The anisotropy gamma of the superconducting state high quality single crystals MgB2 was determined, using torque magnetometry with two different methods. upper critical field found to be temperature dependent, decreasing from approximately 6 at 15 K 2.8 35 K. Reversible data near T(c) reveal a dependent anisotropy, increasing nearly linearly equal 2 in zero 3.7 10 kOe. unusual dependence is true bulk property and can explained by nonlocal effects anisotropic pairing and/or k--> effective mass tensor.

We report scanning tunneling spectroscopy imaging of the vortex lattice in single crystalline MgB2. By parallel to c axis, a superconducting gap (Delta=2.2 meV) associated with pi band is observed. The vortices have large core size compared estimates based on H(c2) and show an absence localized states core. Furthermore, superconductivity between rapidly suppressed by applied field. These results suggest that is, at least partially, induced intrinsically sigma band.

We present the results of first directional point-contact spectroscopy experiments in high-quality ${\mathrm{M}\mathrm{g}\mathrm{B}}_{2}$ single crystals. Because directionality current injection into samples, application a magnetic field allowed us to separate contributions $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ bands total conductance our point contacts. By using this technique, we were able obtain temperature dependency each gap independent other. The consequent, strong reduction...

Growth of carbon substituted magnesium diboride Mg(B1-xCx)2 single crystals with 0<x<0.15 is reported and the structural, transport, magnetization data are presented. The superconducting transition temperature decreases monotonically increasing content in full investigated range substitution. By adjusting nominal composition, Tc can be tuned a wide between 10 39 K. Simultaneous introduction disorder by substitution significant increase upper critical field Hc2 observed. Comparing...

The first direct observation of charge order Ni(3+delta(')) and Ni(3-delta) by resonant x-ray scattering experiments in an epitaxial film NdNiO3 is reported. A quantitative value delta+delta(') = (0.45 +/- 0.04)e was obtained. temperature dependence the deviates significantly from those magnetic moment crystallographic structure. This might be indication a difference their fluctuation time scales. These observations are discussed terms temperature-driven metal-insulator transition RNiO3 family.

We measure phonon dispersion and linewidth in a single crystal of MgB2 along the Gamma-A, Gamma-M, A-L directions using inelastic x-ray scattering. use density functional theory to compute effect both electron-phonon coupling anharmonicity on linewidth, obtaining excellent agreement with experiment. Anomalous broadening E(2g) mode is found all Gamma-A. The dominant contribution always coupling.

The ab-plane thermal conductivity $\kappa$ of single-crystalline hexagonal MgB_2 has been measured as a function magnetic field H with orientations both parallel and perpendicular to the c-axis at temperatures between 0.5 300 K. In mixed state, $\kappa(H)$ constant reveals features that are not typical for common type-II superconductors. observed behavior may be associated field-induced reduction two superconducting energy gaps, significantly different in magnitude. A nonlinear temperature...

We report on measurements of the magnetic moment in superconducting MgB2 single crystals. find \mu_0H_{c2}^c(0) = 3.2 T, \mu_0H_{c2}^{ab}(0) 14.5 \gamma 4.6, \mu_0H_c(0) 0.28 and \kappa(T_c) 4.7. The standard Ginzburg-Landau London model relations lead to a consistent data set indicate that is clean limit superconductor intermediate coupling strength with very pronounced anisotropy effects.

The bulk upper critical field ${H}_{c2}(T)$ of superconducting ${\mathrm{MgB}}_{2}$ and its anisotropy are established by analyzing experimental data on the temperature magnetic-field dependences $\mathrm{ab}$-plane thermal conductivity a single-crystalline sample in external magnetic fields oriented both parallel ${(H}_{c2}^{c})$ perpendicular ${(H}_{c2}^{\mathrm{ab}})$ to c axis hexagonal lattice. From numerical fits we deduce ratio...

Single crystals of ${\mathrm{Mg}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}{\mathrm{B}}_{2}$ have been grown at a pressure 30 kbar using the cubic anvil technique. Precipitation free with $x&lt;0.1$ were obtained as result optimization an already developed ${\mathrm{MgB}}_{2}$ crystal growth procedure. A systematic decrease $c$-axis lattice constant increasing Al content, when $a$-axis is practically unchanged, was observed. Variation critical temperature on content in found to be slightly...

We report measurements of the temperature-dependent anisotropies (gamma(lambda) and gamma(xi)) both London penetration depth lambda upper critical field MgB2. Data for gamma(lambda)=lambda(c)/lambda(a) was obtained from lambda(a) lambda(c) on a single crystal sample using tunnel diode oscillator technique. gamma(xi)=H(perp)c(c2)/H(||c)(c2) deduced field-dependent specific heat same sample. Gamma(lambda) gamma(xi) have opposite temperature dependencies, but close to T(c) tend common value...

The crystal and magnetic structures of brownmillerite-like Sr(2)Co(1.2)Ga(0.8)O(5) with a stable Co(3+) oxidation state at both octahedral tetrahedral sites are refined using neutron powder diffraction data collected 2 K (S.G. Icmm, = 5.6148(6) Å, b 15.702(2) c 5.4543(6) Å; R(wp) 0.0339, R(p) 0.0443, χ(2) 0.775). very large tetragonal distortion CoO(6) octahedra (1.9591(4) Å for Co-O(eq) 2.257(6) Co-O(ax)) could be beneficial the stabilization long-sought intermediate-spin in perovskite-type...

We present neutron scattering from the flux line lattice (FLL) in MgB2. Between 0.5 and 0.9 T FLL undergoes a 30 degrees reorientation, simultaneously scattered intensity falls sharply consistent with weaker superconducting pi band being suppressed increasing field. speculate that sigma bands favor different orientations, reorientation is driven by suppression of band. When c axis crystal rotated 45 to applied field penetration depth anisotropy could be measured, rises both as function temperature.

Single crystals of MgB2 with a size up to 1.5 × 0.9 0.2 mm3 have been grown high pressure cubic anvil technique. The crystal growth process is very peculiar and involves an intermediate nitride, namely MgNB9. BN grow simultaneously by peritectic decomposition Magnetic measurements SQUID magnetometry in fields 1–5 Oe show sharp transitions the superconducting state at 37–38.6 K width ∼0.5 K. quality allowed accurate determination magnetic, transport (electric heat) optical properties as well...

To assess electron correlation and electron-phonon coupling in the recently discovered $\ensuremath{\beta}$-pyrochlores $\mathrm{K}{\mathrm{Os}}_{2}{\mathrm{O}}_{6}$ $\mathrm{Rb}{\mathrm{Os}}_{2}{\mathrm{O}}_{6}$, we have performed specific heat measurements magnetic fields up to $14\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. We present data from high-quality single-crystalline $\mathrm{K}{\mathrm{Os}}_{2}{\mathrm{O}}_{6}$, showing that is a strong-coupling superconductor with parameter...

We report on the effects of neutron irradiation in superconducting ${\mathrm{MgB}}_{2}$ single crystals. Transmission electron microscopy investigations reveal large radiation-induced defects with dimensions comparable to coherence length. Accordingly, measurements magnetic moment show pronounced modifications reversible and irreversible properties after irradiation. In particular, we concentrate emergence a second peak (fishtail), situated near ${H}_{c2}$ at low fluences, but extending over...

We report the basic thermodynamic properties of geometrically frustrated $\ensuremath{\beta}$-pyrochlore bulk superconductor ${\mathrm{RbOs}}_{2}{\mathrm{O}}_{6}$ with a critical temperature ${T}_{c}=6.4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Specific heat measurements are performed in magnetic fields up to $12\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. The electronic density states at Fermi level normal state results...

We report the results of first directional point-contact measurements in Mg(B_{1-x}C_{x})_2 single crystals with 0.047 <= x 0.132. The two-gap superconductivity typical MgB_2 persists up to x=0.105. In this region, values gaps Delta_{sigma} and Delta_{pi} were determined by fitting Andreev-reflection conductance curves a two-band Blonder-Tinkham-Klapwijk (BTK) model, confirmed single-band BTK fit sigma- pi-band conductances, separated means magnetic field. At x=0.132, when T_{c}=19 K, we...

We present the results of measurements dc-magnetic susceptibility $\ensuremath{\chi}(T)$ and ${}^{23}\mathrm{Na}$-NMR response ${\mathrm{Na}}_{0.70}{\mathrm{CoO}}_{2}$ at temperatures between 50 340 K. The data suggest that for $T>75\mathrm{K},$ Co ions adopt an effective configuration ${\mathrm{Co}}^{3.4+}.$ reveals pronounced anomalies near 250 295 K, but no evidence magnetic phase transitions is found in $\ensuremath{\chi}(T).$ Our onset a dramatic change $3d$-electron spin dynamics This...

Single crystals of KOs2O6 have been grown in a sealed quartz ampoule. Detailed single crystal X-ray diffraction studies at room temperature show Bragg peaks that violate Fd-3m symmetry. With comparative structure refinement the is identified as non-centrosymmetric (F-43m). Compared to ideal beta-pyrochlore lattice (Fd-3m), both Os tetrahedral and O octahedral network exhibit breathing mode like volume changes accompanied by strong anisotropic character K channels. The metallic conductivity...

We present the anisotropic optical conductivity of MgB$_{2}$ between 0.1 and 3.7 eV at room temperature obtained on single crystals different purity by spectroscopic ellipsometry reflectance measurements. The bare (unscreened) plasma frequency $\omega_{p}$ is almost isotropic equal to 6.3 eV, which contrasts some earlier reports a very small value $\omega_{p}$. data suggests that $\sigma$-bands are characterized stronger electron-phonon coupling $\lambda_ {tr}$ but smaller impurity...