Inspired by biological neural systems, neuromorphic devices may open up new computing paradigms to explore cognition, learning and limits of parallel computation. Here we report the demonstration of a synaptic transistor with SmNiO 3 , a correlated electron system with insulator-metal transition temperature at 130°C in bulk form. Non-volatile resistance and synaptic multilevel analogue states are demonstrated by control over composition in ionic liquid-gated devices on silicon platforms. The extent of the resistance modulation can be dramatically controlled by the film microstructure. By simulating the time difference between postneuron and preneuron spikes as the input parameter of a gate bias voltage pulse, synaptic spike-timing-dependent plasticity learning behaviour is realized. The extreme sensitivity of electrical properties to defects in correlated oxides may make them a particularly suitable class of materials to realize artificial biological circuits that can be operated at and above room temperature and seamlessly integrated into conventional electronic circuits.

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The thickness and origin of the free charge layer which forms at the LaAlO_{3}/SrTiO_{3} interface is still uncertain. By inserting Mn dopants at different distances from the interface we can locate the position of carriers within the SrTiO3 surface layers. We show that the majority of the carriers in fully-oxygenated samples are confined within 1 unit cell of the interface. This confirms the "polar-catastrophe" mechanism proposed for this system but the low mobility of these carriers demonstrates the need for improved materials for applications and a more complete understanding of the role of the minority of higher mobility carriers identified.

The rare-earth nickelates (RNiO 3 ) exhibit interesting phenomena such as unusual antiferromagnetic order at wavevector q = (½, 0, ½) and a tunable insulator-metal transition that are subjects of active research. Here we present temperature-dependent transport measurements of the resistivity, magnetoresistance, Seebeck coefficient, and Hall coefficient (R H ) of epitaxial SmNiO 3 thin films with varying oxygen stoichiometry. We find that from room temperature through the high temperature insulator-metal transition, the Hall coefficient is hole-like and the Seebeck coefficient is electron-like. At low temperature the Néel transition induces a crossover in the sign of R H to electron-like, similar to the effects of spin density wave formation in metallic systems but here arising in an insulating phase ~200 K below the insulator-metal transition. We propose that antiferromagnetism can be stabilized by bandstructure even in insulating phases of correlated oxides, such as RNiO 3 , that fall between the limits of strong and weak electron correlation.3

The origin of the free charge layer which forms at the LaAlO3/SrTiO3 interface is still uncertain. By varying the doping concentration and the nature of the dopant in SrTiO3 at the LaAlO3/SrTiO3 interface, we show the extreme sensitivity of the system and confirm that the underlying phenomenon accounting for the conduction is most likely an electronic reconstruction. We explain that although doping these interfaces might be useful to induce additional properties such as ferromagnetism or useful to probe the electronic reconstruction, undoped interfaces provide the highest carrier density.