We have performed angle-resolved photoemission spectroscopy (ARPES) of KFeAgTe${}_2$, and revealed the absence of band crossing at the Fermi level ($E_{\mathrm{F}}$) indicative of the unconventional insulating nature of this material. Comparison of the ARPES-derived band dispersions with the first-principles calculations based on local density approximation and the inclusion of electron correlation $U$ demonstrated that the ground state of KFeAgTe${}_2$ is not a simple band insulator. And also, our fitting result on the ARPES experimental density of states near $E_{\mathrm{F}}$ plausibly excludes the possibility of Anderson insulator. We suggest that KFeAgTe${}_2$ is most likely a Mott insulator or a Hund insulator, providing a deep insight into the insulating ground state.

• Received 19 July 2013

DOI:https://doi.org/10.1103/PhysRevB.88.155102