Photo-Induced Transport Properties in Ferroelectric Domains and Domain Walls in Lithium Niobate Single Crystals

Ferroelectric materials exhibit a spontaneous and stable dielectric polarization, resulting in a rich and variable assembly of domain and domain wall structures that is receiving continued attention [1, 2]. Furthermore, the multifield-controlled (electrical, mechanical, optical) electrical transport across these crystals offers many prospects for the vivid application of ferroelectrics into electronic devices, such as ferroelectric sensors, memories, and even ferroelectric synaptic circuits [3-5]. Notably, (external) control of the electronic transport by means of photons is very desirable since being non-invasive and ultrafast, but has been studied only sparsely so far. In particular, polarization switching of domains and domain walls, band gap modulation, or domain wall dynamics, all are susceptible to the photon-electron interaction, and thus need fundamental and profound investigations as basis for further application.<br/>In this work, we combine local-scale scanning probe techniques with analyzing the impact of light irradiation onto lithium niobate domains and domain walls, and vary both intensity and wavelength to probe the (local) electronic conductivity. On this basis, we can also realize the configuration of high density domain pattern array and modulate the domain wall conductivity through scanning probe microscopy and the assistance of UV light. Then, we demonstrate that the enhancement of transport properties and the switching behavior of lithium niobate domain walls can be regulated by illumination adjacent to the band gap. This multi-method approach thus will improve our in-depth knowledge on the local band structure and energy level distribution within domain walls, and will lay the foundation to design integrated electro-optical components thereof.<br/><br/>[1] D. Meier, et al., <i>Nat</i><i>.</i> <i>Rev</i><i>.</i><i> Mater</i><i>.</i> <b>7</b>, 157 (2022)<br/>[2] D. M. Evans, et al., <i>Phys. Sci. Rev.</i> <b>5</b>, 9 (2020)<br/>[3] C. Godau, et al., <i>ACS Nano</i> <b>11</b>, 5 (2017)<br/>[4] E. Singh, et al., <i>Phys. Rev. B</i> <b>106</b>, 144103 (2022)<br/>[5] Z. D. Luo, et al., <i>ACS Nano</i> <b>14</b>, 746 (2020)