Enhanced Field Modulation Sensitivity and Anomalous Polarity-Dependency Emerged in Spatial-Confined Manganite Strips

An anomalous polarity-dependent electrostatic field modulation effect, facilitated by spatial confinement, is found in an oxide-based field-effect prototype device with a spatial-confined Pr_0.7(Ca_0.6Sr_0.4)_0.3MnO₃ channel. It is revealed that the dominant field modulation mode under a small bias field varies from a polarity-independent strain-mediated one to a nonvolatile polarity-dependent one with enhanced modulation sensitivity as the channel width narrows down to several micrometers. Specially, in the structure confined to length scales similar to that of the phase domains, the field modulation exhibits a greatly increased modulation amplitude around the transition temperature and an anomalous bias-polarity dependence that is diametrically opposite to the normal one observed in regular polarization field-effect. Further simulations show that a large in-plane polarization field is unexpectedly induced by a small out-of-plane bias field of 4 kV/cm in the narrow strip (up to 790 kV/cm for the 3 μm strip). Such large in-plane polarization field, facilitated and enhanced by size reduction, drives phase transitions in the narrow channel film, leading to the reconfiguration of percolation channel and nonvolatile modulation of transport properties. Accordingly, the accompanied polarity relationship between the induced in-plane polarization field and the applied vertical bias field well explains the observed anomalous polarity-dependence of the modulation. Our studies reveal a new acting channel in the nanoscale control of lateral configurations of electronic phase separation and macroscopic behaviors by a small vertical electric bias field in spatial-confined field-effect structures. This distinct acting mechanism offers new possibilities for designing low-power all-oxide-based electronic devices and exploiting new types of multifunctionality to other strongly correlated materials where electronic phase competition exists.