Anisotropic superconducting and normal state magnetic properties of single crystals of RNi2B2C compounds (R = Y, Gd, Dy, Ho, Er, and Tm)

The interaction of superconductivity with magnetism has been one of the most interesting and important phenomena in solid state physics since the 1950\u27s when small amounts of magnetic impurities were incorporated in superconductors. The discovery of the magnetic superconductors RNi[subscript]2B[subscript]2C (R = rare earth, Y) offers a new system to study this interaction. The wide ranges of superconducting transition (T[subscript] c) and antiferromagnetic (AF) ordering temperatures (T[subscript] N) ( 0 K ≤ T[subscript]c ≤ 16 K, 0 K ≤ T[subscript]N ≤ 20 K) give a good opportunity to observe a variety of interesting phenomena;Single crystals of high quality with appropriate size and mass are crucial in examining the anisotropic intrinsic properties. Single crystals have been grown successfully by an unusual high temperature flux method and characterized thoroughly by X-ray, electrical transport, magnetization, neutron scattering, scanning electron microscopy, and other measurements. Superconductivity in single crystal DyNi[subscript]2B[subscript]2C is discovered and exhibits T[subscript]c \u3c T[subscript]N, which is the first observation of this ordering of transition temperatures in a crystallographically ordered compound except heavy fermion superconductors. The crystals reveal highly anisotropic behavior for R = Tb, Dy, Ho, Er, and Tm, but not for Gd, in the temperature dependent normal state magnetic susceptibility for 2 K ≤ T ≤ 300 K, which implies that the crystalline electric field (CEF) interaction plays a key role in the anisotropy. Nice fitting of anisotropic magnetization data of HoNi[subscript]2B[subscript]2C was achieved by a detailed CEF analysis, and CEF parameters (B[subscript]sp n m), energy levels, and corresponding eigenstates were determined. The determined data can be used for analyzing magnetism and superconductivity below T[subscript] N and T[subscript] c. The long range magnetic ordering in the magnetic sublattices, investigated by magnetization, specific heat, and magnetoresistivity, are found to be sensitive to the orientation of the applied field. Superconductivity and local magnetic moment ordering coexist below T[subscript] N for R = Dy, Ho, Er, and Tm. The interplay between the two phenomena appears in anisotropic reentrant behavior of the superconductivity and anomalous suppression of the upper critical field (H[subscript] c2)

Structural characterization and phase transformations in metal oxide fi lms synthesized by Successive Ionic Layer Deposition (SILD) method

In this paper the peculiarities of phase composition and morphology of metal oxides synthesized by successive ionic layer deposition (SILD) method are discussed. The main attention is focused on SnO2–based metal oxides, which are promising materials for gas sensor applications. FTIR spectroscopy has shown that the precipitates of metal oxides, deposited by SILD method, are hydroxide, peroxide or hydrated metal oxide-based compounds. After annealing at relatively low temperatures (200–400°C) these compounds release both water and peroxide oxygen and transform into corresponding oxides. According to XRD, SEM and AFM measurements it was confi rmed that deposited fi lms had fi ne-dispersed structures. Only after annealing at Tan>500°C, XRD diffraction peaks, typical for nanocrystalline material with grain size < 6–8 nm, were observed. High roughness and high degree of agglomeration are important peculiarities of metal oxides deposited by SILD. Metal oxide fi lms consist of spherical agglomerates. Degree of agglomeration of the fi lms and agglomerate size could be controlled. It was found that introduction of various additives in the solution for SILD could sufficiently change the microstructure of synthesized metal oxides

Observation of warping effects in the band and angular momentum structures of topological insulator Bi2Te3

We performed angle resolved photoemission (ARPES) experiments on Bi2Te3 with circularly polarized light. ARPES data show very strong circular dichroism, indicating existence of orbital angular momentum (OAM). Moreover, the alignment of OAM is found to have a strong binding energy dependence. Such energy dependence comes from a relatively strong band warping effect in Bi2Te3 compared to Bi2Se3. OAM close to Dirac point has an ideal chiral structure (sin ?) without out-of-plane component. Warping effect comes in as the binding energy decreases and circular dichroism along a constant energy contour can no longer be explained by a simple sin? function but requires a sin3? term. When the warping effect becomes even stronger near the Fermi energy, circular dichroism gains an additional sin6? term. Such behavior is found to be compatible with the theoretically predicted OAM structure

Correlation between Geometrically induced oxygen octahedral tilts and multiferroic behaviors in BiFeO3 films

The equilibrium position of atoms in a unit cell is directly connected to crystal functionalities, e.g., ferroelectricity, ferromagnetism, and piezoelectricity. The artificial tuning of the energy landscape can involve repositioning atoms as well as manipulating the functionalities of perovskites (ABO3), which are good model systems to test this legacy. Mechanical energy from external sources accommodating various clamping substrates is utilized to perturb the energy state of perovskite materials fabricated on the substrates and consequently change their functionalities; however, this approach yields undesired complex behaviors of perovskite crystals, such as lattice distortion, displacement of B atoms, and/or tilting of oxygen octahedra. Owing to complimentary collaborations between experimental and theoretical studies, the effects of both lattice distortion and displacement of B atoms are well understood so far, which leaves us a simple question: Can we exclusively control the positions of oxygen atoms in perovskites for functionality manipulation? Here the artificial manipulation of oxygen octahedral tilt angles within multiferroic BiFeO3 thin films using strong oxygen octahedral coupling with bottom SrRuO3 layers is reported, which opens up new possibilities of oxygen octahedral engineering

Bulk transport paths through defects in floating zone and Al flux grown SmB6

We investigate the roles of disorder on low-temperature transport in SmB6 crystals grown by both the Al flux and floating zone methods. We used the inverted resistance method with Corbino geometry to investigate whether low-temperature variations in the standard resistance plateau arise from a surface or a bulk channel in floating zone samples. The results show significant sample-dependent residual bulk conduction, in contrast to smaller amounts of residual bulk conduction previously observed in Al flux grown samples with Sm vacancies. We consider hopping in an activated impurity band as a possible source for the observed bulk conduction, but it is unlikely that the large residual bulk conduction seen in floating zone samples is solely due to Sm vacancies. We therefore propose that one-dimensional defects, or dislocations, contribute as well. Using chemical etching, we find evidence for dislocations in both flux and floating zone samples, with higher dislocation density in floating zone samples than in Al flux grown samples. In addition to the possibility of transport through one dimensional dislocations, we also discuss our results in the context of recent theoretical models of SmB6

Anisotropic superconducting and normal state magnetic properties of single crystals of RNi2B2C compounds (R = Y, Gd, Dy, Ho, Er, and Tm)

The interaction of superconductivity with magnetism has been one of the most interesting and important phenomena in solid state physics since the 1950's when small amounts of magnetic impurities were incorporated in superconductors. The discovery of the magnetic superconductors RNi[subscript]2B[subscript]2C (R = rare earth, Y) offers a new system to study this interaction. The wide ranges of superconducting transition (T[subscript] c) and antiferromagnetic (AF) ordering temperatures (T[subscript] N) ( 0 K ≤ T[subscript]c ≤ 16 K, 0 K ≤ T[subscript]N ≤ 20 K) give a good opportunity to observe a variety of interesting phenomena;Single crystals of high quality with appropriate size and mass are crucial in examining the anisotropic intrinsic properties. Single crystals have been grown successfully by an unusual high temperature flux method and characterized thoroughly by X-ray, electrical transport, magnetization, neutron scattering, scanning electron microscopy, and other measurements. Superconductivity in single crystal DyNi[subscript]2B[subscript]2C is discovered and exhibits T[subscript]c < T[subscript]N, which is the first observation of this ordering of transition temperatures in a crystallographically ordered compound except heavy fermion superconductors. The crystals reveal highly anisotropic behavior for R = Tb, Dy, Ho, Er, and Tm, but not for Gd, in the temperature dependent normal state magnetic susceptibility for 2 K ≤ T ≤ 300 K, which implies that the crystalline electric field (CEF) interaction plays a key role in the anisotropy. Nice fitting of anisotropic magnetization data of HoNi[subscript]2B[subscript]2C was achieved by a detailed CEF analysis, and CEF parameters (B[subscript]sp n m), energy levels, and corresponding eigenstates were determined. The determined data can be used for analyzing magnetism and superconductivity below T[subscript] N and T[subscript] c. The long range magnetic ordering in the magnetic sublattices, investigated by magnetization, specific heat, and magnetoresistivity, are found to be sensitive to the orientation of the applied field. Superconductivity and local magnetic moment ordering coexist below T[subscript] N for R = Dy, Ho, Er, and Tm. The interplay between the two phenomena appears in anisotropic reentrant behavior of the superconductivity and anomalous suppression of the upper critical field (H[subscript] c2).</p

Branching Ratio Study of Resonant X-Ray Scattering Intensities of GdB4

Resonant X-ray scattering measurements for a GdB4 single crystal have been carried out at Gd L-3- and L-2-edges. Branching ratios between x-ray scattering intensities at two x-ray energies are different for resonance peaks. Their analysis shows different anisotropic characters of 5d electron states of Gd ions corresponding to the peaks.11sciescopuskc

Importance of charge fluctuations for the topological phase in SmB6

Typical Kondo insulators (KIs) can have a nontrivial Z2 topology because the energy gap opens at the Fermi energy (EF) by a hybridization between odd- and even-parity bands. SmB6 deviates from such KI behavior, and it has been unclear how the insulating phase occurs. Here, we demonstrate that charge fluctuations are the origin of the topological insulating phase in SmB6. Our angle-resolved photoemission spectroscopy results reveal that with decreasing temperature the bottom of the d-f hybridized band at the X̄ point, which is predicted to have odd parity and is required for a topological phase, gradually shifts from below to above EF. We conclude that SmB6 is a charge-fluctuating topological insulator. © 2014 American Physical Society.141411sciescopu