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The PhysTEC Program at UA
There is a critical shortage of qualified high school
physics teachers in the U.S., especially in Alabama. The
Physics Teacher Education Coalition (PhysTEC) consists of more
than 260 colleges and universities that are committed to
address this problem. The Department of Physics &
Astronomy has just received a 3-year grant from PhysTEC to
increase the number and quality of certified physics teachers
graduating from UA. Major components of the program are a
Teacher-in-Residence (TiR), a Learning Assistant (LA) program,
and a partnership with Alabama Science in Motion (ASIM) to
provide early teaching experiences.
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The Double Chooz neutrino experiment
The Double Chooz neutrino experiment is designed primarily
to measure the neutrino mixing angle θ13. We
describe the motivation and design of the experiment, review
the results from the first year of data taking, and give an
overview of plans and prospects.
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The age-metallicity relationship of stars in MUGS
galaxy simulations
In the early universe there were no heavy elements
("metals"). Generations of stars fused metals in their core
and spewed them out into the interstellar medium through
supernova explosions and stellar winds, allowing later
generations of stars to incorporate more and more metals in
their composition. Tracing the evolution of stellar
metallicity with age in a galaxy therefore allows us to see
the history of how its stars formed. I will present a study of
the age-metallicity relation of stars in a simulated galaxy
from the MUGS project, which has revealed a wealth of
structure not anticipated by simple models, including abundant
substructure, a broad age-metallicity distribution, and
non-monotonic evolution.
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The CMS Experiment and Activities of the CMS Group at UA
The CMS Experiment at the CERN Large Hadron Collider in
Switzerland is well into its third year of data taking. The
data are being analyzed to perform detailed studies of the
recently observed boson at a mass of 125 GeV, and to actively
continue the exploration of the uncharted energy range that
the LHC is making available. A brief overview of the CMS
experiment and the activities of the CMS group at the
University of Alabama is given.
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Double Beta Decay: EXO-200 and Beyond
Neutrinos are electrically neutral fundamental constituents
of matter. The absence of electrical charge opens the
possibility that neutrinos are their own anti-particles or so
called Majorana particles, an as of yet unobserved feature of
matter. Double beta decay is the rarest known nuclear decay,
its hypothetical neutrinoless variety a sensitive probe for
lepton number violation and the possible neutrino
anti-neutrino identity. The observation of neutrinoless double
beta decay would require physics beyond the standard model.
EXO-200 is an experimental search for double beta decay of
136Xe. It recently reported the first observation of two
neutrino double beta decay of 136Xe and the most stringent
limit on the so called effective Majorana mass of neutrinos.
The experiments and its early results will be discussed along
with the collaboration's plans for a larger follow on project.
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Atomic, Molecular, and Optical Physics: Going Forward
Atomic, Molecular, and Optical Physics (AMOP) is a very broad
field with disparate parts. The speaker's highly personal
perspective of the opportunities and pitfalls for academic
departments will be presented, along with a more specific
discussion of his own research in what has come to be called
‘Terahertz’ physics.
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New Insights Into Hydrogen (water) at the Lunar Poles
The Lunar Prospector (LP) and Lunar Reconnaissance Orbiter
(LRO) orbital neutron spectroscopy datasets represent a unique
comprehensive multi-mission lunar resource. A rigorous
statistical approach has been used to (re-)analyze neutron
data from both missions to provide new details regarding the
relationships between the individual detector datasets, as
well as a new evaluation of enhanced hydrogen deposits at the
lunar poles. Using the multi-mission epithermal neutron
dataset we find water ice distributed broadly across the
poles, yet showing evidence for a dependence on topographical
features. A footprint averaged water equivalent hydrogen (WEH)
abundance of 106+/-11 ppm at each pole, with maxima of 131 ppm
and 112 ppm at the North and South poles, respectively, is
derived from the epithermal neutron data. We also report the
first definitive detection of a fast-neutron signature
consistent with an enhanced hydrogen hypothesis. These data
suggest a highly localized distribution, consistent with
Shackleton Crater, corresponding to a footprint averaged WEH
abundance of 194+/-11. If confined to this crater this
abundance yields a localized deposit of ~0.7% WEH. Details of
the analysis approach are presented along with spatial
distribution maps showing the intriguing enhanced hydrogen
deposits at the lunar poles.
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Walking with Paleozoic Tetrapods: An Astronomer's
Journey into Alabama's Remote Past
For the past 12 years, Prof. Buta has been involved in a
remarkable odyssey of rescue, documentation, and study of
Paleozoic footprints that have been found in the sedimentary
rocks exposed in surface coal mines of Walker County, Alabama.
The footprints date back to the Carboniferous period, 313
million years ago, and are significant because they were made
by some of the earliest known reptiles. The trails were
preserved on a tidal mud flat where a major river once drained
into a tropical inland sea. The river carried sediments from
the Appalachian Mountains, which had been recently uplifted by
the collision of Laurussia with Gondwanaland, forming the
supercontinent of Pangaea. The land that later became Alabama
was just south of the equator and was partly covered by vast
tropical swamp forests populated by strange trees covered with
scales and by unusual seed ferns. These forests grew
episodically and later became the coal seams that are being
mined in Alabama. By the time the first dinosaurs appeared
almost 80 Myr later, the world of the Paleozoic tetrapods of
Walker County was long gone.
Prof. Buta will describe how he, an extragalactic astronomer,
became involved in the study of Paleozoic trace fossils, what
it is like to search the spoil piles of a coal mine for the
elusive footprints of long dead animals for whom no bones have
ever been found, and how the experience has contributed to his
development as a scientist and educator.
Acknowledgments: Prof. Buta thanks the Alabama
Paleontological Society and local geologists and
paleontologists for making this presentation possible.
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Cavity-Enhanced Spectroscopic Measurement of Greenhouse
Gases
A rigorous understanding of light-matter interactions that
involve greenhouse gases (GHGs) is central to physical models
and measurements in atmospheric and climate-change science. In
recent years there has been concerted effort to develop new
ground- and satellite spectrometers designed to measure local
and global distributions of GHGs such as CO2, O2,
CH4, and H2O. Many of these remote
sensing applications require accurate molecular line-by-line
parameter data (0.3% relative uncertainties or less) so that
GHG absorber concentration profiles can be determined from
rotationally resolved observations of light transmission
through the atmosphere. Given the extremely long path lengths
involved in these observations, the most relevant absorption
features are usually weak enough that they do not saturate in
the atmosphere, and consequently they are difficult to measure
in the laboratory with conventional spectroscopy techniques
such as Fourier-Transform Spectroscopy (FTS). In this talk I
will discuss important alternatives to FTS that are based on
cavity-enhanced spectroscopy (CES) and optical-frequency comb
(OFC) technology. These laser-based methods yield
ultra-sensitive, high resolution measurements that enable
unprecedented levels of sensitivity, precision, accuracy and
spectral resolution, thus opening new frontiers in
quantitative spectroscopy of atoms and molecules. In
particular, I will emphasize frequency-stabilized cavity
ring-down spectroscopy, a CES technique recently developed at
NIST that has been used to substantially reduce the
uncertainty in spectroscopic line parameters and other
fundamental physical properties of GHG molecules.
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True Color: QCD Measurements with D0 at the Tevatron
Collider
The Tevatron Collider at Fermilab, which has recently shut
down after taking data for nearly 20 years, leaves a legacy of
physics results and a deeper understanding of the fundamental
particles and forces. The data have given us a much better
understanding of the structure of the proton and of the strong
nuclear force described by Quantum Chromodynamics (QCD).
Although each quark and gluon in the nucleus carries a
``color'' charge, the colors of QCD are never observed
directly due to ``color confinement,'' the fact that quarks
are always bound tightly in groups, so that the properties of
QCD must be understood by observing objects which have no
color. This colloquium will discuss some of the important QCD
measurements that have used data from the D0 detector at the
Fermilab Tevatron Collider. These measurements give insight
into the structure of the nucleon and have the potential of
discovering physics not described by the standard model of
elementary particles and fields. The results will include
precise measurements of the inclusive jet cross section, the
di-jet cross section, and the inclusive photon production
cross section among others.
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Through the Looking Glass: Matching Observational
Diagnostics with Simulations of Star Formation
Forming stars are difficult to observe directly because they
are deeply embedded in dust and gas. To better understand the
star formation process and explore key physics, investigators
perform large-scale, physically detailed numerical
simulations. However, many different simulations that include
many different inputs can reproduce a fundamental
observational result: the initial mass function of stars. In
this talk, I will discuss how I perform and post-process
simulations to compare directly with observational metrics
such as gas linewidths and protostellar kinematics. I will
reflect on what this implies about current simulations and
about the nature of star formation.
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The Luster of Pt
For centuries, platinum metal has been highly valued for its
luster and rarity. With the technological revolution, Pt has
found many applications owing to its high chemical inertness
and catalytic properties. Recently, electronic properties of
Pt have attracted a significant interest for emerging
(spin)electronic applications. By passing an electrical
current through a device comprised of a bilayer of Pt with a
ferromagnet (F), one can modify the dynamic magnetic
properties of F with the pure spin current generated in Pt via
the spin Hall effect. Devices utilizing spin Hall effect do
not require electric current flow through the magnetic layer,
thus minimizing heating and electromigration, and allowing one
to use dielectric and/or semiconducting magnetic materials. I
will describe our recent measurements of spin-current induced
effects in Pt/F heterostructures using several techniques
including electronic spectroscopy, microfocus Brillouin Light
Spectroscopy (mBLS), and x-ray magnetic circular dichroism
microscopy. I will show that one can utilize the spin Hall
effect to significantly suppress or enhance thermal
magnetization fluctuations, modify the dynamical damping
rates, induce magnetization auto-oscillations, reverse the
magnetization in both uniform and vortex states. Finally, I
will describe measurements indicating that not only Pt can
affect the properties of the ferromagnet in Pt/F
heterostructures, but also the ferromagnet can change the
properties of Pt, resulting in an intricate interplay between
magnetism and spin transport.
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Muon Cooling and Future Muon Facilities
Muon colliders and neutrino factories are attractive options
for future facilities aimed at achieving the highest
lepton-antilepton collision energies and precision
measurements of parameters of the Higgs boson and the neutrino
mixing matrix. The performance and cost of these depend
sensitively on how well a beam of muons can be cooled. Recent
progress in muon cooling design studies and prototype tests
nourishes the hope that such facilities can be built during
the next decade. The status of the key technologies and their
various demonstration experiments will be summarized.
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Ultracold molecules - New frontiers in quantum and
chemical physics
Molecules cooled to ultralow temperatures provide fundamental
new insights to molecular interaction and reaction dynamics in
the quantum regime. In recent years, researchers from various
scientific disciplines such as atomic, optical, and condensed
matter physics, physical chemistry, and quantum science have
joined force to explore many emergent and exciting research
topics that are enabled by cold molecules, including cold
chemistry, strongly correlated quantum systems, novel quantum
phases, and precision measurement.
Complete control of molecular interactions has been an
outstanding scientific quest for generations. However,
producing a molecular gas at very low entropy and near
absolute zero has long been hindered by their complex energy
level structure. We have recently developed a number of
technical tools to laser cool and magneto-optically trap polar
molecules, as well as to cool molecules via evaporation.
Another recent experiment has brought polar molecules into the
quantum regime, in which ultracold molecular collisions and
chemical reactions must be described fully quantum
mechanically. We control chemical reaction via quantum
statistics of the molecules, along with their long-range and
anisotropic dipolar interactions. Further, molecules can be
confined in reduced spatial dimensions and their interactions
are precisely manipulated via external electric fields. Those
efforts serve as an important staging ground to explore
strongly interacting and collective quantum effects in an
ultracold gas of molecules.
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Kepler's Exoplanets and Astrophysics: What the
publications didn't tell you …
Nearly four years ago, NASA launched a space telescope with
the sole purpose of finding exoplanets, planets orbiting other
suns. To date, the Kepler mission has discovered nearly 3000
exoplanet candidates, many in multiple planet systems, and
hundreds of which are near the size of the Earth. We will
explore the wide variety of exoplanets discovered and focus on
the most recent and interesting discoveries. Are other worlds
like our Earth out there? We will see that the answer is, so
far, a strong maybe. We will also discuss Kepler's paradigm
changing results in stellar astrophysics. Kepler photometry is
over 100 times the precision of ground-based observations.
Combined with its essentially continuous time coverage, these
data provide a unique and spectacular data set for astronomy.
Some specific examples, near to my heart, will be discussed as
well as recent highlights in astrophysics.
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RR Lyrae Stars in M31, M32, and M33>
I will review some of the recent work on the RR Lyrae
populations in M31, M32 and M33. The capabilities of the
Hubble Space Telescope and 10-meter class ground-based
telescopes have made it possible to reliably identify and
characterize RR Lyrae variables in these two galaxies. This is
important because RR Lyraes are the 'Swiss Army knives' of
astronomy in the sense that they have multiple and varied uses
for probing the formation and evolution of galaxies. I will
describe the diversity of ways that RR Lyraes are useful in
this regard and what they reveal about the properties of M31,
M32, and M33.
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Emergent magnetic properties in hybrid nanostructures:
scratching the surface for new physics
Magnetic nanostructures are considered basic building blocks
in spintronics and high- density data storage applications.
Surface and interface effects in oxide nanoparticle assemblies
have been increasingly found to play significant roles in
controlling the magnetic properties. Modification of the
surface spin structure in magnetic oxide nanoparticles can be
achieved by controlling the particle shapes and forming hybrid
structures. We discuss how these effects often lead to novel
magnetic properties, useful for applications, such as tunable
exchange bias (EB) and enhanced magnetocaloric effect (MCE).
Exchange bias (EB)-like behavior in magnetic nanoparticles has
been observed and reported in a number of systems. However the
origin is not well understood and the results have often been
misinterpreted in numerous reports in the literature. We have
recently done systematic experiments to investigate these
intriguing phenomena using a range of probes such as DC and AC
magnetometry, RF transverse susceptibility, magnetocaloric
effect and small angle neutron scattering (SANS). In this talk
we will emphasize the need for systematic experimental studies
to understand the origin and physics of magnetism in
nanostructures and the correlation between surface anisotropy,
freezing of surface and core spins with exchange bias.
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Magnetic Thin Films and Multilayers: Fabrication and
Analysis
The MINT Center at UA has an assortment of shared vacuum
systems for thin film fabrication. These systems are
periodically refitted and upgraded to meet users' needs. After
a brief introduction of how these capabilities have changed
over the past several years, some examples of research results
will be presented. These include measurements of magnetic
hysteresis behavior of ferromagnet/antiferromagnet/ferromagnet
trilayers, magnetic band structure determinations of epitaxial
films, magnetic periodicities in ferromagnet/antiferromagnet
multilayers, and domain structures in helical
antiferromagnetic multilayers.
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Constraining Cosmological Models with Massive Galaxy
Clusters
Clusters of galaxies are among the most energetic persistent
sources in the extragalactic sky, and observations of their
properties and evolution provide multiple, complementary
probes of cosmology. I will describe recent work on two of
these cosmological tests: the first providing measurements of
the cosmic expansion and its acceleration, and the second
using clusters to trace the growth of structure in the
Universe. These techniques have provided strong, independent
confirmation of the concordance model, in which the dynamics
of the present-day Universe are dominated by a cosmological
constant and cold dark matter, with constraints on dark energy
properties that are competitive with yet highly complementary
to those from other probes. Measurements of the growth of
structure enable a number of additional tests of fundamental
physics, placing limits on the species-summed neutrino mass,
modifications of General Relativity, and departures from
single-field inflation. With recent improvements in the
quality and analysis of gravitational lensing data, a growing
body of multi-wavelength observations, and several ambitious
cluster surveys either ongoing or on the horizon, clusters are
poised to deliver even more powerful cosmological results.
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Exploration of Magnetic Crystals: Macroscopic
Investigation to Topographical Nanoengineering
The energetic interplay in magnetic crystal dictates the
fundamental properties of a broad range of magnetic materials,
for instance the quantum critical fluctuations in strongly
correlated electron system. My research efforts involve dual
approaches where the macroscopic investigations of candidate
materials in bulk are used as guide to create prototype system
of the artificial magnetic crystal via periodic nanoscale
confinement. First part of my talk will discuss the details of
macroscopic investigation of underlying magnetic crystal in an
archetypal heavy electron superconductor CeCu2Ge2,
where the critical spin fluctuations of the antiferromagnetic
spin density wave order was found to dominate the local
fluctuations due to single-site Kondo effect. In second part,
I will show that the artificial magnetic crystal, created
using topographical nanoengineering, helps us develop a new
research arena, which enables exploration of the energetic
interplay and associated physics that are ordinarily found in
bulk materials of strongly correlated electron systems. I will
summarize the talk with a synopsis of future research, which
aims to explore and understand recently discovered anomalous
coupling between the giant thermal hysteresis and the
magnetoresistance oscillation in slightly modified
topographical nanoengineered material with strong implication
to the spin (magnetic) caloritronics devices.
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Charge transport and dynamics in nanomaterials and their
interfaces
Carrier transport and dynamics in nanomaterials and thin
films are both of fundamental interest and of importance for
the development of efficient optoelectronic and energy
conversion devices. Among nanomaterials, graphene and
graphene-based heterostructures are promising nanoscale
systems because of excellent electronic and optical properties
of graphene. To study transport properties by measuring
photoconductivity of these materials, however, is often
hindered by the complication of making contacts to nanoscale
objects. Furthermore, sub-picosecond (sub-ps) to nanosecond
(ns) carrier dynamics plays an important role in efficient
charge separation, transport, and relaxation processes. As I
will discuss in this talk, time-resolved THz spectroscopy
(TRTS) provides a powerful ultrafast, non-contact electrical
probe capable of measuring the photoconductivity in broad
range of material systems. In particular, I will describe our
recent progress in applying this approach to probe of charge
transport properties and photoinduced carrier dynamics in
graphene, at the C60/graphene interface, and films
of the semi-metal bismuth.
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The Higgs Boson – Latest Results from the Large Hadron
Collider
The Higgs boson was proposed in 1964 and is the final and
key undiscovered particle in the Standard Model of particle
physics. The Higgs has been searched for actively for more
than 30 years. On July 4, 2012, the massive CMS and ATLAS
experiments at the Large Hadron Collider at CERN announced the
observation of a new boson with a mass of 125 GeV whose
properties were consistent with the Higgs. In this talk, I
will present a brief history of searches for the Higgs boson
and then discuss the latest experimental results on the 125
GeV boson. I will focus on the results from CMS experiment
including some details of the experimental challenges, but
will include the most recent measurements from ATLAS as well.
I will discuss how close we are to determining whether or not
the new boson is the Higgs boson or something else.
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The Impact of Secular Features on the Evolution of Disk
Galaxies
The role of secular features, such as stellar bars, in
driving the evolution of galaxies is still uncertain. The
fraction of barred galaxies, both in the local and high
redshift universe, is highly debated as well as their role in
building bulges, triggering star formation and active galactic
nuclei (AGN), as well as modulating metallicity gradients
within galaxies. In this talk, I will present some recent
results from the Sloan Digital Sky Survey (SDSS), and HST
COSMOS survey to address these issues. I will contrast the
importance of secular processes with galaxy mergers, which
represents a fundamental building block in the hierarchical
picture of galaxy formation.
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Tuning Electrical and Optical Properties of 2D Atomic
Crystals
Two-dimensional (2D) atomic crystals are recently discovered
materials that are only atoms thick, and yet can span
laterally over millimeters. The diverse family of such
materials includes graphene, a semimetal with massless
relativistic charge carriers, and monolayer molybdenum
disulfide (MoS2), a direct band gap semiconductor
with strong spin-orbit interaction. Since every atom in these
materials belongs to the surface, their physical properties
are greatly affected by the immediate microenvironment.
In my talk, I will demonstrate the wide tunability of the
electrical and optical properties of both graphene and MoS2
and discuss some novel device applications. In the first part
of the talk, I will demonstrate the use of graphene field
effect transistors (FETs) in sensing different physical
parameters of nanometer-thick interfacial liquid
volumes. I will demonstrate sensing of local liquid dielectric
constant, mass flow velocity – with sensitivity 70nL/min, and
ion concentration with sensitivity as low as 40 nM. I will
also show that charge carrier scattering in graphene can be
efficiently suppressed by placing graphene into a liquid
environment. Overall, our results highlight the usefulness of
graphene FETs for applications in ultra-precise fluidic
sensing and as a potential replacement for silicon in next
generation transistors.
In the second part of my talk, I will focus on mononalyer
MoS2 and demonstrate that its optical properties,
fluorescence quantum yield and transparency, can be tuned via
electrical gating. In particular, we have observed a
hundredfold modulation of excitonic photoluminescence from
MoS2 at room temperature by varying the electric fields within
±1.7 MV/cm. Our findings demonstrate that MoS2 is
the thinnest possible electroactive material and suggest the
possibility of diverse applications ranging from nanoscale
electro-optical modulators to quantum computing based on the
spin degree of freedom.
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Understanding Galaxy Evolution with Massive Starburst
Galaxies
We are constantly intrigued by how dramatically galaxies
evolve when we probe closer to the cosmic dawn. Ten billion
years ago, galaxies were forming stars ten times more fiercely
than they do today. This phenomenon can be understood in the
framework of cold dark matter simulations only if star
formation is suppressed in massive dark matter halos. However,
the physical mechanisms responsible for the suppression are
unclear. Starburst galaxies in massive halos offer a unique
laboratory to constrain the suppression processes, because,
unlike most galaxies, such processes have apparently failed to
operate in these starbursts. Thanks to the Herschel Space
Telescope, for the first time we have identified a sample of
gravitationally lensed massive starbursts at the peak epoch of
cosmic star formation. I will show how high-resolution
multi-phase observations in combination with gravitational
lensing have helped us gain a comprehensive understanding of
these unusual galaxies. I will also describe future projects
aimed at constraining the star formation history and the
halo-scale gas supply of such massive starbursts. By
contrasting with normal galaxies, the results of these studies
will be fundamental to a physical understanding of galaxy
evolution. Finally, I will present my vision of this field
with future ground- and space-based observatories.
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Galaxy Evolution in the Thermal Era
Technological advances in ground- and space-based
observatories now allow routine observations of protogalaxies
to within 1 Gyr of the Big Bang. But most of the present-day
stellar mass, along with the familiar pattern of spiral and
elliptical galaxies we see in the nearby universe, in fact
emerged in the latter 10 Gyr of the Universe. Between
0<z<2, a period which I've termed the "thermal era," the
cosmic baryons have become increasingly locked up in
million-degree intergalactic gas and bound, dynamically "hot"
structures like elliptical galaxies and galaxy clusters. Here
I will present some of our ongoing efforts (employing both
large surveys and targeted programs) to trace out the dramatic
evolution of galaxies in the thermal era, quantify the rise of
large-scale structures, and directly probe the physical
mechanisms behind this evolution.
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Studying baryon physics with galaxy groups and clusters
Most of the cosmic baryons are not locked in stars.
Understanding the properties and underlying cause of baryons
that are not locked into stars will shed light on the
formation of galaxies, which only account for ~10% of baryons.
Galaxy groups and clusters are the only systems where the bulk
of the baryons have been detected. This makes them great
objects to study baryon physics, such as cooling, star
formation, heating from supermassive black holes and galactic
winds. Moreover, a better understanding of these baryon
processes is also important for cluster cosmology. In this
talk, I will discuss several topics related to the study of
baryon physics in groups and clusters, including halo
gas/baryon fraction, cool core and AGN heating, ram pressure
and star formation in the stripped gas.
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From new materials to devices for the future: the
interface matters
Advances made in fabricating thin-film materials with
atomic-level control have provided researchers unprecedented
access to investigate new physics and functionalities. The
rapid development in the field of spintronics is largely a
consequence of such improvements. Complex materials can move
these areas into newer directions. The intricate interplay
between charge, spin, lattice and orbital degrees of freedom
in complex materials offer exciting opportunities which impact
both fundamental and technological areas. After a brief
introduction to complex materials, I shall provide two
examples of my research on thin-film materials and
heterostructures. First is a functional spintronic device
showing giant tunnel magnetoresistance (TMR) effect, where
huge changes in electrical resistance is achieved by applying
a small, external magnetic field. The novel mechanism that
helps realize such high TMR values is understood in terms of a
symmetry filtering effect through a crystalline tunnel barrier
((001) oriented MgO, for example), where wavefunctions of
certain symmetries are transmitted preferentially. First
theorized by Butler et al. in 2001 it received
emphatic experimental verification within a few years, which
includes my graduate group. This effect is now being used as
the read head sensor in hard drives. In principle, a similar
functionality is achieved by using a single material which is
both magnetic and insulating. Such are magnetic insulators,
many of which are found in transition metal oxides. The unique
nature of these materials also makes them suitable for
applications in other, newer areas. In the next part of my
talk, I shall focus on my work which combines high quality
thin-film growth, optical absorption spectroscopy and
electronic structure investigations on a high Curie
temperature magnetic oxide in the spinel family (NiFe2O4,
NFO). Spectroscopic measurements on atomically-flat, epitaxial
thin films reveal that NFO is an indirect band gap material
with a gap hierarchy which emanates from its dispersionless
band structure. The band gap value also has a good overlap
with the solar spectrum. I shall conclude with my future
research plans.
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Optical Spectroscopy and Phonon Self-Energy
Renormalizations in Carbon Materials
For over two decades, carbon-based materials have been the
focus of intense research, accumulating two Nobel prizes
(fullerenes-1996 and graphene-2010) and an uncountable number
of solutions that aim, almost always, technological
applications in the nanometer scale such as solar cells,
transistors and gas sensors. In this colloquium, I will
discuss my recent contributions to the development of basic
research in carbon materials. More specifically, I will
explain how optical spectroscopy can be merged with electronic
devices to probe basic properties of carbon materials which
are tightly related to electron, phonons as well as their
mutual interactions. A discussion about phonon self-energy
renormalizations in single and double layer graphene involving
phonons with zero momentum (q = 0) and non-zero momentum (q ≠
0) will be addressed by showing that they have opposite
behaviors with changing the graphene’s Fermi level energy EF.
These different behaviors exhibited by q = 0 and q ≠ 0 phonons
serve as a new and efficient tool to assign phonons,
combination of phonons and phonon overtones. Finally, I will
address some topics related to my work on the development of
new carbon materials and give my perspectives on the next
steps of my research, which includes Near-Field spectroscopy.