Europhys. Lett, 48 (3), pp. 320-325 (1999)
Electron doping in the honeycomb bilayer superconductors (Zr, Hf)NCl
R. Weht 1,2, A. Filippetti 1 and W. E. Pickett 1
1 Department of Physics, University of California -
Davis CA, 95616 USA
2 Departamento de Física, CNEA - Avenida General Paz y Constituyentes
1650 - San Martín, Argentina
(received 24 March 1999; accepted in final form 8 September 1999)
PACS. 74.70Ad - Metals; alloys and binary compounds (including A15, Laves phases, etc.).
PACS. 74.25Jb - Electronic structure.
PACS. 74.25Kc - Phonons.
Based on a virtual crystal treatment, we show that alkali doping introduces electron carriers into a single light mass (m*=0.6), low density of states band in LixZrNCl and NaxHfNCl (which have superconducting up to 25 K) that is a symmetric interlayer combination of dxy, dx2-y2 character. Doping leads to simple K-centered three-fold symmetrical cylindrical Fermi surfaces that concentrate low-energy scattering into distinct regions of momentum. The lack of any observed magnetic tendencies, together with our calculation of small electron-phonon strength, suggests a pairing mechanism that is distinct from known superconductors.
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