We discovered that perovskite (Ba,La)SnO3 can have excellent carrier mobility even though its band gap is large. The Hall mobility of Ba0.98La0.02SnO3 crystals with the n-type carrier concentration of sim 8-10times10 19 cm-3 is found to be sim 103 cm
2 V-1s-1 at room temperature, and the precise measurement of the band gap Delta of a BaSnO3 crystal shows Delta=4.05 eV, which is significantly larger than those of other transparent conductive oxides. The high mobility with a wide band gap indicates that (Ba,La)SnO3 is a promising candidate for transparent conductor applications and also epitaxial all-perovskite multilayer devices.
Competition with magnetism is at the heart of high temperature superconductivity, most intensely felt near a vortex core. To investigate vortex magnetism we have developed a spatially resolved probe using nuclear magnetic resonance. Our spin-lattice-
relaxation spectroscopy is spatially resolved both within a conduction plane as well as from one plane to another. With this approach we have found a spin-density wave associated with the vortex core in Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$, which is expected from scanning tunneling microscope observations of checkerboard patterns in the local density of electronic states.[1] We determine both the spin-modulation amplitude and decay length from the vortex core in fields up to H=30 T.
It has been predicted that superconducting vortices should be electrically charged and that this effect is particularly enhanced for, high temperature superconductors.cite{kho95,bla96} Hall effectcite{hag91} and nuclear magnetic resonance (NMR) exper
imentscite{kum01} suggest the existence of vortex charging, but the effects are small and the interpretation controversial. Here we show that the Abrikosov vortex lattice, characteristic of the mixed state of superconductors, will become unstable at sufficiently high magnetic field if there is charge trapped on the vortex core. Our NMR measurements of the magnetic fields generated by vortices in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+y}$ single crystalscite{che07} provide evidence for an electrostatically driven vortex lattice reconstruction with the magnitude of charge on each vortex pancake of $mathbf{sim 2}$x$mathbf{10^{-3} e}$, depending on doping, in line with theoretical estimates.cite{kho95,kna05}
The study of abrupt increases in magnetization with magnetic field known as metamagnetic transitions has opened a rich vein of new physics in itinerant electron systems, including the discovery of quantum critical end points with a marked propensity
to develop new kinds of order. However, the electric analogue of the metamagnetic critical end point, a metaelectric critical end point has not yet been realized. Multiferroic materials wherein magnetism and ferroelectricity are cross-coupled are ideal candidates for the exploration of this novel possibility using magnetic-field (emph{H}) as a tuning parameter. Herein, we report the discovery of a magnetic-field-induced metaelectric transition in multiferroic BiMn$_{2}$O$_{5}$ in which the electric polarization (emph{P}) switches polarity along with a concomitant Mn spin-flop transition at a critical magnetic field emph{H}$_{rm c}$. The simultaneous metaelectric and spin-flop transitions become sharper upon cooling, but remain a continuous crossover even down to 0.5 K. Near the emph{P}=0 line realized at $mu_{0}$emph{H}$_{rm c}$$approx$18 T below 20 K, the dielectric constant ($varepsilon$) increases significantly over wide field- and temperature (emph{T})-ranges. Furthermore, a characteristic power-law behavior is found in the emph{P}(emph{H}) and $varepsilon$(emph{H}) curves at emph{T}=0.66 K. These findings indicate that a magnetic-field-induced metaelectric critical end point is realized in BiMn$_2$O$_5$ near zero temperature.
