Sept. 16
Silicon Sensors in High Energy Physics Experiments
Frank Hartmann, Karlsruhe Institute of Technology
Semiconductor sensors have been around since the 1950s and today, every high energy physics experiment has one in its repertoire. In Lepton as well as Hadron colliders, silicon vertex and tracking detectors led to the most amazing physics and will continue doing so in the future. This talk tries to depict the history of these devices exemplarily without being able to honor all important developments and installations. The current understanding of radiation damage mechanisms and recent R&D topics demonstrating the future challenges and proposed technical solutions for the HL-LHC detectors will be presented. Consequently semiconductor sensor candidates for an LHC upgrade and a future linear collider are also briefly introduced. The work presented here is a collage of the work of many individual silicon experts spread over several collaborations across the world.
Return to the 2014-2015 Colloquia ScheduleOct. 2
Detection of B-mode Polarization at Degree Scales using BICEP2
Stefan Fliescher, University of Minnesota
Using BICEP2, a specialized Cosmic Microwave Background (CMB) polarimeter operating from the South Pole in Antarctica, our collaboration recently reported the detection of B-mode polarization. By making super sensitive maps of the polarization of microwave light at 150 GHz we find >5 sigma excess of B-mode power above the lensed-LCDM expectation in the angular range here primordial gravitational waves are expected to peak. The theory of Cosmic Inflation postulates such gravitational waves to be produced from quantum fluctuations during an incredibly brief urst of hyper expansion in the very early universe. Upcoming analysis with data at additional frequencies are required to determine how much of the detected signal is due to galactic dust foreground, and how much may be due to gravity waves.
Return to the 2014-2015 Colloquia ScheduleOct. 9
Interface Physics in Hybrid Materials
David Lederman, West Virginia University
Interfaces between materials have different properties from bulk materials because of the different symmetry of the electronic orbitals. The resulting interface electronic interactions can in turn affect the properties inside the bulk material. If the bulk material is thin, the interface physics can dominate the behavior of the entire material, resulting in essentially a new material with unique properties. In my talk, I will illustrate this concept through two very different examples. First, I will discuss the phenomenon of exchange bias, where the magnetic exchange interaction at the interface between an antiferromagnet and a ferromagnet can induce a net shift of the ferromagnetic hysteresis loop. In turn, the antiferromagnetic structure is also affected, especially if magnetic disorder due to impurities or defects is present in the antiferromagnet. Interestingly, a magnetic net polarization is induced in the antiferromagnet at the interface which can persist to temperatures that are much higher than the antiferromagnetic Neel (ordering) temperature. I will also discuss efforts to fabricate bioelectronic devices that rely on biomolecules that can conduct electricity in a way similar to quantum dots, focusing on protein-based single electron transistors and measurements of enzymes immobilized on metallic nanopillars. In these devices, resonant tunneling seems to be an important electrical conduction mechanism. The binding site of the protein and its conformation also play crucial roles, but to date it is not clear how to control these factors, although I will discuss ways in which it may be possible to at least determine the binding site and the structure of the bound protein.
Return to the 2014-2015 Colloquia ScheduleOct. 16
Why Should You Care About Nuclear Fusion?
David Crandall
Three quick answers to that question: you owe everything to fusion (Earth and you are fusion-created stardust and all stars are powered by fusion); fusion energy will be a topic of discussion for your entire life; the science and engineering challenges in obtaining sustained fusion on earth are interesting and conect to nearly all science. The talk will define fusion and how it works in stars. The current efforts to sustain inertial and magnetic fusion in the laboratory will be summarized. The talk will describe in some detail the most interesting endeavor right now, the attempt to reach inertial fusion ignition at the National Ignition Facility in Livermore, California using the world’s largest laser to drive explosion of a tiny fusion fuel target. The world’s largest fusion endeavor, the International Thermonuclear Experimental Reactor (ITER) under construction in Cadarache, France, will be outlined along with the magnetic confinement of plasma that it will rely on. Connections of these fusion concepts to astrophysics and materials science will be described. Why fusion energy is so attractive and so elusive will be discussed.
Return to the 2014-2015 Colloquia ScheduleOct. 23
Observation and control of electronic phases in strongly correlated oxides
Thomas Ward, Oak Ridge National Lab
The strong electronic correlations arising from overlapping spin-charge-orbital-lattice order parameters in complex oxides are of fundamental importance to many desirable characteristics such as metal-insulator transitions, ferroicity, colossal magnetoresistance, and high TC superconductivity. We will discuss our research progression on manganites which has taken us from creating a means of isolating and observing previously hidden mesoscopic phenomena to designing approaches that allow tuning of each of the individual order parameters. These methods will be put into the contexts of allowing us to explore the fundamental mechanisms at play in complex materials and providing a bridge toward next generation device functionality. Supported by the US DOE Office of Basic Energy Sciences, Materials Sciences and Engineering Division.
Return to the 2014-2015 Colloquia ScheduleNov. 06
Observation and control of electronic phases in strongly correlated oxides
Amber Boehnlein, SLAC National Accelerator Laboratory
All experimental and observational science areas are seeing dramatic increases in data volumes and a need for sophisticated data management, analysis and visualization techniques. There is increasing interplay of simulation and experiment observation that requires the ability to treat simulated and experimentally collected data on equal footing. The scale of the computing requirements and the distributed nature of the collaborations in high energy and nuclear physics experiments has led to the development of highly organized computing models. The successful deployment of this computing paradigm was a major factor in the ability of the Large Hadron Collider collaborations to rapidly achieve key physics goals, such as the discovery of the Higgs Boson. The Large Synoptic Space Telescope is an example of a new instrument that will push the boundaries of research data. In contrast, the data rates and computing power traditionally required by experiments mounted at conventional light source end stations have been relatively modest and adequately addressed within the individual experimental groups. Due to advances in detector technology, the use of computer simulations to design experiments and a desire for near real-time feedback during data collection, light source users are experiencing significant increases in data rates and computational needs. This trend, coupled with the development of open data policies, is leading to a need for more formal computing paradigms.
Return to the 2014-2015 Colloquia ScheduleJan. 22
Using Attosecond XUV and Electron Pulses to Control and Image Electronic Motion
Anthony Starace, University of Nebraska-Lincoln
The first part of this talk will focus on signatures of nonlinear attosecond phenomena in single- and double-ionization of the helium atom by an intense, few-cycle extreme ultraviolet (XUV) light pulse with a duration measured in attoseconds (10-18 sec). The magnitudes of these nonlinear signatures are shown to be highly sensitive to the carrier-envelope-phase (i.e., the shape of the laser pulse electric field within the pulse envelope), the duration, and the intensity of the XUV pulse. The second part of this talk will focus on the description of attosecond electron pulse diffraction from a time-varying electronic target state as the coherent scattering of incident electron and target wave packets. The diffraction images are shown to have significant contributions from inelastic processes and to have important differences from the diffraction images produced in the simplest theoretical approximation for ultrafast electron diffraction: elastic electron scattering from a time-varying target charge distribution.
Return to the 2014-2015 Colloquia ScheduleJan. 29
Modeling of ultrashort pulse laser-matter interactions
John Palastro, Naval Research Laboratory
An intense femtosecond laser pulse propagating through matter induces a dynamic, nonlinear dielectric response. Through the dielectric response, the matter modifies propagation of the pulse. This feedback—the laser matter interaction—results in a number of fascinating phenomena: the formation of plasma wakefields and plasma mirrors, nonlinear frequency conversion, collimated pulse propagation over 100’s of meters in atmosphere, pulse compression and amplification, and induced birefringence. Consequently, these pulses are of potential interest to the DoD for applications including, compact x-ray sources for detection of nuclear material, remote radiation generation, light detection and ranging (LIDAR), laser induced breakdown spectroscopy (LIBS), and directed energy beacon beams. Here I will discuss a variety of topics in ultrashort pulse laser-matter interactions from a theoretical and computational standpoint. Primarily, I will demonstrate a single pulse, all-optical Compton scattering configuration consisting of a plasma mirror formed during the ionization of a high-density shaped gas target. Additional topics such as plasma-based particle acceleration and mid-infrared sources, filamentary propagation in atmosphere, and laser-material interactions will be discussed briefly.
Return to the 2014-2015 Colloquia ScheduleFeb. 5
Ferroic domain switching is scale dependent: the hidden role of nano ferroelastic domains
Yachin Ivry, MIT
Ferroics are functional materials with reversible spontaneous electric, mechanical or magnetic strain. Similarly to other ferroic systems, the onset of ferroelectricity is at the border between one and a few domains. That is, ferroelectricity emerges where there are just enough participating interacting electrons and ions to interact collectively and support the existence of a single domain. Practically, the onset of ferroelectricity is deep at the nano scale. Traditionally, ferroelectricity has been considered as a single mechanism that is effective for all length scales, while below a certain critical size the ferroic behavior is suppressed. Although experimental investigation of domains is crucial for the understanding of the phenomenon, observing the static and dynamic configuration of nanometer size domains is a real challenge. Hence, the scalability of ferroelectric behavior has remained somehow elusive by means of direct observations. In addition to the scientific interest, the continuous attempt to miniaturize ferroelectric-based technologies, such as non-volatile switching devices, rf cellular filters and biomedical ultrasound imaging systems signifies the technological importance of nanoscale ferroelectricity. We enhanced the imaging capabilities of the mainstream method to detect micron and submicron size ferroelectric domains—piezoresponse force microscopy (PFM). Using enhanced-PFM, we were able to study the multiscale domain switching mechanism of ferroelectric domains. Specifically, we investigated with enhanced-PFM ferroelectric and ferroelectric domains simultaneously over a broad length scale that ranges from a few dozens of micrometers towards the onset of these phenomena, i.e. at the nanoscale. We demonstrated that ferroelectric domain switching is a complex system that strongly depends on the ferroelectric-ferroelastic interplay, which in turn varies with length scale. Lastly, we discussed parallelism between the multiscale ferroelectric-ferroelastic interplay and ferromagnetic domains.
Return to the 2014-2015 Colloquia ScheduleFeb. 12
Role of Materials in Quantum Information Systems
David Pappas, NIST
An introductory review of quantum information will be given that illustrate the usefulness and of using quantum systems for computing. From this, two examples, ion traps and superconducting qubits, will be given where we have studied the relevant properties that need to be optimized. In particular, for the ion traps we observe that UHV cleaning and surface order helps reduce the ion heating rates that are deleterious to the operation qubit gates, while for superconductors we find that it is necessary to optimize surfaces and interfaces to improve the coherence times.
Return to the 2014-2015 Colloquia ScheduleFeb. 26
Attosecond time-resolved photoelectron emission from atoms and surfaces: the photoeffect revisited
Uwe Thumm, KSU
State-of-the-art streaking spectroscopy experiments enable the resolution in time of photo-ionization processes at the natural time scale of the motion of valence electrons in atoms and solids. This ultrahigh time resolution allows the unprecedented observation of a "time delay" between the absorption of XUV photons and subsequent photoelectron emission. Relative delays for photoemission from different initial states are of the order of tens of attoseconds and thus accurately probe of the entire photoemission dynamics, including the initial XUV-pulse-triggered release, propagation, and detection of the photoelectron. In this talk, I plan to discuss different interpretations of photoemission delay times for gaseous and solid targets, and compare calculated photoelectron spectra with recent experiments, examining, for example, the effect of the Coulomb interaction between the photoelectron and residual ion and on streaking time delays. For photoemission from surfaces, I plan to review the influence of the electron mean-free path, skin depth of the IR streaking field, and surface electronic structure on streaked photoelectron spectra and streaking time delays. Finally, I will examine the influence of the dynamical plasmon response on photoelectron spectra and photoemission time delays, suggesting the time-resolved investigation of collective excitations in solid with streaked photoemission spectroscopy.
Return to the 2014-2015 Colloquia ScheduleMarch 9
Why Isn’t God Ambidextrous?
Tim Gay, UNL
Until 1957, scientists thought that the fundamental laws of Nature must be the same whether they were applied to our Universe or the Universe that is a mirror reflection of our own. The implications of the discovery that this is not true – essentially that Nature is "handed" – will be discussed. Some interesting applications of handedness, or "chirality" in agriculture, biology, chemistry, and physics will be presented. I will also talk about some new physics experiments on chirality that may shed light on how life began on this planet.
Return to the 2014-2015 Colloquia ScheduleMarch 12
Measurements of the Properties of a Higgs Boson using the ATLAS Detector at the LHC
Michael Strauss, University of Oklahoma
In July 2012 the ATLAS and CMS collaborations at the CERN Large Hadron collider announced the discovery of a boson consistent with the predicted standard model Higgs Boson. Since that discovery, further measurements have given insight into the properties of this particle. This talk will discuss the importance of the Higgs Boson within the standard model, the discovery of this new Boson, and subsequent measurements of its properties. Searches for additional Higgs Bosons may also be discussed.
Return to the 2014-2015 Colloquia ScheduleMarch 19
Co-sponsored by NCMN and Physics
2D Transition Metal Dichalcogenide (MoS2, MoSe2, etc.) Films:Transport, Optical Characterization, and Growth on Dielectric/Ferroelectric Substrates
Ludwig Bartels, University of California-Riverside
Transition metal dichalcogenides (TMD) such as MoS2, MoSe2, WS2, etc. present an exciting materials system for applications from spintronics to chemical catalysis. At the single layer limit, these materials attain direct–bandgap semiconducting properties. We have optimized the growth of these materials and their alloys to form single layer films (i.e., ~6Å tall) with lateral domain sizes of ≤ 50 μm, an astonishing aspect ratio. Alloys (e.g., of MoS2 and MoSe2) allow bandgap tuning/engineering. The film composition determines the photoconductivity of the single-layer material. A pronounced and extremely supralinear photoresponse is observed. The use of poled ferroelectric substrates (LiNbO3) can spatially encodes the film growth on the substrate; depending on the poling orientation the transport properties and majority charge carrier of the ensuing films vary.
Ref: J. Mann et al., Advanced Materials 26, 1399 (2014), Q. Ma et al, ACS Nano 8, 4672 (1014), V. Klee et al. Nano Letters, doi: 10.1021/acs.nanolett.5b00190 (2015)
Return to the 2014-2015 Colloquia ScheduleApril 2
Optical Forces and the Momentum of Light
Peter W. Milonni, University of Rochester and Los Alamos National Laboratory
After more than a century, starting with the work of Abraham and Minkowski, there is still discussion and controversy concerning the form of the electromagnetic momentum in a dielectric medium. Following a brief review of the subject, attention will be focused on the forces exerted on bodies in dielectric media, some key experiments, and the physical distinction between the Abraham and Minkowski field momenta.*
*Based in part on P. W. Milonni and R. W. Boyd, "Momentum of Light in a Dielectric Medium," Adv. Opt. Photonics 2, 519 (2010). Another review, among quite a few others, is by D. J. Griffiths, "Resource Letter EM-1: Electromagnetic Momentum," Am. J. Phys. 80, 7 (2012).
Return to the 2014-2015 Colloquia ScheduleApril 7
The Search for MSSM Higgs-bosons at CMS
Matthias Schröder, Deutsches Elektronen-Synchrotron (DESY)
How well do its properties of the newly discover boson conform to those of the Standard Model Higgs? Well-motivated extensions of the Standard Model that solve a number of its problems and introduce dark matter candidates include additional Higgs bosons. Is there any evidence for them? In the minimal super-symmetric extension of the Standard Model (MSSM) the Higgs sector contains two Higgs boson doublets, including, after electroweak symmetry breaking, the CP-odd neutral scalar A0, the two charged scalars H±, and the two CP-even neutral scalars h and H0. This presentation will report on the current status of searches for MSSM Higgs bosons with the data collected by the CMS experiment at LHC.
Return to the 2014-2015 Colloquia ScheduleApril 9
Trapping and Probing Antihydrogen
Jonathan Wurtele, University of California, Berkeley and LBNL
The standard model predicts that hydrogen and antihydrogen should have identical spectra. Major progress has been made on the most direct route to precision measurements of trapped antihydrogen in a series of experiments conducted by the ALPHA Collaboration in CERN. Antihydrogen was synthesized and trapped for a 1000 seconds, resonant microwaves were used to flip the positron spin in the antihydrogen atom, a technique to study the behavior of antihydrogen in the Earth’s gravitational field was developed, and a charge neutrality measurement found antihydrogen to be neutral to (−1.3±1.1±0.4) × 10−8 e. I will describe these advances and the physics challenges in the synthesis of antihydrogen atoms with kinetic energy less than our trap potential of .5K. Plans for ongoing and future experiments will be presented.
Return to the 2014-2015 Colloquia ScheduleApril 23
Room-temperature electronic spin correlations: towards spin-coherent technologies
Michael E. Flatté, University of Iowa
Most room-temperature technologies attempt to marginalize many-body physics, relying on classical, collective degrees of freedom such as magnetic moments to describe their behavior. For example, modern high-volume information storage technology relies on room-temperature electronic spin transport through so-called ``spin valves'', which can have parallel or antiparallel magnetic domains. In such spintronic devices individual electrons experience different scattering rates depending on whether their spins are parallel or antiparallel to a magnetic domain’s magnetization, but the interaction between current-carrying electrons is negligible. In recent years, however, new room-temperature spintronic devices are emerging that rely on the spin correlations of current carriers during transport. A result is nonmagnetic materials whose resistance and luminescence change substantially in magnetic fields as small as a few Gauss! For such magnetic fields single-particle thermodynamic energies are four orders of magnitude smaller than thermal energies, so the origin of this phenomenon must be spin-spin coherent quantum dynamics. Other devices are motivated by the discovery that room-temperature spin-orbit correlations can produce new kinds of spin-polarized currents and voltages as well as electrically tunable spin dynamics. Examples of these effects will be drawn from materials as disparate as organic semiconductors, oxide tunnel junctions and topological insulators.
Return to the 2014-2015 Colloquia Schedule