Events List for the Academic Year
Event Time:
Thursday, October 31, 2019 | 2:00 pm - 3:00 pm
Event Location:
Brimacombe 311
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2019-10-31T14:00:00
2019-10-31T15:00:00
CM Seminar - Linear and nonlinear optical responses in chiral topological semimetals
Event Information:
Abstract: The fundamental difference between electrons in a solid and those in high-energy physics is the absence of Poincare symmetry in lattice systems. This gives rise to a much larger number of possible low energy excitations (known as multi-fold fermions) in solid-state physics. Recent theory and experiments show that semimetals with multi-fold degenerate points could exist in nonmagnetic materials with chiral crystal structures. In my talk, I would like to discuss how do we use light to probe these low-energy excitations near the multi-fold degenerate points by linear and nonlinear optical conductivity measurements.
Short Bio: Liang Wu got his B.S. in Physics from Nanjing University in 2010 and Ph.D in Physics at the Johns Hopkins University in 2015. He was a postdoc fellow at the University of California, Berkeley from 2016 to 2018 before joining the department of Physics and Astronomy at the University of Pennsylvania in July 2018. He has been using terahertz spectroscopy and ultrafast optics to study topological insulators, Weyl semimetals and quantum spin liquids. He received the McMillan Award for outstanding contribution in condensed matter physics from the University of Illinois (2019), the Army Research Office Young Investigator Program (YIP) Award (2019), and the Richard L. Greene Dissertation Award in Experimental Condensed Matter Physics by the American Physical Society (2017).
Event Location:
Brimacombe 311
Event Time:
Thursday, October 31, 2019 | 2:00 pm - 3:00 pm
Event Location:
TRIUMF Auditorium
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2019-10-31T14:00:00
2019-10-31T15:00:00
The Accelerating Universe: Lambda, W, and Beyond
Event Information:
While cosmic acceleration is well-established, the nature of Dark Energy causing it remains unknown. A flat universe dominated by a cosmological constant (Lambda) and cold dark matter (CDM) has been cosmologists' working model of choice for nearly two decades. However, the value of Lambda poses a serious theoretical challenge, exposing a gap in our understanding of the vacuum energy and the way it gravitates. Intriguingly, there appear to be tensions between different datasets within the LCDM framework that would be relieved if Dark Energy density was non-constant. I will discuss the evidence for this, as well as some of the alternatives to Lambda and ways of testing them with future data.
Event Location:
TRIUMF Auditorium
Event Time:
Wednesday, October 30, 2019 | 11:00 am - 1:00 pm
Event Location:
Room 318, Hennings Bldg.
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2019-10-30T11:00:00
2019-10-30T13:00:00
Departmental Doctoral Oral Examination (Thesis Title: "Diffusion and surface trapping of 8Li in rutile TiO2 and the comparison on 8Li and 9Li spin relaxation using β-NMR")
Event Information:
Abstract:
It is well established that the properties of many materials change as their thickness is shrunk to the nanoscale, often yielding novel features at the near-surface region that are absent in the bulk. Even though there are several techniques that can study either the bulk or the surface of these materials, there are very few that can scan the near-surface region of crystals and thin films versus depth. Beta detected NMR (β-NMR) is capable of this and therefore has been established as a powerful tool for
material science.
This thesis aims to further develop the capabilities of β-NMR. By comparing the spin-lattice relaxation rates (SLR) of two radioactive Li isotopes (8;9Li) it is shown that it is possible to distinguish whether the source of SLR in a given situation is driven by magnetic or electric interactions. In addition, by coupling the β-decay signal with the subsequent α-decay of 8Li, a technique able to directly study nanometer-scale lithium diffusion was developed.
The first part of this thesis demonstrates that by studying a material with both 8;9Li-b-NMR, it is possible to distinguish the source of SLR. This is an important development for β-NMR, since there are instances where it is problematic to distinguish whether the measured relaxation is due to magnetic or electric fluctuations. Using this method, it was found that the SLR in Pt is (almost) purely magnetic in origin, whereas the spin relaxation in SrTiO3 is driven (almost) entirely by electric quadrupolar interactions.
The second part of this thesis traces the development of α-radiotracer, that uses the progeny α-particles from the decay of 8Li, in order to directly measure the nanoscale diffusivity of Li+ in Li-ion battery materials. To develop this technique, Monte Carlo simulations of the experimental configuration were carried out, a new apparatus and a new α-detector were designed and used for experiments on rutile TiO2. In rutile, the measurements revealed that Li+ gets trapped at the (001)
surface, a result that helps explain the suppressed intercalation of Li+ in bulk rutile. Moreover, the diffusion rate of Li+ in rutile was found to follow a bi-Arrhenius relationship, with a high-T activation energy in agreement with other reported measurements and a low-T component of similar magnitude with the theoretically calculated diffusion barrier as well as the activation energy of the Li-polaron complex found with β-NMR below 100 K.
Event Location:
Room 318, Hennings Bldg.
Event Time:
Tuesday, October 29, 2019 | 2:00 pm - 3:00 pm
Event Location:
Brimacombe 311
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2019-10-29T14:00:00
2019-10-29T15:00:00
CM Seminar - Current Transport Properties and Phase Diagram of a Kitaev Chain with Long-Range Pairing
Event Information:
Abstract: We describe a method to probe the quantum phase transition between the short-range and the long-range topological phase in the superconducting Kitaev chain with long-range pairing. We show that, when the leads are biased at a voltage V, the Fano factor is either zero or 2e. As a result, we find that the Fano factor works as a directly measurable quantity to probe the quantum phase transition between the two phases, also showing a remarkable "critical fractionalization effect". Finally, we note that a dual implementation of our proposed device makes it suitable as a generator of large-distance entangled two-particle states
Event Location:
Brimacombe 311
Event Time:
Monday, October 28, 2019 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
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2019-10-28T15:00:00
2019-10-28T16:00:00
Sporadic Pulsar Emission at Low Radio Frequencies
Event Information:
Pulsars are unparalleled astrophysical tools, yet, after more than 50 years of research, we still do not fully understand the mechanism responsible for their radio emission. To further complicate the matter, the phenomenon of emission intermittency, where the pulsar radio emission ceases unpredictably, is also a mystery. Through a series of simultaneous wideband observations of three different sporadically emitting pulsars, using the Murchison Widefield Array and other Australian radio telescopes, the importance of low-frequency information when characterizing the radio emission is highlighted.
Event Location:
Hennings 318
Event Time:
Thursday, October 24, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2019-10-24T16:00:00
2019-10-24T17:00:00
How can physicists teach climate science?
Event Information:
Climate and energy are prominent topics in the news and in our daily lives. We hear things like doubling the amount of CO2 in the atmosphere will raise the temperature of the Earth by 3 degrees. UBC's sustainability reports tell us that simply heating our classrooms, offices, and labs produces the equivalent of 42,000 tonnes of CO2 a year.
PHYS 333 - Climate and Energy is a third year course aimed at providing a physicist's view of this type of issue. What are the simple models that lead to these results? What things matter and what things don't? It is a course on thermodynamics and "Fermi problems" in disguise.
In this talk I will present a sampling of concepts I teach in PHYS 333 and demonstrate how to use them to unpack some of the terms and numbers you encounter in your day-to-day lives. I'll also briefly talk about some teaching strategies I use in PHYS 333 to facilitate discussions. Specifically, I'll introduce ComPAIR, learning software that I helped develop, which has been used in over 50 courses here at UBC and across Canada by over 5000 students.
Event Location:
Hennings 201
Event Time:
Thursday, October 24, 2019 | 2:00 pm - 3:00 pm
Event Location:
Brimacombe 311
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2019-10-24T14:00:00
2019-10-24T15:00:00
CM Seminar - Tunneling Probe of 2D Magnetism
Event Information:
The recent discoveries of ferromagnetism in single atomic layers have opened a new avenue for two-dimensional (2D) materials research. Not only do they raise fundamental questions regarding the requirements for long-range magnetic order in low-dimensional systems, but they also provide a new platform for the development of spintronic devices. In this talk, I will present a series of studies on the family of layered ferromagnetic semiconductors, CrX3 (X = I, Br, Cl), in the atomically thin limit. By incorporating these materials as tunnel barriers between graphene electrodes, we are able to achieve extremely large tunnel magnetoresistance as well as robust memristive switching that is tunable with magnetic field. Tunneling spectroscopy further allows for direct observation of their spin wave excitations, or magnons, from which we are able to derive a simple microscopic Hamiltonian for all three spin systems. These results show that strong exchange anisotropy is not necessary to stabilize ferromagnetism in the monolayer limit.
Event Location:
Brimacombe 311
Event Time:
Monday, October 21, 2019 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
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2019-10-21T15:00:00
2019-10-21T16:00:00
Gas contents of the low-redshift Universe from the Sunyaev-Zeldovich effect
Event Information:
The Sunyaev-Zeldovich effect (SZE) provides a promising avenue to explore the properties of gas associated with halos and large-scale structures. However, due to contamination by the primary CMB, as well as foregrounds, projection effects, halo identification, and the beam size of current CMB surveys, it is not a trivial task to extract the signal precisely and accurately. In this talk, I will present some recent results of studying the SZE signal from gas in different environments, and discuss the implications for galaxy formation, as well as the uncertainties and potential systematic effects.
Event Location:
Hennings 318
Event Time:
Thursday, October 17, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2019-10-17T16:00:00
2019-10-17T17:00:00
Composite Fermions and their Fermi Surfaces
Event Information:
The decades following the initial discovery of the integer and fractional quantum Hall effects (IQHE/FQHE) in two-dimensional electrons in a strong perpendicular magnetic field led to a detailed understanding of the rich phase diagram and exotic phenomena characterizing various phases. These include charge fractionalization, Abelian and non-Abelian quantum states, topological spin excitations, charge-density-wave phases, to name a few. This body of work paved the way for the new field of topological materials in the 21st century.
The composite fermion picture developed by Jain provides a natural way to understand the sequence of FQH phases. It also naturally predicts the existence of certain gapless phases at even denominator filling fractions of a Landau level in the midst of the more common gapped FQH phases with odd denominator filling fractions and quantized Hall conductance. In particular, the phase for a half-filled lowest Landau level (filling factor n = 1/2) is seen as a Fermi liquid of composite fermions formed out of electrons bound to two vortices, in the absence of a magnetic field.
After briefly reviewing the arguments for various fractional quantum Hall phases following the picture of composite fermions, we concentrate on the gapless phase at filling factor n = 1/2 and explore the nature of its Fermi surface. We will compare its behavior with that of Fermi surfaces of familiar metals with weak electron-electron interactions which depend sensitively on the electronic structure of the material. We ask questions such as - What is the relationship between the Fermi surface of electrons at zero magnetic field and the composite fermion Fermi surface? How sensitive is the latter to perturbations of the zero- field Hamiltonian? What happens when the system does not have rotational symmetry with a circular Fermi surface at zero magnetic field? Using a combination of analytic and numerical techniques, we show that the answer is both surprising, and amenable to a parameter free experimental test, which it passes with surprising accuracy.
Event Location:
Hennings 201
Event Time:
Thursday, October 17, 2019 | 9:00 am - 10:00 am
Event Location:
AMPEL room 311
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2019-10-17T09:00:00
2019-10-17T10:00:00
MASc Thesis Presentation - "A Tunable Vacuum Ultraviolet Light Source for TR-ARPES"
Event Information:
Abstract:
We detail the initial development of a tunable vacuum ultraviolet light source for time-- and angle--resolved photo emission spectroscopy (TR-ARPES); specifically, the construction and characterization of a ytterbium-fiber based pump source, and a nonlinear broadening and compression stage using gas--filled hollow--core fiber (HCF). The ultimate goal is generating sub-30fs pulses with photon energies between 5eV and 11eV via resonant dispersive wave (RDW) generation in a succeeding HCF. The interim goal, discussed herein, is producing 30fs pulses with sufficient energy (uW level) for RDW generation. Using second harmonic generation frequency resolved optical gating (SHG-FROG) we currently measure 174fs, 4.0uJ pulses. We will provide explanations for the shortcoming and suggest several possible solutions to address it.
Event Location:
AMPEL room 311
Event Time:
Wednesday, October 16, 2019 | 7:30 pm - 9:00 pm
Event Location:
Buchanan A201
1866 Main Mall Block A, UBC campus
1866 Main Mall Block A, UBC campus
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2019-10-16T19:30:00
2019-10-16T21:00:00
Carbon Capture From the Atmosphere: A Solution to Global Warming?
Event Information:
To stem the rise of global temperatures we must reduce CO2 emissions. Recently, a Canadian clean energy company, Carbon Engineering Ltd. has developed an industrially-scalable “Direct Air Capture” technology to address this global problem. This technology removes CO2 directly from the atmosphere and can permanently store it underground. In addition, it can be used to reduce emissions by producing ultra-low carbon synthetic fuels, which can power existing cars, trucks and airplanes without any modifications. This talk will explain basic facts about global warming, the challenges involved in stopping it, the direct air capture process now being developed for this purpose, and how it may be scaled up to deal with global needs.
Event Location:
Buchanan A201
1866 Main Mall Block A, UBC campus
Event Time:
Wednesday, October 16, 2019 | 2:00 pm - 3:00 pm
Event Location:
TRIUMF Auditorium
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2019-10-16T14:00:00
2019-10-16T15:00:00
A brief introduction to glasses
Event Information:
Glassy materials and they way glasses are formed from liquids is an active area of both fundamental and applied research. While it is relatively easy to describe low density disordered materials (gas) and high density ordered materials (crystals), high density disordered materials - especially glassy solids - remains a difficult and unresolved problem. Of particular interest is the concept of an ideal glass, and if such a thing does exist how can it be realised? I will discuss characteristics of glasses and glass forming materials, some simple ways of thinking of the dynamics of these materials, the properties of these materials in nanoscale environments, and some very recent tantalizing observation that bring us close to the realizations of ideal glasses. The samples, which can be prepared in the lab in a few hours, have properties similar to those of samples that have been allowed to age for many thousands, or even millions of years.
Event Location:
TRIUMF Auditorium
Event Time:
Thursday, October 10, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2019-10-10T16:00:00
2019-10-10T17:00:00
Unmasking black holes with the Event Horizon Telescope
Event Information:
Black holes are, without question, one of the most bizarre and mysterious phenomena predicted by Einstein's theory of general relativity. They correspond to infinitely dense, compact regions in space and time, where gravity is so extreme that nothing, not even light, can escape from within. And, their existence raises some of the most challenging questions about the nature of space and time. Over the past few decades, astronomers have identified numerous tantalizing observations that suggested that black holes are real. This past April, the search for confirmation changed dramatically with the publication of the first image ever taken of a black hole, rendering tangible what was previously only the purview of theory and science fiction. I will describe how these observations were made, how the images were generated, how quantitative measurements were obtained, and what they all mean for gravity and black hole astronomy.
Event Location:
Hennings 201
Event Time:
Thursday, October 10, 2019 | 2:00 pm - 3:00 pm
Event Location:
Brim 311
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2019-10-10T14:00:00
2019-10-10T15:00:00
CM Seminar - Topological valleytronics in bilayer graphene
Event Information:
Abstract : The advent of two-dimensional materials with hexagonal crystal symmetry offers a new electronic degree of freedom, namely valley, the manipulation and detection of which could potentially be exploited to form new many-body ground states as well as new paradigms of electronic applications. In this talk, I will describe how we create valley-momentum locked topological 1D channels, aka quantum valley Hall kink states, in Bernal stacked bilayer graphene by electrically generating inverted band structures[1]. This all-electric construction gives us the ability to realize reconfigurable ballistic waveguides and device operations that explicitly explore the valley-momentum locking of the kink states. I will show the working of a topological valley valve, which does not require valley-polarized current to operate but relies on the control of topology, and a continuously tunable electron beam splitter[2], which is akin to the function of a quantum point contact for quantum Hall edge states. The high quality and versatile control of the kink states open the door to many exciting fundamental physics inquiries in 1D. Its realization requires the development of high-precision lithography on BN/graphene/BN heterostructures. Time permitting, I will touch upon other works this technique has enabled.
J. Li, K. Wang, K. J. McFaul, Z. Zern, Y. F. Ren, K. Watanabe, T. Taniguchi, Z. H. Qiao, J. Zhu, “Gate-controlled topological conducting channels in bilayer graphene”, Nature Nanotechnology, 11, 1060 (2016)
Jing Li, Rui-Xing Zhang, Zhenxi Yin, Jianxiao Zhang, Kenji Watanabe, Takashi Taniguchi, Chaoxing Liu, Jun Zhu, “A valley valve and electron beam splitter”, Science 362, 1149 (2018)
Biography : Professor Jun Zhu received her PhD from Columbia University in 2003. She was a postdoc fellow in Cornell University from 2003-2005 before joining Penn State University in 2006. She is currently a Professor of Physics at Penn State. Her research interest focuses on the understanding of new physics and device functionalities arising from reduced dimensionality, many-body interactions and the control of new electronic degrees of freedom in nanoscale materials and devices. Her recent research projects explore the electronic properties of van der Waals materials and interferences, with a particular emphasis on valleytronic, topological, and quantum Hall phenomena. Her lab homepage: https://sites.google.com/view/junzhulab/home
Event Location:
Brim 311
Event Time:
Wednesday, October 9, 2019 | 3:00 pm - 5:00 pm
Event Location:
Room 4524 (Teaching Room), BC Cancer-Vancouver
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2019-10-09T15:00:00
2019-10-09T17:00:00
Departmental Oral Examination (Thesis Title: “A Monte Carlo inverse treatment planning algorithm for trajectory-based VMAT with simultaneous couch and gantry rotation”)
Event Information:
Abstract:
The main objective of this thesis is to present a non-hybrid Monte Carlo (MC) based inverse treatment planning for trajectory-based volumetric modulated arc therapy (TVMAT). With the use of continuous and simultaneous gantry and couch rotation, a higher dosimetric plan quality can be achieved. However, commercial treatment planning systems do not provide such a capability. It has been shown that a full MC based optimization greatly reduces the optimization convergence errors. Previously published approaches to MC based optimization have not been clinically implemented, and none has been proposed for VMAT or TVMAT so far. In this work, the author has developed a method that reflects the dynamic multi-leaf collimator (MLC) and gantry-couch trajectory of the actual beam delivery at all stages of the optimization. Dose optimization is performed in a single MC simulation, thereby greatly reducing calculation time. The author selects the initial trajectory (i.e. the range of the gantry, collimator and couch angles) and the initial set of leaf positions, corresponding to a dynamic beam conformal to the target. The MC simulation starts from a phase space scored at the top of the MLC module and uses ‘source 20’ of DOSXYZnrc. The author modifies DOSXYZnrc in order to generate a four-dimensional dose file that scores individual, time-stamped, energy deposition events in the voxels of the planning target volume (PTV) and organs at risk (OAR). Consequently, a relation is established between the space and time (i.e. MU index) coordinates of source particles in the phase space and their contribution to energy deposition. A direct-aperture optimization, with a dose-volume histogram based quadratic objective function, is performed using an in-house code, taking rigorously into account the continuous movement of the MLC, gantry and couch between adjacent control points. Clinically acceptable PTV coverage and OAR sparing have been achieved with this trajectory-based MC optimization..
Event Location:
Room 4524 (Teaching Room), BC Cancer-Vancouver
Event Time:
Monday, October 7, 2019 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
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2019-10-07T15:00:00
2019-10-07T16:00:00
SPHEREx: An all-sky near infrared spectral survey
Event Information:
Recently selected for implementation as the next medium-class mission in NASA's Explorer line, SPHEREx will produce a Near Infrared spectrum for every 6 arcsecond pixel on the celestial sphere. Through the use of cold wide-field optics combined with linear variable filters, this experiment is optimized to probe for signatures of inflation, imprinted on the large-scale structure of the Universe. Key science goals also include surveying the Milky Way for water and other biogenic ices, as well as tracing the history of cosmic light production through fluctuation studies of the NIR background. In this talk I'll provide an overview of the mission, with a focus on the instrument and mission design.
Event Location:
Hennings 318
Event Time:
Thursday, October 3, 2019 | 4:00 pm - 5:00 pm
Event Location:
Hennings 201
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2019-10-03T16:00:00
2019-10-03T17:00:00
The Restoration of Early Sound Recordings using Optical Metrology and Image Analysis
Event Information:
Sound was first recorded and reproduced by Thomas Edison in 1877. Until about 1950, when magnetic tape use became common, most recordings were made on mechanical media such as wax, foil, shellac, lacquer, and plastic. Some of these older recordings contain material of great historical interest, but may be in obsolete formats, and are damaged, decaying, or are now considered too delicate to play. Unlike print and latent image scanning, the playback of mechanical sound carriers has been inherently invasive. Recently, techniques, based upon non-contact optical metrology and data analysis, have been applied to create and analyze high resolution digital images, and to restore the audio content, of these materials.
This lecture will discuss the characteristics of early sound recordings and the use of this new technology as applied to a number of notable collections: field recordings of Native Americans and Canadians from the early 20th Century, the experimental sound recordings of Alexander Graham Bell, from the 1880s, and ethnographic recordings collected by Milman Parry in Yugoslavia in 1930, which led to the oral-formulaic theory of epic poetry.
The technology and restoration of historic audio recordings will be illustrated with sounds and images. Additional information can be found at http://irene.lbl.gov/
Event Location:
Hennings 201
Event Time:
Thursday, October 3, 2019 | 2:00 pm - 4:00 pm
Event Location:
Room 309, Hennings Bldg
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2019-10-03T14:00:00
2019-10-03T16:00:00
Departmental Oral Examination (Thesis Title: “QED and X-ray Polarization from Neutron Stars and Black Holes”)
Event Information:
Abstract:
The emission from accreting black holes and neutron stars, as well as from the highly magnetized neutron stars called magnetars, is dominated by X-rays. For this reason, spectral and timing studies in the X-rays have been extremely successful in broadening our understanding of compact objects for the past few decades. Soon, a new observational window will open on compact objects: X-ray polarimetry. In this work, I explore how polarized light is generated in black-hole accretion disks, magnetar atmospheres and magnetospheres and in the accretion region of X-ray pulsars. In the different chapters, I show how the polarization signal is sensitive to several unknowns in our theoretical models: the geometry of accretion in X-ray pulsars, the strength and structure of the magnetic field threading accretion disks around black holes, the process of the non-thermal emission in magnetars. For this reason, the future X-ray polarimetry missions will be extremely helpful in constraining our theoretical models. Furthermore, the polarization emission will provide, for the first time, a test of one of the first theoretical prediction of quantum electrodynamics: vacuum birefringence. In this work I show how this effect, previously considered only for neutron stars, plays a crucial role for black holes as well.
Event Location:
Room 309, Hennings Bldg
Event Time:
Thursday, October 3, 2019 | 2:00 pm - 3:00 pm
Event Location:
TRIUMF Auditorium
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2019-10-03T14:00:00
2019-10-03T15:00:00
Identification and control of domain wall patterning in spinel ferrimagnets
Event Information:
Spinel antiferromagnets have long been at the center of research into strong spin-lattice coupling and orbital effects. Among other properties, these materials frequently demonstrate concomitant magnetic and structural phase transitions, heightened magneto-elastic or dielectric response functions, and low-temperature multiferroism. There is very little agreement on the microscopic picture to be associated with these effects, but recent work has shown that mesoscale inhomogeneity can play a key role in raising the susceptibilities of complex materials to external perturbations.
In this talk, I will be discussing recent work at the University of Illinois which establishes the importance of mesoscale heterogeneity in determining bulk magnetic properties of spinel ferrimagnets Mn3O4 and MnV2O4. This will first include a review of Raman and x-ray scattering results which reveal the existence of low-temperature magnetostructural transitions and magnetic force microscopy data which show the existence of stripe-like magnetic domains, before turning to our more recent neutron scattering and muon spin rotation (muSR) measurements. Our muSR work associates the emergence of stripe-like domains in Mn3O4 with a real space separation into magnetically ordered and disordered volumes, and further shows that the ordering fraction can be grown with the application of moderate-sized fields. With small angle neutron scattering, we observe Bragg signatures of domain wall order in the bulk of both materials, with wall separations on the ~100nm scale. Lastly, I will present data that demonstrates how domain wall motion can be used to drive these systems out of their low-temperature ferrimagnetic states, with an Hc which is highly sensitive to the applied field direction. I will correlate these results from microscopic probes to our recent investigation into non-equilibrium effects in the bulk magnetization, and discuss in the context of “colossal” control of magnetic properties of real materials.
Acknowledgments:
Research was supported by the National Science Foundation under Grant NSF DMR 1455264.
Event Location:
TRIUMF Auditorium
Event Time:
Monday, September 30, 2019 | 3:00 pm - 4:00 pm
Event Location:
Hennings 318
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2019-09-30T15:00:00
2019-09-30T16:00:00
Weak lensing, baryons, and deep learning
Event Information:
Baryonic processes that alter the large-scale distribution of gas, and thus the matter power spectrum, such as AGN feedback, are one of the the main systematics in current and future weak lensing surveys. Left uncorrected, these effects will bias the inferred properties of dark matter and dark energy that these surveys are designed to measure. Characterising the distribution of gas is thus of vital importance if these surveys are to be exploited to their full potential.
In this talk, I will present ongoing work on joint analyses of weak lensing and tracers of diffuse gas, specifically the tSZ effect. I will show how a joint analysis of cosmic shear and tSZ cross-correlations breaks degeneracies of the individual probes and can significantly improve the constraints on cosmological parameters compared to cosmic shear alone.
Finally, I will demonstrate how we use a class of machine learning methods - deep generative models - to augment N-body simulations with gas. Specifically, I will show how conditional variational autoencoders and generative adversarial networks trained on the BAHAMAS hydrodynamical simulations can be used "paint" pressure fields on the SLICS suite of N-body simulations to produce consistent lensing and tSZ maps for use in the estimation of the cross-correlation covariance.
Event Location:
Hennings 318