Comparative study of photo-induced electronic transport along ferroelectric domain walls in lithium niobate single crystals
arxiv(2024)
摘要
Ferroelectric domain wall conductivity (DWC) is an intriguing functional
property, that can be controlled through external stimuli such as electric and
mechanical fields. Optical-field control, as a non-invasive flexible handle,
has rarely been applied so far, but significantly expands the possibility for
both tuning and probing DWC. On the one hand, as known from Second-Harmonic,
Raman, and CARS micro-spectroscopy, the optical in-and-out approach delivers
parameters on the DW distribution, the DW inclination, and probes the DW
vibrational modes; on the other hand, photons might be applied also to directly
generate charge carriers within the DW, hence acting as a functional and
spectrally tunable probe to deduce the integral or local absorption properties
and bandgaps of conductive DWs. Here, we report on such an optoelectronic
approach by investigating the photo-induced DWC (PI-DWC) in DWs of the model
system lithium niobate, a material that is well known for hosting conductive
DWs. We compare three different crystals containing different numbers of domain
walls: (A) none, (B) one, and (C) many conductive DWs. All samples are
inspected for their current-voltage (I-V) behavior (i) in darkness, and (ii)
for different illumination wavelengths swept from 500 nm down to 310 nm. All
samples show their maximum PI-DWC at 310 nm, i.e., at the optical bandgap of
lithium niobate; moreover, sample (C) reaches PI-DWCs of several μA.
Interestingly, a noticeable PI-DWC is also observed for sub-bandgap
illumination, i.e., wavelengths as high as 500 nm, hinting towards the
existence and decisive role of electronic in-gap states that contribute to the
electronic transport along DWs. Finally, conductive atomic force microscopy
(c-AFM) investigations under illumination proved that the PI-DWC is confined to
the DW area, and does not originate from photo-induced bulk conductivity.
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