Dresden 2006 – scientific programme

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TT: Tiefe Temperaturen

TT 18: Superconductivity: Borides, Borocarbides, Carbides, ...

TT 18.2: Talk

Tuesday, March 28, 2006, 15:15–15:30, HSZ 02

Superconductivity and electron phonon coupling in doped MgB₂ compounds — •Vivien Petzold¹ and Helge Rosner² — ¹TU Dresden — ²MPI for Chemical Physics of Solids Dresden

Recently, substitutions on the metallic site in MgB₂, e.g. Mg_1−xSc_xB₂ [1], Mg_1−x(AlLi)_xB₂ [2] and Nb_1−xB₂ [3] were investigated intensively. For the achievable doping levels (x=0.12...0.27) in Mg_1−xSc_xB₂, the compound shows only very small structural changes, allowing the separation of lattice and doping effects. On the other hand Mg_1−x(AlLi)_xB₂ is isoelectronical to MgB₂, but varies in lattice constants depending on x. In order to investigate the influence of the degree of substitution on the electronic properties, we present band structure calculations using different levels of approximation: rigid band and virtual crystal approach as well as supercell calculations and coherent potential approximation. We show that the latter two approaches lead to consistent results with respect to lattice expansion and electronic properties (density of states, Fermi surfaces). We demonstrate that in the transition metal (T) diborides the doping dependent changes in the electronic structure are strongly influenced by the sp²(B)-d(T) hybridization. The influence of the doping on the electron phonon coupling is discussed.

[1] Agrestini et al. Phys. Rev. B 70 134514 (2004).

[2] Monni et al. cond-mat 0506162 (2005).

[3] Yamamoto et al. Physica C 383 (2002) 197-206.