressure by means of inelastic x-ray scattering in various families of compounds exhibiting charge-density-waves, from elemental -Uranium [1] to more complex metallic dichalcogenides [2] and high temperature superconducting cuprates [3-5]. [1] S. Raymond, et al. Phys. Rev. Lett. 107 136401 (2011) [2] M. Leroux, et al. Phys. Rev. B 92 140303 (2015) [3] S. M. Souliou, et al. Phys. Rev. B 97 020503 (2018) [4] H. H. Kim, S. M. Souliou et al. Science 362 1040 (2018) [5] H. H. Kim, et al. Phys. Rev. Lett. 126 037002 (2021)   Event Location: Zoom link in description
Event Time: Monday, April 12, 2021 | 3:00 pm - 4:00 pm
Event Location:
Connect via zoom
Add to Calendar 2021-04-12T15:00:00 2021-04-12T16:00:00 Exploring The Transient Sky At Millimeter Wavelengths With SPT-3G Event Information: Large-area transient surveys are a powerful source of information on a wide class of high-energy astrophysical objects, including gamma-ray burst afterglows, the jet launch area of active galactic nuclei, tidal-disruption events, and stellar flares. Current transient surveys operate at nearly every wavelength from gamma rays through radio, but the millimeter wavelength range is comparatively unexplored. However, current generation cosmic microwave observatories have the necessary cadence and daily sensitivity to fill this millimeter-wave gap. I will present the first results of an astronomical transient survey with the South Pole Telescope (SPT), using the SPT-3G camera to observe 1500 square degrees of the southern sky at 95 and 150 GHz. Between March and November 2020 we observed fifteen transient events from sources not previously detected by the SPT. The majority are brief and extremely bright and are associated with variable stars of different types. Another population of detected events last for 2--3 weeks and appear to be extragalactic in origin. I will introduce the SPT-3G instrument, present a selection of events from our first transient survey, and discuss our outlook for 2021 and beyond where we plan to increase our number of detected sources by at least an order of magnitude.  Event Location: Connect via zoom
Event Time: Thursday, April 8, 2021 | 4:00 pm - 5:00 pm
Event Location:
Connect via zoom
Add to Calendar 2021-04-08T16:00:00 2021-04-08T17:00:00 What are scientific abilities and how to help students develop them? Event Information: Many years ago (in 2004), the Rutgers University physics education research group devised a list of most common processes that physicists engage in when creating and applying physics knowledge to operationalize the vague notion of “critical thinking” that we wish our students to develop. This list was based on the observations and interviews of practicing physicists and the studies of the history of physics. The list became the list of "scientific abilities" that students can develop when taking physics courses. We used the term "abilities" instead of science-process skills to underscore that these are not automatic skills, but are instead processes that students need to use reflectively and critically. Once the list was created, we started writing activities to help students develop these abilities. To help students progress, we made self-assessment rubrics for each ability. The rubrics were validated through a rigorous process. Students use those rubrics as they work on the activities to self-assess and improve their work, and instructors  use the rubrics for grading. We conducted numerous studies of student development of various abilities that showed how long it takes for the students to improve, which abilities are the most difficult, how to run professional development for the instructors, and many others.  In my talk I will discuss the philosophy of learning and teaching that promotes the development of these abilities, specific activities and rubrics, and will share findings from several research studies. The website for scientific abilities and rubrics is at https://sites.google.com/site/scientificabilities/ . Event Location: Connect via zoom
Event Time: Thursday, April 8, 2021 | 2:00 pm - 4:00 pm
Event Location:
via Zoom
Add to Calendar 2021-04-08T14:00:00 2021-04-08T16:00:00 Departmental Doctoral Oral Examination (Thesis Title: “Holographic quantum matter: toy models and physical platformsr”) Event Information: Abstract:In recent years a new paradigm has emerged to investigate non-Fermi liquids without quasiparticles, based on the exactly-solvable Sachdev-Ye-Kitaev model which consists of a large number of fermions with all-to-all, random Gaussian interactions. This model exhibits a rich phenomenology at low energy, including power-law decaying spectral functions, maximal chaos and connections to black hole horizons in anti-de Sitter spacetime. These intriguing properties have inspired a broad research program at the intersection of condensed matter physics, quantum information and quantum gravity. In this thesis we explore the phases and phase transitions occurring in Sachdev-Ye-Kitaev models that are coupled in various ways, with an eye on physical platforms that could enable their realization in condensed matter systems. This journey takes us from the investigation of quantum chaos and revival dynamics in traversable wormholes, all the way to the physics of disordered graphene flakes and unconventional superconductivity. Event Location: via Zoom
Event Time: Thursday, April 8, 2021 | 10:00 am - 11:00 am
Event Location:
Zoom link in description
Add to Calendar 2021-04-08T10:00:00 2021-04-08T11:00:00 CM Seminar - Recent Developments in Hybrid and Inorganic Perovskite Halides Event Information: CM Seminar - Thu, April 8th 10am https://ubc.zoom.us/j/64183011430?pwd=U2lFNXEwSmlBRWVBdTR5OG1ZdlVSZz09 Meeting ID: 641 8301 1430 Passcode: 113399 Talk Title: Recent Developments in Hybrid and Inorganic Perovskite HalidesSpeaker: Anthony K. Cheetham - Materials Research Laboratory, UCSB Abstract: Hybrid organic-inorganic perovskites are found in a number of important families, including the lead-based halides (e.g. CH3NH3PbI3) and the formates (e.g. [(CH3)2NH2]Zn(HCOO)3) [1], as well as systems with the ReO3 structure [2]. The lead halide perovskites have attracted a great deal of attention in the last decade on account of their excellent performance as active layers in solar cells and other optoelectronic devices. I shall discuss some of our recent work which has focused on the search for lead-free hybrid and inorganic double perovskites such as (CH3NH3)2AgBiBr6 and Cs2AgSbBr6 [3]. I shall also describe some B-site vacant perovskites based on platinum [4] and ruthenium [5], as well as recent developments in the area of hybrid layered double perovskite halides [6]. Our current work on ruthenium systems is enabling us to explore the influence of chemical bonding on spit-orbit coupling effects.   1. W. Li, Z. M. Wang, F. Deschler, S. Gao, R. H. Friend and A. K. Cheetham, Nature Rev. Mater. 2, 16099 (2017) 2. H. A. Evans, Y. Wu, R. Seshadri and A. K. Cheetham, Nature Rev. Mater. 5, 196 (2020) 3. Wei, Z. Deng, S. Sun, F. Zhang, D. M. Evans, G. Kieslich, S. Tominaka, M. A. Carpenter, P. D. Bristowe, and A. K. Cheetham, Chem. Mater. 29, 1089 (2017); Z. Deng, F. Wei, F. Brivio, Y. Wu, S. Sun, P. D. Bristowe, and A. K. Cheetham, J. Phys. Chem. Lett, 8, 5015 (2017); F. Wei, Z. Deng, S. Sun, N. T. Putri Hartono, H. L. Seng, T. Buonassisi, P. D. Bristowe, and A. K. Cheetham, Chem. Comm. 55, 3721 (2019) 4. H. A. Evans, D. H. Fabini, J. Andrews, M. Koerner, M. Preefer, G. Wu, F. Wudl, A. K. Cheetham and R. Seshadri, Inorg. Chem. 57, 10375 (2018); H. A. Evans, J. L. Andrews, D. H. Fabini, M. B. Preefer, G. Wu, A. K. Cheetham, F. Wudl, and R. Seshadri, Chem. Comm. 55, 588 (2019) 5. P. Vishnoi, J. L. Zhuo, T. A. Strom, G. Wu, S. D. Wilson, R. Seshadri, and A. K. Cheetham, Angew. Chemie Intl. Ed. Eng. 59, 8974 (2020); P. Vishnoi, J. L. Zuo, J. A. Cooley, L. Kautzsch, A. Gómez‐Torres, J. Murillo, S. Fortier, S. D. Wilson, R. Seshadri, A. K. Cheetham, Angew. Chemie Intl. Ed. Eng. 60, 5184 (2021) 6. L. L. Mao, S. Teicher, C. C. Stoumpos, R. M. Kennard, R. A. DeCrescent, G. Wu, J. A. Schuller, M. L. Chabinyc, A. K. Cheetham and R. Seshadri, J. Amer. Chem. Soc. 141, 19099 (2019); H. A. Evans, L. L. Mao, R. Seshadri and A. K. Cheetham, Ann. Rev. Mater. Sc. 51, (2021) Bio: Tony Cheetham is a Research Professor at the University of California, Santa Barbara, and a Distinguished Visiting Professor at the National University of Singapore. He was formerly the Goldsmiths’ Professor of Materials Science at the University of Cambridge (2007-2017) and the Treasurer and Vice-President of the Royal Society (2012-2017). He obtained his D.Phil. at Oxford in 1972 and did post-doctoral work in the Materials Physics Division at Harwell. He joined the Chemistry faculty at Oxford in 1974, and then moved to UC Santa Barbara in 1991 to become Professor in the Materials Department. From 1992-2004 he was the Director of UCSB’s Materials Research Laboratory. Cheetham was knighted by the Queen for “Services to Materials Chemistry, UK Science and Global Outreach” in January 2020   Event Location: Zoom link in description
Event Time: Thursday, April 1, 2021 | 4:00 pm - 5:00 pm
Event Location:
Connect via zoom
Add to Calendar 2021-04-01T16:00:00 2021-04-01T17:00:00 Physics Pranks and Astronomical Antics Event Information: 1st April has traditionally been a day for japes and high jinks in many realms of life - with science not being entirely excluded! In observance of this day I will review the use of humour in physics and astronomy, focusing on some specific examples, particularly those involving April Fool's Day. Event Location: Connect via zoom
Event Time: Thursday, April 1, 2021 | 10:00 am - 11:00 am
Event Location:
Zoom link in description
Add to Calendar 2021-04-01T10:00:00 2021-04-01T11:00:00 CM Seminar - Frontiers in Quantum Information Science Event Information: https://ubc.zoom.us/j/64183011430?pwd=U2lFNXEwSmlBRWVBdTR5OG1ZdlVSZz09 Meeting ID: 641 8301 1430 Passcode: 113399 Title: Frontiers in Quantum Information ScienceSpeaker: Jacob Taylor – University of Maryland  Abstract: Quantum information science (QIS) promises dramatic improvements in our ability to understand the physical world and in our capabilities for measurement, communication, and computation. Over the past five years, a worldwide expansion of government-funded research and development has combined with an unprecedented investment from the private sector to dramatically accelerate progress in realizing the potential of quantum systems. In this talk I will discuss the re-envisioning of the U.S. research and development approach to QIS enacted over the past two years through the National Quantum Initiative and other efforts, and consider future opportunities and challenges for academia, industry, government, and the public.  I will also touch upon several research frontiers of personal interest in the space, specifically the interplay between quantum device development and physical understanding, from probing many-body systems with qubits to searching for dark matter using advanced quantum sensors to even exploring terrestrial tests of the quantum nature of gravity. Bio: Jake Taylor has been doing research in quantum information science and quantum computing for the past two decades, most recently at the National Institute of Standards and Technology and at the Joint Quantum Institute and the Joint Center for Quantum Information and Computer Science at the University of Maryland, College Park. In addition to his research, he spent the last three years as the first Assistant Director for Quantum Information Science at the White House Office of Science and Technology Policy, where he led the creation and implementation of the National Quantum Initiative (quantum.gov) and the COVID-19 High Performance Computing Consortium (covid19-hpc-consortium.org). Now taking a year as a TAPP Fellow at Harvard's Belfer Center for Science and International Affairs, Jake is looking at how lessons learned in implementing science and tech policy for an emerging field can enable public purpose in other areas. He is the author of more than 150 peer reviewed scientific articles, a Fellow of the American Physical Society and the Optical Society of America, and recipient of the Silver and Gold medals from the Department of Commerce. He can be found on twitter @quantum_jake and atquantumjake.org.    Event Location: Zoom link in description
Event Time: Wednesday, March 31, 2021 | 11:00 am - 12:00 pm
Event Location:
Connect via Zoom
Add to Calendar 2021-03-31T11:00:00 2021-03-31T12:00:00 Sub-leading Soft Photons and Gravitons Event Information: Soft factorization has been shown to hold to sub-leading order in QED and to sub-sub-leading order in perturbative quantum gravity, with various loop and non-universal corrections that can be found. In a recent paper, we show that all terms factorizing at tree level can be uniquely identified as boundary terms that exist already in the classical expressions for the electric current and stress tensor of a point particle. Further, it turns out that one cannot uniquely identify such boundary terms beyond the sub-leading or sub-sub-leading orders respectively, providing evidence that the factorizability of the tree level soft factor only holds to these orders. In this talk, I will first introduce and motivate the soft theorems, and then explain our recent results. I'll also show how our new classical intuition is reflected in the calculation of quantum scattering amplitudes. Event Location: Connect via Zoom
Event Time: Monday, March 29, 2021 | 3:00 pm - 4:00 pm
Event Location:
Connect via zoom
Add to Calendar 2021-03-29T15:00:00 2021-03-29T16:00:00 The Quest for High Hubble Constant Harmony Event Information: The most precise of the direct measurements of the current rate of cosmic expansion (the Hubble constant) is inconsistent with the even more precise, but indirect, model-dependent inferences. In particular the Riess et al. (2020) measurement is more than four standard deviations higher than the inference based on the standard cosmological model, with its free parameters constrained by Planck satellite observations of the cosmic microwave background. In this talk I will explain the beautifully simple physics that allows for a prediction of the Hubble constant from observations of temperature and polarization patterns in the sky at millimeter wavelengths and I will entertain the exciting possibility that the origin of this discrepancy is a deficiency of the standard cosmological model. Event Location: Connect via zoom
Event Time: Friday, March 26, 2021 | 12:00 pm - 2:00 pm
Event Location:
via Zoom
Add to Calendar 2021-03-26T12:00:00 2021-03-26T14:00:00 Departmental Doctoral Oral Examination (Thesis Title: “The search for jovian and saturnian irregular moons and a study of their luminosity functions”) Event Information: Abstract: (please see this link) Event Location: via Zoom
Event Time: Thursday, March 25, 2021 | 4:00 pm - 5:00 pm
Event Location:
Connect via zoom
Add to Calendar 2021-03-25T16:00:00 2021-03-25T17:00:00 Attosecond Science Event Information: An electron that multiphoton ionizes is immediately subject to the light's electric field that will control its short-term future.  This control enables a gas of atoms to produce intense VUV or soft X-ray beams.  Since we can precisely control the infrared beam, we can synthesize attosecond soft X-ray pulses - pulses that are the shortest controlled events ever systematically produced.  For a complex atom (such as xenon), the recollision electron shares its energy in any multi-electron interaction.  Measuring the energy share encodes multielectron dynamics such as the Fano resonance structure in helium and the Giant Plasmon resonance in Xenon. Event Location: Connect via zoom
Event Time: Thursday, March 25, 2021 | 10:00 am - 11:00 am
Event Location:
Zoom link in description
Add to Calendar 2021-03-25T10:00:00 2021-03-25T11:00:00 CM Seminar - Spin, Charge, and Phonon Coupling Effects in 2D Materials Event Information: CM Seminar - Thu, March 25, 10am (PST)https://ubc.zoom.us/j/64183011430?pwd=U2lFNXEwSmlBRWVBdTR5OG1ZdlVSZz09Meeting ID: 641 8301 1430Passcode: 113399 Abstract: The coupling between spin, charge, and lattice degrees of freedom plays an important role in a wide range of fundamental phenomena. 2D material is an emerging platform for studying these coupling effects. In this talk, I will present a couple examples along this direction. I will firstly discuss the observation of antiferromagnetic exciton and multiple exciton phonon bound states in zigzag antiferromagnet NiPS3. I will then present the observation of valley phonons, i.e. phonons with momentum vectors pointing to the corners of Brillouin zone, and their interaction with spins in a monolayer semiconductor WSe2. We identified the efficient intervalley scattering of quasi particles in both exciton formation and light emission process. These understandings enable us to unravel a series of photoluminescence peaks as valley phonon replicas of neutral and charged dark excitons. Short Bio: Xiaodong Xu is a Boeing Distinguished Professor in the Department of Physics and the Department of Materials Science and Engineering at the University of Washington. He received his PhD (Physics, 2008) from the University of Michigan and then performed postdoctoral research (2009-2010) at the Center for Nanoscale Systems at Cornell University. His nanoscale quantum-optoelectronics group at University of Washington focuses on creation, control, and understanding of novel device physics based on low-dimensional quantum materials. Event Location: Zoom link in description
Event Time: Thursday, March 25, 2021 | 9:00 am - 11:00 am
Event Location:
via Zoom
Add to Calendar 2021-03-25T09:00:00 2021-03-25T11:00:00 Final PhD Oral Examination (Thesis Title: “Scanning Tunnelling Microscopy of Topological Materials”) Event Information: Abstract: Topological materials have been at the forefront of condensed matter physics research over the past few decades. Characterised by electronic bands with non-trivial topological invariants, topological materials exhibit a number of interesting electronic properties, such as conducting chiral boundary states and linear electronic dispersions, and have been theorised for use in a variety of applications ranging from spintronic devices to quantum computing. Recently, topological semimetals were discovered, where the bulk electronic bands are understood in the framework of the high-energy relativistic Dirac equation and its conditional variations, the Weyl and Majorana equations. Furthermore, the vast permutations of material compounds available results in a nearly infinite sandbox for researchers to study, which has resulted in topological semimetals that have no high-energy analogue. One of such material classifications is the nodal-line semimetal, characterised by linear electronic band crossings that form lines or loops in momentum space. These nodal-line semimetals also exhibit exotic surface states, named drumhead states, which are an interesting and exciting new state with promises in high-temperature superconductivity and quantum computation. A large effort is being placed to find materials that can be used to study the fundamental properties of these materials and their resultant surface states. Scanning tunnelling microscopy (STM) provides a perfect tool to study the topological properties of materials, able to atomically resolve the surface structure and also provide insight into scattering selection rules, which are deeply dependent on the band topology. Two topological materials were studied using STM in this thesis: the topological nodal-line semimetal ZrSiTe and the topological insulator (Bi$_x$Sb$_{1-x}$)$_2$Te$_3$. ZrSiTe was studied with an emphasis on the quasiparticle scattering characteristics, measured using Fourier-transform scanning tunnelling spectroscopy. Two main scattering features are examined, one relating to the nodal line, and the other arising from the drumhead surface state. These studies mark the first time a drumhead state has been observed using a real space measurement. (Bi$_x$Sb$_{1-x}$)$_2$Te$_3$ was studied with an emphasis on the nano-scale transport characteristics, measured using 4-probe STM and scanning tunnelling potentiometry. Effects of step edges and domain boundaries on the local resistance are studied for a fractional substitution of $x = 0.19$. Event Location: via Zoom
Event Time: Monday, March 22, 2021 | 3:00 pm - 4:00 pm
Event Location:
Connect via zoom
Add to Calendar 2021-03-22T15:00:00 2021-03-22T16:00:00 The Magnetic Milky Way in Three Dimensions Event Information: Magnetic fields thread our Milky Way Galaxy, influencing interstellar physics from cosmic ray propagation to star formation. The magnetic interstellar medium is also a formidable foreground for experimental cosmology, particularly for the quest to find signatures of inflation in the polarized cosmic microwave background (CMB). Despite its importance across scientific realms, the structure of the Galactic magnetic field is not well understood. Observational tracers like polarized dust emission yield only sky-projected, distance-integrated measurements of the three-dimensional magnetic structure. I will discuss new ways to probe interstellar magnetism in three dimensions, by combining high-resolution observations of Galactic neutral hydrogen with recent insights into how gas morphology encodes properties of the ambient magnetic field. These 3D maps are a new tool for understanding the magnetic interstellar medium and the polarized foreground to the CMB. Event Location: Connect via zoom
Event Time: Monday, March 22, 2021 | 9:00 am - 11:00 am
Event Location:
via Zoom
Add to Calendar 2021-03-22T09:00:00 2021-03-22T11:00:00 Final PhD Oral Examination (Thesis Title: “Development of a Single Vacuum Ultra-Violet Photon-Sensing Solution for nEXO”) Event Information: Event Location: via Zoom
Event Time: Thursday, March 18, 2021 | 4:00 pm - 5:00 pm
Event Location:
Connect via zoom
Add to Calendar 2021-03-18T16:00:00 2021-03-18T17:00:00 The entropy of Hawking Radiation Event Information: Black holes are interesting spacetime configurations predicted by general relativity. When quantum mechanics is taken into account, black holes are found to emit thermal radiation, called "Hawking radiation". During the past couple of years a surprising new way to compute its entropy has emerged. This result indicates that the black hole formation and evaporation is consistent with standard quantum mechanical laws. Event Location: Connect via zoom