Abstract:
My work explores novel materials whose properties are inherently tied to their electronic structure. I focus on the experimental study of three systems undertaken during my PhD. First, Mg-doped CuRhO2, which displays a high value of the thermoelectric coefficient owing to its unique electronic structure. Second, thin films of the correlated metal CaVO3, which undergo a metal-to-insulator transition (MIT) below a critical film thickness. Lastly, a heterostructure of 2D magnetic transition metal dihalide FeCl2 on top of an Au(111) surface, with unique electronic states near the Fermi level.
CuRhO2 is an insulating material with a high value of the thermopower coefficient. Hole doping the material with Mg makes it conductive while still retaining a relatively high thermopower. The origin of the high thermopower has been theoretically proposed as originating from the "pudding-mold" band structure of the material. Through ARPES, we experimentally verify that the observed bands in the 10% Mg-doped CuRhO2 match the DFT-calculated bands and are of the "pudding-mold" type.
Thin films of CaVO3 are observed to undergo an MIT as a function of film thickness. Films of CaVO3 with thicknesses ranging from 90 u.c. to 15 u.c. grown on an SrTiO3 substrate were measured by ARPES, and changes in the electronic structure were tracked. An MIT was observed when transitioning from a metallic 20 u.c. film to an insulating 15 u.c. film, with the disappearance of the conduction band and the appearance of an insulating flat band at ~ -0.9 eV. We conclude that the increased epitaxial strain, rather than dimensionality, is the driver of the MIT, in agreement with previous studies.
The 2D magnetic transition metal halide FeCl2 on Au(111) is observed to host novel states at the Fermi level. A monolayer (ML) of FeCl2 deposited on an Au(111) surface was characterized by STM. Quasi-particle interference (QPI) measurements revealed the presence of novel dispersing bands arising from the heterostructure, whose exact origin remains unclear. We also directly observe the magnetic order on the ML film, which we find to be directly correlated with the topological structure observed with STM.