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Register a new userUnveiling AC electronic properties at ferroelectric domain walls
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Added by
Jan Schulthei{\\ss}
Publication date
2021
fields
Physics
and research's language is
English
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Ferroelectric domain walls exhibit a range of interesting electrical properties and are now widely recognized as functional two-dimensional systems for the development of next-generation nanoelectronics. A major achievement in the field was the development of a fundamental framework that explains the emergence of enhanced electronic direct-current (DC) conduction at the domain walls. In this Review, we discuss the much less explored behavior of ferroelectric domain walls under applied alternating-current (AC) voltages. We provide an overview of the recent advances in the nanoscale characterization that allow for resolving the dynamic responses of individual domain walls to AC fields. In addition, different examples are presented, showing the unusual AC electronic properties that arise at neutral and charged domain walls in the kilo- to gigahertz regime. We conclude with a discussion about the future direction of the field and novel application opportunities, expanding domain-wall based nanoelectronics into the realm of AC technologies.
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Ferroelectric domain walls represent multifunctional 2D-elements with great potential for novel device paradigms at the nanoscale. Improper ferroelectrics display particularly promising types of domain walls, which, due to their unique robustness, are the ideal template for imposing specific electronic behavior. Chemical doping, for instance, induces p- or n-type characteristics and electric fields reversibly switch between resistive and conductive domain-wall states. Here, we demonstrate diode-like conversion of alternating-current (AC) into direct-current (DC) output based on neutral 180$^{circ}$ domain walls in improper ferroelectric ErMnO$_3$. By combining scanning probe and dielectric spectroscopy, we show that the rectification occurs for frequencies at which the domain walls are fixed to their equilibrium position. The practical frequency regime and magnitude of the output is controlled by the bulk conductivity. Using density functional theory we attribute the transport behavior at the neutral walls to an accumulation of oxygen defects. Our study reveals domain walls acting as 2D half-wave rectifiers, extending domain-wall-based nanoelectronic applications into the realm of AC technology.
The ease with which domain walls (DWs) in ferroelectric materials can be written and erased provides a versatile way to dynamically modulate heat fluxes. In this work we evaluate the thermal boundary resistance (TBR) of 180$^{circ}$ DWs in prototype ferroelectric perovskite PbTiO$_3$ within the numerical formalisms of nonequilibrium molecular dynamics and nonequilibrium Greens functions. An excellent agreement is obtained for the TBR of an isolated DW derived from both approaches, which reveals the harmonic character of the phonon-DW scattering mechanism. The thermal resistance of the ferroelectric material is shown to increase up to around 20%, in the system sizes here considered, due to the presence of a single DW, and larger resistances can be attained by incorporation of more DWs along the path of thermal flux. These results, obtained at device operation temperatures, prove the viability of an electrically actuated phononic switch based on ferroelectric DWs.
The domain structure of uniaxial ferroelectric lithium niobate single crystals is investigated using Raman spectroscopy mapping. The influence of doping with magnesium and poling at room temperature is studied by analysing frequency shifts at domain walls and their variations with dopant concentration and annealing conditions. It is shown that defects are stabilized at domain walls and that changes in the defect structures with Mg concentration can be probed by the shift of Raman modes. We show that the signatures of polar defects in the bulk and at the domain walls differ.
Transition metal oxides hold great potential for the development of new device paradigms because of the field-tunable functionalities driven by their strong electronic correlations, combined with their earth abundance and environmental friendliness. Recently, the interfaces between transition-metal oxides have revealed striking phenomena such as insulator-metal transitions, magnetism, magnetoresistance, and superconductivity. Such oxide interfaces are usually produced by sophisticated layer-by-layer growth techniques, which can yield high quality, epitaxial interfaces with almost monolayer control of atomic positions. The resulting interfaces, however, are fixed in space by the arrangement of the atoms. Here we demonstrate a route to overcoming this geometric limitation. We show that the electrical conductance at the interfacial ferroelectric domain walls in hexagonal ErMnO3 is a continuous function of the domain wall orientation, with a range of an order of magnitude. We explain the observed behaviour using first-principles density functional and phenomenological theories, and relate it to the unexpected stability of head-to-head and tail-to-tail domain walls in ErMnO3 and related hexagonal manganites. Since the domain wall orientation in ferroelectrics is tunable using modest external electric fields, our finding opens a degree of freedom that is not accessible to spatially fixed interfaces.
Ferroelectric domain walls are boundaries between regions with different polarization orientations in a ferroelectric material. Using first principles calculations, we characterize all different types of domain walls forming on ($11bar{1}$), ($111$) and ($1bar{1}0$) crystallographic planes in thermoelectric GeTe. We find large structural distortions in the vicinity of most of these domain walls, which are driven by polarization variations. We show that such strong strain-order parameter coupling will considerably reduce the lattice thermal conductivity of GeTe samples containing domain walls with respect to single crystal. Our results thus suggest that domain engineering is a promising path for enhancing the thermoelectric figure of merit of GeTe.
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