First principles electronic structure of spinel LiCr2O4: A possible half-metal?

We have employed first-principles electronic structure calculations to examine the hypothetical (but plausible) oxide spinel, LiCr2O4 with the d^{2.5} electronic configuration. The cell (cubic) and internal (oxygen position) structural parameters have been obtained for this compound through structural relaxation in the first-principles framework. Within the one-electron band picture, we find that LiCr2O4 is magnetic, and a candidate half-metal. The electronic structure is substantially different from the closely related and well known rutile half-metal CrO2. In particular, we find a smaller conduction band width in the spinel compound, perhaps as a result of the distinct topology of the spinel crystal structure, and the reduced oxidation state. The magnetism and half-metallicity of LiCr2O4 has been mapped in the parameter space of its cubic crystal structure. Comparisons with superconducting LiTi2O4 (d^{0.5}), heavy-fermion LiV2O4 (d^{1.5}) and charge-ordering LiMn2O4 (d^{3.5}) suggest the effectiveness of a nearly-rigid band picture involving simple shifts of the position of E_F in these very different materials. Comparisons are also made with the electronic structure of ZnV2O4 (d^{2}), a correlated insulator that undergoes a structural and antiferromagnetic phase transition.Comment: 9 pages, 7 Figures, version as published in PR

Pump-probe method for investigating laser ablation and optical damage threshold mechanisms in optical materials

The method developed for investigating laser-surface interactions by measuring the ratio of ablation threshold fluence for a pair of picosecond or subpicosecond laser pulses to the single-pulse ablation threshold, was applied to ZnS (wurtzite)and to the borosilicate glass BK-7. Each sample was exposed to 1000 pulse pairs of 580-nm dye laser radiation. For ZnS, linear absorption was found to be the cause of the cumulative optical damage mechanism; the linear absorption is probably caused by defects states (such as color centers) near the surface. The nonlinear behavior of BK-7 suggests that avalanche ionization could be the damage mechanism. Results for both materials show that intrinsic multiphoton absorption mechanisms may not be significant indicators of optical damage mechanisms even when they lead to very high free-carrier densities and energy absorption

MATERIALS FOR DIODE PUMPED SOLID STATE LASERS

The advantages of semiconductor diode lasers and laser arrays as pump sources for solid state lasers are reviewed. The properties desired for solid state laser media for various diode pumping applications are discussed, and the characteristics of several promising media are summarized

Emission cross sections and energy extraction for the mid-infrared transitions of Er, Tm, and Ho in oxide and fluoride crystals

Emission cross sections have been measured for the transitions between the two lowest spin orbit multiplets of Er, Tm, and Ho in several fluoride and oxide crystals. Properties affecting energy extraction efficiency are summarized and pulsed extraction performance is calculated for several of these quasi-three-level laser media. 4 refs., 9 figs

Soft x-ray emission studies of the electronic structure in silicon nanoclusters

Density of states changes in the valence and conduction band of silicon nanoclusters were monitored using soft x-ray emission and absorption spectroscopy as a function of cluster size. a progressive increase in the valence band edge toward lower energy is found fro clusters with decreasing diameters. A similar but smaller shift is observed in the near-edge x-ray absorption data of the silicon nanoclusters