Emergent Phenomena at the (111) LaAlO3/SrTiO3 Interface

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In his Nobel lecture Herbert Kroemer famously stated that “The interface is the device”. While he made this statement in the context of semiconducting heterostructures, it has proven to be just as relevant for more complex materials, such as the transition metal oxides. In particular, the 2-D conducting gas that forms at the interface between two transition metal oxides LaAlO3 and SrTiO3 (LAO/STO) has shown that a system containing a rich phase space of phenomena can arise from the interface of two relatively boring insulators. These phenomena include superconductivity, magnetism, gate tuned metal to insulator and superconductor to insulator transitions as well as evidence of large spin-orbit coupling at the interface. While the observation of these effects has produced more than a decade of fervent research on the LAO/STO interface, these previous efforts have focused mainly on the (001) crystal orientation of the LAO/STO interface. This thesis presents the results of some of the first studies on the (111) orientation of the LAO/STO interface, which not only has a more complex interfacial symmetry, but also shows new emergent phenomena. The most striking of which is the observation of strong, in-plane, anisotropy in the almost all of interface’s electrical transport properties. The thesis will identify not only identify where this anisotropy “lives” in the (111) LAO/STO interface, but also examine the energy scale at which it onsets. These results are evidence of an electronic nematic state that breaks the rotational symmetry of the sample. Finally, it will explore how this anisotropy impacts the other phenomena present at the interface, superconductivity and ferromagnetism.

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  • 01/16/2019
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