Entangled States Induced by Electron-Phonon Interaction in Two-Dimensional Materials.

We report on the effects of electron-phonon interaction in materials such as graphene, showing that it enables the formation of a gap bridged by unique edge states. These states exhibit a distinctive locking among propagation direction, valley, and phonon mode, allowing for the generation of electron-phonon entangled states whose parts can be easily split. We discuss the effect of the chiral atomic motion in the zone boundary phonons leading to this effect. Our findings shed light on how to harness these unconventional states in quantum research.

Inducing a topological transition in graphene nanoribbon superlattices by external strain.

Armchair graphene nanoribbons, when forming a superlattice, can be classified into different topological phases, with or without edge states. By means of tight-binding and classical molecular dynamics (MD) simulations, we studied the electronic and mechanical properties of some of these superlattices. MD shows that fracture in modulated superlattices is brittle, as for unmodulated ribbons, and occurs at the thinner regions, with staggered superlattices achieving a larger fracture strain than inline superlattices. We found a general mechanism to induce a topological transition with strain, related to the electronic properties of each segment of the superlattice, and by studying the sublattice polarization we were able to characterize the transition and the response of these states to the strain. For the cases studied in detail here, the topological transition occurred at ∼3-5% strain, well below the fracture strain. The topological states of the superlattice - if present - are robust to strain even close to fracture. The topological transition was characterized by means of the sublattice polarization of the states.

A chemical theory of topological insulators.

Research on topological insulators (TIs) has experienced an exponential growth in the last few years, promising new technological applications in fields ranging from electronics to quantum computing. However, the strong condensed matter physical background that is needed to understand the exotic electronic structure of TIs has precluded its dissemination into the chemistry community. In this work we use chemistry-like models (e.g. the Hückel model) to bridge this gap. By taking bond alternating polyacetylenes as a starting point, we show how several key concepts about TIs, such as chiral symmetries or topologically-protected edge states, may be rephrased in terms of traditional chemical concepts by using Lewis resonance structures and bonding descriptors that characterize electron delocalization in real space. Overall, this Highlight should provide the background for understanding the properties of topological insulators to a broad chemistry readership.