Research on the electronic structure of pure electronic and topological phases in electride Gd2C

Abstract

Electrides are unique ionic crystal in which interstitial anionic electrons (IAEs) decoupled from the atomic orbitals acts as anion. By virtue of this unique electrical property, free electron-like electron layers are expected to float on the surface of 2D electride materials. In addition to that, topological surface states are also predicted in electride materials, following the bulk topological states. However, those surface state has not been sufficiently investigated in. In this thesis, the electronic structure of the 2D electride material Gd2C has been investigated using angle-resolved photoemission spectroscopy (ARPES). With the electronic structure calculations and the ARPES measurements, the realization of a 2D pure floating electron system in an electron liquid state could be captured, and it was found to be a quantum state with a large electron density. Furthermore, the surface deposition of alkali metals allowed the control of the electron density to induce a transition to the hexatic phase which exhibits non-Fermi liquid behavior. In addition, the electronic structure corresponding to the Weyl state –Weyl cones and Fermi arcs – was successfully captured. Interestingly, the calculation indicate that the Fermi arc surface state exists at the topmost atomic layer, separated from the floating electrons, forming a heterosurface state. Therefore, these results show not only interesting properties of a new exotic material, but also possibilities as a new platform to study pure electron systems, strongly correlated systems, and topological superconductors, and more.