Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 18: Superconductivity: Borides, Borocarbides, Carbides, ...
TT 18.6: Vortrag
Dienstag, 28. März 2006, 16:30–16:45, HSZ 02
Soft-mode behavior in superconducting MgB2-like ternary silicides MAlSi (M=Ca,Sr,Ba) — •R. Heid1, K.-P. Bohnen1, B. Renker1, P. Adelmann1, D. Ernst1, and H. Schober2 — 1Forschungszentrum Karlsruhe, Institut für Festkörperphysik — 2Institut Laue-Langevin, Grenoble
The discovery of superconductivity with Tc≈ 39K in MgB2 has led to an intensive search for new superconductors with similar layered structures. Among them, the ternary silicides MAlSi with M=Ca,Sr,Ba exhibit interesting electronic and superconducting properties. With increasing mass of the M ion, Tc drops from 7.8K (Ca) to 5.1K (Sr) to <2K (Ba). Electronic structure calculations suggest that all three compounds possess very similar electronic properties [1], thus pointing to significant differences in the phonons and electron-phonon coupling (EPC).
Here we present results of a combined experimental and theoretical investigation of the lattice dynamics and EPC of the series MAlSi, M=Ca,Sr,Ba. Inelastic neutron-scattering measurements of the generalized phonon density of states show evidence for a low-frequency phonon mode in CaAlSi, which stiffens with increasing mass of the M ion. Using density-functional perturbation calculations of the phonons and EPC, we could identify this mode as an out-of-plane Al vibration with a large EPC. Contrary to a previous theoretical study [2], we do not find evidence for a dynamical instability. We will discuss implications for the observed superconducting trends among the MAlSi series.
[1] I. I. Mazin et al., Phys. Rev. B69, 180512 (2004)
[2] G. Q. Huang et al., Phys. Rev. B69, 064509 (2004)