Physics Department News

Quantum systems can often be found to exhibit wave-like properties. As such, matter waves are known to interfere just as water waves, leading to regions of destructive interference - an absence of matter - while in regions of constructive interference, matter can become "localized". However, this behavior is not only true for matter properties of quanta, but also for their other intrinsic properties such a spin: certain spin projections can be shown to vanish while others remain measurable: this is the basis of so-called spin filters. In a recent paper, we show that this behaviour can also be found in systems with higher spins such as spin-1, spin-3/2 and so on. In Phys. Rev. B 100, 161108(R), we demonstrate how this allows the construction of spin filters and, indeed, spin "cages" in which certain spin projections remain "imprisoned" and can no longer contribute to transport. Such studies show the many surprises one is expecting for so-called spintronics devices.

The XMaS beamline is a materials science facility located at the European Synchrotron (ESRF) in Grenoble (France) and managed by the universities of Liverpool and Warwick.

The ESRF is currently undergoing a massive upgrade that will deliver the most brilliant x-ray beam in the world in 2020 and the beamline has been upgraded to take full advantage of the exciting new opportunities presented by the new source.

The beamline is organising its annual User Meeting at Radcliffe on 27th November.

This year’s User Meeting will be rather special as it will focus on what new research users will be able to do with the upgraded beamline. The in-house team will describe the new XMaS capabilities and a range of scientific talks will also illustrate the broad research portfolio covered by our user community.

If you are not a user but are interested in finding out more about the facility, please register and come along!

Topology has played a central role in modern physics. New phases of matter and phase transitions (1, 2), as well as electronic band theory (3), are understood in terms of topological concepts. On page 1449 of this issue, Tai and Smalyukh (4) harness topology to create a fundamentally new type of crystal, built with knots tied in a chiral fluid (see the figure). They used a liquid crystal doped with a chiral molecule, which caused all of the molecules to rotate like a corkscrew along a preferred direction, the helical axis. Using electric fields, they created vortex lines in the helical axis and tied them into knots that act like “atoms” but on the micrometer scale. Different knotted particles were created by careful illumination with laser tweezers, and their interactions were tuned so that they spontaneously assembled into two- or three-dimensional lattices.

Gareth Alexander's paper appears in Science, Vol. 365, Issue 6460, pp. 1377

DOI: 10.1126/science.aaz0479

The LHCb collaboration has, this week, published long-awaited results on matter-antimatter asymmetries in B+ → π+π+π− decays, explaining the curious variation of the asymmetry across the phase space.