Physics & Astronomy News
"Faint UBVRI Standard Star Fields at +50° Declination," Astronomical Journal, Volume 152, Issue 4, article id. 91,13 pp. (2016). Published by Clem, J.L., and Landolt, A.U.
Precise and accurate CCD-based UBVRI photometry is presented for ~2000 stars distributed around the sky in a declination zone centered approximately at +50°. Their photometry has been calibrated to the standard Johnson UBV and Kron–Cousins RI systems through observations of the UBVRI standard stars presented in the various works of Landolt. The magnitude and color range for these stars are 12 V 22 and −0.3 (B − V) 1.8, respectively. Each star averages 13 measures in each UBVRI filter from data taken on 41 different photometric nights obtained over a 21 month period. Hence, there now exists a network of faint UBVRI photometric standard stars centered on the declination zones δ = −50°, 0°, and +50°.
PhD Student Lydia Jagetic Teaches Students in Mexico about Radiation in Medicine.
Lydia Jagetic is a medical physics PhD student at LSU who combined her passions for research, teaching and travel this summer in Ensenada, Mexico.
“Hidden Phases Revealed at the Surface of Double-Layered Sr3 (Ru1-xMnx)2O7”, Phys. Rev. 94, 085420 (2016). Published by Chen, Jin, Zhang, & Plummer et al.
Double-layered Sr3Ru2O7 has received phenomenal consideration because it exhibits a plethora of exotic phases when perturbed. New phases emerge with the application of pressure, magnetic field, or doping. Here we show that creating a surface is an alternative and effective way to reveal hidden phases that are different from those seen in the bulk by investigating the surface properties of Sr3(Ru1-xMnx)2O7. Driven by the tilt distortion of RuO6 octahedra, the surface of Sr3Ru2O7 is less metallic than the bulk. In contrast, because of the vanishing of tilt and enhanced rotation with Mn-doping, the surface of Sr3(Ru0.84Mn0.16)2O7 is metallic while the bulk is insulating. Our result demonstrates that the electronic and structural properties at the surface are intimately coupled and consistent with quasi two-dimensional character.
"The Role of SrTiO3 Phonon Penetrating into thin FeSe Films in the Enhancement of Superconductivity" Published by Zhang and Plummer et al.
The significant role of interfacial coupling on the superconductivity enhancement in FeSe films on SrTiO3 has been widely recognized. But the explicit origination of this coupling is yet to be identified. Here by surface phonon measurements using high resolution electron energy loss spectroscopy, we found electric field generated by Fuchs-Kliewer (F-K) phonon modes of SrTiO3 can penetrate into FeSe films and strongly interact with electrons therein. The mode-specific electron-phonon coupling (EPC) constant for the ~92 meV F-K phonon is ~0.25 in the single-layer FeSe on SrTiO3. With increasing FeSe thickness, the penetrating field intensity decays exponentially, which matches well the observed exponential decay of the superconducting gap. It is unambiguously shown that the SrTiO3 F-K phonon penetrating into FeSe is essential in the interfacial superconductivity enhancement.
Student Spotlight - Rory Bentley
In Pursuit of Mystery: LSU Physics Student Rory Bentley On Why He Chose Astrophysics
"Emerging single-phase state in small manganite nanodisks" published by Jian Shao & E.W. Plummer, et. al
Electronic phase separation (EPS) is a common phenomenon in complex oxides systems. However, little is known regarding how EPS responds when the size of the system is smaller than the characteristic size of EPS. This issue is not only important for understanding the physical origin of EPS but also for oxides device applications in which oxides have to be fabricated into small-sized structures. Our work on manganites shows a surprising transition from the EPS state to a single phase state when the spatial size of the system is smaller than the characteristic length scale of EPS. This observation paves a way to manipulate EPS, which is potentially useful for oxides electronic and spintronic device applications.
LSU faculty members are closing in on bringing their inventions to market with funds from the university’s LIFT2 grant program
Physics Professor Shane Stadler is among the 22 faculty members at the flagship campus in Baton Rouge that have been awarded a combined $830,000 through the Leverage Innovation and Technology Transfer Fund, or LIFT2, to help bring their inventions to market. Photography courtesy LSU
Meet New Faculty Member Manos Chatzopoulos
Welcome to our New Faculty, Manos Chatzopoulos, a new faculty member in the LSU Department of Physics & Astronomy. Manos received his Ph.D. in 2013 from the University of Texas at Austin and he came to LSU this year as a theoretical and computational astrophysicist. Read about his exciting research, his interactive teaching methods and his inspirational hobbies here! http://lsuscienceblog.squarespace.com/blog/2016/9/20/what-happens-when-a-star-explodes-meet-new-faculty-member-manos-chatzopoulos
"Hubble Finds Planet Orbiting Pair of Stars" in collaboration with Tabetha Boyajian.
When astronomers found an extrasolar planet orbiting a neighboring star, a detailed analysis of the data uncovered a third body. But astronomers couldn't definitively identify whether the object was another planet or another star in the system. Now, nine years later, astronomers have used ultra-sharp images from the Hubble Space Telescope to determine that the system consists of a Saturn-mass planet circling two diminutive, faint stars in a tight orbit around each other. The system, called OGLE-2007-BLG-349, resides 8,000 light-years away. Astronomers teased the signature of the three objects using an observational technique called gravitational microlensing. This occurs when the gravity of a foreground star bends and amplifies the light of a background star that momentarily aligns with it. The particular character of the light magnification can reveal clues to the nature of the foreground star and any associated planets.
Amber Stuver Talks Gravitational Waves and Impact of Science Communication
Amber Stuver, a physics instructor in the LSU Department of Physics & Astronomy and a scientist at the LIGO (Laser Interferometer Gravitational-Wave Observatory) Livingston Observatory. LIGO just celebrated the first anniversary of the detection of gravitational waves, commonly known as ripples in fabric of spacetime. The first detection showed up as a very distinguishable series of blips on computers at LIGO, and sounded something like an electronic bird chirping. Amber talks about her research at LIGO, her visit to the Fermi National Accelerator Laboratory (Fermilab) and more.
“CALET Upper Limits on X-Ray and Gamma-Ray Counterparts of GW 151226” has been published by the CALET collaboration including Nick Cannady, Mike Cherry, Greg Guzik, Amir Javaid, John Wefel et al. in Astrophysical Journal Letters, 829:L20 (2016).
The CALET experiment aboard the International Space Station has placed upper limits for counterpart emission in the 7-1000 keV and 1-100 GeV bands associated with the gravitational wave event GW 151226 corresponding to a luminosity of 3-4 ×1049 erg s−1, which is significantly lower than typical short gamma ray bursts.
“Ripples in Reality” has been published by Don Lincoln and Amber Stuver. Phys. Teach. 54, 398 (2016).
In a deep and dark corner of space, a cataclysm loomed. Two cosmic nemeses circled one another, locked in a macabre dance of death. Unfolding over millennia, the deadly waltz began leisurely enough. But with the dance came radiation and the energy loss that it implies. Orbit after orbit, the distance between the two protagonists shrank as their grip on each other tightened. Radiation carried away energy, but not angular momentum, so the orbital velocity grew to incomprehensible levels—well into the realm where Einstein’s theory of special relativity reigns supreme. With the closing distances, the inevitable occurred as the two twisted knots of spacetime approached each other and merged in a spasm that shook the universe so violently that the energy output briefly outshone the electromagnetic energy output of the entire universe. The two adversaries become one, finally merged together for all eternity. The traces of their ordeal died away, leaving only a fading death scream that spread throughout the cosmos, growing ever fainter. That is, until they passed through Earth. That was the moment that changed everything.
"Efficacy of the SU(3) scheme for ab initio large-scale calculations beyond the lightest nuclei" has been published by Tomas Dytrych, Kristina Launey, and Jerry Draayer et. al. Comp. Phys. Commun. 207 (2016) 202; doi: 10.1016/j.cpc.2016.06.006
We discuss the computational characteristics of ab initio nuclear structure calculations in the symmetry-adapted no-core shell model (SA-NCSM) framework. We examine the computational complexity of the current implementation of the SA-NCSM approach, dubbed LSU3shell, by analyzing ab initio results for Li-6 and C-12 in large harmonic-oscillator model spaces and symmetry-selected subspaces. We demonstrate LSU3shell's strong-scaling properties achieved with highly-parallel methods for computing the many-body matrix elements. In particular, a well-chosen symmetry-adapted basis affords memory savings in calculations of states with a fixed total angular momentum in large model spaces while exactly preserving translational invariance.
Physics Students Named 2016 Astronaut Scholars
For more than 30 years, the Astronaut Scholarship Foundation has supported hundreds of top performing students pursuing degrees in science, technology, engineering or mathematics. This year, LSU physics majors Harvey Shows and Amy LeBleu are among the top performing scholars to receive the 2016 ASF award.
"Quantum self-gravitating collapsing matter in a quantum geometry". by Campiglia, Gambini, Olmedo, and Pulin. Classical and Quantum Gravity, Volume 33, Number 18
The problem of how space–time responds to gravitating quantum matter in full quantum gravity has been one of the main questions that any program of quantization of gravity should address. Here we analyze this issue by considering the quantization of a collapsing null shell coupled to spherically symmetric loop quantum gravity. We show that the constraint algebra of canonical gravity is Abelian both classically and when quantized using loop quantum gravity techniques. The Hamiltonian constraint is well defined and suitable Dirac observables characterizing the problem were identified at the quantum level. We can write the metric as a parameterized Dirac observable at the quantum level and study the physics of the collapsing shell and black hole formation. We show how the singularity inside the black hole is eliminated by loop quantum gravity and how the shell can traverse it. The construction is compatible with a scenario in which the shell tunnels into a baby universe inside the black hole or one in which it could emerge through a white hole.
"Ultrathin two-dimensional superconductivity with strong spin–orbit coupling" by Nam, Kim and Adams, et. al. doi: 10.1073/pnas.1611967113. September, 2016
We report on a study of epitaxially grown ultrathin Pb films that are only a few atoms thick and have parallel critical magnetic fields much higher than the expected limit set by the interaction of electron spins with a magnetic field, that is, the Clogston–Chandrasekhar limit. The epitaxial thin films are classified as dirty-limit superconductors because their mean-free paths, which are limited by surface scattering, are smaller than their superconducting coherence lengths. The uniformity of superconductivity in these thin films is established by comparing scanning tunneling spectroscopy, scanning superconducting quantum interference device (SQUID) magnetometry, double-coil mutual inductance, and magneto-transport, data that provide average superfluid rigidity on length scales covering the range from microscopic to macroscopic. We argue that the survival of superconductivity at Zeeman energies much larger than the superconducting gap can be understood only as the consequence of strong spin–orbit coupling that, together with substrate-induced inversion-symmetry breaking, produces spin splitting in the normal-state energy bands that is much larger than the superconductor’s energy gap.
In Pursuit of Mystery: Undergraduate student Rory Bentley talks why he chose Astrophysics
Rory Bentley talks why he chose Astrophysics
LSU Medical Physicist Works to Improve Treatment Outcomes for Postmasectomy Patients
LSU Assistant Professor of Physics Rui Zhang was awarded a grant from the National Cancer Institute to improve treatment outcomes for breast cancer patients.
"Schrödinger-like quantum dynamics in loop quantized black holes" by Gambini, Rodolfo, Javier Olmedo, and Jorge Pullin. • Int.J.Mod.Phys. D25 (2016) no.08, 1642006 arXiv:1605.00969
We show, following a previous quantization of a vacuum spherically symmetric spacetime carried out in [R. Gambini, J. Olmedo and J. Pullin, Class. Quantum Grav. 31 (2014) 095009.] that this setting admits a Schrödinger-like picture. More precisely, the technique adopted there for the definition of parametrized Dirac observables (that codify local information of the quantum theory) can be extended in order to accommodate different pictures. In this new picture, the quantum states are parametrized in terms of suitable gauge parameters and the observables constructed out of the kinematical ones on this space of parametrized states.
LSU Physicists Collaborate on T2K CP Violation Results to Explain Workings of Universe
Why the universe is dominated by matter today, instead of being comprised of equal parts matter and antimatter, is one of the most intriguing questions in all of science. One of the conditions required for the observed dominance of matter over antimatter to develop is the violation of Charge-Parity (CP) symmetry, which is the principle that the laws of physics should be the same if viewed upside-down in a mirror, with all matter exchanged with antimatter. If CP violation occurs in neutrinos, it will manifest itself as a difference in the oscillation probabilities of neutrinos and antineutrinos.