Coherent dipole units and ferroelectric correlations in asymmetric atomic-layer superlattices
Phys. Rev. B 114, 165126 – Published 17 September, 2026
DOI: https://doi.org/10.1103/7sl3-371j
Abstract
We analyze the dielectric response of superlattice samples composed of titanate phases: calcium titanate, strontium titanate, and barium titanate, stacked at the ultimate atomic layer limit to break inversion symmetry. High temperature susceptibility measurements extracted from low-frequency () ac capacitance measurements indicate that the asymmetric strain field provides an effective polarizing field that polarizes the samples even at high temperature with the sign of the polarization consistent with the sign of the stacking asymmetry. From the combined temperature, frequency, and electric field dependence, we provide evidence that the size of the dynamically coherent dipole units that persist at high temperatures has little variability from sample to sample and have a volume of perovskite unit cells. As temperature is lowered, below a crossover temperature the dielectric response deviates from that expected of activated reorientation of two-state switchable dipoles governed by kinetics. This deviation points to the further growth of dynamically coherent dipole units. Pyrocurrent and dc transient current measurements indicate an unusual asymmetric hysteretic response at low temperatures with a temperature-dependent shift of the loops resulting in a low temperature offset polarization. We argue that the responding dipole units above are correlated only along the superlattice stacking direction by the built-in strain field resulting in nanopillars of single unit cell cross-sectional areas. The growth of the dynamically coherent dipole units below points to the emergence of lateral correlations and an unusual ferroelectric response is observed subject to the built-in asymmetric strain field.
