By Robin Roenker
It’s an exciting time to be part of the Physics and Astronomy faculty at UK.
“I think we are in the midst of a pretty steep upward curve, particularly in terms of our research but also in terms of our education,” said the department’s Chair, Sumit Das, a high-energy physicist whose research interests focus on string theory and black hole physics.
As evidence of UK’s increasingly high-profile national reputation, Das points to the unprecedented 70 percent acceptance rate of the department’s top-choice graduate students this spring — 16 of the 22 students accepted will enroll in the fall.
“I think word is getting around that we have an active, engaged Physics and Astronomy faculty performing some of the best work in their prospective fields,” Das said.
Condensed Matter & Materials Physics
UK is indisputably leading the nation in the development of novel materials.
The Center for Advanced Materials, directed by Physics and Astronomy professor Gang Cao, is one of only one or two such centers in the nation charged with the discovery and development of new materials.
Along with Cao, the center’s faculty, including Physics and Astronomy professors Lance De Long, Joseph Brill, Ambrose Seo, Doug Strachan, and Kwok-Wai Ng, work to develop and understand the properties of new materials, including transition metal alloys and compounds, heavy transition element oxides, and thin film superconductors.
While future applications of these new materials will undoubtedly lead to advancements in technology, Cao’s group is primarily interested in simply understanding the fundamental properties of the new materials that they are producing in their labs —including a class of electric insulators made from transition metal oxides.
Through ultra low-temperature, high pressure, and high-magnetic field testing of single-crystal samples of the new materials they are developing, UK’s researchers push the boundaries of science’s understanding of electron behavior in elements like the so-called 4-d and 5-d transition metal oxides (a reference to their position on the period table) like strontium and iridium, for example.
“People take for granted that copper is a conductor and plastic is an insulator, but we are trying to answer the fundamental question: why are certain materials insulating, and others are conducting,” explained Cao, whose 2008 groundbreaking research paper outlined a new, previously unrecognized role that “spin-orbit coupling” plays in determining a material’s electric conductivity.
Since the publication of Cao’s paper, physics driven by spin-orbit coupling is “one of the most actively pursued fields now in condensed matter physics,” he said.
“UK has established itself as the leader in the development of heavy transition metal oxides,” Cao said. “We have close to 50 collaborations going on with institutes all over the world, including all of the U.S. National Labs as well as some in Germany and China.”
The majority of faculty involved in nuclear physics research at UK are divided into two primary interests. One group, the so-called “fundamental interactions group” or “medium-energy group,” conducts their research entirely off campus, at higher-energy particle accelerators found at national labs like those in Oak Ridge, Tenn., and Fermilab, near Chicago.
The other group uses UK’s own in-house particle accelerator, the Van de Graaff Accelerator, situated in the rounded silo-like portion of the Chemistry-Physics Building, to conduct experiments using lower-energy particle collisions.
Fundamental Interactions Group
UK Physics and Astronomy professor Tim Gorringe, who is part of the fundamental interactions group, is currently part of a prominent, large-scale multi-university collaborative project, along with UK professor Renee Fatemi, called the Muon g-2 experiment, which is being conducted at the Fermilab.
Mainstream media has covered work at the Large Hadron Collider at CERN, which in 2012 documented the discovery of the Higgs Particle. “That is what we call the energy frontier, where you’re colliding particles at higher and higher energies to produce new particles,” explained Gorringe. “But our work is not at the energy frontier. Our work is what we call the precision frontier, or the intensity frontier. It’s where you don’t use the highest energy beams of particles, but instead use the most intense beams of particles to make the most precise measures of things.”
The Muon g-2 project is charged with measuring the magnetic moment of the muon—a term that describes the strength of its magnetic interaction. The muon, similar in many ways to the more familiar electron that makes up ordinary matter, is one of the 17 particles of nature that described the Standard Model.
If Gorringe’s team is able to establish that the muon’s magnetic moment (measured on a scale of 1/10th of a part in a billion) differs statistically from the value that is predicted by the Standard Model, then their results could potentially offer evidence for the existence of dark matter or other new matter. This dark matter/new matter is postulated by physicists to exist but has not yet been directly measured, and the Standard Model currently does not account for it. Their results could potentially be truly ground-breaking.
“The Standard Model has held up well for physics since the 1960s,” Gorringe said. “But there’s an increasing belief that it must be incomplete, and that astrophysical observations have revealed that dark matter and so-called dark energy likely do exist.”
Several other UK faculty involved in fundamental interactions research are working on another high-profile, multi-university collaborative research project called the nEDM experiment, which stands for neutron electric dipole moment. The project’s goal is to measure a precise electrical characteristic of a neutron, called the electric dipole moment, which may or may not exist. If it is found to exist, that discovery may lead to an understanding of a major question of modern physics: why it is that the universe is made of vastly more matter than anti-matter.
“If the electric dipole moment exists, it signals a breakdown of what in physics is called time reversal symmetry, which is a basic symmetry of nature,” Gorringe explained. “The breaking of time reversal symmetry is thought to be a crucial ingredient in answering why there is such an asymmetry in the universe between matter and anti-matter.”
On campus, at the Chemistry and Physics Building’s Van de Graaff Accelerator, joint UK Physics and Astronomy/Chemistry professor Steve Yates and Physics and Astronomy emeritus professor Marcus McAllister and their colleagues work on projects that require lower-energy particle collisions.
One of the very few facilities in the country specializing in neutron physics research of a particular type, UK’s Van de Graaf Accelerator has been continually funded since 1963 by prestigious National Science Foundation (NSF) and Department of Energy (DOE) grants for research on an array of nuclear physics investigations as well as Homeland Security and corporate applications.
“Neutron physics is a very difficult area, and there are few specialized facilities in the world that do the kind of precision work that we do here,” Yates said. “That is what sets UK apart. We have really carved out a niche for ourselves; we do the kind of measurements nobody else can do.”
One research interest of the “low-energy” group, classified as nuclear structure research, aims to identify and answer ancillary questions involved in the worldwide research effort to measure the mass of the neutrino, which has not previously been identified. “It’s one of the big unknowns in physics,” Yates said.
Other projects seek to inform the design of better — i.e., safer and more efficient — nuclear reactors. “Part of what is being measured in our laboratory is determining what materials and properties can be used most effectively in new nuclear reactors,” said Yates. The research is particularly timely, as the nation’s pool of current reactors has passed the 40-year age mark.
“We’re measuring the neutron reaction probabilities of materials like iron that could be used in new reactor construction and fuel assemblies, as well as materials like sodium that could be used for the coolants,” Yates said, adding that improved modern reactor designs would prevent future nuclear disasters like those in Chernobyl or Three Mile Island.
Two recent additions to UK’s astrophysics and astronomy faculty have deepened the department’s interest in the study of star formation and galaxy evolution.
Having joined the UK Physics and Astronomy Department within the last two years, both Renbin Yan and Dale Kocevski research the ways in which black holes at the center of galaxies may play a regulatory role in the galaxy’s star formation.
New stars can only form when gas clouds within a galaxy cool and condense, but super massive black holes that exist at the heart of most, if not every galaxy (it is believed) emit radiation that heats the gas in space surrounding them, thereby slowing or even altogether stopping the formation of new stars.
At least, “that is the current theory we’re all trying to prove right or wrong,” Kocevski said.
While the role of the black hole in the process of galaxy evolution is still being studied, one fact is certain: over the last half of the universe’s life (roughly the last seven billion years of its nearly 14 billion years of existence) the rate of new star formation has decreased dramatically.
“We call it the ‘quenching’ of star formation,” said Yan. “This is one of the major problems in astrophysics and astronomy today, namely, why the star formation stops, sometimes in a very sharp and abrupt manner across these galaxies.”
Both Yan and Kocevski are involved in ground-breaking, international sky survey projects that aim to offer a glimpse of galaxies’ evolution over time.
Kocevski is involved with the CANDELS (Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey) project, which uses the new infrared Wide Field Camera 3 (added to the Hubble Space Telescope by shuttle astronauts in 2008 as one of their last missions) to view distant galaxies so far away that their light is no longer in the visible spectrum. Instead, their light is detectable only as infrared wavelengths.
With the infrared camera, the CANDELS project will take images of roughly 250,000 galaxies, capturing a glimpse of what they looked like 10 billion years ago, when they were in the early stages of their development, Kocevski said.
In 2018, NASA will launch the James Web Space Telescope (JWST), a fully optimized, purely infrared telescope that will allow astronomers to glimpse galaxies at just 200 million years after the Big Bang. “By the end of the decade, with the JWST, we’ll be able to see a glimpse of the Milky Way Galaxy as it was originally forming,” Kocevski said.
While Kocevski’s research focuses primarily on “high red-shift” galaxies which are extremely far away from our own, and whose light has, therefore, shifted further into the infrared spectrum, Yan instead focuses on “lower red-shift” galaxies, which are closer to our own Milky Way Galaxy.
Yan is the survey scientist for a project called MANGA (Mapping Nearby Galaxies at Apache Point Observatory), which is part of an international collaboration project called Sloan Digital Sky Survey IV. “The advantage of looking at galaxies that are more nearby is that you can spatially resolve them,” said Yan.
Using hexagonally-packed fiber bundles, Yan and his colleagues will obtain spatially-resolved spectroscopy (3D spectroscopy) to understand how star formation rates vary in the center versus outskirts of various galaxies, he said. Yan’s research will be conducted over six years using a dedicated 2.5-meter telescope at Apache Point Observatory in New Mexico.
While previous 3-D spectroscopy sky surveys have been done for 100 galaxies or so at a time, Yan’s MANGA project is on a more massive scale, surveying 10,000 galaxies in the nearby universe.
Both Yan and Kocevski agreed that advances in technology have made this an exciting time in astronomy’s history. “This really is the golden age for our field,” Kocevski said. “Technology has always driven advances in astronomy — from the development of the telescope onward — but we’re seeing a faster pace of advancement of technology in our field today than perhaps at any time in recent memory.”