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Mon Jan 15, 2018

Physics Colloquium: Dr. Rebecca Milot, Oxford University

4:00 PM - 5:00 PM
118 Nieuwland Science Hall

Optoelectronics of Hybrid Metal Halide Perovskites for Photovoltaics

Dr. Rebecca Milot
Oxford University

This lecture has been generously funded through The IBM Corporate Lecture Series, created to foster women's inclusion in science, technology, engineering and mathematics (STEM).

 

Hybrid metal halide perovskites have shown extraordinary success as active layers in solar cells, with power conversion efficiencies rivalling existing silicon technologies. A benefit of perovskites is that they are comprised of low-cost, earth abundant materials, and perovskite thin films are easily synthesized with simple starting materials. Additionally, they exhibit exceptional optoelectronic properties, which include strong absorption across the entire visible spectrum, long charge-carrier lifetimes, and high charge-carrier mobilities. Optical-pump/THz-probe (OPTP) spectroscopy has proven to be an essential technique for studying the charge-carrier dynamics and charge-carrier mobility in many of these materials including lead-based, tin-based, two-dimensional, and mixed-halide/mixed-cation perovskites. These studies have determined that the charge-carrier mobility and charge-carrier recombination dynamics are strongly dependent on chemical composition, defect density, band structure, and crystallinity.

Posted In: Colloquia

Wed Jan 17, 2018

Physics Colloquium: Dr. Fahad Mahmood, Johns Hopkins University

4:00 PM - 5:00 PM
118 Nieuwland Science Hall

Illuminating and manipulating quantum materials with femtosecond light

Dr. Fahad Mahmood
Johns Hopkins University

Uncovering and controlling emergent phenomena in quantum materials through external stimuli is a central goal of modern condensed matter physics. However, a major challenge lies in disentangling many different yet closely coupled interactions and fluctuating orders. Moreover, since many quantum processes in these materials are coherent only over ultrashort time scales, it is difficult to probe them using conventional static techniques. In this talk, I will demonstrate how ultrafast femtosecond optical techniques can selectively decipher and alter collective behavior in two of the most intensely researched quantum materials in the past decade, high-Tc superconducting cuprates and topological insulators. For superconducting cuprates, ultrafast infra-red pump-probe and time-domain THz spectroscopy are used to detect elementary excitations and short-lived fluctuating orders. For topological insulators, time-and-angle resolved photoemission spectroscopy is used to dynamically engineer new light-induced ‘Floquet-Bloch’ electronic states. Such studies lay the foundation for utilizing coherent light-matter interaction to steer materials into a desired quantum phase.

Posted In: Colloquia

Mon Jan 22, 2018

Nuclear Physics Seminar: Prof. Elias Garratt

4:00 PM - 5:00 PM
124 Nieuwland Science Hall

Understanding and controlling material properties through focused ion beam technology

Prof. Elias Garratt
Michigan State University

Hosted by Prof. Simon

Posted In: Nuclear Seminar

Tue Jan 23, 2018

Our Universe Revealed: Dr. Jason Kalirai, Multi-Mission Project Scientist, Space Telescope Science Institute

7:30 PM - 8:30 PM
101 Jordan Hall of Science

Hubble’s Recent Hits and a Look Forward to the James Webb Space Telescope

Dr. Jason Kalirai, Multi-Mission Project Scientist, Space Telescope Science Institute

Part of the Our Universe Revealed Lecture Series

Posted In: Special Lectures and Events

Wed Jan 24, 2018

Physics Colloquium: Dr. Jason Kalirai, STScI

4:00 PM - 5:00 PM
118 Nieuwland Science Hall

Seeing Galaxies as Collections of Stars

Dr. Jason Kalirai
STScI

Since the pioneering work of Henry Norris Russell 100 years ago, the study of nearby stellar populations in the Milky Way has served as a foundation for our quest to understand the nature of galaxies in the Universe. Today, studies of resolved stellar populations constrain fundamental relations that define how stars form, how they evolve over time, and how they dramatically transform themselves in the final stages of stellar death.  Understanding these processes give us a prescription to interpret all light from the Universe and to measure the physical state of galaxies. In this talk, I'll present new highest-precision observations that we've taken of nearby stellar populations, using the biggest ground and space based telescopes such as the Keck 10-meter telescope on Mauna Kea and the Hubble Space Telescope in orbit. These data are providing unprecedented constraints on our understanding of how stars evolve, and act as a bridge between studies of the nearby and distant Universe. I'll also discuss new opportunities for stellar population studies with an impressive suite of astronomical tools that are now on our horizon - GAIA, JWST, LSST, WFIRST, 30-meter telescopes.

Posted In: Colloquia

Thu Jan 25, 2018

Physics Colloquium: Dr. Chunhui Du, Harvard University

4:00 PM - 5:00 PM
123 Nieuwland Science Hall

Control and local measurements of the spin chemical potential in a magnetic insulator

Dr. Chunhui Du
Postdoctoral Fellow, Department of Physics, Harvard University

This lecture has been generously funded through The IBM Corporate Lecture Series, created to foster women's inclusion in science, technology, engineering and mathematics (STEM).

In recent decades, a large scientific effort has focused on harnessing spin transport for providing insights into novel materials and low-dissipation information processing. We introduce single spin magnetometry based on nitrogen-vacancy (NV) centers in diamond as a new and generic platform to locally probe spin chemical potentials which essentially determine the flow of spin currents. We use this platform to investigate magnons in a magnetic insulator yttrium iron garnet (YIG) on a 100 nanometer length scale. We demonstrate that the local magnon chemical potential can be systematically controlled through both ferromagnetic resonance and electrical spin excitation, which agrees well with the theoretical analysis of the underlying multi-magnon processes. Our results open up new possibilities for nanoscale imaging and manipulation of spin-related phenomena in condensed-matter systems.

Posted In: Colloquia

Mon Jan 29, 2018

Nuclear Physics Seminar: Dr. Sophia Han

4:00 PM - 5:00 PM
124 Nieuwland Science Hall

Neutron star seismology: damping of oscillation modes via phase conversion

Dr. Sophia Han
University of Tennessee Knoxville

Hosted by Prof. Surman
 …

Posted In: Nuclear Seminar

Tue Jan 30, 2018

Astrophysics Seminar: Mr. Steven Villanueva, OSU

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

A Year with the DEdicated MONitor of EXotransits and Transients (DEMONEXT), an Automated and Robotic Telescope for Exoplanet and Transient Follow Up

Mr. Steven Villanueva
The Ohio State University

DEMONEXT is a 0.5-m robotic telescope that has been in operation since May 2016. Fully automated, DEMONEXT has observed over 200 transits of exoplanet candidates for the KELT survey, including confirmation observations of KELT-20b. DEMONEXT achieves 2-4 mmag precision with unbinned, 20-120 second exposures, on targets orbiting V<13 host stars. Millimagnitude precision can be achieved by binning the transits on 5-6 minute timescales. During observations of 8 hours with hundreds of consecutive exposures, DEMONEXT maintains sub-pixel (<0.5 pixels) target position stability on the CCD during good observing conditions, with degraded performance during poor observing conditions (<1 pixel). DEMONEXT achieves 1% photometry on targets with V<17 in 5 minute exposures, with detection limits of V~21. In addition to the 150 transits observed by DEMONEXT, 50 supernovae and transients haven been observed for the ASAS-SN supernovae group, as well as time-series observations of Galactic microlensing, active galactic nuclei, stellar variability, and stellar rotation.

Posted In: Astrophysics Seminar

Particle Physics Seminar: Allie Reinsvold Hall, University of Notre Dame

4:00 PM - 5:00 PM
415 Nieuwland Science Hall

Search for general gauge mediated SUSY in final states with photons

Allie Reinsvold Hall
Graduate Student
Department of Physics, University of Notre Dame…

Posted In: Particle Physics Seminar

Wed Jan 31, 2018

Physics Colloquium: Prof. Dean Lee, MSU

4:00 PM - 5:00 PM
118 Nieuwland Science Hall

Lattice simulations for nuclear physics

Prof. Dean Lee
Department of Physics and Astronomy
MSU

This colloquium talk is an introduction to how atomic nuclei and other quantum few- and many-body systems can be studied using lattice simulations. The first part of the talk explains the basic formalism called lattice effective field theory. The rest of the talk is a discussion of novel methods and the new physics insights one gains with each.  The methods discussed are the adiabatic projection method for scattering and reaction calculations, pinhole algorithm for probing structure, and eigenvector continuation for extending calculations to regions of parameter space where things otherwise break down.

Posted In: Colloquia

Mon Feb 5, 2018

Nuclear Physics Seminar: Mr. Cory Thornsberry

4:00 PM - 5:00 PM
124 Nieuwland Science Hall

Proton transfer reactions studied using the VANDLE Neutron Detector Array

Mr. Cory Thornsberry
University of Tennessee Knoxville

Hosted by Prof. Ahn

Posted In: Nuclear Seminar

Tue Feb 6, 2018

Astrophysics Seminar: Dr. Claudia Scarlata, University of Minnesota

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

News from the WFC3 IR Spectroscopic Parallel Survey (WISP)

Dr. Claudia Scarlata
Associate Professor and Director of Graduate Studies
School of Physics and Astronomy
University of Minnesota

I will present recent results from the WFC3 Infrared Spectroscopic Parallel Survey (WISP) that we are conducting on the Hubble Space Telescope. This large program is identifying thousands of galaxies across a wide range of redshifts,  spanning more than two thirds of the age of the universe. In this talk, I will focus on our most recent results on the evolution of the Lyman alpha luminosity function out to redshift 7, and discuss implications for the sources of reionizing photons. I will also discuss our results in the context of future space  based surveys such as Euclid and WFIRST-AFTA.

Posted In: Astrophysics Seminar

Particle Physics Seminar: Dr. Andrew Long, Kavli Institute for Cosmological Physics

4:00 PM - 5:00 PM
415 Nieuwland Science Hall

Testing baryons from bubbles with colliders and cosmology

Dr. Andrew Long
Fellow, Kavli Institute for Cosmological Physics
University of Chicago…

Posted In: Particle Physics Seminar

Our Universe Revealed: Jared Coughlin

7:00 PM - 8:00 PM
101 Jordan Hall of Science

To Infinity and Beyond: An Exploration of Travel Between the Stars

Mr. Jared Coughlin
Graduate Student, Department of Physics, University of Notre Dame

From warp drives to generation ships, science fiction is rife with creative ways that humanity may end up travelling among the stars. In this talk we explore the feasibility of some of the more popular proposed methods and, assuming that they are possible, what the pros and cons of each may end up being.

Posted In: Special Lectures and Events

Wed Feb 7, 2018

Physics Colloquium: Dr. Long Ju, Cornell University

4:00 PM - 5:00 PM
118 Nieuwland Science Hall

Tunable Berry Phase and Berry Curvature Effects in 2D and 3D Materials

Dr. Long Ju
Kavli Institute of Nano Science
Cornell University

Berry phase played an important role in quantum mechanics and underlay the physics of a wide range of materials from topological phases of matters to various 2D materials. While the effect of Berry phase has been extensively shown as quantized conductance in transport experiment, the geometric aspect of wave function— determined by Berry curvature has remained much less understood experimentally. In this talk, I will use bilayer graphene as a model system to demonstrate effects of Berry phase and Berry curvature on materials’ electronic and optical properties. I will first show our study of topological valley transport in the stacking domain walls of bilayer graphene, where near field infrared nanoscopy is combined with low temperature transport measurement. Then I will report our study of excitons in the tunable bandgap of bilayer graphene using advanced spectroscopy tools. These excitons obey unusual valley-dependent optical selection rules and very large magnetic moment, both originate from the tunable pseudospin and Berry curvature effect. Finally I will discuss our recent efforts on probing the low energy electron dynamics in Weyl semimetals, and the possibility of detecting related Berry phase effects in these 3D topological material.  

Posted In: Colloquia

Tue Feb 13, 2018

Astrophysics Seminar: Mr. Jared Coughlin, University of Notre Dame

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

Cosmic acceleration and large scale structure

Mr. Jared Coughlin
Graduate Student, University of Notre Dame

Cosmic acceleration was first discovered in the late nineties. Ever since then discovering the nature of the mechanism responsible for this acceleration has stood as one of the most prominent goals of cosmology. In this talk I present a brief overview of the observational evidence supporting the existence of cosmic acceleration and establish the need for additional, complimentary probes. I then discuss several of the most popular mechanisms that have been proposed to explain cosmic acceleration, with a particular focus put on various dark energy models. These include the cosmological constant, quintessence, and k-essence. Having established the need for additional observational constraints in order to further narrow down the list of cosmic acceleration candidates, I conclude with a discussion of the feasibility of employing the Lyman alpha forest as such a probe, highlighting my preliminary results on this question.

Posted In: Astrophysics Seminar

Particle Physics Seminar: Mr. Kevin Zhang, University of Michigan

4:00 PM - 5:00 PM
415 Nieuwland Science Hall

Reshaping effective field theory analyses: new challenges at the LHC and new tools for one-loop matching

Mr. Kevin Zhang
Graduate Student, Theoretical Physics
University of Michigan…

Posted In: Particle Physics Seminar

Wed Feb 14, 2018

Physics Colloquium: Dr. Emrah Turgut, Cornell University

4:00 PM - 5:00 PM
118 Nieuwland Science Hall

Spin dynamics of topological spin textures in chiral magnets

Dr. Emrah Turgut
Postdoctoral Associate, Applied and Engineering Physics
Cornell University

The chiral spin textures are a consequence of the anti-symmetric exchange interaction, which presents in the material systems with broken inversion symmetry, such as B20 FeGe. This interaction enables chiral magnetic order, including topologically non-trivial magnetic skyrmions, which display rich new magnetic phenomena and require low critical current densities to manipulate.  This makes magnetic skyrmions a promising platform for power-efficient spintronics applications. Therefore, a deeper understanding of the static and dynamic magnetic properties of these materials will be a key step toward their application in spintronic devices. In this talk, I will present our study of both sputtered, epitaxial B20 FeGe and B20 FeGe grown using vapor transport. In particular, I will discuss microwave absorption spectroscopy (MAS) of bulk, single crystal FeGe with which we identify the spin dynamics of all magnetic phases. These results reveal the critical role of substrate-induced strain on the magnetic phases of B20 FeGe.  To gain better control over strain and to tune the strength of anti-symmetric exchange, I grew B20 FeGe and MnxFe1-xGe on Si with MBE. After characterization using electron and X-ray diffraction, magnetometry, and cryo-Lorentz-STEM imaging, we study MAS of these films. We identify a new spin wave mode along the film thickness, with a wavelength that matches its helical period, enabling a new, simple method of quantitatively characterizing the anti-symmetric exchange.

Posted In: Colloquia

Mon Feb 19, 2018

Nuclear Physics Seminar: Mr. Rodney Orford, McGill University, Canada

4:00 PM - 5:00 PM
124 Nieuwland Science Hall

Trapping at CARIBU: An overview of mass measurements with the Canadian Penning Trap

Mr. Rodney Orford
McGill University, Canada

Hosted by Prof. Aprahamian

Posted In: Nuclear Seminar

Tue Feb 20, 2018

Astrophysics Seminar: Prof. J. Christopher Howk, University of Notre Dame

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

What I Learned During My Sabbatical

Prof. J. Christopher Howk
Department of Physics
University of Notre Dame

Posted In: Astrophysics Seminar

Particle Physics Seminar: Dr. Raymond Co, University of Michigan

4:00 PM - 5:00 PM
415 Nieuwland Science Hall

QCD Axion Dark Matter with f_a as Low as 10^8 GeV

Dr. Raymond Co
Research Fellow
University of Michigan…

Posted In: Particle Physics Seminar

Our Universe Revealed: Dr. Jonathan Crass, University of Notre Dame

7:00 PM - 8:00 PM
101 Jordan Hall of Science

The Next Decade in Astronomy

Dr. Jonathan Crass, Research Assistant Professor, University of Notre Dame

“What’s next in astronomy?” Join us as we look back at what we’ve discovered in the last decade to see just how quickly astronomy is moving forward and what are the big remaining questions we need to solve. We’ll discuss the next generation of tools currently under construction to answer questions including ‘Are we alone in the Universe?’, ‘How did we get here?’ and ‘Do we really understand how the Universe works’?

Posted In: Special Lectures and Events

Wed Feb 21, 2018

Physics Colloquium: Dr. Yingjie Zhang, University of Illinois at Urbana-Champaign

4:00 PM - 5:00 PM
118 Nieuwland Science Hall

Charge transport in artificial solids: from percolation to miniband conduction

Dr. Yingjie Zhang
Beckman Postdoctoral Fellow
Department of Physics
University of Illinois at Urbana-Champaign…

Posted In: Colloquia

Mon Feb 26, 2018

Nuclear Physics Seminar: Dr. Mark Roberts, Woods Hole Oceanographic Institution

4:00 PM - 5:00 PM
124 Nieuwland Science Hall

Why does an Oceanography Institution have a Particle Accelerator?

Dr. Mark Roberts
National Ocean Sciences AMS Facility
Woods Hole Oceanographic Institution

Hosted by Prof. Peaslee

Posted In: Nuclear Seminar

Tue Feb 27, 2018

Astrophysics Seminar: Dr. Gen Chiaki, Georgia Tech

12:30 PM - 1:30 PM
184 Nieuwland Science Hall

Formation criterion and process of extremely metal-poor stars: the role of first supernovae

Dr. Gen Chiaki
Postdoctoral Researcher, Georgia Tech

Metal-poor stars are living fossils with records of the metal enrichment in the early Universe. They are classified primarily into C-enhanced metal-poor (CEMP) stars and C-normal metal-poor (CNMP) stars according to their carbon abundances. Recently, the new classification of CEMP stars is presented. Their carbon and iron abundances show lower limits of A_cr(C) ~ 6 and [Fe/H]_cr ~ -5, respectively. This suggests the critical elemental abundances above which thermal emission cooling of carbon and silicate grains operates to induce the fragmentation of their parent gas clouds, and low-mass stars are likely to be formed. Since the dust cooling rate depends on the condensation efficiency of metal and grain size distribution with a given metallicity, we estimate them from the observed lower-limits of carbon and iron abundances. Then, we derive the critical condition of the formation of EMP stars. The different classes of CEMP stars are well-explained as the difference of main grain species for their formation.

     We also present results of numerical simulations of the metal-enrichment process and EMP star formation. From their small metal content, they are considered to acquire heavy elements from a single or several supernovae (SNe) of first-generation (Pop III) stars. We simulate the feedback effects of photoionization and SNe with a range of masses of Pop III stars and hosting minihalos (MHs). For pair-instability supernovae (PISNe) with large explosion energy ~30x10^{51} erg, the ejected gas reaches to the neighboring halos, i.e., external enrichment (EE) takes place in all relevant mass range of MHs. Yet, the metals cannot penetrate into the central part of halos, and the resulting metallicity is [Fe/H] < -5. This is consistent with no observational sign of PISNe among EMP stars. For core-collapse supernovae (CCSNe) with normal explosion energy ~1x10^{51} erg, the ejected gas falls back into minihalos and internal enrichment (IE) occurs. The metallicities in the recollapsing region are -5 < [Fe/H] < -3 in most cases. We can conclude that IE by CCSNe can explain the metallicity range and elemental abundance ratios of EMP stars.

Posted In: Astrophysics Seminar

Anna Woodard PhD Defense

1:00 PM - 3:30 PM
Room 202

Anna Woodard Defense Announcement

Posted In: Ph.D. Defense

Particle Physics Seminar: Prof. Radovan Dermisek, Indiana University

4:00 PM - 5:00 PM
415 Nieuwland Science Hall

Understanding parameters of the standard model from the MSSM extended by a complete vectorlike family

Prof. Radovan Dermisek
Theoretical Particle Physics
Indiana University…

Posted In: Particle Physics Seminar

Wed Feb 28, 2018

Physics Colloquium: Prof. John LoSecco, University of Notre Dame

4:00 PM - 5:00 PM
118 Nieuwland Science Hall

The history of supernova neutrinos

Prof. John LoSecco
Department of Physics
University of Notre Dame

Supernovae, the largest explosions in the universe, mark the end of nuclear burning for massive stars. This talk traces our understanding of stellar mechanisms from the mid 19'th century to the present. In many cases progress in astrophysics was delayed until future physics discoveries were made. Somewhat surprisingly, the neutrino, a relatively poorly understood elementary particle, plays a critical role in these mechanisms.

Posted In: Colloquia

Mon Mar 5, 2018

Nuclear Physics Seminar: Dr. Nicole Vassh, University of Notre Dame

4:00 PM - 5:00 PM
124 Nieuwland Science Hall

Fission and the formation of the rprocess rare-earth abundance peak in neutron star mergers

Dr. Nicole Vassh, Postdoc
University of Notre Dame

Hosted by Prof. Surman

Posted In: Nuclear Seminar

Tue Mar 6, 2018

Edward Lamere PhD Defense

2:00 PM - 4:30 PM
Room 124 Nieuwland Science

Lamere Edward PhD Defense Announcement

Posted In: Ph.D. Defense

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