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Abstract:
Two new ternary compounds TaRuB and NbOsB were synthesized by arc-melting and annealing at 1500–1850 °C. They crystallize in orthorhombic primitive structures with space group Pbam . Magnetic susceptibility, electrical resistivity, and specific heat measurements reveal bulk superconductivity for metallic TaRuB with a IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn001.gif] {{T}_{̑ext{c}}}≈ 4} K. Electronic structure calculations by DFT methods show that 4 d and 5 d transition-metal states dominate the density of states (DOS) at the Fermi level IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn002.gif] {{{E}_{̑ext{F}}}} with a pronounced quasi one-dimensional behaviour along the [0 0 1] direction. Comparison of the calculated DOS at IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn003.gif] {{{E}_{̑ext{F}}}} with specific heat data reveals a moderate electron–phonon coupling. Possible small boron vacancies could significantly reduce the DOS at IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn004.gif] {{{E}_{̑ext{F}}}} , hence decrease IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn005.gif] {{{T}_{̑ext{c}}}} for samples annealed at higher temperatures. For NbOsB, the DOS( IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn006.gif] {{{E}_{̑ext{F}}}} ) is strongly reduced due to an increase of covalent bonding interactions between Os and B. Accordingly, a lower IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn007.gif] {{{T}_{̑ext{c}}}} IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn008.gif] {≈ 1 K is observed.
