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Ferroelectricity at the extreme thickness limit in the archetypal antiferroelectric PbZrO3
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Melting of charge order in the low-temperature state of an electronic ferroelectric-like system
Strong electronic interactions can drive a system into a state with a symmetry breaking. Lattice frustration or competing interactions tend to prevent symmetry breaking, leading to quantum disordered phases. In spin systems frustration can produce a spin liquid state. Frustration of a charge degree of freedom also can result in various exotic states, however, experimental data on these effects is scarce. In this work we demonstrate how in a Mott insulator on a weakly anisotropic triangular lattice a charge ordered state melts on cooling down to low temperatures. Raman scattering spectroscopy finds that κ -(BEDT-TTF) 2 Hg(SCN) 2 Cl enters an insulating “dipole solid” state at T =30K, but below T =15K the order melts, while preserving the insulating energy gap. Based on these observations, we suggest a phase diagram relevant to other quantum paraelectric materials.
Dzyaloshinskii–Moriya-like interaction in ferroelectrics and antiferroelectrics
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Electro-thermal actuation in percolative ferroelectric polymer nanocomposites
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Interfacial ferroelectricity in rhombohedral-stacked bilayer transition metal dichalcogenides
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Electrically switchable anisotropic polariton propagation in a ferroelectric van der Waals semiconductor
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To switch or not to switch – a machine learning approach for ferroelectricity
The introduced two-dimensional representation of two-parameter signal dependence allows for clear interpretation and classification of the measured signal upon using machine learning methods.
Towards ferroelectricity-inducing chains of halogenoantimonates( iii ) and halogenobismuthates( iii )
A discovered abundance of structures with rare and highly-desired anionic chains is examined to identify structural factors leading to the chains' formation.
Quantifying non-centrosymmetric orthorhombic phase fraction in 10 nm ferroelectric Hf0.5Zr0.5O2 films
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Identification of structural phases in ferroelectric hafnium zirconium oxide by density-functional-theory-assisted EXAFS analysis
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Active and passive defects in tetragonal tungsten bronze relaxor ferroelectrics
Tetragonal tungsten bronze (TTB) based oxides constitute a large family of dielectric materials which are known to exhibit complex distortions producing incommensurately modulated superstructures as well as significant local deviations from their average symmetry. The local deviations produce diffuse scattering in diffraction experiments. The structure as well as the charge dynamics of these materials are anticipated to be sensitive to defects, such as cation or oxygen vacancies. In this work, in an effort to understand how the structural and charge dynamical properties respond to these two types of vacancy defects, we have performed measurements of dielectric susceptibilities and single crystal diffraction experiments of two types of TTB materials with both ‘filled’ (Ba 2 NdFeNb 4 O 15 and Ba 2 PrFeNb 4 O 15 ) and ‘unfilled’ (Sr 0.5 Ba 0.5 Nb 2 O 6 ) cation sublattices. We also perform these measurements before and after oxygen annealing, which alters the oxygen vacancy concentrations. Surprisingly, we find that many of the diffuse scattering features that are present in the unfilled structure are also present in the filled structure, suggesting that the random fields and disorder that are characteristic of the unfilled structure are not responsible for many of the local structural features that are reflected in the diffuse scattering. Furthermore, oxygen annealing clearly affected both color and dielectric properties, consistent with a diminishment of the oxygen vacancy concentration, but had little effect on observed diffuse patterns.
Comment on “Superconductivity at low density near a ferroelectric quantum critical point: Doped SrTiO 3 ”
Wölfle and Balatsky have proposed a microscopic pairing mechanism for doped SrTiO 3 (STO) based on the gradient coupling of electronic density to the soft transverse optical (TO) phonon mode. Since this coupling to TO phonons is usually weak, this conclusion is surprising, especially for a low-density superconductor such as STO, where the density of states is small. A crucial step in the argument made by Wölfle and Balatsky is that the displacement vector of the TO mode is not strictly perpendicular to the momentum vector, making a deformation coupling possible. We show that they have made a mistake in computing the eigenvector and have grossly overestimated this lack of orthogonality. When corrected, the coupling is negligible. We also use transport data to put upper bounds on the coupling constant which are much smaller than the estimate by Wölfle and Balatsky. Lastly, we also object to their use of the Eliashberg equation when the phonon frequency is larger than the Fermi energy.
Improper ferroelectricity in 134-type $AA_3'B_4\text{O}_{12}$ perovskites
The 134-type $\textit{A}$-site ordered LaMn 3 Cr 4 O 12 , that belongs to the family of $AA_3'B_4\text{O}_{12}$ perovskites, with cubic structure and magnetically driven improper polarization is puzzling because the conventional mechanisms leading to the creation of polarization in type-II multiferroics do not apply. By symmetry analysis and first-principles simulations in this work, we discover an original and previously overlooked energetic term that naturally explains the origin of improper polarization in LaMn 3 Cr 4 O 12 . In addition, we demonstrate the existence of three other energetic invariants in $AA_3'B_4\text{O}_{12}$ perovskites, for which other physical quantities (such as oxygen tiltings or shear strain) mediate the interaction between $\textit{G}$-type antiferromagnetic vectors to create and even enhance improper polarization.
From first- to second-order phase transitions in hybrid improper ferroelectrics through entropy stabilization
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