Proximate Two-Dimensional Electron and Hole Gases in Ambipolar Cuprates

Cornell University, Ithaca NY

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: The laws that govern how atoms interact differ significantly from what we are used to in everyday life such as how baseballs fly through the air or ocean waves move and interact with each other. For atoms, our notions of particles and waves merge together and quantum mechanics are used to describe their interactions. Although commonly relegated to atomic scales, behavior that is only explainable with the use of quantum mechanics can transcend from the microscopic to the macroscopic world and produce some spectacular effects. Examples include superconductivity, superfluidity, and coherent matter waves. The long-term goal of this work is to achieve coherent waves of moving pairs of opposite charges in a solid at a temperature where they could be of practical importance. Matter within which coherent waves of opposite charge pairs move could provide society with behaviors useful for the next generation of electronics. Toward this end, the PI will create targeted structures containing copper and oxygen atom-by-atom with precise control of their arrangement and the spacing between the atoms. The broader impact of this research includes the training of undergraduate and graduate students to use one of the most sophisticated techniques known for creating new materials with atom-by-atom control of how they are assembled. TECHNICAL DETAILS: The technical objective of this project is to grow new copper-oxide-based superconductors with tunable hole or electron mobile carrier concentrations. Achieving a superconductor that can be doped with holes or electrons in a way that can switch abruptly from hole to electron doping is an important step on the path to synthesizing proximal two-dimensional electron liquids and two-dimensional hole liquids. A key advantage of this approach is that the resulting excitonic system created is in its ground state; it does not rely on optical excitation for its creation, is not subject to recombination, and can thus, in principle, access much higher exciton carrier concentrations, a completely uncharted state of matter where unusual behavior (e.g., Bose condensation) is expected. Although oxide systems are known that can support either two-dimensional electron liquids or two-dimensional hole liquids, there are only a few oxides in which the same parent phase can be highly doped in an ambipolar manner. A standout among these is SrCuO2, the so-called "infinite-layer" cuprate, which is the parent structure of all high transition temperature (high Tc) cuprate superconductors. The broader impact of this research includes the training of students to use one of the most sophisticated synthesis techniques, molecular-beam epitaxy known for creating oxide materials with atomic-level control of the constituent atoms.