Electron-phonon coupling and superconductivity in LiB${}_{1+x}$C${}_{1-x}$

Abstract

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. LiB${}_{1+x}$C${}_{1-x}$), with $x$ 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 LiB${}_{1.8}$C${}_{0.2}$ is a two-gap superconductor, whose superconducting transition temperature, T${}_c$, may exceed the experimentally observed value of MgB${}_2$. Similar to MgB${}_2$, the two-dimensional bond-stretching $E_{2g}$ phonon modes along $\Gamma$-$A$ line have the largest contribution to electron-phonon coupling. More importantly, we find that the first two acoustic phonon modes $B_1$ and $A_1$ around the midpoint of $K$-$\Gamma$ line play a vital role for the rise of T${}_c$ in LiB${}_{1.8}$C${}_{0.2}$. The origin of strong couplings in $B_1$ and $A_1$ 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 $\sigma$-bonding electronic states.

7 pages, 10 figures, accepted for publication in EPL

References in corpus (4)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• EPW: Electron-phonon coupling, transport and superconducting properties using maximally localized Wannier functions
• Evolution of multi-gap superconductivity in the atomically thin limit: Strain-enhanced three-gap superconductivity in monolayer MgB${}_2$
• Prediction of superconducting properties of CaB2 using anisotropic Eliashberg theory

Cited by in corpus (2)

• First-principles prediction of phonon-mediated superconductivity in XBC (X= Mg, Ca, Sr, Ba)
• Properties and challenges of hot-phonon physics in metals: MgB${}_2$ and other compounds