Carrier localization in perovskite nickelates from oxygen vacancies

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Abstract

Point defects, such as oxygen vacancies, control the physical properties of complex oxides, relevant in active areas of research from superconductivity to resistive memory to catalysis. In most oxide semiconductors, electrons that are associated with oxygen vacancies occupy the conduction band, leading to an increase in the electrical conductivity. Here we demonstrate, in contrast, that in the correlated-electron perovskite rare-earth nickelates, RNiO ₃ ( R is a rare-earth element such as Sm or Nd), electrons associated with oxygen vacancies strongly localize, leading to a dramatic decrease in the electrical conductivity by several orders of magnitude. This unusual behavior is found to stem from the combination of crystal field splitting and filling-controlled Mott–Hubbard electron–electron correlations in the Ni 3 d orbitals. Furthermore, we show the distribution of oxygen vacancies in NdNiO ₃ can be controlled via an electric field, leading to analog resistance switching behavior. This study demonstrates the potential of nickelates as testbeds to better understand emergent physics in oxide heterostructures as well as candidate systems in the emerging fields of artificial intelligence.

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A correlated nickelate synaptic transistor.

Jian Shi, Sieu D Ha, You zhou … (2013)

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 SmNiO₃, 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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Colossal resistance switching and band gap modulation in a perovskite nickelate by electron doping.

Jian Shi, You zhou, Shriram Ramanathan (2014)

The electronic properties of correlated oxides are exceptionally sensitive to the orbital occupancy of electrons. Here we report an electron doping strategy via a chemical route, where interstitial dopants (for example, hydrogen) can be reversibly intercalated, realizing a sharp phase transition in a model correlated perovskite nickelate SmNiO3. The electron configuration of eg orbital of Ni(3+) t2g(6)eg(1) in SmNiO3 is modified by injecting and anchoring an extra electron, forming a strongly correlated Ni(2+) t2g(6)eg(2) structure leading to the emergence of a new insulating phase. A reversible resistivity modulation greater than eight orders of magnitude is demonstrated at room temperature. A solid-state room temperature non-volatile proton-gated phase-change transistor is demonstrated based on this principle, which may inform new materials design for correlated oxide devices. Electron doping-driven phase transition accompanied by large conductance changes and band gap modulation opens up new directions to explore emerging electronic and photonic devices with correlated oxide systems.