Abstract
Ferroelectric domain walls have continued to attract widespread attention due to both the novelty of the phenomena observed and the ability to reliably pattern them in nanoscale dimensions. However, the conductivity mechanisms remain in debate, particularly around nominally uncharged walls. Here, we posit a conduction mechanism relying on field-modification effect from polarization re-orientation and the structure of the reverse-domain nucleus. Through conductive atomic force microscopy measurements on an ultra-thin (001) BiFeO3 thin film, in combination with phase-field simulations, we show that the field-induced twisted domain nucleus formed at domain walls results in local-field enhancement around the region of the atomic force microscope tip. In conjunction with slight barrier lowering, these two effects are sufficient to explain the observed emission current distribution. These results suggest that different electronic properties at domain walls are not necessary to observe localized enhancement in domain wall currents.
Highlights
Ferroelectric domain walls have continued to attract widespread attention due to both the novelty of the phenomena observed and the ability to reliably pattern them in nanoscale dimensions
Given that the studies on wall conduction are often conducted using conductive atomic force microscope (c-AFM) technique, progress in reconciling experiments to possible mechanisms requires a strong appreciation of the role of the junction between the metal-coated AFM tip and the domain wall[7]
The topography of the (001) ~10 nm-thick BiFeO3 (BFO) thin film is shown in Fig. 1a, and indicates a smooth surface with low roughness (RMS~200 pm) (Method)
Summary
Ferroelectric domain walls have continued to attract widespread attention due to both the novelty of the phenomena observed and the ability to reliably pattern them in nanoscale dimensions. There has been renewed interest in exotic domain topologies, spurred by the discovery of closure states[30,31,32], quadrupole chains[33], and continuous polarization rotations[34, 35] in ferroelectric thin films and, very recently, experimental demonstration of vortex-anti-vortex arrays in an oxide superlattice heterostructure[36]. Key to these novel states is the existence of non-zero curl of polarization. Distinguishing between the conduction at the domain walls and the bulk of the film would benefit from ultra-thin samples (~30 nm)
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