Emergence of low-energy electronic states in oxygen-controlled Mott insulator Ca$_{2}$RuO$_{4+δ}$

Takeo Miyashita; Hideaki Iwasawa; Tomoki Yoshikawa; Shusuke Ozawa; Hironoshin Oda; Takayuki Muro; Hiroki Ogura; Tatsuhiro Sakami; Fumihiko Nakamura; Akihiro Ino

doi:10.1016/j.ssc.2020.114180

paper

Emergence of low-energy electronic states in oxygen-controlled Mott insulator Ca $_{2}$ RuO $_{4 + δ}$

arXiv:2102.01396 · doi:10.1016/j.ssc.2020.114180

Abstract

Insulator-to-metal transition in Ca $_{2}$ RuO $_{4}$ has drawn keen attention because of its sensitivity to various stimulation and its potential controllability. Here, we report a direct observation of Fermi surface, which emerges upon introducing excess oxygen into an insulating Ca $_{2}$ RuO $_{4}$ , by using angle-resolved photoemission spectroscopy. Comparison between energy distribution curves shows that the Mott insulating gap is closed by eV-scale spectral-weight transfer with excess oxygen. Momentum-space mapping exhibits two square-shaped sheets of the Fermi surface. One is a hole-like $α$ sheet around the corner of a tetragonal Brillouin zone, and the other is an electron-like $β$ sheet around the $Γ$ point. The electron occupancies of the $α$ and $β$ bands are determined to be $n_{α} = 1.6$ and $n_{β} = 0.6$ , respectively. Our result indicates that the insulator-to-metal transition occurs selectively in $d_{x z}$ and $d_{y z}$ bands and not yet in $d_{x y}$ band. This orbital selectivity is most likely explained in terms of the energy level of $d_{x y}$ , which is deeper for Ca $_{2}$ RuO $_{4 + δ}$ than for Ca $_{1.8}$ Sr $_{0.2}$ RuO $_{4}$ . Consequently, we found substantial differences from the Fermi surface of other ruthenates, shedding light on a unique role of excess oxygen among the metallization methods of Ca $_{2}$ RuO $_{4}$ .

9 pages, 6 figures

References in corpus (1)

Manifestations of Broken Symmetry: The Surface Phases of Ca(2-x)Sr(x)RuO4

Emergence of low-energy electronic states in oxygen-controlled Mott insulator Ca2​RuO4+δ​

Abstract

References in corpus (1)

Emergence of low-energy electronic states in oxygen-controlled Mott insulator Ca $_{2}$ RuO $_{4 + δ}$