Interplay between Ferroelasticity, Electron Pairing, and Magnetism in LaAlO3/SrTiO3 Nanostructures

The LaAlO3/SrTiO3 interface exhibits a wide range of rich physical properties including superconductivity, electron pairing without superconductivity, magnetism, and ferroelasticity. However, the microscopic origin of the low temperature transport properties is not well understood. A long-standing question involves the unknown interrelations between structural distortions, electron pairing, and low temperature magnetotransport properties at the LaAlO3/SrTiO3 interface. In this thesis, we delineate experimental signatures of interplay between ferroelastic domains, preformed electron pairs, magnetism and electronic nematicity in LaAlO3/SrTiO3 nanostructures. Low-temperature magnetotransport measurements on quasi-one dimensional (1D), cross-shaped electron waveguides, “nanocrosses” are reported. The nanocross devices exhibit quantized ballistic transport of electron and electron pairs and serves as a building block for understanding the 1D electron physics at the LaAlO3/SrTiO3 interface. First, a highly reproducible inhomogeneous energy landscape across the nanocrosses is reported, and ferroelastic domain models are provided to explain the observed inhomogeneity. Second, Hall measurements across the nanocross devices show an abrupt change in slope of the Hall resistance which is directly correlated to the depairing and subsequent spin polarization of preformed electron pairs. Angle-dependent measurements of nonlinear Hall effect also reveals an onset of electronic nematicity at high magnetic fields that again coincides with the electron pairing transition, strengthening the connection between the two phenomena. Potential correlations between ferroelastic domains and preformed electron pairs at the LaAlO3/SrTiO3 interface is further discussed. Finally, results indicating an unconventional electromechanical gating mechanism at the interface is presented. The results reported in this thesis highlights the significance of preformed pairs in the overall phase diagram of LaAlO3/SrTiO3 heterostructures. Functional interrelations between ferroelastic domains, electron pairing, and unusual transport signatures such as nonlinear Hall effect and electronic nematicity at the interface is explored. The given results provide a step forward in understanding the pairing mechanism and the rich correlated electron physics at the LaAlO3/SrTiO3 interface