Department Colloquia

Spring 2019 Schedule

All talks will be in the Physics Department Library (accessed from 3438 Ingersoll Hall) unless otherwise stated.

Check here for updates to the schedule as the semester progresses.

Wednesday, March 13, 12:30 p.m.

Speaker: Anatoly Kuklov, Department of Physics & Astronomy, College of Staten Island (CUNY) and The Graduate Center (CUNY)

Title: Superfluidity beyond Helium-4

Abstract: The remarkable phenomena of Bose-Einstein condensation and superfluidity were first observed in liquid Helium-4 about 80 years ago. Then, at the end of 20th century, these effects were realized in ultra cold clouds of atoms Rb-87, Na-23 and Li-7. Similar effects were also observed in exciton-polariton media. I will argue that the condensation of pure light in 2D geometry produced by the photonic group in Bonn University 9 years ago provides a new platform for studying novel phases and phase transitions some of which have no analogy in other systems. The combination of low effective mass of the confined light and the presence of the dye molecules with randomly oriented dipolar transition engages a competition between disorder and the tendency to forming algebraic off-diagonal order. The phase diagram of possible phases is constructed at the mean field level. One of such novel phases is the condensate of photon pairs induced solely by the orientational disorder.

Thursday, March 21, 12:30 p.m.

Graduate Student Seminar (2 Speakers)

Speaker 1: Nikesh Maharjan, Department of Physics, Brooklyn College (CUNY) and Physics Program The Graduate Center (CUNY)

Title: Electroreflectance studies of GaAs/AlGaAs multiple quantum well based resonant Bragg structure at excited states

Abstract: Electroreflectance (ER) Spectroscopy was employed to study the optical properties of GaAs/AlGaAs multiple quantum well (MQW) based resonant Bragg structure (RBS). The sample used in this experiment consists of 60 periods of quantum well structures with GaAs well and AlGaAs barrier layers grown by molecular beam expitaxy on a semi-insulating GaAs substrate. The sample structure was designed to achieve a double resonance condition to coincide the Bragg resonance peak with the exciton transitions at the second quantum state. Bragg peak can significantly be tuned by changing the angle of incidence of the light. Exciton energies can be tuned by changing the temperature and external electric field. The exciton energies are very sensitive to the thickness of the quantum wells. We performed low temperature ER measurements of the RBS samples of different thicknesses by tuning the angle of incidence of the light for double resonance and observed ER features related to the exciton transitions at excited states such x(e2-hh2), x(e2-hh1), x(e2-hh3) x(e2-lh1) and x(e1-hh3) exciton transitions along with the sharp features of x(e1-hh1) and x(e1-lh1) ground state exciton transitions. Details about the origin of the ER features related to the transitions will be presented.

Speaker 2: Anthony Tantillo, Department of Physics, Brooklyn College (CUNY) and Physics Program The Graduate Center (CUNY)

Title: The Use of Magnetically Hard Materials in Thermomagnetic Power Generation Cycles

Thursday, April 4, 2:30 p.m.

Speaker: António M. dos Santos, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee

Title: An illustrated guide to high pressure research at the Spallation Neutron Source

Abstract: Neutron scattering is a unique tool in materials sciences. It allows studies on problems mostly inaccessible through other techniques, such as direct interrogation on the location of light elements, unveiling complex magnetic structures, or the non-destructive testing of large engineering parts. Unlike visible light (Lasers) and X-rays, neutrons beams for materials research can only be produced in dedicated facilities, such as nuclear reactors or spallation sources. The Oak Ridge National Laboratory is unique in that it houses both neutron sources, the Spallation Neutron Source (SSNS)) and the High Flux Isotope Reactor (HHFIR), making it arguably the leading laboratory in the world for neutron scattering research. Since early in the development of neutron scattering, the coupling of this technique with high pressure was identified as an avenue with great potential. The SNAP instrument at the SNS, a diffractometer dedicated to high pressure research, is the flagship extreme conditions beamline in the US, delivering record high neutron flux to minute samples Since this facility has been made available to the high pressure user community, a broad range of materials systems have been investigated, in the form of powders, glasses and single crystals. Here we will illustrate the promise of neutron diffraction to physics and chemistry research, with examples from the SNAP research. We will show examples of compression mechanisms of amorphous solids, magnetic phase diagrams in lanthanides, phase competition in manganites and structural studies of clathrate hydrates. These examples will highlight how the use of the neutron scattering can assist in pursuing exciting science. Finally, ongoing improvements and additions to the SNS and SNAP capabilities will be discussed; facility capabilities, instrument improvements and new record-breaking pressure devices that open a new frontier in high pressure neutron scattering.

Monday, April 15, 12:30 p.m.

Speaker: Ron Koder, City College (CUNY) and The Graduate Center (CUNY)

Title: Using Information Theory and Supercharging in Functional Protein Design

Abstract: TBC

Thursday, May 2, 12:30pm

Speaker: Matthew O'Dowd, Lehman College (CUNY) and The Graduate Center (CUNY)

Title: The Heart of the Quasar

Abstract: Quasars provide one of the few observable manifestations of the extreme behavior of matter near black holes and they are an important factor in the energetic evolution of the Universe. Yet due to their vast distances and compact sizes, we have only a crude understand the physics behind their powerful emission processes. I will discuss an extremely promising technique to map the inner structure of quasars through gravitational microlensing. This technique takes advantage of size-dependent magnification fluctuations in multiply-imaged quasars that result from the gravitational substructure of the intervening lensing galaxy. With our new Hubble Space Telescope observations we apply this technique to make the most reliable-to-date measurement of quasar accretion disk temperature gradients.

Tuesday, May 14, 12:30pm

Speaker: Kimani Stancil, US Merchant Marine Academy

Title: The Langmuir Isotherm: an Interdisciplinary Tool for Nanoparticle Assembly

Abstract: On the path to scientific discovery, all students solve a lot of problems. And in introductory physics courses, problems are presented as simple or ideal, and possibly too complex or theoretical in the ‘real world’ cases. Some students become expert solvers without developing a real world connection to their solutions. The maturity of a scientist is established through these necessary connections. In this talk, I discuss one example of a problem from class – a gas in contact with an adsorbing surface in thermal equilibrium (i.e. constant temperature). How does the surface adsorption change with concentration? Using the Langmuir Isotherm, the physical adsorption of molecules can be measured by a coverage ratio that increases with concentration or pressure. And under ideal conditions, the isotherm details the eventual saturation or full surface coverage by adsorbed molecules. In two published experiments – 1) using polymer gels to adsorb metal ions; and 2) assembling CdSe nanorods via their dipole interaction, I demonstrate the usefulness of the equation that defines the Langmuir isotherm. Additionally, I discuss the Langmuir isotherm’s potential to serve as a more robust analysis and modeling tool for evaporation driven nanoparticle assembly. Note that Irving Langmuir first developed the isotherm equation to describe the adsorption of gases on metal substrates in the early 20th Century. A century later, Langmuir’s work lives on in polymer and nanoscience.

[1] Langmuir, I. The Adsorption of Gases on Plane Surfaces of Glass, Mica and Platinum. J. Am. Chem. Soc. 1918, 40, 1361−1403.
[2] Onsager, L. The Effects of Shape on the Interaction of Colloidal Particles. Ann. N.Y. Acad. Sci. 1949, 51, 627−659.
[3] Pande, V.; Grosberg, A. Yu; Tanaka, T. Rev. Mod. Phys. 2000, 72, 259.
[4] Tanaka, T.; et al. Phys. Chem. 1998, 102, 1529.
[5] Kimani A. Stancil, Michael S. Feld, Mehran Kardar, ‘Correlation and Crosslinking Effects in Imprinting sites for Divalent Adsorption by gels’, J. Phys. Chem. B; 2005, 109(14); 6636-6639
[6] Kevin M. Ryan, Alexander Mastrioanni, Kimani A. Stancil, Haitao Liu, A. P. Alivisatos, ‘Electric – Field Assisted Assembly of Perpendicularly Oriented Nanorod Superlattices’, Nano Letters, 6, (7), 1479, (2006)
[7] Kimani A. Stancil, Evaporation Assisted CdSe Nanorod Assembly by Small Angle X-ray Scattering and Langmuir Adsorption’, J. Phys. Chem. B, 118 (50), pp 14695–14702, November 2014