Frequency regulation in alternation-current transports across metal to insulator transitions of thin film correlated perovskite nickelates

Abstract

Although the metal to insulator transition (MIT) observed in d-band correlated metal oxides enables promising applications (e.g., correlated logical devices and Mottronic devices), its present recognition is mainly limited on the direct current (DC) electrical transports. Up to date, the MIT from the perspective of alternation current (AC) transport and its potential electronic applications remains yet unclear. Herein, we demonstrate the frequency (fAC) dependence in the impedance (Z = Z’+iZ’’) of typical MIT materials, such as thin film rare-earth nickelates (ReNiO3), across the critical MIT temperature (TMIT). Apart from the abrupt change in the impedance modulus (|Z|) across the critical temperature (TMIT) similar to the DC transport, the MIT also triggers non-continuous variation in the impedance phase (θ), and this enables the fAC-regulations in the Z’-T tendencies (Z’=|Z|cosθ). At the critical fAC range (e.g., 104–106 Hz), the conversing variations in |Z|-T and cosθ-T across TMIT result in non-monotonic delta-shape Z’-T tendency in SmxNd1-xNiO3, the full width half maximum of which is effectively narrowed compared to the situation with the absence of MIT. Further imparting lower or higher fAC elevate the domination in |Z|-T and cosθ-T, respectively, but also enables abrupt Z’-T tendencies across TMIT showing negative temperature coefficient of resistance (NTCR) or positive temperature coefficient of resistance (PTCR). By introducing fAC as a new freedom, the MIT behavior can be more comprehensively regulated electronically, and this extends the vision in exploring the new electronic applications based on the correlated MIT materials from the AC perspective.