UMD CMNS Physics S1 Color


The Spring 2016 colloquia will be held in the lobby of the Physical Sciences Complex

Each week during the semester, the Department of Physics invites faculty, students and the local community to hear prominent scientists discuss intriguing physics research. The Spring 2016 colloquia will be held Tuesdays in the Physical Sciences Complex lobby at 4:00 p.m. (preceded by light refreshments at 3:30 p.m.)

Parking is available in the Regents Drive Parking Garage (PG2). An attendant will direct visitors within the garage. Additionally, a free ShuttleUM bus runs between the College Park Metro Station and Regents Drive at about eight-minute intervals.

For further information, please contact the Physics Department at 301-405-5946 or email This email address is being protected from spambots. You need JavaScript enabled to view it..

February 2
Dan Hooper, Fermi Lab
Hosted by: Kaustubh Agashe

Dark Matter Annihilation in the Gamma-Ray Sky

In many models, dark matter particles can undergo self-annihilation, generating gamma-rays and other high-energy particles. One of the missions of the Fermi Gamma-Ray Space Telescope is to search for these annihilation products. Over the past several years, Fermi's data has been shown to contain a spatially extended excess of ~1-3 GeV gamma rays from the region surrounding the Galactic Center, consistent with the signal expected from annihilating dark matter. Recent improvements in the analysis techniques have found this excess to be robust and highly statistically significant, with a spectrum, angular distribution, and overall normalization that is in good agreement with that predicted by simple annihilating dark matter models. I will discuss the characteristics of this signal, and ways to test its origin. In particular, the dwarf galaxies recently discovered by DES provide a potently important tool to test a dark matter origin of the Galactic Center excess.

February 9
Sankar Das Sarma, University of Maryland

Quantum Many Body Localization

How does an isolated quantum system come to thermal equilibrium due to interaction between its constituent subsystems? Or does it? What underlies the condition for quantum ‘ergodicity’? These are some of the basic questions to be discussed in this talk. The topic is of fundamental importance since it deals with the applicability of thermodynamics and statistical mechanics to isolated quantum systems, and asks the extent to which an isolated (macroscopic) quantum system can be considered to be acting as its own heat bath.

February 16
Dimtry Pushin, NIST
Hosted by: Vlad Manucharyan

The Quantum Neutron

The neutron, one of the most common building blocks of matter, is also a unique probe for studying materials and fundamental interactions. The only electrically-neutral nucleus, the neutron passes through most materials with ease, even at the lowest energies. Nowadays neutrons, even with their ~ 15 minute lifetime, are used to study problems ranging from current flow in common batteries to cosmological dark energy. I focus on the neutron as a quantum particle. We use a Mach-Zehnder neutron interferometer to fork a neutron into superposition states separated by decimeters, to exploit macroscopic quantum interference. I discuss recent experimental searches for dark energy, the use of quantum information concepts to enhance coherence, and the twisting of neutron waves.

February 23 
in Physics, ROOM 1412
Peter Shawhan, University of Maryland

The Remarkable Story of LIGO's Detection of Gravitational Waves

On February 11, LIGO scientists announced the direct detection of gravitational waves, confirming a century-old prediction of Einstein's general theory of relativity. This milestone fulfills a dream which started here on the UMD campus with Joseph Weber, and was finally made possible with the incredibly sensitive Advanced LIGO detectors, combined with a certain measure of luck. I will share both the scientific meaning of the discovery and some of the personal stories behind it.

March 1
Sami Mitra, APS
Hosted by: Vlad Manucharyan

PRL Today

How do the editors of Physical Review Letters determine which of the approximately 10,000 papers that it receives each year should be published? Science journals are being transformed by the internet: now their role appears to be to validate research, not to disseminate it. How is PRL in particular adapting to this changing environment? What guidelines would be helpful to you as an author and a referee? Why should you submit your work to PRL? I plan to address -- with plenty of interspersed Q & A -- these and related issues.

March 8
Raman Sundrum, University of Maryland

Particle Physics, the Large Hadron Collider, and Beyond

The central successes and puzzles of particle physics will be reviewed, the discovery of the Higgs boson at the CERN Large Hadron Collider (LHC) illustrating both aspects. The grand principle of Naturalness will be introduced as the dominant organizing principle behind many searches for new physics beyond the Standard Model. The challenging task of testing naturalness will be summarized, especially the interplay between deep theoretical ideas, such as Supersymmetry, Compositeness, Extra Dimensions and Hidden Naturalness, and experimental strategies at the LHC and even more powerful future colliders. The LHC is beginning its second phase of operations, at significantly higher energies than before, and this talk will give a satellite view of the big issues at stake in the coming years.

March 22
Richard Lebed, Arizona State University
Hosted by: Tom Cohen

The X,Y,Z Affair: A Tale of the Third and Fourth Hadrons

In the past 13 years, many new particles have been discovered that are clearly hadrons (interacting via the strong nuclear force), but do not seem to fit into either of the known hadron categories of meson (quark-antiquark) or baryon (3 quarks). Several species of these ``exotic’’ particles, called X, Y, and Z, are now believed to be tetraquarks, and last July the LHC announced the discovery of pentaquark states, P_c. We begin by reviewing the basics of QCD (quarks, color, confinement, etc.), and then turn to the question of how conventional mesons are identified, which allows one to identify exotics. After reviewing their experimental discovery, we consider the question of how exotics are assembled. Several competing physical pictures attempt to describe the structure of exotics: as molecules of known hadrons, as the result of kinematical effects, and others. I propose that they arise due to the formation of compact diquarks, a well-known but under-appreciated phenomenon of QCD. The competing facts of kinematics and diquark confinement create an entirely new kind of bound state: not a molecule with well-defined orbits, but an extended object that lasts only as long as it takes for quantum mechanics to allow the separated quarks and antiquarks to “find” one another, and allow decays to occur. I will discuss several observed effects that support this picture.

March 29
Robert Brown, American Institute of Physics
Hosted by: Ken Gertz

Fundamental Physics into High Impact Applications

Dr. Robert G. W. Brown is chief executive officer of the American Institute of Physics, a federation of 10 Member Societies in the physical sciences, which in total serve 120,000 members in the United States and around the world. As a trained physicist and engineer, Brown has made substantial contributions in research, product and business development, teaching, publishing, editorial direction, and administration. He has held various leadership positons in the corporate, non-profit, academic, and government sectors, principally in the United Kingdom, the United States, and Northern Ireland, with additional ventures throughout Europe and Asia. His research interests extend from nanotechnology to photonics, optics, medical physics, fluid dynamics, and beyond. Brown has authored more than 120 articles in peer-reviewed journals and holds 34 patents, several of which have been successfully commercialized. As CEO, he serves as an ex-officio member on the boards of AIP and AIP Publishing, a wholly owned subsidiary of the institute.

Brown is an elected member of the European Academy of the Sciences and Arts (Academia Europaea) and a special professor at the University of Nottingham in the UK. He also retains an adjunct full professorship at the University of California, Irvine in the Beckman Laser Institute and Medical Clinic and is a visiting professor in the Department of Computer Science, also at UC Irvine.

Before coming to AIP, Brown most recently led the nano-plasmonic research activities at Rockwell Collins’ Advanced Technology Center, and was chief technology officer to Ostendo Technologies, a specialist display company, in Carlsbad, California. He served for various years as professor and director of nanotechnology for Northern Ireland; executive director of the UK Institute of Physics; and head of optoelectronics research and development for Sharp Laboratories of Europe, the world’s third largest optoelectronics corporation. As a principal scientist in the UK Ministry of Defence’s Royal Radar Establishment, Brown was responsible for inventing new detector, electronic correlator, APD photo-detector, laser-diode, liquid-crystal display and optical-fiber technologies that have since been developed into successful products for experiments related to jet engines, macro-molecules, US submarines, and space shuttle instrumentation.

Brown has been recognized for his entrepreneurship with the United Kingdom’s Ministry of Defence Prize for ‘Outstanding Technology Transfer,’ Sharp Corporation’s (Japan) prize for his novel laser-diode invention, and, together with his team at the UK Institute of Physics, a Queen’s Award for Enterprise, the highest honor that can be bestowed on a UK company.

Brown is editor-in-chief of the Handbook of Optoelectronics published by CRC Press and is co-editor-in-chief of the CRC Press book series in ‘Optics and Optoelectronics’. He has been co-chairman for four of OSA’s International Photon Correlation Conferences, and editor of subsequent related special issues of Applied Optics. He has served as a consultant to many companies and government research centers in the USA and UK, most notably on NASA’s Microgravity Experimental Advisory Board and on the UK Home Office (Homeland Security Department equivalent) Science and Technology Reference Committee.

Brown is a citizen of the United States and the United Kingdom.

April 5
Peter Armitage, Johns Hopkins University
Hosted by: Vlad Manucharyan

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 1D Ising model. 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.

April 12
M Zahid Hasan, Princeton University
Hosted by: Jay Sau

Discovery of Weyl Fermion and Topological Nodal-line Fermions as Emergent Excitations in Topological Materials

Topological materials can host Dirac, Majorana and Weyl fermions as quasiparticle modes on their boundaries or bulk. First, I briefly mention the basic theoretical concepts defining insulators and superconductors where topological surface state modes are robust only in the presence of a gap (Rev. of Mod. Phys. 82, 3045 (2010)). In these systems topological protection is lost once the gap is closed turning the system into a trivial metal. A Weyl semimetal is the rare exception in this scheme which is a topologically robust conductor (semimetal) whose low energy emergent bulk excitations are Weyl fermions. In a Weyl semimetal, the chiralities associated with the Weyl nodes can be understood as topological charges, leading to split monopoles and anti-monopoles of Berry curvature in momentum space. This gives a measure of the topological strength of the system. Due to this topology a Weyl semimetal is expected to exhibit 2D Fermi arc quasiparticles on its surface (Wan, 2011). These arcs (``fractional'' Fermi surfaces) are discontinuous or disjoint segments of a two dimensional Fermi contour with non-trivial spin textures, which are terminated onto the projections of the Weyl fermion nodes on the surface observed recently in experiments. Our theoretical predictions (Nature Commun. 2015) and experimental demonstrations (Xu, Science 349, 613 (2015), Nature Physics 2015, Science Advances 2015) reveal that these Fermi arc quasiparticles can only live on the boundary of a 3D crystal which collectively represents the realization of a new state of quantum matter beyond our earlier work on spin-textured Fermi arcs in topological materials (Xu, Science 347, 294 (2015)). We provide a comparison. Very recently, we theoretically and experimentally discovered a related state of matter, a topological nodal-line semimetal state in (Pb/Tl)TaSe2 (which also superconduct at low temperatures) where the Fermi surface is a protected nodal-line loop in three dimensional momentum space (Bian et,al., Nature Commun. 7:10556 (2016)) possibly suggesting a new platform to investigate the interplay of superconductivity and non-trivial topology.

April 19
Marc Kamionkowski, Johns Hopkins University
Hosted by: Raman Sundrum

Symmetry, Geometry, Cosmology

Our existing physical laws are unable to explain several features of the observed Universe. The nature of the dark matter that holds individual galaxies together and of the dark energy that drives different galaxies away from each other both require new physics beyond the Standard Model and general relativity. The preponderance of matter over antimatter likewise requires some new baryon-number violation beyond that in the Standard Model. Explanations for the primordial density inhomogeneities observed in the cosmic microwave background all involve new physics. I will review these questions, discuss some existing avenues to make progress, emphasizing several ways in which considerations of symmetry and geometry may play a role in the quest for new cosmological physics.

April 26
Carr Lecture
in Physics, Room 1410
Art Hebard, University of Florida
Hosted by: Chris Lobb

Ah-ha Moments Inspired by the Scaling/Collapse of Experimental Data

Condensed matter experimentalists are often confronted with multivariable data sets in which dependent variables such as resistance, susceptibility, or magnetization are measured as a function of independent variables such as temperature, magnetic field or frequency. When the data can be plotted in such a way that all of the data fall onto either a small subset of curves or even a single curve, an “ah ha” moment is close at hand. This talk will trace the speaker’s experience with such “ah ha” moments when confronted with data collapse in collaborative investigations on: (1) the disorder driven two-dimensional superconductor-insulator transition in thin films of indium oxide, (2) the disorder driven three-dimensional metal-insulator transition in ferromagnetic thin films of gadolinium, (3) a multivariable power-law scaling collapse of the dielectric constant in complex oxide manganites near the percolation transition and (4) a self-similar scaling behavior of the hysteretic magnetization of a wide variety of magnetic thin-film systems. Among these examples, the first two rely on insightful theoretical guidance to extract fundamental understanding, whereas the second two have no apparent theoretical interpretation but do provide rather spectacular and surprising scaling collapses of multivariable data sets.

May 3


Anwar Shaikh, New School for Social Research
Hosted by: Victor Yakovenko

Economic Inequality: Piketty versus Econophysics

The study of income inequality is back in vogue. Thomas Piketty's empirical investigations have led him to conclude that capitalist inequality is structural, and is likely to revert to its nineteenth century, much more unequal stage of "patrimonial capitalism". For him, the best way to compensate for this intrinsic tendency is to use global capital taxation to fund national welfare states. He admits that this is an "utopian ideal”, but hopes that it could spark regional or continental moves in that direction. The classical tradition rooted in Smith, Ricardo, and Marx is grounded in a structural analysis of actual capitalism, in which the laws governing market-determined (i.e. pre-tax and transfer) labor and property incomes are fundamentally different. Yakovenko and his co-authors have shown that labor income tends to follow an exponential probability distribution, while property incomes tend to follow a power law, such as the Pareto distribution. In this approach, the overall degree of inequality, as measured by the Gini coefficient, depends on the share of property income in total personal income. The presented paper shows that, in the postwar US, the property income share is determined by the balance of power in the ongoing struggle over the relation of real wages to productivity and by the degree to which financial capital is given free rein to exercise its inherent tendency to create bubbles and troubles. From this point of view, the post 1980s increases in the profit share and the degree of financialization are political outcomes which can be reversed, so there is no need to believe that the future of inequality should look like the past.

Dr. Anwar Shaikh is Professor of Economics and Chair of Economics Department at the Graduate Faculty of Political and Social Science of the New School University in New York. He earned B.S. in Engineering at Princeton University in 1965 and Ph.D. in Economics at Columbia University in 1973. Currently he is an Associate Editor of the "Cambridge Journal of Economics", and was a Senior Scholar and member of the Macro Modeling Team at the Levy Economics Institute of Bard College from 2000-2005. His most recent book (2016) is "Capitalism: Competition, Conflict, Crises" by Oxford University Press. In 2014 he was awarded the Social Science Prize of the NordSud International Prize for Literature and Science by the Fondazione Pescarabruzzo in Italy. His intellectual biography appears in the most recent edition of the book "Eminent Economists II" published by Cambridge University Press in 2014, along with similar essays from 30 prominent economists, including seven current Nobel Prize Laureates. He is the author of three other books, including "Globalization and the Myths of Free Trade" (2007, Routledge). More information is available at