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PHYSICS COLLOQUIUM SCHEDULE
Fall 2016

The Colloquia are in Room 1002 NPB on Thursday at 4:05 PM
Refreshments will be served starting at 3:15 PM in NPB 2205

Contact: A. Hebard afh@phys.ufl.edu)
Department of Physics Colloquium Committee:
Hebard (chair), Fry, Matcheva, Mitselmakher, Furic, Zhang (members)


AUGUST 25

  Speaker Graduate Student Meeting with Dr. Guido Mueller 4:00pm in 1002 NPB

SEPTEMBER 1 - CANCELLED

  Speaker Jian Sheng Xia, UF Physics
  Title High B/T Facility and Experiments
  Abstract The High B/T Facility is a cutting edge experimental equipment of NHMFL, collaborated with department of physics, University of Florida, opened to the scientist worldwide who needs to do the experiment in high magnetic field and at ultra-low temperatures simultaneously. It is a highly demand system for thermal dynamic transport measurements and quantum phenomenon studies since it was opened to the users. Many specific devices, sensors and probes, unique low temperature techniques and methods have been well developed by our low temperature group. The details and experience of cooling various samples at ultra-low temperatures and high magnetic fields will be presented and shared. Some of the significant results of the experiments will be demonstrated as well.
  Host

SEPTEMBER 8

  Speaker Xiaoguang Zhang, UF Physics
  Title Quantum transport theory: Counting electrons and their (wave function) shapes
  Abstract Quantum transport theory relies fundamentally on counting and keeping track of electrons. The famed Landauer-Buttiker conductance formula can be derived by counting the number of electrons passing through a sample. Exotic but technologically important physical phenomena such as the giant magnetoresistance effect can be understood by simply counting electrons in the multilayer material. Tunneling magnetoresistance, on the other hand, arises from symmetry filtering in magnetic tunnel junctions, which requires both counting electrons and taking account of the symmetry of electron wave functions. Counting electrons is also the basis for understanding the shot noise of a tunnel junction. Spin-flip induced shot-noise-like feature in magnetic tunnel junctions again requires combining electron counting with symmetry filtering. Finally I will discuss a simple way to generalize the Landauer-Buttiker conductance formula to finite voltages.
  Host


SEPTEMBER 15

  Speaker Jian Sheng Xia, UF Physics
  Title High B/T Facility and Experiments
  Abstract The High B/T Facility is a cutting edge experimental equipment of NHMFL, collaborated with department of physics, University of Florida, opened to the scientist worldwide who needs to do the experiment in high magnetic field and at ultra-low temperatures simultaneously. It is a highly demand system for thermal dynamic transport measurements and quantum phenomenon studies since it was opened to the users. Many specific devices, sensors and probes, unique low temperature techniques and methods have been well developed by our low temperature group. The details and experience of cooling various samples at ultra-low temperatures and high magnetic fields will be presented and shared. Some of the significant results of the experiments will be demonstrated as well.
  Host


SEPTEMBER 22

  Speaker Dan Desseau, University of Colorado
  Title “Phun” with Photoelectrons or What Sets the Tc in Cuprate High-Temperature Superconductors?
  Abstract Angle-resolved photoemission spectroscopy (ARPES) has recently emerged as one of the most powerful probes of the electronic structure of a solid, directly giving the detailed energy-momentum dispersion relations (band structures), Fermi surfaces, etc. – properties that are the starting point for almost all analyses of the physical properties of a solid. Going more deeply, ARPES also has unique abilities to uncover the dynamical interaction effects or “self energies” that dominate the physical properties of correlated electron materials. Perhaps the most famous and exotic of correlated electron materials are high-temperature cuprate superconductors, which have exotic “normal” and superconducting states, neither of which are understood. Here I show our latest results on this problem, focusing not just on the pairing energy scale (the gap ?) but also the pair-breaking energy scale ?. In contrast to conventional superconductors in which the superconducting transition temperature Tc is set by the pairing energy alone, I show that Tc in the cuprates is set by a crossover between the pairing and pair-breaking energy scales, each of which is strongly temperature-dependent. I then discuss how this is likely related to the strong interactions present in the normal state, with many of these interactions “undressing” as the material goes superconducting.
Host David Tanner and Peter Hirschfeld

SEPTEMBER 29

  Speaker Seiji Kawamura, ICCR, U Tokyo
  Title Current status of KAGRA
  Abstract KAGRA is a 3 km cryogenic gravitational wave detector. It is being built underground in Kamioka for a better seismic environment. Sapphire mirrors are cooled down to 20 K to reduce the thermal noise. The detuned RSE interferometer is used to optimize the quantum noise. The first stage of KAGRA (called iKAGRA), a 3 km room-temperature Michelson interferometer with a modest seismic isolation system, was operated and the engineering run was held in March/April, 2016. We are now upgrading it to the final stage of KAGRA (called bKAGRA).
Host David Tanner, Guido Mueller

OCTOBER 6

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OCTOBER 13

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OCTOBER 20

  Speaker Arnoldo Valle-Levinson, UF Coastal Engineering
  Title Sea-level changes and hot spots along the U.S. Atlantic coast in the most recent ~100 years
  Abstract Sea-level rise (SLR) accelerated in a “hot spot” along the north of Cape Hatteras over the past several decades, including an abrupt rise of ~13 cm in 2009-2010. This regional acceleration in SLR has been attributed to weakening in the circulation of the North Atlantic, although this causal link remains debated. I will talk about a striking shift in the pattern of SLR along the U.S. Atlantic coast during 2011-2016, whereby SLR decelerated north of Cape Hatteras and accelerated south of the Cape to 10 times the global rates (>20 mm/yr). These changes occurred despite continued decline in strength of the North Atlantic circulation. Tide-gauge records, 95-yr long, show that similar SLR intervals have occurred repeatedly over ~1500-km stretches of coastline. These records reveal that hot spots of SLR have migrated northward since the 1940s and suggest that the reappearance of the hot spot in the southeastern U.S. may represent a re-initiation of a ~65-year cycle. Causes for ! this variability are likely associated with climate indices. The regional expression of SLR hot spots documented here is a key factor in determining coastal vulnerability in the context of continued global mean sea-level rise and should be captured in global climate models of regional sea-level change.
Host Peter Hirschfeld

OCTOBER 27

  Speaker Robin Stebbins
  Title The Universe in Gravitational Waves
  Abstract On the 100th anniversary of Einstein’s prediction of gravitational waves, great things happened. Gravitational waves were detected, the technology for a space detector was spectacularly demonstrated, and the future for both ground- and space-based detectors brightened. After 100 years of struggle with the theory and 50 years of struggle with the measurements: Where is the science of gravitational waves going? What can we learn about the Universe from gravitational waves? What are the challenges ahead? What might a young researcher do? This talk will give an old researcher’s answers to these questions.
Host Guido Mueller

NOVEMBER 3

  Speaker Kurt Gibble, Penn State
Title Laser-cooled Atomic Clocks : The Most Accurate Measurements
  Abstract Atomic clocks realize the most accurate measurements of any physical observable – the frequency of an atomic transition. I will give an overview of state-of-the-art atomic clocks and how they work. There are a number of interesting physics problems in current microwave and optical frequency clocks. Several involve the scattering of coherent superpositions of atomic states, including novel collisions of ultracold fermions in optical lattice clocks, using a microwave clock to precisely probe quantum scattering phase shifts, and frequency shifts that related to the momentum of microwave photons. Because optical frequency transitions enable large improvements in stability and accuracy, a future redefinition of the SI second is widely anticipated. There are a number of attractive candidates, including a promising prospect, an optical lattice clock based on cadmium.
Host David Tanner

NOVEMBER 10

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NOVEMBER 17

  Speaker Axel Hoffmann, Argonne National Lab
  Title Room Temperature Generation and Manipulation of Magnetic Skyrmion
  Abstract The field of spintronics, or magnetic electronics, is maturing and giving rise to new subfields [1]. An important ingredient to the vitality of magnetism research in general is the large complexity due to competitions between interactions crossing many lengthscales and the interplay of magnetic degrees of freedom with charge (electric currents), phonon (heat), and photons (light) [2]. One perfect example, of the surprising new concepts being generated in magnetism research is the recent discovery of magnetic skyrmions. Magnetic skyrmions are topologically distinct spin textures that are stabilized by the interplay between applied magnetic fields, magnetic anisotropies, as well as symmetric and antisymmetric exchange interactions. Due to their topology magnetic skyrmions can be stable with quasi-particle like behavior, where they can be manipulated with very low electric currents. This makes them interesting for extreme low-power information technologies, where it is envisioned that data will be encoded in topological charges, instead of electronic charges as in conventional semiconducting devices. Towards the realization of this goal we demonstrated magnetic skyrmions in magnetic heterostructures stable at room temperature, which can be manipulated using spin Hall effects [3]. Furthermore, using inhomogeneous electric charge currents allows the generation of skyrmions in a process that is remarkably similar to the droplet formation in surface-tension driven fluid flows [4]. However, detailed micromagnetic simulations show that depending on the electric current magnitude there are at least two regimes with different skyrmion formation mechanisms [5]. Lastly, we demonstrated that the topological charge gives rise to a transverse motion on the skyrmions, i.e., the skyrmion Hall effect, which is in analogy to the ordinary Hall effect originating from the motion of electrically charged particles in the presence of a magnetic field [6].
Host Hai-Ping Cheng/ Xiaoguang Zhang

DECEMBER 1

  Speaker Art Hebard, UF
  Title A personal perspective on the 2016 Nobel Prize in Physics: "Topological phase transitions and topological phases of matter"
  Abstract The 2016 Nobel Prize in Physics was recently awarded to David Thouless, Duncan Haldane and Michael Kosterlitz for their work on identifying novel states of matter and associated phase transitions in which topological defects play a crucial role. This talk will begin with a description of the theoretical accomplishments of each of these laureates and show how present-day understanding of superconducting and superfluid films, two-dimensional magnetic systems, the precise quantization of the Hall conductance in two dimensional electron gases, and the behavior of one-dimensional chains of integer and half-integer spins are all affected by topological constraints. My personal perspective is based on collaborative experimental work performed at AT&T Bell Laboratories (1972-1996) confirming the Kosterlitz-Thouless vortex-antivortex unbinding transition in thin-film superconductors. A circulating current carrying a quantum of flux is the topological defect in this system. Follow up work on related transitions will also be described and comments on the unique “hands-off” working environment at Bell Labs will be made.
Host Peter Hirschfeld



PHYSICS COLLOQUIUM SCHEDULE

Spring 2017

The Colloquia are in Room 1002 NPB on Thursday at 4:05 PM
Refreshments will be served starting at 3:15 PM in NPB 2205

Contact: A. Hebard afh@phys.ufl.edu)
Department of Physics Colloquium Committee:
Hebard (chair), Fry, Matcheva, Mitselmakher, Furic, Zhang (members)

JANUARY 5

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Host

JANUARY 12

  Speaker Graduate Student Meeting with Guido Mueller
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  Host

JANUARY 19

  Speaker Andreas Ringwald
  Title The Quest for the Axion and Axion-Like Particles
  Abstract Many theoretically well-motivated extensions of the Standard Model of particle physics predict the existence of very weakly interacting ultralight particles, such as the axion and similar Nambu-Goldstone bosons. They may constitute the mysterious dark matter in the Universe and solve some puzzles in stellar and high-energy astrophysics. There are new, relatively small experiments around the globe, which started to hunt for these elusive particles and complement the search for physics beyond the Standard Model at the Large Hadron Collider.
  Host Guido Mueller

JANUARY 26

  Speaker Jeremy Levy, University of Pittsburgh
  Title Etch-a-Sketch Nanoelectronics
  Abstract The study of strongly correlated electronic systems and the development of quantum transport in nanoelectronic devices have followed distinct, mostly non-overlapping paths. Electronic correlations of complex materials lead to emergent properties such as superconductivity, magnetism, and Mott insulator phases. Nanoelectronics generally starts with far simpler materials (e.g., carbon-based or semiconductors) and derives functionality from doping and spatial confinement to two or fewer spatial dimensions. In the last decade, these two fields have begun to overlap. The development of new growth techniques for complex oxides have enabled new families of heterostructures which can be electrostatically gated between insulating, ferromagnetic, conducting and superconducting phases. In my own research, we use a scanning probe to "write" and "erase" conducting nanostructures at the LaAlO3/SrTiO3 interface. The process is similar to that of an Etch-a-Sketch toy, but with a preci! sion of two nanometers. A wide variety of nanoscale devices have already been demonstrated, including nanowires, nanoscale photodetectors, THz emitters and detectors, tunnel junctions, diodes, field-effect transistors, single-electron transistors, superconducting nanostructures and quantum point contacts. These building blocks may form the basis for novel technologies, including a platform for complex-oxide-based quantum computation and quantum simulation.
  Host Peter Hirschfeld

FEBRUARY 2

  Speaker Yong-Baek Kim, Toronto
  Title Topology and Correlation in Quantum Materials
  Abstract In the last several years, there has been tremendous progress in understanding topological phases of quantum materials. While most of the past progress concerned about weakly interacting electron systems, more recent efforts uncover the subtle connection between electron interaction and topological properties of the quantum ground state. Taking some examples of quantum materials with strong spin-orbit coupling, we explain what kinds of new topological phases can be obtained and where we stand in terms of experimental detection of such phases.
  Host Yoonseok Lee

FEBRUARY 9

  Speaker Thomas Shulthess
  Title Challenges in scientific computing at the dusk of Moore’s Law
  Abstract Today’s scientific computing systems are massively parallel processing arrays with multi-threaded compute nodes that have complex memory hierarchies. In some cases, compute nodes have heterogeneous memory and compute resources, such as GPU accelerators or high-bandwidth/non-volatile memory. This diversity of architectures will further increase, as we approach the end of Moore’s Law. Scientific application software has to be portable across all these architectures and at the same time perform optimally on each individually. We will discuss software strategies that allow us to tackle this challenge while maintaining high productivity of scientists who have to use and further develop application software. Specific examples will be given for codes used to study electronic structure in condensed matter physics and materials science.
  Host Hai-Ping Cheng/ Xiaoguang Zhang (sponsored by Physics Department and Quantum Theory Project)

FEBRUARY 16

  Speaker Can Kilic, University of Texas
  Title Adding a Little Flavor to Dark Matter
  Abstract The physics of the known elementary particles is very well described by the Standard Model (SM) down to distance scales of 10^-18 m. Despite its successes however, the SM is known to be an incomplete theory, as there are several observed phenomena that it cannot account for, among them the existence of “Dark Matter” (DM), which has been firmly established by astrophysical observations over the last few decades. I will begin by describing the SM and its shortcomings, followed by two popular paradigms for the particle nature of DM and how they connect to the aforementioned shortcomings. I will then highlight the more recent scenario of “Flavored Dark Matter” where DM exists in three generations, as is true of all visible matter particles, and I will go over some novel theoretical and phenomenological aspects of this scenario, including its experimental signatures in direct detection and indirect detection experiments as well as at the Large Hadron Collider.
  Host Konstantin Matchev

FEBRUARY 23

  Speaker Aparna Baskaran, Brandeis
  Title Active Matter: Using the soft materials paradigm to understand biology"
  Abstract : In this talk I will introduce and discuss a new class of microscopically driven materials that have been termed active materials. Drawing lessons from both biology and in vitro experimental systems, I will discuss theoretical challenges and different approaches that have proved fruitful so far. In particular, I will discuss the physics of active brownian particles and active nematics.
  Host Jim Dufty

MARCH 2

  Speaker Prof. Nomura, Tokyo Institute of Technology
  Title 4He Crystals in Superfluid out of Equilibrium Ryuji Nomura, Tokyo Institute of Technology
  Abstract 4He quantum crystals grow from superfluid liquid very rapidly at low temperatures. This is because mass and heat transport processes in the bulk are negligible due to the swift superflow and the minimal release of the latent heat. High mobility of the crystal-superfluid interface allows one to observe novel interfacial phenomena which are sometimes hidden in the classical systems by the dissipations.
Acoustic radiation pressure is the second order acoustic effect which is usually small but can push an object in the direction of the acoustic waves. Crystal-superfluid interface of 4He is so mobile that such tiny force was enough to induce both crystallization and melting. It was used as a tool to deform 4He crystals largely and relaxation of the highly anisotropic interface was investigated after the deformation. Anomalous relaxation shapes such as needle-like or irregular shapes were observed depending on temperature. Relaxation time was highly dependent on the direction of the deformation whether it was crystalized or melted, indicating a significant influence of superflow on the relaxation. Effect of the superflow on the crystal shape was also investigated by observing 4He crystals falling in superfluid. During the falling, upper surface of the crystal became rough and lower surface became facetted. This is caused by the superflow around the crystal which induced the melting in the upper surface and the crystallization in the lower surface. When it collided with the bottom, pulse-like wave traveled around the surface from the impact point and the crystal transformed itself quickly to adjust to a new boundary condition.
To see the effect of disorder on dynamics of the first order phase transition at very low temperatures, crystallization of 4He in silica-aerogels was visualized. The way of the crystallization in aerogels by pressurization showed a dynamical transition due to the competition between thermal fluctuation and disorder: crystals grew via creep at high temperatures and via avalanche at low temperatures. Avalanche size distribution followed a power law and thus the crystallization showed the self-organized criticality. Recently, it was also observed that crystallization can be induced below a clear onset temperature on cooling at constant pressure. This crystallization on cooling requires mass flow from the surrounding bulk crystals into the aerogel and is possibly related to the “supersolidity” which is at issue in the quantum crystals. Other phenomena such as rising of a superfluid droplet in 4He crystals by buoyancy, and ripening and equilibrium shapes in zero gravity will also be presented.
  Host Yoonseok Lee

MARCH 9

  Speaker Spring Break
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MARCH 16

  Speaker Astrophysics search/APS Meeting
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  Host Guido Mueller

March 23

  Speaker Astrophysics search
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  Host Guido Mueller

March 30

  Speaker Bangalore Sathyaprakash, Penn State
  Title Testing the black hole no-hair theorem
  Abstract In the words of nobel laureate Subrahmanyan Chandrasekhar "/The black holes of nature are the most perfect macroscopic objects there are in the universe: the only elements in their construction are our concepts of space and time/". In other words, black holes are spacetime warpage with no other attributes. Indeed, according to general relativity, black holes, no matter how big or small, are characterised by just three numbers: their mass, spin magnitude and electric charge, which essentially the statement of the /black hole no-hair theorem/. Astrophysical black holes are likely characterised by only their mass and spin as they are not likely to possess any electric charge. The most direct way of confirming if an astrophysical object is a black hole is to gather evidence that the only properties that describe the object are their mass and spin magnitude. In this talk I will discuss how gravitational wave observations of black holes, such as the ones that LIGO discovered in September and December 2015, will allow us to test the no-hair theorem and if we can already tell with great confidence that what we have seen are indeed black holes.
  Host David Tanner

April 6

  Speaker Astrophysics search
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  Host Guido Mueller

APRIL 13

  Speaker Yoonseok Lee, UF Physics
  Title Exotic Excitations in Superfluid 3He
Abstract Superfluid phase of helium three has been the paradigm for symmetry-breaking phase transition in condensed matter physics. Unlike conventional condensed matter system, liquid helium three possesses maximal symmetry and almost all of them are broken below 2 mK where it enters p-wave spin triplet superfluid. In this talk, I will guide a walking tour of the progresses and developments made in this field in the past decade including the results from UF. This colloquium will be given in memory of Dr. Pradeep Bhupathi.
  Host

APRIL 20

  Speaker Viktor Tsepelin, Lancaster University
  Title Visualizing Quantum Turbulence in Superfluid 3He-B using Quasiparticles
Abstract We present experimental studies of quantum turbulence in superfluid 3He-B, the coldest fermionic liquid available. While the flow of bulk superfluid must be irrotational, it can mimic classical turbulence by supporting singly quantised vortices. Measurements were carried at low temperatures where the thermal excitations in the superfluid comprise ballistic quasiparticles. Fermionic excitations in addition to the normal scattering can undergo Andreev reflection, which underpins non-invasive imaging of structures present in the superfluid such as quantum vortices or textures. The topological structures in superfluid could be produced via analogues of cosmological processes, for example Kibble mechanism, or by exceeding the Landau critical velocity and breaking the condensate. We created a rudimentary quasiparticle camera operating at 150 microkelvin and show two-dimensional 'images' of a quasiparticle beam and of a tangle of quantised vortices (quantum turbulence), that we created by a mechanical oscillator. Quasiparticle imaging technique could be used to observe the other defects and to investigate pair-breaking processes in 3He.
  Host Yoonseok Lee