Conductance quantization and quantum-point-contact formation in hBN/HfO₂bilayer memristive devices

We report quantized conductance and quantum point contact (QPC) formation in memristive devices comprising exfoliated hexagonal boron nitride (hBN) over HfO₂as the active layer. The scattered hBN flakes locally enhance oxygen vacancy concentration, forming the filamentary paths beneath Ag top electrodes (TEs). These topographical inhomogeneities create atomically narrow constrictions that act as QPCs. X-ray diffraction measurements indicate strain in the hBN stacks, whereas the RamanE2gmode shows a small shift (1364-1366 cm^-1) and broadening indicative of strain and substrate coupling. Electrical characterization exhibits conductance plateaus close to integer and half-integer multiples ofG0=2e2/h, along with hysteretic current-voltage behavior consistent with filament evolution. We propose a unified morphological-ionic model where randomly distributed hBN flakes create nanoscale topography that steers oxygen-vacancy accumulation and produces QPCs at the TE/hBN interface. The results highlight van-der-Waals/oxide heterostructures as promising platforms for atomic-scale memristive devices and secure stochastic hardware primitives.