Anisotropic superconducting gaps in YNi${}_2$B${}_2$C: A first-principles investigation

Abstract

We calculate superconducting gaps and quasiparticle density of states of YNi${}_2$B${}_2$C in the framework of the density functional theory for superconductors to investigate the origin of a highly anisotropic superconducting gaps in this material. Calculated phonon frequencies, the quasiparticle density of states, and the transition temperature show good agreement with experimental results. From our calculation of superconducting gaps and orbital character analysis, we establish that the orbital character variation of the Fermi surface is the key factor of the anisotropic gap. Since the electronic states that consist of mainly Ni $3d$ orbitals couple weakly with phonons, the superconducting gap function is suppressed for the corresponding states, which results in the anisotropy observed in the experiments. These results are hints to increase the transition temperature of materials in the borocarbide family.

31 pages, 16 figures

References in corpus (3)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Improved tetrahedron method for the Brillouin-zone integration applicable to response functions
• Phonons and electron-phonon coupling in the phonon-mediated superconductor YNi2B2C

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