Low-Voltage Domain-Wall LiNbO3 Memristors.

Application of conducting ferroelectric domain walls (DWs) as functional elements may facilitate development of conceptually new resistive switching devices. In a conventional approach, several orders of magnitude change in resistance can be achieved by controlling the DW density using supercoercive voltage. However, a deleterious characteristic of this approach is high-energy cost of polarization reversal due to high leakage current. Here, we demonstrate a new approach based on tuning the conductivity of DWs themselves rather than on domain rearrangement. Using LiNbO3 capacitors with graphene, we show that resistance of a device set to a polydomain state can be continuously tuned by application of subcoercive voltage. The tuning mechanism is based on the reversible transition between the conducting and insulating states of DWs. The developed approach allows an energy-efficient control of resistance without the need for domain structure modification. The developed memristive devices are promising for multilevel memories and neuromorphic computing applications.

Hall effect in charged conducting ferroelectric domain walls.

Enhanced conductivity at specific domain walls in ferroelectrics is now an established phenomenon. Surprisingly, however, little is known about the most fundamental aspects of conduction. Carrier types, densities and mobilities have not been determined and transport mechanisms are still a matter of guesswork. Here we demonstrate that intermittent-contact atomic force microscopy (AFM) can detect the Hall effect in conducting domain walls. Studying YbMnO3 single crystals, we have confirmed that p-type conduction occurs in tail-to-tail charged domain walls. By calibration of the AFM signal, an upper estimate of ∼1 × 1016 cm-3 is calculated for the mobile carrier density in the wall, around four orders of magnitude below that required for complete screening of the polar discontinuity. A carrier mobility of∼50 cm2V-1s-1 is calculated, about an order of magnitude below equivalent carrier mobilities in p-type silicon, but sufficiently high to preclude carrier-lattice coupling associated with small polarons.

Neurological examination is possible using telemedicine.

To compare the reliability of neurological examination performed by telemedicine and face to face, a junior doctor examined 23 patients face to face, these examinations being witnessed either by one or by two telemedicine observers using a telemedicine video-link at 384 kbit/s. The gold standard was a face-to-face examination from a panel of six consultant neurologists. Power, deep tendon reflexes, plantar responses, coordination, sensation, eye movements, facial strength, tongue movements, sitting balance and gait were studied. Seventeen patients satisfied the inclusion criteria, and a total of 1,084 matched pairs of observations were made. The reliability of the telemedicine examination ranged from fair to moderate for deep tendon reflexes, coordination and eye movement, to near perfect for plantar responses. Overall, examination by telemedicine compared favourably with face-to-face examination. Telemedicine examination was more sensitive in detecting abnormalities than face-to-face examination for all the neurological tests studied and more specific for all but one (plantar responses). The study showed that neurological examination using telemedicine is at least as good as face-to-face examination performed by a junior doctor.