Speaker: Dr. Xia Hong, Department of Physics and Astronomy, University of Nebraska-Lincoln.
Title: Emergent Phenomena in Ferroelectric Oxide/van der Waals Heterostructures
Abstract: The heterointerfaces between ferroelectric oxides and two-dimensional (2D) van der Waals materials present a versatile platform for achieving novel interfacial coupling, nonvolatile field effect control, and nanoscale programmable functionalities. In this talk, I will discuss a range of emergent phenomena in ferroelectric/vdW heterostructures mediated by interfacial coupling of charge, lattice, and polar symmetry. By combining polarization doping with nanoscale domain patterning in a ferroelectric Pb(Zr,Ti)O3 (PZT) gate, we create one-dimensional graphene superlattice in the high Kronig-Penney potential limit [1]. Negative capacitance (NC) transistors are developed based on polycrystalline PZT gated MoS2, which exhibits ultralow subthreshold swing of 9.7 mV/decade at 300 K. Theoretical modeling and PFM studies suggest that the NC mode is enabled by the metastable polar states within the domain walls [2]. We observe enhanced polar alignment, piezoelectricity, and Curie temperature in thin CuInP2S6 flakes prepared on PZT, which can be attributed to the tilt of the free-energy quadruple well via interfacial strain coupling [3]. An unconventional tuning effect of second harmonic generation signal is enabled by the polar coupling of monolayer MoS2 with either the polar domain or the chiral dipole rotation at the domain wall surface in PZT thin films and free-standing membranes [4]. Our study showcases the rich research opportunities offered by integrating ferroelectric oxides with 2D materials.
[1] T. Li et al., Phys. Rev. Lett. 132, 056204 (2024).
[2] Song et al., npj 2D Mater. Appl. 6, 77 (2022).
[3] K. Wang et al., ACS Nano 17, 15787 (2023).
[4] D. Li et al., Nat. Commun. 11, 1422 (2020); D. Li et al., Adv. Mater. 35, 2208825 (2023).