Room Temperature Optically and Magnetically Active Edges in Phosphorene Nanoribbons

Abstract

Nanoribbons – nanometer wide strips of a two-dimensional material – are a unique system in condensed matter. They combine the exotic electronic structures of low-dimensional materials with an enhanced number of exposed edges, where phenomena including ultralong spin coherence times1–4, quantum confinement5 and topologically protected states6–8 can emerge. An exciting prospect for this new material concept is the potential for both a tunable semiconducting electronic structure and magnetism along the nanoribbon edge. This combination of magnetism and semiconducting properties is the first step in unlocking spin-based electronics such as non-volatile transistors, a route to low-energy computing9, and has thus far typically only been observed in doped semiconductor systems and/or at low temperatures10–15. Here, we report the magnetic and semiconducting properties of phosphorene nanoribbons (PNRs). Static (SQUID) and dynamic (EPR) magnetization probes demonstrate that at room temperature, films of PNRs exhibit macroscopic magnetic properties, arising from their edge, with internal fields of ~ 240 to 850 mT. In solution, a giant magnetic anisotropy enables the alignment of PNRs at modest sub-1T fields. By leveraging this alignment effect, we discover that upon photoexcitation, energy is rapidly funneled to a dark-exciton state that is localized to the magnetic edge and coupled to a symmetry-forbidden edge phonon mode. Our results establish PNRs as a fascinating system for studying the interplay of magnetism and semiconducting ground states at room temperature and provide a stepping-stone towards using low-dimensional nanomaterials in quantum electronics.

Production of Magnetic Arsenic–Phosphorus Alloy Nanoribbons with Small Band Gaps and High Hole Conductivities

“…52 Solid-state AsPNRs drop-cast from DMF solutions (selected due to the higher propensity to form ribbons) show significantly different behavior from the paramagnetic Li-(AsP) 9 , with no diamagnetic component and a vanishing coercive field, typical of small-domain nanomagnets, attributed to the formation of edge-states. We have recently measured similar behaviors in the related PNRs, 43 although the atypical ferromagnetic-like hysteresis of PNRs does not appear to be present here, possibly due to the lack of the crystallographically clean, zigzag-only edges. The SQUID magnetometry also provides insight into the mechanism of formation of AsPNRs; the persistence of a diamagnetic component in Li(AsP) 9 implies that it does not contain individual ribbons (stacked or encased in amorphous lithium phosphide/arsenide) but 2D sheets, which are then cut into paramagnetic ribbons during exfoliation.…”