APS Physics Tip Sheet – Sep 30, 2013
In this issue: The Weak Side of the Proton, Finding New Superconductors, Trapping Atoms in Magnetic Vortices
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The Weak Side of the Proton
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An international collaboration has measured for the first time the weak charge of the proton – the parameter characterizing the strength of its interaction with the weak force.
In the same way that the electric charge of a particle determines the response to an electromagnetic force, the so-called "weak charge" characterizes the strength of the “weak force” – the fundamental interaction responsible for radioactive decay or nuclear fusion. The weak charge is hard to measure, since its effects outside the sub-atomic world are masked by the stronger electromagnetic interaction. Now, the Qweakcollaboration has measured the proton’s weak charge using a spin-polarized electron beam at the Thomas Jefferson National Accelerator Facility in Virginia. By analyzing how the beam was scattered by the protons contained in liquid hydrogen, the researchers were able to determine the proton’s weak charge, finding a value in good agreement with the theoretical prediction of the standard model.
* Qweak collaboration (contact author: Roger D. Carlini), “First determination of the weak charge of the proton”, Physical Review Letters (expected publication date: Oct 2)
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Finding New Superconductors
Theoretical calculations have lead to the successful design of a new iron-based superconductor.
Designing new materials that exhibit complex properties, such as superconductivity, is a notoriously challenging task, but computational and theoretical advances in solid-state physics are beginning to change this trend. A team of researchers from Europe and the US, guided by the conclusions of a previous theoretical study, was able to synthesize a superconducting iron-based compound. Their characterization showed the material behaved as calculations predicted: it exhibits low-temperature superconductivity, combined with an unusual hardness that may be advantageous for applications. The result provides an encouraging step in the quest for materials by design.
* Huiyang Gou, Natalia Dubrovinskaia (contact author) et al, “Discovery of a superhard iron tetraboride superconductor”, Physical Review Letters (expected publication date: Oct 7)
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Trapping Atoms in Magnetic Vortices
In optical lattices, ultracold atoms are trapped by lasers in periodic arrangements that can be used to simulate the physics of crystals. But atoms cannot be trapped too closely, as the separation is limited by the wavelength of light. According to a new proposal by a research group at the Max Planck Institute for Quantum Optics in Germany, atoms could be trapped by magnetic, rather than optical, means, using the magnetic vortices that can be generated in a thin superconducting sheet. The scheme could trap atoms at distances as small as few tens of nanometers, allowing the study of conditions in which mutual interactions are much stronger than in conventional optical lattices.
* Oriol Romero-Isart (contact author) et al, “Superconducting Vortex Lattices for Ultracold Atoms”, Physical Review Letters (expected publication date: Oct 4)
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Journal articles and preprints are available to journalists on request.
Matteo Rini, PhD
Deputy Editor, Physics
