Emergence of low-energy electronic states in oxygen-controlled Mott insulator Ca2RuO 4 + δ

2020/12/30 by Takeo Miyashita, Hideaki Iwasawa, Tomoki Yoshikawa +8
Chemistry · Materials Science · Physics and Astronomy · #Advanced Condensed Matter Physics #Angle-resolved photoemission spectroscopy #Brillouin zone #Chemistry #Condensed matter physics #Electron #Electronic and Structural Properties of Oxides #Electronic structure #Fermi level #Fermi surface #Magnetic and transport properties of perovskites and related materials #Materials science #Mott insulator #Nuclear magnetic resonance #Photoemission spectroscopy #Physics #Quantum mechanics #Superconductivity #Tetragonal crystal system #X-ray photoelectron spectroscopy #cond-mat.str-el

paper · pdf · doi:10.1016/j.ssc.2020.114180

published as Solid State Communications 326, 114180 (2021) · 9 pages, 6 figures

openalex publication_date 2020/12/30 · openalex created_date 2021/01/05 · arxiv created 2021/02/03 · arxiv updated 2021/02/04 · openalex updated_date 2026/08/05

Abstract

Insulator-to-metal transition in Ca₂RuO₄ 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 Ca₂RuO₄, 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_xz and d_yz bands and not yet in d_xy band. This orbital selectivity is most likely explained in terms of the energy level of d_xy, which is deeper for Ca₂RuO_4+δ than for Ca_1.8Sr_0.2RuO₄. 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 Ca₂RuO₄.

Citations

• Possible highT c superconductivity in the Ba?La?Cu?O system
• Observation of a Novel Orbital Selective Mott Transition inCa1.8Sr0.2RuO4
• Anisotropic uniaxial pressure response of the Mott insulator Ca<mml:mrow/>2RuO<mml:mrow/>4
• Destruction of the Mott insulating ground state ofCa2RuO4by a structural transition