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Crystal structures and microstructural features, such as structural phase transitions, defect structures, and chemical and structural inhomogeneities, are known to have profound effects on the physical properties of superconducting materials. Recently, many studies on the structural properties of Fe-based high-Tc superconductors have been published. This review article will mainly focus on the typical microstructural features in samples that have been well characterized by physical measurements. (i) Certain common structural features are discussed, in particular, the crystal structural features for different superconducting families, the local structural distortions in the Fe2Pn2 (Pn = P As, Sb) or Fe2Ch2 (Ch = S, Se, Te) blocks, and the structural transformations in the 122 system. (ii) In FeTe(Se) (11 family), the superconductivity, chemical and structural inhomogeneities are investigated and discussed in correlation with superconductivity. (iii) In the K0.8Fe1.6+xSe2 system, we focus on the typical compounds with emphasis on the Fe-vacancy order and phase separations. The microstructural features in other superconducting materials are also briefly discussed. [ABSTRACT FROM AUTHOR]

The I-V characteristics of In2O3:SnO2/TiO2/In2O3:SnO2 junctions with different interfacial barriers are investigated by comparing experiments. A two-step resistance switching process is found for samples with two interfacial barriers produced by specific thermal treatment on the interfaces. The nonsynchronous occurrence of conducting filament formation through the oxide bulk and the reduction in the interfacial barrier due to the migration of oxygen vacancies under the electric field is supposed to explain the two-step resistive switching process. The unique switching properties of the device, based on interfacial barrier engineering, could be exploited for novel applications in nonvolatile memory devices. [ABSTRACT FROM AUTHOR]

Based on a recent loopless mounting method, a simplified loopless and bufferless crystal mounting method is developed for macromolecular crystallography. This simplified crystal mounting system is composed of the following components: a home-made glass capillary, a brass seat for holding the glass capillary, a flow regulator, and a vacuum pump for evacuation. Compared with the currently prevalent loop mounting method, this simplified method has almost the same mounting procedure and thus is compatible with the current automated crystal mounting system. The advantages of this method include higher signal-to-noise ratio, more accurate measurement, more rapid flash cooling, less x-ray absorption and thus less radiation damage to the crystal. This method can be extended to the flash-freeing of a crystal without or with soaking it in a lower concentration of cryoprotectant, thus it may be the best option for data collection in the absence of suitable cryoprotectant. Therefore, it is suggested that this mounting method should be further improved and extensively applied to cryocrystallographic experiments. [ABSTRACT FROM AUTHOR]

Trapped ions, under electromagnetic confinement and Coulomb repulsion, can behave as non-interacting particles in one-dimensional lattices. Here we explore analytically the possible effects regarding Anderson localization in a chain of trapped ions experiencing laser Bessel beams. Under an experimentally feasible condition, we predict an analytical form of the energy-dependent mobility edges, which is verified to be in good agreement with the exact numerical results except for the top band. Some other important properties regarding the phonon localization in the ion chain are also discussed both analytically and numerically. Our results are relevant to experimental observation of localization–delocalization transition in the ion trap and helpful for deeper understanding of the rich phenomena due to long-range phonon hopping. [ABSTRACT FROM AUTHOR]

Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increasing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional (2D) systems, few-layer h-BN and indium iodide (InI). We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the competition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect. [ABSTRACT FROM AUTHOR]

Lorentz transmission electron microscopy (TEM) is a powerful tool to study the crystal structures and magnetic domain structures in correlation with novel physical properties. Nanometric topological magnetic configurations such as vortices, bubbles, and skyrmions have received enormous attention from the viewpoint of both fundamental science and potential applications in magnetic logic and memory devices, in which understanding the physical properties of magnetic nanodomains is essential. In this review article, several magnetic imaging methods in Lorentz TEM including the Fresnel and Foucault modes, electron holography, and differential phase contrast (DPC) techniques are discussed, where the novel properties of topological magnetic domains are well addressed. In addition, in situ Lorentz TEM demonstrates that the topological domains can be efficiently manipulated by electric currents, magnetic fields, and temperatures, exhibiting novel phenomena under external fields, which advances the development of topological nanodomain-based spintronics. [ABSTRACT FROM AUTHOR]

We investigate the performances of the pairwise correlations (PCs) in different quantum networks consisting of four-wave mixers (FWMs) and beamsplitters (BSs). PCs with quantum correlation in different quantum networks can be verified by calculating the degree of relative intensity squeezing for any pair of all the output fields. More interestingly, the quantum correlation recovery and enhancement are present in the FWM+BS network and the repulsion effect phenomena (signal (idler)–frequency mode cannot be quantum correlated with the other two idler (signal)–frequency modes simultaneously) between the PCs with quantum correlation are predicted in the FWM + FWM and FWM + FWM + FWM networks. Our results presented here pave the way for the manipulation of the quantum correlation in quantum networks. [ABSTRACT FROM AUTHOR]

In this work, ultrathin pure HfO2 and Al-doped HfO2 films (about 4-nm thick) are prepared by atomic layer deposition and the crystallinities of these films before and after annealing at temperatures ranging from 550 °C to 750 °C are analyzed by grazing incidence x-ray diffraction. The as-deposited pure HfO2 and Al-doped HfO2 films are both amorphous. After 550-°C annealing, a multiphase consisting of a few orthorhombic, monoclinic and tetragonal phases can be observed in the pure HfO2 film while the Al-doped HfO2 film remains amorphous. After annealing at 650 °C and above, a great number of HfO2 tetragonal phases, a high-temperature phase with higher dielectric constant, can be stabilized in the Al-doped HfO2 film. As a result, the dielectric constant is enhanced up to about 35. The physical mechanism of the phase transition behavior is discussed from the viewpoint of thermodynamics and kinetics. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy (TEM) study of SrPt2As2 reveals two incommensurate modulations appearing in the charge-density-wave (CDW) state below TCDW ≈ 470 K. These two structural modulations can be well explained in terms of condensations of two-coupled phonon modes with wave vectors of q1 = 0.62a* on the a*−b* plane and q2 = 0.23a* on the a*−c* plane. The atomic displacements occur along the b-axis direction for q1 and along the c-axis direction for q2, respectively. Moreover, the correlation between q1 and q1 can be generally written as q1 = (q2 + a*)/2 in the CDW state, suggesting the presence of essential coupling between q1 and q2. A small fraction of Ir doping on the Pt site in Sr(Pt1–xIrx)2As2 (x ≤ 0.06) could moderately change these CDW modulations and also affect their superconductivities. [ABSTRACT FROM AUTHOR]

The crystallographic temperature factors (B factor) of individual atoms contain important information about the thermal motion of the atoms in a macromolecule. Previously the theory of flexibility of active site has been established based on the observation that the enzyme activity is sensitive to low concentration denaturing agents. It has been found that the loss of enzyme activity occurs well before the disruption of the three-dimensional structural scaffold of the enzyme. To test the theory of conformational flexibility of enzyme active site, crystal structures were perturbed by soaking in low concentration guanidine hydrochloride solutions. It was found that many lysozyme crystals tested could still diffract until the concentration of guanidine hydrochloride reached 3 M. It was also found that the B factors averaged over individually collected data sets were more accurate. Thus it suggested that accurate measurement of crystal temperature factors could be achieved for medium-high or even medium resolution crystals by averaging over multiple data sets. Furthermore, we found that the correctly predicted active sites included not only the more flexible residues, but also some more rigid residues. Both the flexible and the rigid residues in the active site played an important role in forming the active site residue network, covering the majority of the substrate binding residues. Therefore, this experimental prediction method may be useful for characterizing the binding site and the function of a protein, such as drug targeting. [ABSTRACT FROM AUTHOR]