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Electron-phonon coupling and superconductivity in LiBC
By means of the first-principles density-functional theory calculation and
Wannier interpolation, electron-phonon coupling and superconductivity are
systematically explored for boron-doped LiBC (i.e. LiBC), with
between 0.1 and 0.9. Hole doping introduced by boron atoms is treated
through virtual-crystal approximation. For the investigated doping
concentrations, our calculations show the optimal doping concentration
corresponds to 0.8. By solving the anisotropic Eliashberg equations, we find
that LiBC is a two-gap superconductor, whose superconducting
transition temperature, T, may exceed the experimentally observed value of
MgB. Similar to MgB, the two-dimensional bond-stretching
phonon modes along - line have the largest contribution to
electron-phonon coupling. More importantly, we find that the first two acoustic
phonon modes and around the midpoint of - line play a
vital role for the rise of T in LiBC. The origin of strong
couplings in and modes can be attributed to enhanced
electron-phonon coupling matrix elements and softened phonons. It is revealed
that all these phonon modes couple strongly with -bonding electronic
states.Comment: 7 pages, 10 figures, accepted for publication in EP
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