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Oxygen modulated quantum conductance for ultra-thin HfO$_2$-based memristive switching devices

Memristive switching devices, candidates for resistive random access memory technology, have been shown to switch off through a progression of states with quantized conductance and subsequent non-integer conductance (in terms of conductance quantum $G_0$). We have performed calculations based on density functional theory to model the switching process for a Pt-HfO$_2$-Pt structure, involving the movement of one or two oxygen atoms. Oxygen atoms moving within a conductive oxygen vacancy filament act as tunneling barriers, and partition the filament into weakly coupled quantum wells. We show that the low-bias conductance decreases exponentially when one oxygen atom moves away from interface. Our results demonstrate the high sensitivity of the device conductance to the position of oxygen atoms.