Yasuyuki Hirata, Makoto Nakajima, Tohru Suemoto, Hiroyuki Tajima, Keiko Asoh, Yoko Kiuchi, Yoshitaka Matsushita, Kenya Ohgushi
The structural, electronic, and optical properties of pyrochlore-type
Pb$_{2}$Ir$_{2}$O$_{6}$O'$_{0.55}$, which is a metal without spatial inversion
symmetry at room temperature, were investigated. Structural analysis revealed
that the structural distortion relevant to the breakdown of the inversion
symmetry is dominated by the Pb-O' network but is very small in the Ir-O
network. On the other hand, gigantic second harmonic generation signals due to
the noncentrosymmetricity of the conducting Ir 5$d$ electrons were observed,
which were comparable to that of GaAs. The mediation between the Pb-O' network
and the Ir-O conducting network by low-energy optical phonon modes is suggested
as its origin. These results stimulate theoretical study of inversion-broken
iridates, where exotic quantum states such as a topological insulator and Dirac
semimetal are anticipated.
View original:
http://arxiv.org/abs/1201.6410
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