Conductance Quantization and Quantum-Point-Contact Formation in hBN/HfO ₂ Bilayer Memristive Devices

We report quantized conductance and quantum point contact (QPC) formation in memristive devices comprising exfoliated hexagonal boron nitride (hBN) over HfO 2 as the active layer. The scattered hBN flakes that locally enhance oxygen vacancy concentration, forming the filamentary paths beneath Ag top electrodes. These topographical inhomogeneities create atomically narrow constrictions that act as QPCs. X-ray diffraction measurements indicate strain at the hBN stacks, where the Raman " E 2g " mode 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 of G 0 =2e 2 /h and hysteretic current-voltage behavior consistent with filament evolution. We propose a unified morphological-ionic model where scattered hBN flakes create nanoscale topography that steers oxygen-vacancy accumulation and produces QPCs at the top electrode/HfO 2 interface. The results highlight van-der-Waals/oxide heterostructures as promising platforms for atomic-scale memristive devices and secure stochastic hardware primitives.