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1. Fluid Ferroelectric Filaments

   https://doi.org/10.1002/advs.202305950  

   Máthé, Marcell_T; Perera, Kelum; Buka, Ágnes; Salamon, Péter; Jákli, Antal (December 2023, Advanced Science)

   Abstract Freestanding slender fluid filaments of room‐temperature ferroelectric nematic liquid crystals are described. They are stabilized either by internal electric fields of bound charges formed due to polarization splay or by external voltage applied between suspending wires. The phenomenon is similar to those observed in dielectric fluids, such as deionized water, except that in ferroelectric nematic materials the voltages required are three orders of magnitudes smaller and the aspect ratio is much higher. The observed ferroelectric fluid threads are not only unique and novel but also offer measurements of basic physical quantities, such as the ferroelectric polarization and viscosity. Ferroelectric nematic fluid threads may have practical applications in nano‐fluidic micron‐size logic devices, switches, and relays. 

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2. Modeling and Comparative Analysis of Hysteretic Ferroelectric and Anti-ferroelectric FETs

   https://doi.org/10.1109/DRC.2018.8442136  

   Saha, Atanu K.; Gupta, Sumeet K. (June 2018, Device Research Conference)
3. Ferroelectric Domain Wall Memristor

   https://doi.org/10.1002/adfm.202000109  

   McConville, James_P_V; Lu, Haidong; Wang, Bo; Tan, Yueze; Cochard, Charlotte; Conroy, Michele; Moore, Kalani; Harvey, Alan; Bangert, Ursel; Chen, Long‐Qing; et al (May 2020, Advanced Functional Materials)

   Abstract A domain wall‐enabled memristor is created, in thin film lithium niobate capacitors, which shows up to twelve orders of magnitude variation in resistance. Such dramatic changes are caused by the injection of strongly inclined conducting ferroelectric domain walls, which provide conduits for current flow between electrodes. Varying the magnitude of the applied electric‐field pulse, used to induce switching, alters the extent to which polarization reversal occurs; this systematically changes the density of the injected conducting domain walls in the ferroelectric layer and hence the resistivity of the capacitor structure as a whole. Hundreds of distinct conductance states can be produced, with current maxima achieved around the coercive voltage, where domain wall density is greatest, and minima associated with the almost fully switched ferroelectric (few domain walls). Significantly, this “domain wall memristor” demonstrates a plasticity effect: when a succession of voltage pulses of constant magnitude is applied, the resistance changes. Resistance plasticity opens the way for the domain wall memristor to be considered for artificial synapse applications in neuromorphic circuits. 

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4. Vibrational fingerprints of ferroelectric HfO2

   https://doi.org/10.1038/s41535-022-00436-8  

   Fan, Shiyu; Singh, Sobhit; Xu, Xianghan; Park, Kiman; Qi, Yubo; Cheong, S. W.; Vanderbilt, David; Rabe, Karin M.; Musfeldt, J. L. (December 2022, npj Quantum Materials)

   Abstract Hafnia (HfO 2 ) is a promising material for emerging chip applications due to its high- κ dielectric behavior, suitability for negative capacitance heterostructures, scalable ferroelectricity, and silicon compatibility. The lattice dynamics along with phononic properties such as thermal conductivity, contraction, and heat capacity are under-explored, primarily due to the absence of high quality single crystals. Herein, we report the vibrational properties of a series of HfO 2 crystals stabilized with yttrium (chemical formula HfO 2 :  x Y, where x  = 20, 12, 11, 8, and 0%) and compare our findings with a symmetry analysis and lattice dynamics calculations. We untangle the effects of Y by testing our calculations against the measured Raman and infrared spectra of the cubic, antipolar orthorhombic, and monoclinic phases and then proceed to reveal the signature modes of polar orthorhombic hafnia. This work provides a spectroscopic fingerprint for several different phases of HfO 2 and paves the way for an analysis of mode contributions to high- κ dielectric and ferroelectric properties for chip technologies. 

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5. Electrically Activated Ferroelectric Nematic Microrobots

   Máthé, Marcell Tibor; Nishikawa, Hiroya; Araoka, Fumito; Jákli, Antal; Salamon, Péter (July 2024, Nature communications)

   Ferroelectric nematic liquid crystals are fluids exhibiting spontaneous electric polarization, which is coupled to their long range orientational order. Due to their inherent property of making bound and surface charges, the free surface of ferroelectric nematics becomes unstable in electric fields. Here we show that ferroelectric liquid bridges between two electrode plates undergo distinct interfacial instabilities. In a specific range of frequency and voltage, the ferroelectric fluid bridges move as active interacting particles resembling living organisms like swarming insects, microbes or microrobots. The motion is accompanied by sound emission, as a consequence of piezoelectricity and electrostriction. Statistical analysis of the active particles reveals that the movement can be controlled by the applied voltage, which implies the possible application of the system in new types of microfluidic devices. 

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