Angle-Resolved Photoemission Spectroscopy Of Sr1-Xlaxcuo2 Thin Films Grown By Molecular-Beam Epitaxy
Among the multitude of known cuprate material families and associated structures, the archetype is "infinite-layer" ACuO2 , where perfectly square and flat CuO2 planes are separated by layers of alkaline earth atoms. The infinite-layer structure is free of magnetic rare earth ions, oxygen chains, orthorhombic distortions, incommensurate superstructures, ordered vacancies, and other complications that abound among the other material families. Furthermore, it is the only cuprate that can be made superconducting by both electron and hole doping, making it a potential platform for decoding the complex many-body interactions responsible for high-temperature superconductivity. Research on the infinite-layer compound has been severely hindered by the inability to synthesize bulk single crystals, but recent progress has led to high-quality superconducting thin film samples. Here we report in situ angle-resolved photoemission spectroscopy measurements of epitaxially-stabilized Sr1[-]x Lax CuO2 thin films grown by molecular-beam epitaxy. At low doping, the material exhibits a dispersive lower Hubbard band typical of other cuprate parent compounds. As carriers are added to the system, a continuous evolution from Mott insulator to superconducting metal is observed as a coherent low-energy band develops on top of a concomitant remnant lower Hubbard band, gradually filling in the Mott gap. For x = 0.10, our results reveal a strong coupling between electrons and ([pi], [pi] ) antiferromagnetism, inducing a Fermi surface reconstruction that pushes the nodal states below the Fermi level and realizing nodeless superconductivity. Electron diffraction mea- surements indicate the presence of a surface reconstruction that is consistent with the polar nature of Sr1[-]x Lax CuO2 . Most knowledge about the electron-doped side of the cuprate phase diagram has been deduced by generalizing from a single material family, Re2[-]x Cex CuO4 , where robust antiferromagnetism has been observed past x [ALMOST EQUAL TO] 0.14. In contrast, in all hole-doped cuprates, N´ el order is rapidly suppressed by x [ALMOST EQUAL TO] 0.03, with superconductivity following at higher e doping levels. Studies of cuprates, however, often yield material-specific features that are idiosyncratic to particular compounds. By studying a completely different electrondoped cuprate, we can for the first time independently confirm that the cuprate phase diagram is fundamentally asymmetric and provide a coherent framework for understanding the generic properties of all electron-doped cuprates.
ARPES; MBE; superconductivity
Shen, Kyle M.
Muller, David Anthony; Mueller, Erich
Ph.D. of Physics
Doctor of Philosophy
dissertation or thesis