Electronic Structure ofMgB2from Angle-Resolved Photoemission Spectroscopy

Abstract

The first angle-resolved photoemission spectroscopy results from MgB2 single crystals are reported. Along the GammaK and GammaM directions, we observed three distinct dispersive features approaching the Fermi energy. These can be assigned to the theoretically predicted sigma (B 2p(x,y)) and pi (B 2p(z)) bands. In addition, a small parabolic-like band is detected around the Gamma point, which can be attributed to a surface-derived state. The overall agreement between our results and the band calculations suggests that the electronic structure of MgB2 is of a conventional nature, thus implying that electron correlations are weak and may be of little importance to superconductivity in this system.

Raman study on the effects of sintering temperature on the Jc(H) performance of MgB2 superconductor

“…Further research has found that MgB 2 exhibits a rich multiple-band structure, which has been observed by a number of experimental techniques, such as angleresolved photoemission spectroscopy, the de Haas-van Alphen effect, and the Hall resistivity. [5][6][7] These results confirm previous band structure calculations 8,9 and reveal strongly two-dimensional sp x p y ͑ ͒ bands, as well as threedimensional p z ͑ ͒ bands. Owing to the simple hexagonal structure ͑space group P6 / mmm͒, four optical modes at the G point of the Brillouin zone are predicted for MgB 2 : a silent B 1g mode ͑at 87.1 meV, Ϸ700 cm −1 ͒, the E 2g Raman mode ͑at 74.5 meV, Ϸ600 cm −1 ͒, and the infrared active E 2u ͑at 40.7 meV, Ϸ330 cm −1 ͒, and A 2u ͑at 49.8 meV, Ϸ400 cm −1 ͒ modes, where only the E 2g mode is Raman active and strong coupling to the electronic conduction bands is predicted.…”

Momentum-dependent multiple gaps in magnesium diboride probed by electron tunnelling spectroscopy

“…There is a finite coupling between the π and σ bands, and both gaps vanish at a common T c . Besides the two widely observed gaps [9][10][11][12] , first-principles calculations taking into account the fully anisotropic electron-phonon interaction predict that there should also be an intraband anisotropy within the σ and π gaps 1,2 . In an earlier work Choi et al solved the Eliashberg equation in the clean limit, using an anisotropic electron-phonon interaction λ(k,k′), and found an energy gap ∆(k) that spreads between 1.2 and 3.7 meV for the π bands and from 6.4 to 7.2 meV for the σ bands 1,13 .…”

Strong interaction between electrons and collective excitations in the multiband superconductorMgB2

“…MgB 2 15-20 is a notable exception: it is a layered material with multigap, phonon-mediated superconductivity at T c = 39K with some quasi-two-dimensional bands, making it an ideal candidate to study the temperature dependence of the dispersion renormalization due to electron-phonon coupling. LDA calculations 17 predict four bands crossing Fermi level in MgB 2 : two quasi 2D σ-bands from p x , p y orbitals around Γ and two 3D π-bands from p z orbital 27,31,32 . The superconductivity is believed to caused by the E 2g phonon mode at 75meV that couples strongly to the 2D σ-bands, but more weakly to the π-bands 19 , leading to two different gaps, ∆ σ = 6.5 meV and ∆ π = 1.5meV, as revealed by previous tunneling 26 and ARPES studies 27 .…”