Monday, December 3, 2012

1211.7176 (Hidetomo Usui et al.)

Large Seebeck effect in the electron-doped FeAs$_2$ driven by quasi one
dimensional pudding-mold type band

Hidetomo Usui, Kazuhiko Kuroki, Seiya Nakano, Kazutaka Kudo, Minoru Nohara
We investigate the thermoelectric propeties of the electron-doped FeAs$_2$ both experimentally and theoretically. Electrons are doped by partially substituting Se for As, which leads to a metallic behavior in the resistivity. A Seebeck coefficient of about $-$200 $\mu$V/K is reached at 300 K for 1% doping, and about $-$120 $\mu$V/K even at 5% doping. The origin of this large Seebeck coefficient despite the metallic conductivity is analyzed from a band structure point of view. The first-principles band calculation reveals the presence of a pudding-mold type band just above the band gap, somewhat similar to Na$_x$CoO$_2$, but with a quasi-one-dimensional nature. We calculate the Seebeck coefficient using a tightbinding model that correctly reproduces this band structure, and this gives results close to the experimental observations. The origin of this peculiar band shape is also discussed.
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