The escalating and unpredictable cost of oil, the concentration of major oil resources in the hands of a few politically sensitive nations, and the long-term impact of CO 2 emissions on global climate constitute a major challenge for the 21 st century. They also constitute a major incentive to harness alternative sources of energy and means of vehicle propulsion. Today's lithium-ion batteries, although suitable for small-scale devices, do not yet have sufficient energy or life for use in vehicles that would match the performance of internal combustion vehicles. Energy densities 2 and 5 times greater are required to meet the performance goals of a future generation of plug-in hybrid-electric vehicles (PHEVs) with a 40-80 mile all-electric range, and all-electric vehicles (EVs) with a 300-400 mile range, respectively. Major advances have been made in lithium-battery technology over the past two decades by the discovery of new materials and designs through intuitive approaches, experimental and predictive reasoning, and meticulous control of surface structures and chemical reactions. Further improvements in energy density of factors of two to three may yet be achievable for current day lithiumion systems; factors of five or more may be possible for lithium-oxygen systems, ultimately leading to our ability to confine extremely high potential energy in a small volume without compromising safety, but only if daunting technological barriers can be overcome.

Periodic intensity variations in the measured Compton profile anisotropies of ordinary ice Ih correspond to distances of 1.72 and 2.85 Å, which are close to the hydrogen bond length and the nearestneighbor O-O distance, respectively. We interpret this result as direct evidence for the substantial covalent nature of the hydrogen bond. Very good quantitative agreement between the data and a fully quantum mechanical bonding model for ice Ih and the disagreement with a purely electrostatic (classical) bonding model support this interpretation and demonstrate how exquisitely sensitive Compton scattering is to the phase of the electronic wave function. [S0031-9007(98)08227-1]

Determining the nature of the electronic phases that compete with superconductivity in high-transition-temperature (high-T(c)) superconductors is one of the deepest problems in condensed matter physics. One candidate is the 'stripe' phase, in which the charge carriers (holes) condense into rivers of charge that separate regions of antiferromagnetism. A related but lesser known system is the 'spin ladder', which consists of two coupled chains of magnetic ions forming an array of rungs. A doped ladder can be thought of as a high-T(c) material with lower dimensionality, and has been predicted to exhibit both superconductivity and an insulating 'hole crystal' phase in which the carriers are localized through many-body interactions. The competition between the two resembles that believed to operate between stripes and superconductivity in high-T(c) materials. Here we report the existence of a hole crystal in the doped spin ladder of Sr14Cu24O41 using a resonant X-ray scattering technique. This phase exists without a detectable distortion in the structural lattice, indicating that it arises from many-body electronic effects. Our measurements confirm theoretical predictions, and support the picture that proximity to charge ordered states is a general property of superconductivity in copper oxides.

We report resonant inelastic x-ray measurements of insulating La2CuO4 and Sr2CuO2Cl2 taken with the incident energy tuned near the Cu K absorption edge. We show that the spectra are well described in a shakeup picture in 3rd order perturbation theory which exhibits both incoming and outgoing resonances, and demonstrate how to extract a spectral function from the raw data. We conclude by showing q-dependent measurements of the charge transfer gap.PACS numbers: 78.70. Ck, 74.25.Jb Inelastic x-ray scattering (IXS) has shown promise as a practical probe of electronic excitations in condensed matter because of its broad kinematic range and direct coupling to the electron charge. However, since x-rays are strongly absorbed in high density materials, successful applications of the technique have been limited to low-Z systems [1,2,3,4,5].Several recent studies [6,7,8,9], have shown that by that by tuning the incident energy near an x-ray absorption edge a Raman effect could be measured, despite the high absorption, because of the resonant enhancement. These studies have emphasized the role of coulomb interactions in the scattering process. Since it involves coupling between highly excited virtual states and strongly correlated valence states, it is important to characterize the resonance process well for the technique to be useful.With emphasis on systematics, we have measured resonant inelastic x-ray scattering at moderate resolution (∆E=0.9 eV) near the CuK absorption edge in the high-T c parent insulator La 2 CuO 4 (LCO) as a function of incident photon energy. Based on the changes of inelastic intensity and peak position with incident energy we show that the scattering is well described in a "shakeup" picture in 3rd order perturbation threoy [10]. We also present higher resolution measurements (∆E=0.45 eV) on another insulator, Sr 2 CuO 2 Cl 2 (SCOC), as a function of momentum transfer, q, which show some new features, such as the 2 eV optical charge transfer gap.Experiments were carried out at the X21 wiggler line at the National Synchrotron Light Source and the 3ID (SRI-CAT) undulator line at the Advanced Photon Source. At X21 the energy resolution was 0.45 eV and typical count rates were 0.4 Hz. At 3ID with 0.9 eV resolution 9 Hz was typical. The scattered light was collected with a spherical, diced, Ge(733) analyzer and imaged onto a detector. Energy analysis was done by rotating the analyzer and translating the detector in coincidence. The momentum transfer was varied by rotating the entire apparatus around the scattering center (exact experimental geometries are indicated in the figure captions). −1 parallel toĉ. The upper frame shows the raw spectra plotted against transferred energy (curves are offset for clarity). In the lower frame the open and filled circles are the inelastic peak height and position, respectively, plotted against incident energy. The black line is the fluorescence yield which peaks at the Cu1s → 4p energy.The LCO and SCOC crystals were grown by techniques described previously [11,12]....