Electronic Structure of Two-Dimensional CoO₂

The transition metal oxide CoO₂ forms layered bulk “pseudo-two-dimensional” structures that exhibit correlated electronic states and a complex interplay between superconductivity and charge/spin ordering. Recently, it has been shown [1] that CoO₂ can be stabilized in the single-layer limit. However, little has been known about the single layer’s electronic structure. We have now studied the crystalline and electronic structure of single-layer epitaxial CoO₂/Au(111). Angle-resolved photoemission spectroscopy (ARPES) reveals a band structure with parallels to that of the superconducting layered bulk material Na_0.35CoO₂ ● 1.3H₂O. Using x-ray photoelectron diffraction, we have obtained detailed information about the crystal structure, and have used this information as a basis for density functional theory calculations to support the interpretation of our ARPES data. The results emphasize the interest of oxides as a new subject within two-dimensional materials research. They also contribute to our understanding of the electronic properties of layered bulk crystals based on CoO₂. [1] ACS Nano 9 (2015) 2445