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Physics Colloquium


Fall 2014 Colloquium Schedule

Date Speaker Title Host
August 25 Bob Svoboda
UC Davis
WATCHMAN: Neutrino Physics and Nuclear Non-Proliferation – Oh . . . Really? Tom Handler
September 8 Jaideep Singh
Technische Universität München
Trapping Atoms the "Old-Fashioned" Way: New Results & Opportunities Nadia Fomin
September 15 Peng Xiong
Florida State University
Ultrathin Pb Films in a Magnetic Field: New Physics from an Old Superconductor Haidong Zhou
September 22      
September 29      
October 6      
October 13      
October 20      
October 27      
November 3      
November 10      
November 17      
November 24      
December 1      


August 25, 2014

Bob Svoboda
University of California, Davis

WATCHMAN: Neutrino Physics and Nuclear Non-Proliferation – Oh . . . Really?

Monitoring nuclear non-proliferation treaties is a challenging technological problem. Since the “fast lane” to nuclear weapons is the production of plutonium in small nuclear reactors, an important (but difficult) problem is how to monitor reactors built for research to ensure they are not being used for weapons production. Recent experiments in neutrino physics and dedicated demonstration projects at commercial nuclear plants have shown that it may be possible to use neutrinos to determine the operational cycle of such reactors from moderately distant locations. At the same time, the particle physics community is developing technology that may make such monitoring both feasible and cost effective. The WATCHMAN Project is a collaborative effort between scientists and engineers that will not only advance neutrino detector technology, but also demonstrate the ability to effectively monitor nuclear reactors for weapons production.

September 8, 2014

Jaideep Singh
Technische Universität München

Trapping Atoms the "Old-Fashioned" Way: New Results & Opportunities

Inert gases frozen at cryogenic temperatures have been used to trap and study atoms and molecules for over 60 years. In particular, noble gas solids (NGS) are a promising medium for the capture, detection, and manipulation of atoms and nuclear spins. They provide stable, chemically inert, & efficient confinement for a wide variety of guest species. Because NGS are transparent at optical wavelengths, the guest species can be probed using lasers. Longitudinal and transverse nuclear spin relaxation times of a guest species can be made very long under well understood and feasible conditions. Potential applications include measurements of rare nuclear reactions and tests of fundamental symmetries.

In this talk, I will present the results of our optical spectroscopic study of ytterbium atoms embedded in a frozen neon matrix, which includes the first experimental determination of the 23 second lifetime of the metastable atomic state of Yb-171 that is used for next generation atomic clocks. I will conclude with our efforts to demonstrate (1) optical single atom detection for studying rare nuclear reactions and (2) optical pumping of Yb-171 nuclei in solid neon for a test of time-reversal symmetry.

September 15, 2014

Peng Xiong
Florida State University Department of Physics

Ultrathin Pb Films in a Magnetic Field: New Physics from an Old Superconductor

Even in materials where the origin of superconductivity is known to be conventional, dimensional confinement, disorder, electron correlation, external magnetic field, and magnetic impurities often combine to induce novel electronic phases and quantum phase transitions, many of which remain poorly understood and controversial. We have carried out a detailed examination of the superconductivity and superconductor-insulator transitions in ultrathin amorphous Pb films as functions of disorder, magnetic field, and paramagnetic pair-breaking. The Pb films are grown via quench-condensation in a modified dilution refrigerator under ultrahigh vacuum at low temperature, and all the electrical measurements are performed in situ. Here I describe and discuss two intriguing observations from these experiments: i) A perpendicular magnetic field induces features suggestive of mesoscale phase separation near the critical field and an insulating state with localized superconductivity.1 ii) In the same films, a parallel magnetic field is found to enhance superconductivity, increasing the mean-field Tc by as much as 13% in field as high as 8 T. The Tc enhancement is progressively suppressed, eventually eliminated, by incremental deposition of magnetic impurity on the film.2

1. J.S. Parker, D. Read, A. Kumar, and P. Xiong, Europhys. Lett. 75, 950 (2006).
2. H.J. Gardner, A.S. Kumar, L. Yu, P. Xiong, M. Warusawithana, L. Wang, O. Vafek, D.G. Schlom, Nature Physics 7, 895 (2011).

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