LAUSR

In 1861, Maxwell conceived the idea of the displacement current, which then made laws of electrodynamics more complete and also resulted in the realization of devices exploiting such displacement current. Interestingly, it is presently unknown if such displacement current can result in large intrinsic ac current in ferroic systems possessing domains, despite the flurry of recent activities that have been devoted to domains and their corresponding conductivity in these compounds. Here, we report first-principles-based atomistic simulations that predict that the transverse (polarization-related) displacement currents of 71° and 109° domains in the prototypical BiFeO3 multiferroic material are significant at the walls of such domains and in the GHz regime, and, in fact, result in currents that are at least of the same order of magnitude than previously reported dc currents (that are likely extrinsic in nature and due to electrons). Such large, localized and intrinsic ac currents are found to originate from low-frequency vibrations at the domain walls, and may open the door to the design of novel devices functioning in the GHz or THz range and in which currents would be confined within the domain wall.Domain wall electronics: More robust at high frequenciesDomain walls in bismuth ferrite are predicted to have high a.c. conductivity, which could be exploited to develop giga- and terahertz devices. The observation of conducting domain walls in otherwise insulating functional materials has raised the prospect of forming reconfigurable electronic circuits. Unfortunately, it has been difficult to definitively identify the mechanism driving d.c. domain wall conduction, although it appears to arise from material defects, making precisely controlled devices difficult to fabricate. Sergey Prosandeev and co-workers from the University of Arkansas, USA, and Southern Federal University, Russia, have used numerical modeling to show that high frequency domain wall conductivity can occur in multiferroic bismuth ferrite due to the intrinsic physics of the walls. By avoiding reliance on extrinsic factors this mechanism should provide a more robust platform for developing gigahertz regime electronics.