TY - JOUR
T1 - High tc of aA5 compounds
T2 - Linear chains or cubic symmetry?
AU - Weger, M.
PY - 1978
Y1 - 1978
N2 - Intermetallic compounds with the A15 crystal structure are frequently excellent superconductors, with Tc considerably exceeding the value expected for the electron/atom ratio. This high value of Tc has been attributed to the linear chain structure of the transition metal atoms. However, uniaxial stress experiments point to the importance of the cubic symmetry, rather than of the chain structure per se. The high Tc may be due to sharp peaks in the electronic density of states or to the softening of some phonons due to nesting of the Fermi surface or probably to both of these effects. Band structure calculations indicate that the large cubic unit cell, with its high symmetry, is essential for the large Van Hove peaks in the electronic density of states. Disorder thus reduces Tc drastically, as is found experimentally. The positron annihilation method has been employed to determine the shape of the Fermi surface and several planar sections have been observed. The high Tc is attributed to the reduction in the group velocity over large regions in k space by the destructive interference due to multiple scattering by the various equivalent transition metal atoms in the unit cell. Thus Matthias' claim that cubic symmetry is essential for high Tc is indeed accounted for.
AB - Intermetallic compounds with the A15 crystal structure are frequently excellent superconductors, with Tc considerably exceeding the value expected for the electron/atom ratio. This high value of Tc has been attributed to the linear chain structure of the transition metal atoms. However, uniaxial stress experiments point to the importance of the cubic symmetry, rather than of the chain structure per se. The high Tc may be due to sharp peaks in the electronic density of states or to the softening of some phonons due to nesting of the Fermi surface or probably to both of these effects. Band structure calculations indicate that the large cubic unit cell, with its high symmetry, is essential for the large Van Hove peaks in the electronic density of states. Disorder thus reduces Tc drastically, as is found experimentally. The positron annihilation method has been employed to determine the shape of the Fermi surface and several planar sections have been observed. The high Tc is attributed to the reduction in the group velocity over large regions in k space by the destructive interference due to multiple scattering by the various equivalent transition metal atoms in the unit cell. Thus Matthias' claim that cubic symmetry is essential for high Tc is indeed accounted for.
UR - http://www.scopus.com/inward/record.url?scp=0018032009&partnerID=8YFLogxK
U2 - 10.1016/0022-5088(78)90014-0
DO - 10.1016/0022-5088(78)90014-0
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AN - SCOPUS:0018032009
SN - 0022-5088
VL - 62
SP - 39
EP - 48
JO - Journal of the Less-Common Metals
JF - Journal of the Less-Common Metals
IS - C
ER -