The recent surge of interest in moir & eacute; superlattices of twisted van der Waals compounds has spotlighted the emergence of unconventional superconductivity and novel electronic phases. However, the range of moir & eacute; phenomena can be dramatically expanded by incorporating complex oxide materials into twisted heterostructures. In this study, motivated by the recent breakthroughs in the synthesis of freestanding oxide membranes, we explore the emergent structural and electronic properties of twisted oxide bilayers. We focus on the classic perovskite oxide, SrTiO3, and design SrTiO3 bilayers with a relative twist between the individual layers. Using density functional theory calculations, we predict the appearance of vortex-antivortex polarization patterns at the interface of the SrTiO3 bilayers driven by twist. We also predict charge modulation of the interfacial Ti ions induced by varying local coordination, which follow the moir & eacute; pattern. Furthermore, we forecast the emergence of flat bands at large twist angles and the associated localized electronic states with moir & eacute;-periodic charge density, originating from the interlayer bonding effects resulting in the formation of dangling bonds. Finally, we predict that hole doping induces unconventional d0 magnetism in otherwise nonmagnetic SrTiO3, driven by the exchange splitting of the high-density O-p bands and producing the spin density with moir & eacute; periodicity. These results demonstrate a broad landscape of emergent phenomena that may occur in moir & eacute;-engineered oxide heterostructures showing far-reaching perspectives of these material systems for further fundamental studies and potential applications.

Deterministic control of coupled ferroelectric and antiferromagnetic orders remains a central challenge in multiferroics, limiting their integration into functional magnetoelectrics and magnonic-devices. (111)pc BiFeO3 with a robust single spin cycloid, offers direct magnetoelectric-coupling and a platform for efficient spin transport, yet multi-magnetic domains and ferroelectric-fatigue have prevented reproducible control. Here, we show that anisotropic-compressive in-plane strain stabilizes a single antiferromagnetic domain with unique spin-cycloid vector, by breaking the symmetry of the (111)pc plane. Epitaxial BiFeO3 films grown on orthorhombic NdGaO3 (011)o [(111)pc] substrates impose the required anisotropic in-plane strain and stabilizes single antiferromagnetic domain, as confirmed through direct imaging with scanning NV microscopy and non-resonant-x-ray-magnetic-scattering. Remarkably, these engineered films exhibit deterministic and non-volatile 180° switching of ferroelectric and single antiferromagnetic domains over 1,000 cycles. The monodomain state also enables anisotropic and threefold enhanced magnon transport with reduced scattering. Thus, symmetry-designed (111)pc monodomain BiFeO3 offers a robust platform for advanced magnetoelectric and magnonic applications.

Using an advanced technique combining pulsed laser deposition growth of LaAlO3, LaTiO3, and SrTiO3 we effectively constructed half-integer unit cell number LaAlO3-SrTiO3 heterostructures where all interfaces are of LaO-TiO2 type, and where a two-dimensional electron gas (2DEG) forms a symmetric n-type bilayer. Using ultrahigh-vacuum scanning tunneling microscopy we investigated the properties of the surface 2DEG in these heterostructures. Our results indicate that the surface 2DEG is strongly, within one unit cell, confined at the interface. Tunneling spectroscopy of the surface 2DEG reveals thickness-dependent band-gap changes attributed to the quantum size effect.

Submitted for the MAR14 Meeting of The American Physical Society Spin-orbit engineering of LaAlO3/SrTiO3 nanowires 1 PATRICK IRVIN, MEGAN KIRKENDALL, JEREMY LEVY, University of Pittsburgh, SANGWOO RYO, CHANG-BEOM EOM, University of Wisconsin-Madison — LaAlO3/SrTiO3 heterostructures possess a tunable spin-orbit coupling that strongly influences other properties such as magnetism and superconductivity. Lowtemperature transport experiments with nanowires created by conductive AFM show a sizeable non-zero resistance in the superconducting state. Here we present lowtemperature magnetotransport of nanowires with 1D corrugations (e.g., triangular and rectangular lattices). We find that these “zig-zag” nanostructures possess a robust, fully superconducting state as compared to conventional “straight” nanowires. The most likely explanation relates to an effective spin-orbit interaction in which the effective magnetic fields of segments within the zig-zag “unit cell” cancel. We discuss implications for engineering spin-orbit couplings in superconducting nanostructures capable of supporting Majorana zero modes. 1We gratefully acknowledge support for this work from AFOSR (FA9550-10-1-0524, FA9550-12-1-0057, FA9550-12-1-0268, and FA9550-12-1-0342) and ONR (N0001413-1-0806). Patrick Irvin Univ of Pittsburgh Date submitted: 15 Nov 2013 Electronic form version 1.4