Substitutional doping of Cu in diamond: Mott physics with pp orbitals

Discovery of superconductivity in the impurity band formed by heavy doping of boron into diamond (C:B) as well as doping of boron into silicon (Si:B) has provided a rout for the possibility of new families of superconducting materials. Motivated by the special role played by copper atoms in high temperature superconducting materials where essentially Cu $d$ orbitals are responsible for a variety of correlation induced phases, in this paper we investigate the effect of substitutional doping of Cu into diamond. Our extensive first principle calculations averaged over various geometries based on density functional theory, indicates the formation of a mid-gap band, which mainly arises from the $t_{2g}$ and $4p$ states of Cu. For impurity concentrations of more than $\sim 1$2p$bands of neighboring carbon atoms can be ignored. Based on our detailed analysis, we suggest a two band model for the mid-gap states consisting of a quarter-filled hole like$t_{2g}$band, and a half-filled band of$4p$states. Increasing the concentration of the Cu impurity beyond$\sim 5%, completely closes the spectral gap of the host diamond.Comment: 5 figure

Effect of the Surface on the Electron Quantum Size Levels and Electron g-Factor in Spherical Semiconductor Nanocrystals

The structure of the electron quantum size levels in spherical nanocrystals is studied in the framework of an eight--band effective mass model at zero and weak magnetic fields. The effect of the nanocrystal surface is modeled through the boundary condition imposed on the envelope wave function at the surface. We show that the spin--orbit splitting of the valence band leads to the surface--induced spin--orbit splitting of the excited conduction band states and to the additional surface--induced magnetic moment for electrons in bare nanocrystals. This additional magnetic moment manifests itself in a nonzero surface contribution to the linear Zeeman splitting of all quantum size energy levels including the ground 1S electron state. The fitting of the size dependence of the ground state electron g factor in CdSe nanocrystals has allowed us to determine the appropriate surface parameter of the boundary conditions. The structure of the excited electron states is considered in the limits of weak and strong magnetic fields.Comment: 11 pages, 4 figures, submitted to Phys. Rev.

Superhard Phases of Simple Substances and Binary Compounds of the B-C-N-O System: from Diamond to the Latest Results (a Review)

The basic known and hypothetic one- and two-element phases of the B-C-N-O system (both superhard phases having diamond and boron structures and precursors to synthesize them) are described. The attention has been given to the structure, basic mechanical properties, and methods to identify and characterize the materials. For some phases that have been recently described in the literature the synthesis conditions at high pressures and temperatures are indicated.Comment: Review on superhard B-C-N-O phase

High-Pressure, High-Temperature Synthesis of Nanodiamond from Adamantane

International audienceAbstract— We have studied the high-pressure, high-temperature behavior of adamantane (C10H16) and the associated formation of diamond nano- and microcrystals. Diamond microcrystals have been synthesized at a pressure of 8 GPa and temperatures above 1300–1400°C, whereas large-scale synthesis of nanodiamond has been carried out at higher pressures, near 9.4 GPa, in the narrow temperature range 1250–1330°C. Our experimental data suggest that diamond microcrystals are formed in a fluid growth medium as a result of recrystallization of graphite, an intermediate carbonization product, and that nanodiamond formation is a direct result of adamantane carbonization. © 2019, Pleiades Publishing, Ltd

High-Pressure Synthesis of Boron-Doped Ultrasmall Diamonds from an Organic Compound

International audienceThe first application of the high-pressure-high-temperature (HPHT) technique for direct production of doped ultrasmall diamonds starting from a one-component organic precursor is reported. Heavily boron-doped diamond nanoparticles with a size below 10 nm are produced by HPHT treatment of 9-borabicyclo [3,3,1]nonane dimer molecules. © 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

High-pressure synthesis and characterization of superconducting boron-doped diamond

Microcrystalline powders of boron-doped diamond were produced in the C–H–B system under a pressure of 8 GPa and at a temperature of more than 2000 K. The presence of boron in the C–B–H system was shown to decrease the temperature–pressure parameters for diamond synthesis compared with those for the binary C–H system (naphthalene). A decrease in the parameters for synthesis in the system with boron may be due to the formation of graphite with less perfect crystal structure during an intermediate stage of diamond formation. Superconducting diamond microcrystals are synthesized in the C–H–B system with boron content of about 5–10 at% in a mixture with naphthalene. Superconductivity below 3.5 K in boron-doped diamond powder is detected in AC magnetic susceptibility measurements

Superconductivity - PuCoGa5 to Diamond

We review experimental and theoretical studies of two new superconductors, B-doped diamond and PuMGa5 (MZCo, Rh). The pairing mechanism responsible for superconductivity in these materials remains ambiguous. Though electron phonon pairing in B-doped diamond is a viable candidate, the Coulomb interaction in this poor metal must be understood before definitive conclusions can be drawn. The 5f electrons of Pu appear to play a decisive, but uncertain, role in producing superconductivity in PuMGa5. The possibility of magnetically mediated superconductivity in these materials is suggested by analogy to the evolution of superconductivity and magnetism in isostructural Ce- and actinide-based materials.JRC.E.6-Actinides researc

High-Pressure, High-Temperature Synthesis of Nanodiamond from Adamantane

Abstract— We have studied the high-pressure, high-temperature behavior of adamantane (C10H16) and the associated formation of diamond nano- and microcrystals. Diamond microcrystals have been synthesized at a pressure of 8 GPa and temperatures above 1300–1400°C, whereas large-scale synthesis of nanodiamond has been carried out at higher pressures, near 9.4 GPa, in the narrow temperature range 1250–1330°C. Our experimental data suggest that diamond microcrystals are formed in a fluid growth medium as a result of recrystallization of graphite, an intermediate carbonization product, and that nanodiamond formation is a direct result of adamantane carbonization. © 2019, Pleiades Publishing, Ltd

Superconductivity: PuCoGa5 to Diamond.

Abstract not availableJRC.E-Institute for Transuranium Elements (Karlsruhe