Epitaxial growth and the magnetic properties of orthorhombic YTiO3 thin films

High-quality YTiO3 thin films were grown on LaAlO3 (110) substrates at low oxygen pressures (<10-8 Torr) using pulsed laser deposition. The in-plane asymmetric atomic arrangements at the substrate surface allowed us to grow epitaxial YTiO3 thin films, which have an orthorhombic crystal structure with quite different a- and b-axes lattice constants. The YTiO3 film exhibited a clear ferromagnetic transition at 30 K with a saturation magnetization of about 0.7 uB/Ti. The magnetic easy axis was found to be along the [1-10] direction of the substrate, which differs from the single crystal easy axis direction, i.e., [001].Comment: 14 pages, 4 figure

Scanning tunneling spectroscopic studies of the pairing state of cuprate superconductors

Quasiparticle tunneling spectra of both hole-doped (p-type) and electron-doped (n-type) cuprates are studied using a low-temperature scanning tunneling microscope. The results reveal that neither the pairing symmetry nor the pseudogap phenomenon is universal among all cuprates, and that the response of n-type cuprates to quantum impurities is drastically different from that of the p-type cuprates. The only ubiquitous features among all cuprates appear to be the strong electronic correlation and the nearest-neighbor antiferromagnetic Cu2+-Cu2+ coupling in the CuO2 planes

New heat treatment to prepare high quality polycrystalline and single crystal MgB2 in single process

We report here on a new heat treatment to prepare both dense polycrystalline and single crystal MgB2 high quality samples in one single process. Resistivity measurements for polycrystalline part of the sample gives a residual resistivity ratio RRR=16.6 and a very low normal state resistivity rho(40K)= 0.28 microOhmcm. Both SEM and SQUID study on polycrystals reveal the high quality, dense character and well coupling of grain boundaries. On the other hand, the high quality single crystals have a unique shape that resembles the hexagonal crystal structure. SQUID measurements reveals very weak flux pinning character implying our single crystals to be very clean. In this study, we conclude that heat treatment is playing a major rule on the characteristics of both polycrystalline and single crystal MgB2. Samples are thoroughly characterized by x-ray, resistivity, dc SQUID and SEM

Microstructure and pinning properties of hexagonal-disc shaped single crystalline MgB2

We synthesized hexagonal-disc-shaped MgB2 single crystals under high-pressure conditions and analyzed the microstructure and pinning properties. The lattice constants and the Laue pattern of the crystals from X-ray micro-diffraction showed the crystal symmetry of MgB2. A thorough crystallographic mapping within a single crystal showed that the edge and c-axis of hexagonal-disc shape exactly matched the (10-10) and the (0001) directions of the MgB2 phase. Thus, these well-shaped single crystals may be the best candidates for studying the direction dependences of the physical properties. The magnetization curve and the magnetic hysteresis for these single crystals showed the existence of a wide reversible region and weak pinning properties, which supported our single crystals being very clean.Comment: 5 pages, 3 figures. submitted to Phys. Rev.

On some notions of good reduction for endomorphisms of the projective line

Let $\Phi$ be an endomorphism of \SR(\bar{\Q}), the projective line over the algebraic closure of \Q, of degree $\geq2$ defined over a number field $K$. Let $v$ be a non-archimedean valuation of $K$. We say that $\Phi$ has critically good reduction at $v$ if any pair of distinct ramification points of $\Phi$ do not collide under reduction modulo $v$ and the same holds for any pair of branch points. We say that $\Phi$ has simple good reduction at $v$ if the map $\Phi_v$, the reduction of $\Phi$ modulo $v$, has the same degree of $\Phi$. We prove that if $\Phi$ has critically good reduction at $v$ and the reduction map $\Phi_v$ is separable, then $\Phi$ has simple good reduction at $v$.Comment: 15 page

The Staudinger Ligation

While the Staudinger reaction has first been described a hundred years ago in 1919, the ligation reaction became one of the most important and efficient bioconjugation techniques in the 1990s and this century. It holds the crucial characteristics for bioorthogonal chemistry: biocompatibility, selectivity, and a rapid and high-yielding turnover for a wide variety of applications. In the past years, it has been used especially in chemical biology for peptide/protein synthesis, posttranslational modifications, and DNA labeling. Furthermore, it can be used for cell-surface engineering, development of microarrays, and drug delivery systems. However, it is also possible to use the reaction in synthetic chemistry for general formation of amide bonds. In this review, the three major types, traceless and nontraceless Staudinger Ligation as well as the Staudinger phosphite reaction, are described in detail. We will further illustrate each reaction mechanism and describe characteristic substrates, intermediates, and products. In addition, not only its advantages but also stereochemical aspects, scope, and limitations, in particular side reactions, are discussed. Finally, the method is compared to other bioorthogonal labeling methods