Topological zoo of free-standing knots in confined chiral nematic fluids

Knotted fields are an emerging research topic relevant to different areas of physics where topology plays a crucial role. Recent realization of knotted nematic disclinations stabilized by colloidal particles raised a challenge of free-standing knots. Here we demonstrate the creation of free-standing knotted and linked disclination loops in the cholesteric ordering fields, which are confined to spherical droplets with homeotropic surface anchoring. Our approach, using free energy minimization and topological theory, leads to the stabilization of knots via the interplay of the geometric frustration and intrinsic chirality. Selected configurations of the lowest complexity are characterized by knot or link types, disclination lengths and self-linking numbers. When cholesteric pitch becomes short on the confinement scale, the knotted structures change to practically unperturbed cholesteric structures with disclinations expelled close to the surface. The drops with knots could be controlled by optical beams and may be used for photonic elements.

Superconductivity in CuxBi2Se3 and its implications for pairing in the undoped topological insulator

Bi2Se3 is one of a handful of known topological insulators. Here we show that copper intercalation in the van der Waals gaps between the Bi2Se3 layers, yielding an electron concentration of approximately 2x10{20} cm{-3}, results in superconductivity at 3.8 K in CuxBi2Se3 for 0.12<or=x<or=0.15. This demonstrates that Cooper pairing is possible in Bi2Se3 at accessible temperatures, with implications for studying the physics of topological insulators and potential devices.