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

Abstract

For the 40 K superconductor MgB2, 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, MgB2 has holes in the bonding σ bands, which contribute 42% to the density of states: N(0)=0.355 states/(MgB2)(eV)(spin). The total interaction strength, λ=0.87 and λtr=0.60, is dominated by the coupling of the σ holes to the bond-stretching optical phonons with wave numbers in a narrow range around 590 cm−1. Like the holes, these phonons are quasi-two-dimensional and have wave vectors close to ΓA, where their symmetry is E. The π electrons contribute merely 0.25 to λ and to λtr. With Eliashberg theory we evaluate the normal-state resistivity, the density of states in the superconductor, and the B-isotope effect on Tc and Δ0, and find excellent agreement with experiments, when available. Tc=40 K is reproduced with μ*=0.10 and 2Δ0/kBTc=3.9. MgB2 thus seems to be an intermediate-coupling e-ph pairing s-wave superconductor.

Source-reported materials — not catalogue approval

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