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This Week at Physics

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Events on Thursday, April 12th, 2012

R. G. Herb Condensed Matter Seminar
The modulated spin liquid and hidden order in URu2Si2
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: SĂ©bastien Burdin, University of Bordeaux, France
Abstract: We have shown that near a Kondo breakdown critical point, a spin liquid with spatial modulations is likely to be formed. Unlike its uniform counterpart, we find that this occurs via a second order phase transition. The amount of entropy quenched when this ordering is manifest is of the same magnitude as for an antiferromagnet. Moreover, these two states are in direct competition with each other, and at low temperatures they are separated by a first order phase transition. This suggests that the modulated spin liquid is indeed a viable candidate for the unique phase of matter which is observed in the hidden order phase of URu2Si2. We investigate the modulated spin liquid proposal taking full account of the tetragonal-body-centered lattice structure which characterizes URu2Si2. We find that the physical quantities predicted from the model are in very good qualitative and quantitative agreement with recent experiments, including thermodynamic properties, inelastic neutron scattering, and Fermi surface measurements. We also present an overview of other f-electron compounds where similar phases have been observed.

C. Pepin, M.R. Norman, S. Burdin, and A. Ferraz, Phys. Rev. Lett. 106, 106601 (2011)

C. Thomas, S. Burdin, C. Pepin, and A. Ferraz, in preparation.
Host: Perkins
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Observation of Reactor Antineutrino Disappearance at RENO
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Soo-Bong Kim, Seoul National University
Abstract: The RENO experiment has observed the disappearance of reactor electron antineutrinos, consistent with neutrino oscillations, with a significance of 4.9 standard deviations. Antineutrinos from six reactors at Yonggwang Nuclear Power Plant in Korea, are detected by two identical detectors located at 294 m and 1383 m, respectively, from the reactor array center. In the 229 day data-taking period of 11 August 2011 to 26 March 2012, the far (near) detector observed 17102 (154088) electron antineutrino candidate events with a background fraction of 5.5% (2.7%). A ratio of observed to expected number of antineutrinos in the far detector is 0.920+-0.009(stat.)+-0.014(syst.). From the deficit, we find sin^2(2theta_13)=0.113+-0.013(stat.)+-0.019(syst,) based on a rate-only analysis. In this talk, its detailed analysis will be presented.
Host: Karsten Heeger
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Astronomy Colloquium
Plasma physics in the intracluster medium on large scales
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Aurora Simionescu, Stanford University
Abstract: Measurements of the thermodynamic properties of the faint cluster outskirts have become possible only recently due to the unique capabilities of the Suzaku satellite. This has opened a new window for the exploration of the ongoing virialization and equilibration processes that occur as part of large-scale structure formation. I will summarize some of the most interesting conclusions regarding the physics of the intracluster medium beyond the bright cluster cores. I will focus on results from several recently finalized and ongoing Key/Large programs with the Suzaku satellite, targeting the outskirts of the Perseus, Virgo, and Coma clusters, which are the nearest, brightest clusters of galaxies, and are thus ideal targets for studying in detail the physics of the hot X-ray emitting plasma near the virial radii of these systems.
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