title: Mechanism of enhanced optical second-harmonic generation in the conducting pyrochlore-type Pb2Ir2O7-x oxide compound.
abstract: 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. At the same time, gigantic second-harmonic generation signals were observed, which can only occur if the local environment of the Ir 5d electrons features broken inversion symmetry. First-principles electronic structure calculations reveal that the underlying mechanism for this phenomenon is the induction of the noncentrosymmetricity in the Ir 5d bands by the strong hybridization with O' 2p orbitals. Our results stimulate theoretical study of inversion-broken iridates, where exotic quantum states such as a topological insulator and Dirac semimetal are anticipated.
authors.affiliation: Institute for Solid State Physics, The University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Hirata
authors.forename: Makoto
authors.initials: M
authors.lastname: Nakajima
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Nomura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tajima
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Matsushita
authors.forename: Keiko
authors.initials: K
authors.lastname: Asoh
authors.forename: Yoko
authors.initials: Y
authors.lastname: Kiuchi
authors.forename: Adolfo G
authors.initials: AG
authors.lastname: Eguiluz
authors.forename: Ryotaro
authors.initials: R
authors.lastname: Arita
authors.forename: Tohru
authors.initials: T
authors.lastname: Suemoto
authors.forename: Kenya
authors.initials: K
authors.lastname: Ohgushi
mesh_terms: D007495:Iridium / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D009556:Niobium / Q000737:chemistry*; D055095:Optics and Photonics / Q000379:methods; D011789:Quantum Theory; D014961:X-Ray Diffraction
chemical_list: D009556:Niobium; C044458:iridium oxide; C016709:pyrochlore; D007854:Lead; D007495:Iridium