Collective magnetism at multiferroic vortex domain walls

Topological defects have been playgrounds for many emergent phenomena in complex matter such as superfluids, liquid crystals, and early universe. Recently, vortex-like topological defects with six interlocked structural antiphase and ferroelectric domains merging into a vortex core were revealed in multiferroic hexagonal manganites. Numerous vortices are found to form an intriguing self-organized network. Thus, it is imperative to find out the magnetic nature of these vortices. Using cryogenic magnetic force microscopy, we discovered unprecedented alternating net moments at domain walls around vortices that can correlate over the entire vortex network in hexagonal ErMnO3 The collective nature of domain wall magnetism originates from the uncompensated Er3+ moments and the correlated organization of the vortex network. Furthermore, our proposed model indicates a fascinating phenomenon of field-controllable spin chirality. Our results demonstrate a new route to achieving magnetoelectric coupling at domain walls in single-phase multiferroics, which may be harnessed for nanoscale multifunctional devices.Comment: 18 pages, 10 figure

The decay of the new neutron-rich isotope 217^{217}Bi

Exotic, neutron-rich proton-induced spallation products of /sup 232 /Th and /sup 238/U obtained from the PS Booster ISOLDE facility have been investigated by gamma - gamma , alpha - gamma coincidence and spectrum-multiscaling measurements. A new method for he reduction of isobaric contamination enabled to study the unknown region beyond /sup 208/Pb for the decay chain A=217. A new isotope /sup 217/Bi with a half-life of 98.5+or-0.8 s was discovered and its beta -decay studied. For the first time, a half-life value of 1.53+or-0.03 s for the alpha -decay of /sup 217/Po was measured. (12 refs)

Imaging chiral symmetry breaking from Kekulé bond order in graphene

Chirality-or 'handedness'-is a symmetry property crucial to fields as diverse as biology, chemistry and high-energy physics. In graphene, chiral symmetry emerges naturally as a consequence of the carbon honeycomb lattice. This symmetry can be broken by interactions that couple electrons with opposite momenta in graphene. Here we directly visualize the formation of Kekule bond order, one such phase of broken chiral symmetry, in an ultraflat graphene sheet grown epitaxially on a copper substrate. We show that its origin lies in the interactions between individual vacancies in the copper substrate that are mediated electronically by the graphene. We show that this interaction causes the bonds in graphene to distort, creating a phase with broken chiral symmetry. The Kekule ordering is robust at ambient temperature and atmospheric conditions, indicating that intercalated atoms may be harnessed to drive graphene and other two-dimensional materials towards electronically desirable and exotic collective phases.11Nsciescopu