天美传媒

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.

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 鈥渁toms鈥� 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+ 鈫� 蟺+蟺+蟺鈭� decays, explaining the curious variation of the asymmetry across the phase space.

Professor Sandra Chapman is part of the Centre for Fusion, Space and Astrophysics in the Physics Department and is taking part in the British Science Festival happening on campus in September.

Click for a short video featuring Sandra explaining her research, and details of the event at the British Science Festival.