Electron-phonon interaction in the normal and superconducting states of MgB2

作者：Yong Kong, O. V. Dolgov, Ove Jepsen, O. K. Andersen · 发表于：Physical review. B, Condensed matter · 年份：2001 · DOI：10.1103/physrevb.64.020501 · 被引用次数：556 · 研究领域：Superconductivity in MgB2 and Alloys、Iron-based superconductors research、Physics of Superconductivity and Magnetism

For the 40 K superconductor ${\mathrm{MgB}}_{2},$ we have calculated the electronic and phononic structures and the electron-phonon (e-ph) interaction throughout the Brillouin zone ab initio. In contrast to the isoelectronic graphite, ${\mathrm{MgB}}_{2}$ has holes in the bonding \ensuremath{\sigma} bands, which contribute $42%$ to the density of states: $N(0)=0.355$ $\mathrm{states}/({\mathrm{MgB}}_{2})(\mathrm{eV})(\mathrm{spin}).$ The total interaction strength, $\ensuremath{\lambda}=0.87$ and ${\ensuremath{\lambda}}_{\mathrm{tr}}=0.60,$ is dominated by the coupling of the \ensuremath{\sigma} holes to the bond-stretching optical phonons with wave numbers in a narrow range around $590 {\mathrm{cm}}^{\ensuremath{-}1}.$ Like the holes, these phonons are quasi-two-dimensional and have wave vectors close to $\ensuremath{\Gamma}A,$ where their symmetry is E. The \ensuremath{\pi} electrons contribute merely 0.25 to \ensuremath{\lambda} and to ${\ensuremath{\lambda}}_{\mathrm{tr}}.$ With Eliashberg theory we evaluate the normal-state resistivity, the density of states in the superconductor, and the B-isotope effect on ${T}_{c}$ and ${\ensuremath{\Delta}}_{0},$ and find excellent agreement with experiments, when available. ${T}_{c}=40 \mathrm{K}$ is reproduced with ${\ensuremath{\mu}}^{*}=0.10$ and $2{\ensuremath{\Delta}}_{0}{/k}_{B}{T}_{c}=3.9.$ ${\mathrm{MgB}}_{2}$ thus seems to be an intermediate-coupling e-ph pairing s-wave superconductor.