Regensburg 2002 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 16: Neue und unkonventionelle Supraleiter II
TT 16.10: Vortrag
Mittwoch, 13. März 2002, 16:45–17:00, H18
Multiband effects in the normal and superconducting state of MgB2 — •Jens Kortus1, O. V. Dolgov1, O. Jepsen1, O. K. Andersen1, I. I. Mazin2, and A. A. Golubov3 — 1MPI für Festkörperforschung Stuttgart — 2Center for Computational Materials Science, Washington DC, USA — 3University of Twente, Department of Applied Physics, 7500 AE Enschede, The Netherlands
The electronic structure of MgB2 contains four Fermi surface sheets. Two of them, with 2D character emerging from bonding σ bands, form small cylindrical sheets around Γ - A. The other two, originating from bonding and antibonding π bands, have 3D character and form a tubular network [1]. From a first-principles calculation of the electron-phonon coupling it has been concluded that the superconducting gap is different for the σ- and π-sheets and one can derive an effective two-band model with two different order parameters [2]. The optical conductivity (or reflectivity) can be understood within this model by assuming different intraband impurity scattering rates in the σ- and π-bands and negligible interband scattering. This also explains the surprisingly small correlation between the residual resistivity and Tc. The same model explains the reduced heat capacity anomaly at Tc and the low temperature behavior of the specific heat. Our model also gives the conditions for observing one or two gaps in point-contact spectroscopy, depending on tunneling direction, barrier type and amount of impurities.
[1] J. Kortus, I.I. Mazin, K.D. Belashchenko, V.P. Antropov, L.L. Boyer, Phys. Rev. Lett. 86 4656 (2001)
[2] A. Y. Liu, I. I. Mazin, J. Kortus, Phys. Rev. Lett. 87 087005 (2001)