Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 16: Neue und unkonventionelle Supraleiter II

TT 16.12: Vortrag

Mittwoch, 13. März 2002, 17:15–17:30, H18

Two-Gap Scenario for the 40K Superconductor MgB₂ from Heat Capacity Experiments — •R. K. Kremer, K.S. Ahn, B.J. Gibson und A. Das — MPI für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart

The order-parameter of the 40K superconductor MgB₂ has been intensively investigated by tunneling and point contact spectroscopy as well as by high-resolution PES. While these techniques show an energy gap most likely of s-wave symmetry the magnitude of the gap, Δ(0), itself remained an open question: Tunneling experiments initially revealed a distribution of energy gaps with lower boundary and upper boundary 2Δ(0)/k_BT_C≈ 1.1 and 4.5, respectively. These controversial findings have been discussed in terms of a gap anisotropy or more recently been attributed to the presence of two gaps or multiple gaps. We present and discuss the results of heat capacity measurements which indicate MgB₂ to be in the moderately strong coupling regime with 2Δ_u(0)/k_BT_C≈ 4.3 and which evidence a second gap with 2Δ_l(0)/k_BT_C≈ 1.