Regensburg 2002 – scientific programme

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TT: Tiefe Temperaturen

TT 9: Neue und unkonventionelle Supraleiter I

TT 9.3: Talk

Tuesday, March 12, 2002, 10:00–10:15, H19

Prediction of High T_c Superconductivity in Hole-doped LiBC — •Helge Rosner, Alex Kitaigorodsky, and Warren E. Pickett — University of California, Davis, CA, 95616, USA

The layered lithium borocarbide LiBC, isovalent with and structurally similar to the superconductor MgB₂, is an insulator due to the modulation within the hexagonal layers (BC vs. B₂). Using LDA band structure calculations for super-cells and in virtual crystal approximation, we show that hole-doping of LiBC results in Fermi surfaces of B-C pσ character that couple very strongly to B-C bond stretching modes. These are precisely the features that lead to superconductivity at T_c ≃ 40 K in MgB₂. Comparison of Li_0.5BC with MgB₂ indicates the former to be a prime candidate for electron-phonon coupled superconductivity at substantially higher temperature than in MgB₂. At this doping level, the densities of states and the phonon frequencies of both compounds are comparable, whereas the deformation potential is 40% larger in Li_0.5BC, resulting in an about twice as large electron phonon coupling λ in the latter. Due to its layered structure, LiBC seems to be a prime candidate for field-effect doping, offering a wide field of basic research for the whole compound family, and the possibility of technical applications.