Control of electronic phase co-existence in hydrogen-doped perovskite nickelates for photonic computing

Quantum materials such as perovskite nickelates undergo colossal electronic phase transitions from electron doping with donors such as hydrogen. The resulting changes in optical gap can be as large as 3eV. The hydrogen resides as a proton in interstitial sites while the electrons anchor to Ni-O orbitals. Using asymmetric two-terminal electrodes such as Pt and Au, it is possible to create a doping gradient by catalytic spillover of hydrogen proximal to Pt electrode. The gradient in dopant density allows for electric field modulation of the effective channel conductance and optical refractive index (n) and extinction coefficient (k) in a non-volatile manner. Here, we will describe the doping physics of nickelates followed by fabrication of solid-state devices to manipulate the electronic phases in an epitaxial perovskite NdNiO3 thin film channel on LaAlO3 substrate. Spatially-resolved probing of the phase distribution by synchrotron spectroscopy allows us to obtain length scale information on the conducting and insulating phases and re-distribution under electric field stimulus. Using the measured (n, k) of the fabricated thin film, we simulate the light propagation through such media and compare it to experimental data. Non-volatile correlated perovskite electronic systems could serve as excellent tunable optical weights for photonic neural networks and the ability to read out signals by electric and optical modality opens up new directions for energy-efficient non-Von Neumann computing. (M.I. and F.A. contributed equally)