Events List for the Academic Year
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Thursday, May 13, 2021 | 4:00 pm - 5:00 pm
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2021-05-13T16:00:00
2021-05-13T17:00:00
Application of Generalized Quantum Formalisms in Cognitive Science and Humor Research
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Many branches of mathematics were first used to describe some aspect of the physical world, and later applied more broadly in other fields. It is in this spirit that the field of quantum cognition draws upon the formalisms of quantum mechanics. Quantum cognition does not posit that phenomena at the quantum level affect the brain; rather, it uses abstract formal structures that, as it happens, found their first application in quantum mechanics. The approach enables us to explain findings in several areas of psychology—including decision making and concept combination—that are otherwise difficult to account for. More generally, it suggests a new approach to understanding and modeling psychological phenomena that involve ambiguity and/or contextuality. After briefly reviewing the rationale for quantum cognition, and summarizing some notable applications, we will focus on its application to humor. Humor often involves the ‘bisociation’ of incongruous interpretations of an ambiguous situation or word. In jokes, a first interpretation (which is often tendentious, or lewd) is suggested by the set-up, while a second (often more innocent) interpretation is suggested by the punchline. Using a verbal pun as an example we will see how these interpretations can be modeled as a linear superposition of a set of basis states in a complex Hilbert space. We will look at a study involving 85 participant responses to 35 jokes (as well as variants) that investigated whether humor involves violation of the Law of Total Probability. The results suggest that quantum cognition may provide a viable new approach to modeling humor.
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Thursday, May 6, 2021 | 4:00 pm - 5:00 pm
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2021-05-06T16:00:00
2021-05-06T17:00:00
Optimization predicts neutrino flavor evolution, a junior prom date, and the best means to escape from an awkward party
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The multi-messenger astrophysics of compact objects presents a vast range of environments where neutrino flavor transformation may occur and may be important for nucleosynthesis and a detected neutrino signal. Developing efficient techniques for surveying flavor evolution solution spaces in these environments, which augment existing computational tools, could leverage progress in this field. To this end, we explore statistical data assimilation (SDA) to identify solutions to a small-scale model of neutrino flavor transformation. SDA is an optimization formula, akin to machine learning, wherein a dynamical model is assumed to generate any measured quantities. Specifically, we use an optimization formulation of SDA wherein a cost function is extremized via the variational method. Regions of state space in which the extremization identifies the global minimum of the cost function will correspond to parameter regimes in which a model solution can exist. Our study seeks to infer the flavor transformation histories of two mono-energetic neutrino beams coherently interacting with each other and with a matter background. We show how the procedure efficiently identifies solution regimes and rules out regimes where solutions are infeasible. Overall, results intimate the promise of this “variational annealing” methodology to efficiently probe an array of fundamental questions that traditional numerical simulation codes render difficult to access. Finally, on a personal note, optimization has also predicted for me how things might have turned out had I mustered the nerve to ask Barry Cottonfield to the Junior Prom back in 1997, *and* it helped me sneak away from a really awkward departmental holiday party without getting caught.
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Wednesday, May 5, 2021 | 3:30 pm - 5:30 pm
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2021-05-05T15:30:00
2021-05-05T17:30:00
Departmental Doctoral Oral Examination (Thesis Title: “Low-dimensional quantum systems from novel constituents”)
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Abstract:
Recent decades have seen a proliferation of unconventional quasiparticles in condensed matter systems. Majorana fermions, theoretically predicted in several setups and of great interest in topological quantum computation, are a focus of intense research efforts. Higher-spin moments, relevant for both solid-state compounds and cold atoms, are of great theoretical interest as they interpolate between the quantum and classical limits but sometimes show surprising behavior. In the meantime, successful fabrication and characterization of low-dimensional systems have brought new phenomenology and physical insights. In this dissertation I will theoretically explore a few low-dimensional models using Majorana fermions and higher-spin moments as building blocks. I will first discuss a generalized family of the celebrated Sachdev-Ye-Kitaev model, a zero-dimensional all-to-all Majorana model that exhibits non-Fermi liquid behavior and is holographically dual to a black hole. The generalized model has a phase transition between a non-Fermi liquid and a disordered Fermi liquid. Then I will discuss the Heisenberg model with higher spins, with a focus on chaos and information scrambling. Using matrix-product-state-based methods, we are able to obtain numerical results for spin up to 4 and characterize the Lyapunov growth. After that I will discuss a generalization of the Hubbard model to Majorana fermions on the honeycomb lattice. Unlike previous similar models, we find topological phases with (anti-)chiral edge modes for weak interaction.
Finally, I will show a construction of explicit supersymmetric Majorana model on the kagome lattice, where a family of exact solutions is found and the nature of supersymmetry breaking is explored.
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Wednesday, May 5, 2021 | 11:00 am - 12:00 pm
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2021-05-05T11:00:00
2021-05-05T12:00:00
Neutron stars as gravitational-wave sources: dense matter and stellar mass
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Astronomical observations of neutron stars inform our understanding of matter at the highest densities. Already, we have used the gravitational-wave data of GW170817 - the first signal from merging neutron stars - to constrain the equation of state of dense matter in neutron stars. The heavy neutron-star merger GW190425 indicated that the gravitational-wave population may include heavier stars not previously observed in galactic double neutron star binaries. For more distant sources, the distribution of masses in neutron-star mergers will be a key observable in the coming years of gravitational-wave astronomy. In this talk, I will discuss methods being used to explore matter and mass properties for LIGO/Virgo neutron stars. I will discuss how these results fit with other neutron-star observations, outline prospects of learning about matter in the current Advanced-detector era, and extrapolate to the potential of next-generation gravitational-wave observatories to map the phase diagram of dense neutron-rich matter and the endpoints of stellar evolution.
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Monday, May 3, 2021 | 3:00 pm - 4:00 pm
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2021-05-03T15:00:00
2021-05-03T16:00:00
Reducing Errors in Derived Planetary Radii Caused by Undetected Stellar Companions via Adaptive Optics
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The calculated planet radii for TESS Objects of Interest (TOIs) presume that the stellar flux collected is only coming from known stars. However, any undetected stellar companions will provide additional flux and result in the transit depth being underestimated, leading to the planet radius also being underestimated. Radial velocity follow-up can identify companion stars on short orbits, and high-resolution imaging can identify companion stars with sufficient angular separations. There remains, however, a population of stellar companions that cannot be detected by either of these methods, and will still cause planetary radii to be underestimated. If the planet radii are larger than inferred from the transit depths alone, this can lead to a significant overestimation of the planetary density, and thus, for planets that are close to the boundary between rocky and gaseous planets, quantifying the frequency and properties of unknown stellar companions is critical to our understanding of planetary properties. We explore the likelihood of the presence of companions that may have escaped detection after vetting with adaptive opics (AO) imaging and the impact these potentially undetected companions have on derived planetary radii.
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Thursday, April 29, 2021 | 4:00 pm - 5:00 pm
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2021-04-29T16:00:00
2021-04-29T17:00:00
New phases of matter in quantum materials
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Abstract: Condensed matter is the science of stuff you can touch: if you can hold it in your hand, it's a condensed matter system. Phases of matter and phase transitions are central concepts in condensed matter physics. Think how important the solid, liquid, and vapor phases of water are to human society. But there are many more phases of matter and phase transitions than these three! From the liquid crystal displays of our computer screens, to the foams of bread and shaving cream, the suspension we know as milk, and the granular matter known as peanut butter, phases beyond the simple solid/liquid/gas permeate our lives. Some of the most dramatic technological advances have come through controlling the behavior of electrons inside of materials. These electrons have their own phases of matter and phase transitions, such as magnet, semiconductor, metal, and many other exotic phases of electrons which have thus far defied a unified theoretical description. We discuss a new conceptual framework for describing the behavior of electrons when they acquire self-similar structure on multiple length scales, i.e. fractal electronic textures. I will discuss the application of these ideas to quantum materials such as cuprate superconductors and Mott metal-insulator transition materials. [Nat. Commun. 10, 4568 (2019); Nat. Phys. 14, 1056 (2018); PRL 116, 036401 (2016); Nat. 529, 329 (2015); Nat. Commun. 3, 915 (2012)]
Bio: Erica W. Carlson, Ph.D., is Professor of Physics at Purdue University. Prof. Carlson holds a B.S. in Physics from the California Institute of Technology (1994), as well as a Ph.D. in Physics from UCLA (2000). A theoretical physicist, Prof. Carlson researches electronic phase transitions in quantum materials. In 2015, she was elected a Fellow of the American Physical Society "for theoretical insights into the critical role of electron nematicity, disorder, and noise in novel phases of strongly correlated electron systems and predicting unique characteristics." Prof. Carlson has been on the faculty at Purdue University since 2003, where she was recently named a "150th Anniversary Professor" in recognition of teaching excellence. Her latest work popularizing science can be found at thegreatcourses.com/courses/understanding-the-quantum-world and youtube.com/QuantumCoffeehouse
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Thursday, April 29, 2021 | 10:00 am - 11:00 am
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2021-04-29T10:00:00
2021-04-29T11:00:00
CM Seminar - A review and recent progress in quantum error - mitigation
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April 29, Thu 10am
https://ubc.zoom.us/j/64183011430?pwd=U2lFNXEwSmlBRWVBdTR5OG1ZdlVSZz09
Meeting ID: 641 8301 1430
Passcode: 113399
Speaker: Kristan Temme - IBM
Talk Title: A review and recent progress in quantum error - mitigation
Abstract: Near-term applications of early quantum devices, such as quantum simulations, rely on accurate estimates of expectation values to become relevant. Decoherence and gate errors lead to wrong estimates. This problem was, at least in theory, remedied with the advent of quantum error correction. However, the overhead that is needed to implement a fully fault-tolerant gate set with current codes and current devices seems prohibitively large. In turn, steady progress is made in improving the quality of the quantum hardware. This leads to the question: what computational tasks could be accomplished with only limited, or no error correction? In this talk we first review two simple techniques for quantum error mitigation that increase the quality of short-depth quantum simulations. The first method, extrapolation to the zero noise limit, subsequently cancels powers of the noise perturbations by an application of Richardson’s deferred approach to the limit. The second method cancels errors by resampling randomized circuits according to a quasi-probability distribution. The two schemes are presented and we will discuss their application in experiments. Furthermore we will discuss recent progress on applying error mitigation techniques to logical qubits that don't support a universal gate set
and show how to implement encoded Clifford+T circuits. Here the Clifford gates are protected from noise by error correction while errors introduced by noisy encoded T-gates are mitigated using the quasi-probability method. As a result, Clifford+T circuits with a number of T-gates inversely proportional to the physical noise rate can be implemented on small error-corrected devices without magic state distillation. We argue that such circuits can be out of reach for state-of-the-art classical simulation algorithms.
Short Bio: Kristan Temme is a Principal Research Staff Member and the manager of the Theory of Quantum Algorithms group at IBM's T.J. Watson Research Center. His research currently centers around quantum algorithms and noise in complex quantum systems with a focus on the applications of noisy intermediate scale quantum devices.
Kristan has received a diploma in Physics from the University of Heidelberg in 2007. He completed his Ph.D in Physics at the University of Vienna in 2011 under the supervision of Frank Verstraete. During this time he studied quantum Markov processes and complex quantum many-body systems. Between 2012 and 2014 he was a postdoctoral fellow at the Massachusetts Institute of Technology. Between March 2014 and September 2015 Kristan held the IQIM postdoctoral Fellowship of the Gordon and Betty Moore Foundation at the California Institute of Technology. He joined IBM research in the fall of 2015.
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Event Time:
Wednesday, April 28, 2021 | 11:00 am - 12:00 pm
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2021-04-28T11:00:00
2021-04-28T12:00:00
Apocalyptic quantum gravity
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Quantum gravity is hard, but it's not the end of the world. Or is it? In this talk, I'll give a high-level overview of recent work involving end-of-the-world branes in AdS/CFT. Gravitationally, these branes are simple hypersurfaces cutting off spacetime. Quantum-mechanically, however, they encode non-perturbative features of the dual CFT, and exhibit surprising information-theoretic properties. I'll explain how these branes are constructed, how to test the genericity and consistency of the construction, and finally, how to use it to peer inside black holes and track their evaporation. I end with some prospects for post-apocalyptic quantum gravity.
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Tuesday, April 27, 2021 | 1:00 pm - 3:00 pm
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2021-04-27T13:00:00
2021-04-27T15:00:00
Departmental Doctoral Oral Examination (Thesis Title: “Axion Quark Nugget Dark Matter Model: Developments in Model Building and Observations”)
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Abstract:
The axion quark nugget (AQN) model was initially proposed with the motivation to explain the observed similarity between the visible and dark matter abundances in the Universe. AQNs are dense objects made of standard model quarks in color superconducting (CS) phase. AQNs can be made of matter as well as antimatter. Matter AQNs and antimatter AQNs together form the dark matter, while the disparity between them will lead to the observed matter-antimatter asymmetry. Thus, the similarity between visible and dark matter abundances can be naturally explained since they have the same origin in the AQN framework.
This thesis focuses on recent developments in model building and some potential observational evidence of AQNs. First, we show how the coherent nonzero axion field in the early Universe generates the disparity between matter and antimatter AQNs. Then, we calculate the real-time evolution of an AQN from its initial state as a closed axion domain wall with baryon charge trapped inside to its final CS state.
Next, we show that for the most part of axion parameter space, AQNs are the dominant part of dark matter compared to the contribution of the free axions from the misalignment mechanism. After that, we calculate the size distribution of AQNs based on percolation theory. We also demonstrate that after formation, the size distribution can survive the subsequent evolution in the early Universe. Finally, we study potential observational evidence of the AQN model, focusing on the following two phenomena: the impulsive radio events in quiet solar corona recorded by the Murchison Widefield Array and the seasonal variation of the near-Earth X-ray background observed by the XMM-Newton observatory.
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Monday, April 26, 2021 | 3:00 pm - 4:00 pm
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2021-04-26T15:00:00
2021-04-26T16:00:00
Innovative Approaches in mm-Wavelength Cosmology: From Inflation to the Epoch of Reionization and Beyond
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I will describe how we use mm-wavelength instruments (both spectrometers and photometers) to explore our universe across cosmic time and to probe fundamental physics. I will discuss how we seek to understand the epoch of reionization, star formation across cosmic time, and cosmology using the cosmic microwave background (probing inflation and neutrino physics), and discuss the development of instrumentation and data analysis tools to study these areas. I will focus on TIME, a pathfinder instrument I am leading for studying reionization with mm-wavelength line intensity mapping. I will discuss models for expected signals from this instrument and discuss what we may be able to learn from combining data from mm-wavelength spectrometers with other instruments, such 21 cm instruments in the future. I will also briefly mention CMB-S4, a next generation cosmic microwave background experiment that will probe cosmology, the early universe, and neutrino physics.
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Thursday, April 22, 2021 | 4:00 pm - 5:00 pm
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2021-04-22T16:00:00
2021-04-22T17:00:00
Cosmic Bell Experiments: Using Quasars to Test Quantum Theory
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Abstract: For decades, physicists have conducted experimental tests of quantum entanglement, a phenomenon that Albert Einstein once dismissed as "spooky action at a distance." Despite Einstein's misgivings, the experiments have consistently found results compatible with quantum theory; today entanglement is at the heart of next-generation devices like quantum computers and quantum encryption. Yet every experimental test has been subject to one or more "loopholes," which (in principle) could account for the results even in the absence of genuine quantum entanglement. This talk describes the latest experimental tests of quantum entanglement, including my group's recent "Cosmic Bell" experiments that used real-time astronomical measurements of light from high-redshift quasars to address the most stubborn of the remaining loopholes. Our experiments provided compelling evidence that quantum entanglement is a robust feature of our world while constraining certain classes of alternative models more thoroughly than ever before.
Bio: David Kaiser is Germeshausen Professor of the History of Science and Professor of Physics at the Massachusetts Institute of Technology,
where he also serves as Associate Dean for Social and Ethical Responsibilities of Computing. He is the author of several award-winning books about modern physics. His latest book, "Quantum Legacies: Dispatches from an Uncertain World" (2020), was honored as among the best books of the year by "Physics Today" and "Physics World" magazines. A Fellow of the American Physical Society, Kaiser has received MIT's highest awards for excellence in teaching. His work has been featured in "Science", "Nature", the "New York Times", and the "New Yorker" magazine. His group's recent efforts to conduct a "Cosmic Bell" test of quantum entanglement were featured in a documentary film, "Einstein's Quantum Riddle", which premiered in 2019.
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Thursday, April 22, 2021 | 1:00 pm - 3:00 pm
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2021-04-22T13:00:00
2021-04-22T15:00:00
Departmental Doctoral Oral Examination (Thesis Title: “The Interfacial Dynamics of Amorphous Materials as Revealed By β-NMR Measurements and Molecular Simulations”)
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Abstract:
The free surface interface is important for developing a fundamental understanding of dynamical length scales in glasses. We first investigate the relaxation of freestanding atactic polystyrene (aPS) thin films with molecular dynamics simulations. As in previous coarse-grained simulations, relaxation times for backbone segments and phenyl rings are linked to their bulk relaxation times via a power law coupling relation. Variation of the coupling exponent with distance from the surface is consistent with depth-dependent activation barriers. We also quantify a reduction of dynamical heterogeneity at the interface which can be interpreted in the framework of cooperative models for glassy dynamics. Capable of depth-resolved measurements near the surface, implanted-ion β-detected nuclear magnetic resonance (β-NMR) has been a powerful probe of the dynamics in aPS thin films. We have completed and commissioned an upgrade to the β-NMR spectrometer, extending the accessible upper temperature, and enabling a direct comparison between this experimental technique and the molecular dynamics simulations. We demonstrate that the modified spectrometer is now capable of operation to at least 400 K, an improvement of more than 80 K.
We also demonstrate the application of β-NMR as a probe of ionic liquid molecular dynamics through the measurement of 8Li spin-lattice relaxation (SLR) and resonance in 1-ethyl-3-methylimidazolium acetate. The motional narrowing of the resonance, and the local maxima in the SLR rate, 1/T1 , imply a sensitivity to sub-nanosecond Li+ solvation dynamics. From an analysis of 1/T1 , we extract an activation energy and Vogel-Fulcher-Tammann constant in agreement with the dynamic viscosity of the bulk solvent. Near the melting point, the line shape is broad and intense, and the form of the relaxation is non-exponential, reflective of our sensitivity to heterogeneous dynamics near the glass transition. We also employ the depth resolution capabilities of this technique to probe the subsurface dynamics with nanometer resolution. We show modified dynamics near the surface in, and above, the glassy state.
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Thursday, April 22, 2021 | 10:00 am - 12:00 pm
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2021-04-22T10:00:01
2021-04-22T12:00:00
Departmental Doctoral Oral Examination (Thesis Title: “Topological quantum phase transitions and topological quantum criticality in superfluids and superconductors”)
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Abstract:
Quantum phases of different topologies exist in superfluids and superconductors. These phases can be either fully gapped or gapless with nodal structures. Topological quantum phase transitions exist between these gapped phases or between gapped and nodal phases. The two phases on both sides of the phase transitions have the same local order but differ in topology. These topological quantum phase transitions cannot be described by the Landau paradigm of symmetry breaking. It is well-known that surface states change across these phase transitions as a result of change of topology in the bulk. However, a complete theory of topological quantum phase transitions has not been developed before. Here we construct an effective field theory to study the universality class of these topological quantum phase transitions. We find that quantum phase transitions between fully gapped phases with different topologies belong to the emergent relativistic Majorana field universality class. Quantum phase transitions between gapped and nodal phases belong to what we call quantum Lifshitz Majorana field universality classes. We also study the bulk signatures and energetics of these phase transitions. We find non-analyticities in certain thermodynamic quantities across these phase transitions, which can be viewed as a collective signature of Majorana fermions in the bulk. These topological quantum phase transitions only exist at zero temperature. At finite temperature, different states are connected by smooth crossovers. There exists a quantum critical region where physical properties are dictated by the topological quantum critical points (QCPs) at zero temperature. Thermodynamic quantities have universal scaling dependence on temperature that are also unique to each universality class. These temperature scalings can be used to probe and differentiate different topological QCPs.We also find that topological QCPs can exist on surfaces when time-reversal symmetry is broken. These surface topological QCPs belong to the emergent relativistic Majorana field universality class. These topological quantum phase transitions exist in various concrete models, such as chiral and time-reversal invariant $p$-wave superfluids, topological superconductors of emergent Dirac fermions, and topological superconducting model of Cu$_x$Bi$_2$Se$_3$.
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Event Time:
Thursday, April 22, 2021 | 10:00 am - 11:00 am
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2021-04-22T10:00:00
2021-04-22T11:00:00
CM Seminar - ZnO: Ultrafast generation and decay of a surface metal
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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)
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Tuesday, April 20, 2021 | 2:00 pm - 4:00 pm
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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”)
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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.
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Monday, April 19, 2021 | 3:00 pm - 4:00 pm
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2021-04-19T15:00:00
2021-04-19T16:00:00
The Southern Stellar Stream Spectroscopic Survey: Overview and Latest Science Results
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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.
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Thursday, April 15, 2021 | 4:00 pm - 5:00 pm
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2021-04-15T16:00:00
2021-04-15T17:00:00
First Results from the Fermilab Muon g-2 Experiment!
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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.
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Thursday, April 15, 2021 | 10:00 am - 11:00 am
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2021-04-15T10:00:00
2021-04-15T11:00:00
CM Seminar - Pressure Control of Competing Orders in Superconductors
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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)
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Monday, April 12, 2021 | 3:00 pm - 4:00 pm
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2021-04-12T15:00:00
2021-04-12T16:00:00
Exploring The Transient Sky At Millimeter Wavelengths With SPT-3G
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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.
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Thursday, April 8, 2021 | 4:00 pm - 5:00 pm
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2021-04-08T16:00:00
2021-04-08T17:00:00
What are scientific abilities and how to help students develop them?
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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/ .
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