Physics and Astronomy Colloquia, Academic Year 2017-2018

Colloquium committee: Leonardo Rastelli (Chair),  Marivi Fernandez-Serra, Eden Figueroa, Krishna Kumar, Mengkun Liu, Rosalba Perna, and Giacinto Piacquadio

Coffee & Tea served at 3:45 pm.

Talk begins at 4:15 pm.

Location: Harriman 137 (bottom of square C4 on the campus map)

Movies:  To watch the recorded movies, please  read the instructions here.

Fall 2017 colloquia

Sept. 12

Chair Colloquium

Chair’s Colloquium

   [recorded movies] on Firefox-ESR or VLC / rtsp://.

Sept. 19

Philip B. Allen

Stony Brook University

Electrons and Phonons in Solids
Electrons and phonons are the “quasiparticles” that determine the behavior of crystalline solids.  Quasiparticles are excitations with analogs to free particles.  Electrons in crystals, for example, have the same charge as free electrons, but altered mass.  They are accelerated by electric fields, obey Fermi statistics, and have hybrid particle/wave features like free electrons.  But they are also very different from free electrons.  In pure semiconductors, they disappear at low temperatures, emerging as electron-hole pairs, analogous to electron-positron pairs.  In metals at low temperature, they are constrained by a sharp Fermi surface, form Cooper pairs, and carry supercurrents.  Phonons are vibrational-wave particles that cannot be freed from their crystal host.  They are a lot like photons in vacuum, but more complicated.  We are still learning how to think about quasiparticles in crystals.  We want to understand how they evolve in time, temperature, and as their interaction strength varies.  The incredible diversity of crystalline matter gives us new surprises, challenges, and opportunities to deepen our understanding.

  [recorded movies] 


Sept. 26

Matthew Sfeir

Center for functional nanomaterials, BNL

Manipulating Excitons Dynamics for Energy Conversion Applications
The promise of nanotechnology lies in the emergence of novel electronic and photonic phenomena with the potential for new device technologies. For example, optical transitions at the nanoscale frequently result from strongly absorbing excitons, whose electronic structure and dynamics are shape, size, and morphology dependent. However, since excitons are bound
states, device concepts that exploit the unique photophysics of excitons, for example, organic photovoltaics or multiple exciton generation solar cells, depend critically on the ability to direct specific favorable conversion processes and suppress unfavorable ones. Here I will discuss
how optical spectroscopy is an important tool to understand the success (and failure) of nanoscale device concepts. In this talk, I will discuss how the unique optical signature of excitons allow for dynamical tracking of energy conversion processes on ultrafast time scales. These optical signatures can be used to understand the harvesting of excitons in
nanoscale lasers, photocatalytic water splitting devices, and photovoltaics. I will show how the first few picoseconds after absorption are crucial to understanding the overall performance of a
nanomaterial-based energy device.

  [recorded movies] 


Oct. 3

Richard Averitt


Ultrafast Dynamics and Control in Complex Materials

The past decade has seen enormous advances in materials and ultrafast optical spectroscopy spanning from classical to quantum physics. On the classical front, metamaterials are artificial composites with unique electromagnetic properties that derive from their sub-wavelength structure. Metamaterials enable new ways to control light with negative refractive index and cloaking as two examples of continuing interest. Further, it is possible to use metamaterials to localize and enhance incident electromagnetic fields well below the diffraction limit. Moving to the quantum realm, correlated electron materials exhibit fascinating phenomena ranging from superconductivity to metal-insulator transitions.  Many of these materials exhibit colossal changes to small perturbations, which includes electromagnetic excitation. This opens up exciting possibilities such as photoinduced phase transitions with the goal to create novel states with unique properties. To illustrate the richness of this still emerging field, I will show examples from our work such as terahertz induced field-emission and carrier acceleration from metamaterial split ring resonators, nonlinear plasmonics, optically induced metastable insulator-to-metal phase transitions, and very recent work on photoinduced phenomena in superconductors.

  [recorded movies] 


Oct. 10

Mike Williams


Searching for physics beyond the Standard Model at the LHCb experiment
The LHCb experiment at the Large Hadron Collider (LHC) at CERN has been the world's premier laboratory for studying processes in which the quark types (or flavors) change since 2011. Such processes are highly sensitive to quantum-mechanical contributions from as-yet-unknown particles, e.g. supersymmetric particles, even those that are too massive to produce at the LHC. I will discuss the status of these searches, including some intriguing anomalies. I will also present searches for the proposed dark matter analogs of the photon and the Higgs boson. Planned future upgrades and the resulting physics prospects will also be discussed, including our plans to process the full 5 terabytes per second of LHCb data in real time in the next LHC run.

  [recorded movies] 


Oct. 17

Giuseppe Mussardo

Yang-Lee Zeros of the Yang-Lee Model

We address in a very pedagogical way the Yang-Lee formalism for statistical models, finally focusing the attention  on the zeros of the grand canonical partition in the fugacity variable of the simplest integrable quantum field theory,  the so called Yang-Lee model. 

The colloquium will take place in the Simons Center auditorium. 

Refreshments after the colloquium at 5:30pm in the Simons Center lobby. 

Screening of Mussardo’s movie “Galois: Story of a Revolutionary Mathematician” will follow at 6pm in the Simons Center Auditorium.

  [recorded movies] 


Oct. 24

Jon Simon

University of Chicago

Building Correlated and Topological Quantum Matter from Light

In this talk I will discuss ongoing efforts in my group exploring topological and strongly-interacting phases of light. I will begin with our observation of photonic Landau levels in curved space, created by trapping light in twisted (non-planar) optical cavities, and culminating in the first measurement of the mean orbital spin of integer Hall state, a normally-inaccessible quantum number, along with a direct measurement of the Chern number using Kitaev’s real-space formalism. I will then discuss our recent demonstration of colliding cavity Rydberg polaritons, plus ongoing efforts to load the polaritons into a twisted cavity to create Laughlin states. I will conclude by summarizing a collaboration with the Schuster lab where we have recently created both a photonic Chern insulator and a dissipatively stabilized photonic Mott insulator.

  [recorded movies] 



Joanna Kiryluk

Stony Brook University

IceCube: Understanding the High Energy Universe with Cosmic Neutrinos

IceCube is a one cubic kilometer telescope, buried deep in the ice at the South Pole. With this unique instrument IceCube scientists have discovered a flux of high energy (1015 eV) cosmic neutrinos, elusive sub-atomic particles, originating from outside of our Galaxy.  Such neutrinos are expected to be produced in the most violent astrophysical processes:  events like exploding stars, gamma ray bursts, and other phenomena that accelerate particles to ultra-high energies.  However, the astrophysical sources of these neutrinos still remain a mystery.   I will discuss the IceCube experiment, highlight its most important and recent scientific results, and will outline plans for future neutrino astronomy

  [recorded movies] 

Nov. 7

Gordon Cates
University of Virginia

Neutrons, Nephrology and Nuclear Imaging:  MRI with a millionfold increase in sensitivity 

The technique of spin-exchange optical pumping has found extensive use in both fundamental research and a variety of applications. For example, high-density polarized He-3 targets have played an important role in elucidating  the spin structure of the nucleon, and more recently, enabling form-factor measurements at very high momentum transfer. Phenomena such as the role of quark orbital angular momentum, and the importance of diquark-like structures, are among the physics that has resulted from such work.  MRI using polarized He-3 and Xe-129 have provided the highest resolution images of the gas space of lungs ever produced.  And very recently, polarized Xe-129, dissolved into the blood following inhalation, has been used to try to visualize, in real time, the function of the kidney. However, the strategy of somehow combining magnetic resonance with the use of tiny quantities of a tracer is limited by the poor signal-to-noise that results when very few nuclei are involved. I will describe a new technique we call Polarized Nuclear Imaging (PNI) in which magnetic resonance techniques play a key role, but imaging data are acquired not through detecting weak electromagnetic signals, but through the detection of gamma rays.  The net effect is to increase the sensitivity of magnetic resonance by factors of between a million and a billion. The techniques described may also be useful in the  study of exotic nuclei.

  [recorded movies] 


Nov. 14

Pedro Vieira

Perimeter Institute and ICTP-SAIFR

Holography and Haute Couture

Superstrings in five dimensional hyperbolic space and a strongly coupled four dimensional conformal theory known as maximally supersymmetric Yang-Mills theory (or simply the Darth Vader theory) are related by a remarkable duality known as holography. Solving these theories would tell us a great deal about quantum gravity and about the nature of strongly coupled field theories. Since they are both strongly coupled quantum field theories, this is quite a challenge. One promising approach is based on tailoring ideas. As I will review in this colloquium,  various observables in these theories are cut into fundamental building blocks which are then stitched back together into beautiful haute couture physical quantities at finite coupling.

  [recorded movies] 


Nov. 21

Neelima Sehgal

Stony Brook University

Measuring Gravitational Lensing of the Cosmic Microwave Background to Probe Neutrino Mass, Dark Energy, Dark Matter, and Primordial Gravitational Waves

In this talk I will discuss the next frontier of research on the Cosmic Microwave Background (CMB): precisely measuring the gravitational lensing of the CMB.  This CMB lensing signal encodes a wealth of statistical information about the distribution of matter in the Universe, which is sensitive to the total mass of the neutrinos, the nature of dark energy, and the particle properties of dark matter.   CMB lensing also obscures our view of the newborn Universe, limiting our ability to constrain gravitational wave signals from the epoch of inflation.  By removing this lensing “noise”, any inflationary signatures would be brought into sharper focus. I will discuss recent progress in probing neutrino mass, dark energy, and primordial gravitational waves using data from the Atacama Cosmology Telescope Polarimeter (ACTPol), and forecasts of what can be expected from the upcoming AdvACT, Simons Observatory, and CMB-S4 experiments. I will also discuss a novel and powerful way to probe dark matter particle properties using very high resolution CMB lensing measurements, which can distinguish between cold dark matter and alternative dark matter models that suppress small-scale structure. 

  [recorded movies] 

Nov. 28

Scott Dodelson

University of Chicago

Cosmology with the Dark Energy Survey

The Dark Energy Survey released its first cosmological results this summer. Using the positions and shapes of millions of galaxies, DES has obtained the most accurate measurement to date of clustering in the late universe. Comparing these results with those obtained by cosmic microwave background experiments enables us to test a zero parameters prediction of the so-called Lambda CDM model. I will present the motivation, details of the analysis, a video of the profanity-laced unblinding telecon … and the results.

  [recorded movies] 

Dec. 5

Marivi Fernandez-Serra

Stony Brook University

Understanding liquid water from first principles: a tale of two liquids

Despite the simplicity of its molecular structure, condensed phases of water present a complicated phase diagram that has not yet been fully completed. Liquid water as we know it is not a simple liquid. The anomalies of water manifest in many thermodynamic and structural ways. Because of this the complete understanding of the phase diagram of liquid water and ice is still an active area of research in the chemical physics community. In this talk I will present how this problem can be addressed using density functional theory. Our results show that the anomalies of water are strongly linked to the coupling between vibrational and electronic degrees of freedom in the hydrogen bond interaction. And that both electronic and nuclear quantum effects play a role in the second critical point conjecture. In addition, I will show how the second critical point scenario also connects to the interaction of water with functional semiconductor and metallic surfaces. I will present the state of the art of current simulations and the challenges we face, focusing on two specific problems: the description of aqueous solvated electrode surfaces and the simulation of photocatalytic surfaces in aqueous environments.

  [recorded movies] 


  Spring 2018 colloquia

Jan. 23

Sally Dawson

BNL and Stony Brook University

Precision measurements for the LHC

The discovery of the Higgs boson at the LHC in 2012 was a triumph for particle physics and demonstrated the basis correctness of the Glashow-Weinberg theory of weak interactions. I will discuss the next phase of our understanding of the mechanism of electroweak symmetry breaking at the LHC and how progress requires the delicate interplay of experiment and theory.


Jan. 30

Peter Armitage 

Johns Hopkins University

On Ising's model of ferromagnetism

The 1D Ising model is a classical model of great historical significance for both classical and quantum statistical mechanics. Developments in the understanding of the Ising model have fundamentally impacted our knowledge of thermodynamics, critical phenomena, magnetism, conformal quantum field theories, particle physics, and emergence in many-body systems. Despite the theoretical impact of the Ising model there have been very few good 1D realizations of it in actual real material systems. However, it has been pointed out recently, that the material CoNb2O6, has a number of features that may make it the most ideal realization we have of the Ising model in one dimension.  In this talk I will discuss the surprisingly complex physics resulting in this simple model and review the history of "Ising’s model” from both a scientific and human perspective.  In the modern context I will review recent experiments by my group and others on CoNb2O6.  In particular I will show how low frequency light in the THz range gives unique insight into the tremendous zoo of phenomena arising in this simple material system.


Feb. 6

Jim Lattimer

Stony Brook University


Feb. 13

Thomas Hartman

Cornell University


Feb. 20

Bruce Remington

Lawrence Livermore National Lab


Feb. 27

Carter Hall

University of Maryland


March 6

March 13

Spring Break: No classes and no colloquium

March 20

March 27

Mehran Kardar


April 3

Monica Olvera de la Cruz

Northwestern University


April 10

April 17

April 24

May 1

Graduate Director