Periodically folded graphene sheets with enhanced spin-orbit interaction due to curvature effects can carry spin-polarized currents and have gaps in the electronic spectrum in the presence of weak magnetic fields. Results indicate that such origami-like structures can be used efficiently in spintronic applications.
Scientists have theoretically shown that a bandgap can be opened in graphene by folding 2D graphene sheets origami-style and exposing them to a magnetic field. In addition to opening up a bandgap, this method also produces spin-polarized current in the graphene sheets, making them attractive for spintronics applications.
(a) To grow graphene fin-like structures, the researchers draped a graphene sheet over a patterned stamp. Below, (b) a scanning electron micrograph and (c) an atomic force microscope image show a small portion of the folded graphene surface. Credit: A. T. Costa, et al. ©2013 EPL
Since the bandgap is an energy range where no electron states exist, opening a bandgap in graphene transforms it from a conducting material to a semiconducting material. Semiconducting graphene would be more useful, and could have particularly interesting applications for spintronics devices, which exploit the electron’s quantum mechanical property of spin in addition to its property of electric charge.
One reason that graphene is a promising spintronics material is that, compared to other materials, it has an extremely small spin-orbit interaction (SOI). This means that its spin interacts very little with its orbital motion, and so spin dissipation is practically negligible in graphene. As a result, information stored in graphene’s spin can be retained for considerably longer times than in other materials. A small SOI also means that the information can travel over long distances with very little loss.
Although a small SOI has many advantages, here the scientists wanted to increase the SOI in parts of graphene because doing so is necessary for opening a bandgap. Recent research has demonstrated that SOI is enhanced when graphene is mechanically bent. Here, the researchers theoretically showed that a 2D graphene sheet molded into periodic ridges and troughs has an enhanced SOI in the curved regions.
Increasing the SOI is half of the process to inducing a bandgap; the other half is applying a magnetic field. As the researchers explain, the SOI and magnetic field complement each other in such a way that both quantities must be enhanced to induce a bandgap. The magnitude of the bandgap is ultimately determined by the smaller of these two quantities.
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