2017 Fall Archive

September 8, 2017 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Fan Zhang, University of Texas
Host: E. Rossi
Title: Symmetry Protected Topological Matter
Abstract: In history, solid states are characterized by the symmetries they respect and also by those they break. Not only does this idea distinguish graphite and diamond, but also ferromagnets and superconductors. Recently, the discovery of topological insulators has revealed a new paradigm that solid states respecting the same symmetries can be topologically distinct. The same idea relates a cup and a donut, yet distinguishes a sphere and a torus. Such a topological viewpoint has created a revolution in condensed matter science that has far ranging implications over coming decades. In this talk, I will introduce how the topological insulators arise from band inversion, and how they are protected by symmetries and enriched under symmetry breaking. I will then generalize these essential ideas to other experimentally feasible systems such as superconductors with Weyl and Majorana excitations. Fascinating and significant implications including experimental signatures and potential applications will be discussed.

September 15, 2017 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Deyu Lu, Center for Functional Nanomaterials, Brookhaven National Laboratory
Host: S. Zhang
Title: First principles modeling of electronic excitations: From basic understanding to materials
applications
Abstract: Electronic excitations are fundamental physical processes. Spectroscopic information, including absorption and emission spectra, from electron or photon probes is crucial for materials characterization and interrogation. When experimental data are supplemented and interpreted by first principles atomic modeling, a coherent physical picture can be established to provide physical insights into the intriguing structure-property-function relationship of functional materials. In this talk, the significance of the first principles modeling of electronic excitations is highlighted with three examples. In the first example, we investigated the oxygen 1s corelevel binding energy shift of bilayer silica films on Ru(0001) under different surface oxygen coverages in the X-ray photoelectron spectroscopy (XPS) measurement. Our study revealed that the binding energy shift is an electrostatic effect caused by the interplay of the surface and interface dipole moments. In the second example, we applied ab intio X-ray absorption near edge structure (XANES) modeling for spinel lithium titanate (Li4/3Ti5/3O4), an appealing lithium ion battery material. We identified key spectral features as fingerprints for quantitative assessment of the structural transformation during lithiation. In the third example, we are motivated to develop a local representation of the microscopic dielectric response function of valence electrons, which is a central physical quantity that captures the many-electron correlation effects. Although the response function is non-local by definition, a local representation in real space can provide insightful understanding of its chemical nature and improve the computational efficiency of first principles excited state methods. We applied the local dielectric theory to calculate the molecular polarizability of water and investigated the effects of the local field and hydrogen bonds. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DESC0012704.

September 22, 2017 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker:
Marc Sher, William & Mary Physics
Title:
The Higgs Boson, five years later
Abstract:
The discovery of the Higgs boson in 2012, almost fifty years after it had been predicted, was an extraordinary achievement.    It explained the origin of mass for all elementary particles.   In this talk, I will discuss the Standard Model and explain the importance of the Higgs and describe its properties.   The experimental results since the discovery will be reviewed.    I will then discuss the next steps in exploring the properties of the Higgs, future prospects and physics “beyond the Standard Model”.   This talk should be accessible to undergraduate juniors

October 6, 2017 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker:
Natalia Noginova, NSU
Host: Irina Novikova
Title:
Plasmon Drag and Optical Magnetism in Plasmonic Structures and Metasurfaces
Abstract:
Plasmonic systems and metamaterials attract much attention due to their unusual properties and new opportunities for various applications. Such systems are also extremely interesting from fundamental point of view as they demonstrate novel or strongly modified effects associated with light matter interactions.  In this talk I will discuss two directions of my research: Coupling of photons,  plasmons and electrons in nanostructured metal, and Probing of optical magnetism in plasmonic systems and metasurfaces.

October 27, 2017 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker:
Kent Yagi, UVA
Host:
Marc Sher
Title:
Welcome to the Era of Gravitational Wave Astronomy!
Abstract:
Recent direct detections of gravitational waves from binary black hole mergers opened a completely new type of astronomy. Very recently, gravitational waves from binary neutron star mergers were detected, followed up by roughly 70 electromagnetic telescopes. Such multimessenger astronomy already brought us very important and new implications in various aspects of physics. In this talk I will give an overview of the current status of this new gravitational wave astronomy and what we have learnt so far in terms of astrophysics, nuclear physics, gravitational physics and cosmology. I will then explain what we expect to find in future in terms of fundamental physics with the up-coming multimessenger astronomy.

November 3, 2017 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker:
Wes Gohn, Kentucky
Host:
Wouter Deconinck
Title:
Breaking the Standard Model with Precision
Abstract: While colliding particles at the highest energies provides an important frontier in which to look for physics beyond the standard model, we can also search for new physics by pushing the precision at which the theory is tested, and with sufficiently high precision, we can probe energy scaled far beyond those of the LHC. New experiments will push that boundary by performing precision measurements with muons such as the Muon g-2 experiment at Fermilab and precision electron scattering measurements such as the QWeak and M{\o}ller experiments at Jefferson Lab. Muon g-2 will improve the uncertainty on the anomalous magnetic moment of the muon $a_\mu$ by a factor of four over Brookhaven experiment E821, and M{\o}ller will improve the uncertainty on $A_{PV}$ by a factor of five on the previous E158 experiment at SLAC. Both of the previous experiments measured 3$\sigma$ discrepancies which could be reconciled in the new experiments. These improvements in precision, combined with recent improvements in our understanding of the QCD contributions to the muon $a_\mu$, could provide a better than 5$\sigma$ discrepancy with the standard model, a clear indication of new physics.

November 10, 2017 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker:
Host:
E. Rossi
Title:
Does God play dice?
Abstract:
Quantum mechanics does not deal with individual events and all its predictions are of a statistical nature. For example, if we have radioactive nuclei or molecules in excited states we can, in principle, predict the average rate of decay but not when exactly this given nucleus or molecule passes to its ground state. This situation leads to long-time and very hot debates on “completeness”

of quantum mechanics, its applicability or inapplicability for macroscopic objects, existence or nonexistence of underlying classical reality (“hidden parameters”), role of measurement devices and observes, and so on, and so forth. Discussions involved the greatest physicists of twentieth century and can be briefly summarized as an exchange of mottos:

Albert Einstein: God doesn’t play dice.
Niels Bohr: Einstein, don’t tell God what to do.

Recently, we proposed [1-4] a purely phenomenological way to build the quantum theory as the most robust description of reproducible experiments and have shown that this may be done independently on any assumptions on underlying ontology, based purely on logical inference approach and a minimal amount of additional physical postulates, such as applicability of classical physics at the average.

Basic experiments of quantum physics, such as Stern - Gerlach or Einstein - Podolsky - Rosen - Bohm experiments can be analyzed within this framework, without any presumptions on wave function and Born rule. In a sense, our approach is a formalization of a well-known quasi-philosophical motto, "quantum theory describes our knowledge of atomic world rather than the atomic world itself"' which can be now analysed by conventional powerful tools of mathematical physics. Basic equations of quantum mechanics can be derived in this way.

In the context of the question in the title, one can say: We do not know what He is doing and, of course, we do not dare to tell Him what to do but our human way of thinking forces us to describe the reality as if He would play dice.

[1] H. De Raedt, M. I. Katsnelson, and K. Michielsen, Quantum theory as the most robust description of reproducible experiments. ANN PHYS (NY) 347, 45 (2014)

[2] H. De Raedt, M. I. Katsnelson, H. C. Donker, and K. Michielsen, Quantum theory as a description of robust experiments: Derivation of the Pauli equation. ANN PHYS (NY) 359, 166 (2015)

[3] H. C. Donker, M. I. Katsnelson, H. De Raedt, and K. Michielsen, Logical inference approach to relativistic quantum mechanics: derivation of the Klein-Gordon equation. ANN PHYS (NY) 372, 74 (2016)

[4] H. De Raedt, M.I. Katsnelson, and K. Michielsen, Quantum theory as plausible reasoning applied to data obtained by robust experiments. PHIL TRANS ROYAL SOC A 374, 20150233 (2016)

December 8, 2017 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker:
Marko Horbatsch, York University, Toronto, Canada
Host:
K. Griffioen
Title:
Quantum interference in hydrogen spectroscopy and the proton charge radius puzzle
Abstract: For some years now the size of the proton charge radius has been in question. Atomic hydrogen spectroscopy was thought to be consistent with elastic electron-proton scattering determinations and yielding a radius of about 0.88 fm. The CREMA collaboration produced a 2S-2P Lamb shift measurement in muonic hydrogen (and later in muonic deuterium) from which the charge radius follows to have a value of 0.841 fm. This questions the accuracy of e-p scattering determinations of the charge radius. I will describe a recent fluorescence measurement from Garching (T. Haensch group, Science 2017) in regular hydrogen for the 2S-4P intervals, which when corrected for quantum interference yields a result that is consistent with the muonic hydrogen determination of the proton charge radius. The role of quantum interference in spectroscopy is a phenomenon that is becoming more important as the demand of determining the center of the resonance as a tiny fraction of its width is attempted.