Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session E30: Topological and Correlation Effects in Oxide HeterostructuresFocus

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Sponsoring Units: DMP Chair: James Rondinelli, Northwestern University Room: 329 
Tuesday, March 15, 2016 8:00AM  8:36AM 
E30.00001: Design of Mott and topological phases on buckled \textit{3d}oxide honeycomb lattices Invited Speaker: Rossitza Pentcheva The honeycomb lattice, as realized e.g. in graphene, has rendered a robust platform for innovative science and potential applications. A much richer generalization of this lattice arises in (111)oriented bilayers of perovskites, adding the complexity of the strongly correlated, multiorbital nature of electrons in transition metal oxides. Based on first principles calculations with an onsite Coulomb repulsion, here we provide trends in the evolution of ground states versus band filling in (111)oriented (La$X$O$_{\mathrm{3}})_{\mathrm{2}}$/(LaAlO$_{\mathrm{3}})_{\mathrm{4}}$ superlattices, with $X$ spanning the entire \textit{3d} transition metal series. The competition between local quasicubic and global triangular symmetry triggers unanticipated broken symmetry phases, with mechanisms ranging from JahnTeller distortion, to charge, spin, and orbitalordering. LaMnO$_{\mathrm{3}}$ and LaCoO$_{\mathrm{3}}$ bilayers, where spinorbit coupling opens a sizable gap in the Diracpoint Fermi surface, emerge as much desired oxidebased Chern insulators, the latter displaying a gap capable of supporting roomtemperature applications [1] Further realizations of the honeycomb lattice and geometry patterns beyond the perovskite structure will be addressed. [1] D. Doennig, S. Baidya, W.E. Pickett and R. Pentcheva, arXiv: 1510.09177. [Preview Abstract] 
Tuesday, March 15, 2016 8:36AM  8:48AM 
E30.00002: Topological magnetic phase in LaMnO$_3$ ($111$) bilayer Yakui Weng, Xin Huang, Yugui Yao, Shuai Dong Candidates for correlated topological insulators, originated from the spinorbit coupling as well as Hubbard type correlation, are expected in the ($111$) bilayer of perovskitestructural transitionmetal oxides. Based on the firstprinciples calculation and tightbinding model, the electronic structure of a LaMnO$_3$ ($111$) bilayer sandwiched in LaScO$_3$ barriers has been investigated. For the ideal undistorted perovskite structure, the Fermi energy of LaMnO$_3$ ($111$) bilayer just stays at the Dirac point, rendering a semimetal (graphenelike) which is also a halfmetal (different from graphene nor previous studied LaNiO$_3$ ($111$) bilayer). The Dirac cone can be opened by the spinorbit coupling, giving rise to nontrivial topological bands corresponding to the (quantized) anomalous Hall effect. For the realistic orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard repulsion (or equivalent JahnTeller distortion). Finally, a Mott gap opens, establishing a phase boundary between the Mott insulator and topological magnetic insulator. Our calculation finds that the gap opened by spinorbit coupling is much smaller in the orthorhombic distorted lattice ($\sim$$1.7$ meV) than the undistorted one ($\sim$$11$ meV). [Preview Abstract] 
Tuesday, March 15, 2016 8:48AM  9:00AM 
E30.00003: Electronic structure of two dimensional electron gases at the (111)  surface of KTaO$_{\mathrm{3}}$ and SrTiO$_{\mathrm{3}}$ Flavio Bruno, S. McKeown Walker, A. de la Torre, S. Ricco, A. Tamai, Z. Wang, M. Shi, T. K. Kim, M. Hoesch, M.S. Bahramy, P. D. C. King, F. Baumberger Doping the band insulators KTaO$_{\mathrm{3}}$ (KTO) and SrTiO$_{\mathrm{3}}$ (STO) by chemical substitution or by the creation of oxygen defects induces metallicity and even superconductivity at exceptionally low carrier densities. A promising strongly correlated model system emerged when it was discovered that a 2D electron gas (2DEG) can be stabilized in KTO by field effect, and in STO by interfacing with other oxides. These materials also support a similar 2DEG formed by an electron accumulation layer screening positively charged oxygen vacancy defects that are created in the surface by irradiating the samples with photons of appropriate energy. [Adv. Mat. 27, 3894 (2015)] Here, we will report on direct measurements of the 2DEG band structure stabilized on the (111)  surface of KTO and STO using high resolution angleresolved photoemission (ARPES) [Phys. Rev. Lett. 113, 177601 (2014)]. The differences and similarities between the electronic structure of these two systems in terms of the strong and weak spin orbit coupling found in KTO and STO respectively will be discussed. [Preview Abstract] 
Tuesday, March 15, 2016 9:00AM  9:12AM 
E30.00004: Nitride Multilayers as a Platform for Parallel TwoDimensional ElectronHole Gases: MgO/ScN(111) Antia S. Botana, Victor Pardo, Warren E. Pickett At interfaces between insulating oxides LaAlO$_3$ and SrTiO$_3$, a two dimensional electron gas has been observed and well studied, while the predicted hole gas has not been realized due to the strong tendency of holes in O2p orbitals to localize. Here we propose, via ab initio calculations, an unexplored class of materials for the realization of parallel two dimensional (2D), two carrier (electron+hole) gases: nitrideoxide heterostructures, with (111)oriented ScN and MgO as the specific example. Beyond a critical thickness of five ScN layers, this interface hosts spatially separated conducting Sc3d electrons and N2p holes, each confined to about two atomic layers the transition metal nitride provides both gases. A guiding concept is that the N$^{3}$ anion should promote robust two carrier 2D hole conduction compared to that of O$^{2}$: metal mononitrides are mostly metallic and even superconducting while most metal monoxides are insulating. Our results, provide guidance for new exploration, both experimental and theoretical, on nitridebased conducting gases that should promote study of long sought exotic states viz. new excitonic phases and distinct, nanoscale parallel superconducting nanolayers[1].\newline [1]A.S. Botana, V. Pardo, W.E. Pickett, arXiv/1509.08518(2015) [Preview Abstract] 
Tuesday, March 15, 2016 9:12AM  9:24AM 
E30.00005: Low temperature transport at the \{111\} LaAlO$_3$/SrTiO$_3$ interface. S. Davis, V. Chandrasekhar, Z. Huang, K. Han, Ariando ., T. Venkatesan For the last ten years the interface between epitaxially grown \{001\} LaAlO$_{3}$(LAO) and SrTiO$_{3}$ (STO) has provided a rich playground for exotic physics, including a gatetuned metal to insulator transition, a gatetuned superconductorinsulator transition, and the coexistence of 2D superconductivity and magnetism. Recently the interfaces in other orientations of LAOSTO, namely the \{110\} and \{111\} orientations, have received increased attention after they were shown to become conducting. The \{111\} interface is particularly interesting due to its potential for topological effects as well as its complex Fermi surface. Here we present the results of low temperature electrical transport studies along two crystal directions of a \{111\} LAOSTO interface grown in intermediate oxygen partial pressures via PLD. More specifically we measure the longitudinal resistance as well as the transverse (Hall) resistance to elucidate the difference between the \{111\} and \{001\} LAO/STO interfaces. [Preview Abstract] 
Tuesday, March 15, 2016 9:24AM  9:36AM 
E30.00006: Anisotropic superconducting properties of nanowires at the LaAlO$_3$/SrTiO$_3$ (110) interface Mengchen Huang, Anil Annadi, Kalon Gopinadhan, Thirumalai Venkatesan, Ariando Ariando, Guanglei Cheng, Patrick Irvin, Jeremy Levy Quasi1D nanowires are created using conductive AFM (cAFM) lithography\footnote{C. Cen \textit{et al.}, Nat. Mater. \textbf{7}, 298 (2008)} at the LaAlO$_3$/SrTiO$_3$ (110) interface along the (001) and (1$\bar{1}$0) crystallographic directions. The superconducting properties of nanowires were investigated under transport measurements with respect to the crystallography and orbital hierarchy. We observe anisotropic superconductivity where the upper critical magnetic field along the (001) and (1$\bar{1}$0) directions are markedly different with a superconducting dome that is shifted for the two orientations as a function of gate voltages. The superconducting dome shift can be explained by anisotropic band structures along the two different directions combined with the Lifshitz transition\footnote{A. Joshua \textit{et al.}, Nat. Commun. \textbf{3}, 1129 (2012)}. [Preview Abstract] 
Tuesday, March 15, 2016 9:36AM  9:48AM 
E30.00007: Heteroepitaxially lifting Diracdegeneracy in topological semimetallic perovskite SrIrO$_{\mathrm{3}}$ Jian Liu Crystal symmetrybreaking and timereversal symmetry breaking in epitaxial thin films and heterostructures of the topological semimetallic perovskite SrIrO$_{\mathrm{3}}$ were investigated by experimental growth, characterizations and theoretical calculations. Structure refinement on ultrathin films and firstprinciples calculations show that the symmetryprotected Dirac line nodes in the topological semimetallic perovskite SrIrO$_{\mathrm{3}}$ can be lifted simply by applying epitaxial constraints. In particular, the Dirac nodal ring is found to be gapped in epitaxial film structure where the nglide symmetry of the bulk Pbnm space group is removed while the mirror symmetry is preserved. Our symmetrybreaking analysis shows that the nglide operation protects the nodal ring and the bglide operation provides addition protection for a pair of highsymmetry Dirac points of the nodal ring. These symmetry operations can be selectively broken by different epitaxially strained structures, leading to different semimetallic band crossing. Timereversal symmetry is further investigated under epitaxial confinement by ferromagnetic La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$. The resulted control over the magnetic anisotropy and spinorbit coupling will be discussed. The results highlight the vital role of symmetry in spinorbitcoupled correlated oxides. [Preview Abstract] 
Tuesday, March 15, 2016 9:48AM  10:00AM 
E30.00008: Tunneling Spectroscopy of Strongly Correlated Electron Liquids in SrTiO$_{\mathrm{3}}$ Patrick Marshall, Evgeny Mikheev, Santosh Raghavan, Susanne Stemmer Tunneling spectroscopy is used to probe the electronic structure of the twodimensional electron liquid confined in $R$TiO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$/$R$TiO$_{\mathrm{3}}$ quantum wells ($R \quad =$ Gd, Sm). The conductance spectra of metallic quantum wells exhibit power law behavior at high energies, reflecting the influence of disorder on the density of states. At low energies a pseudogap is observed in quantum wells containing 5 SrO layers and fewer, coinciding with the quantum phase transition in this system. As the quantum well thickness is reduced the DOS around the Fermi level vanishes in quantum wells embedded in GdTiO$_{\mathrm{3}}$, consistent with the metalinsulator transition occurring at thicknesses of 2 SrO layers and fewer. In SmTiO$_{\mathrm{3}}$embedded quantum wells the metallic state persists down to the lowest thickness and temperature, with the emergence of coherence peaks indicating the onset of an ordered phase in the itinerant state with possible density wave order. The results shed light on the interplay of disorder, electronelectron interactions, and electronlattice coupling in strongly correlated systems. [Preview Abstract] 
Tuesday, March 15, 2016 10:00AM  10:12AM 
E30.00009: Internal Charge Transfer and QuasiTwo Dimensional Electron Gases at NdTiO$_{3}$/SrTiO$_{3}$ interfaces Peng Xu, Timothy C. Droubay, Jong Seok Jeong, K. Andre Mkhoyan, Peter V. Sushko, Scott A. Chambers, Bharat Jalan Twodimensional (2D) ultrahigh carrier densities are of considerable current research interest for novel plasmonic and high chargegain devices. However, the highest 2D electron density obtained is thus far limited to 3x10$^{14}$ cm$^{2}$ (\textonehalf electron/unit cell/interface) at GdTiO$_{3}$/SrTiO$_{3}$ interfaces, and is typically an order of magnitude lower at LaAlO$_{3}$/SrTiO$_{3}$ interfaces. In this work, we will present detailed study that carrier densities much higher than expected based on resolution of the polar discontinuity at perovskite oxide heterojunctions can be achieved via band engineering and internal charge$^{\, [1]}$. The SrTiO$_{3}$(8 u.c.)/NdTiO$_{3}$(2 u.c)/SrTiO$_{3}$(8 u.c.)/LSAT(001) heterostructure shows the expected electronic reconstruction behavior starting at t $=$ 2 u.c., but then exhibits a higher carrier density regime at t $\ge $ 6 u.c. due to additional charge transfer from band alignment. Combining DFT modeling and experiments using xray photoelectron spectroscopy, scanning transmission electron microscopy, electron energy loss spectroscopy, energy dispersive xray spectroscopy and electronic transport measurements, we will discuss the origin of these carriers, dimensionality and transport mechanisms. [1] Peng Xu, et al. Advanced Material Interface (2015), in press. [Preview Abstract] 
Tuesday, March 15, 2016 10:12AM  10:24AM 
E30.00010: Onedimensional Electron Gases at Oxide Interfaces Yanwei Cao, Zhicheng Zhong, P. Shafer, Xiaoran Liu, M. Kareev, S. Middey, D. Meyers, E. Arenholz, Jak Chakhalian Emergence of twodimensional electron gases (2DEG) at the oxide interfaces of two dissimilar insulators is a remarkable manifestation of interface engineering. With continuously reduced dimensionality, it arises an interesting question: could onedimensional electron gases (1DEG) be designed at oxide interfaces? So far there is no report on this. Here, we report on the formation of 1DEG at the carefully engineered titanate heterostructures. Combined resonant soft Xray linear dichroism with electrical transport and the firstprinciples calculations have confirmed the formation of 1DEG driven by the interfacial symmetry breaking. Our findings provide a route to engineer new electronic and magnetic states. [Preview Abstract] 
Tuesday, March 15, 2016 10:24AM  10:36AM 
E30.00011: Controlled Confinement of Halfmetallic 2D Electron Gas in BaTiO$_3$/Ba$_2$FeReO$_6$/BaTiO$_3$ Heterostructures: A Firstprinciples Study Tanusri SahaDasgupta, Santu Baidya, Umesh Waghmare, Arun Paramekanti Using density functional theory calculations, we establish that the halfmetallicity of bulk Ba$_2$FeReO$_6$ survives down to 1 nm thickness in BaTiO$_3$/Ba$_{2}$FeReO$_6$/BaTiO$_3$ heterostructures grown along the (001) and (111) directions. The confinement of the twodimensional (2D) electron gas in this quantum well structure arises from the suppressed hybridization between Re/Fe $d$ states and unoccupied Ti $d$ states, and it is further strengthened by polar fields for the (111) direction. This mechanism, distinct from the polar catastrophe, leads to an order of magnitude stronger confinement of the 2D electron gas than that at the LaAlO$_3$/SrTiO$_3$ interface. We further show lowenergy bands of (111) heterostructure display nontrivial topological character. Our work opens up the possibility of realizing ultrathin spintronic devices. \vskip .2in Journal Ref: Phys. Rev. B 92, 161106(R) (2015) [Preview Abstract] 
Tuesday, March 15, 2016 10:36AM  10:48AM 
E30.00012: Electronic and magnetic phenomena at the interface of LaAlO$_{\mathrm{3}}$ and Rudoped SrTiO$_{\mathrm{3}}$ Matthew Gray, Ted Sanders, Catherine Jenkins, Padriac Shafer, Elke Arenholz, Yuri Suzuki The emergence of a quasitwo dimensional electron gas with hints of magnetic order at the interface between bulk diamagnetic, band gap insulators LaAlO$_{\mathrm{3}}$ (LAO) and SrTiO$_{\mathrm{3}}$ (STO) has led to intensive research of this interface. We doped magnetic, isovalent Ru onto the Ti site of the STO side of the interface. 010 nm of SrTi$_{\mathrm{0.98}}$Ru$_{\mathrm{0.02}}$O$_{\mathrm{3}}$ were deposited on TiO$_{\mathrm{2}}$ terminated (001) STO singlecrystal substrates and then capped with 117 nm of LAO. Insertion of more than 7 unit cells of Rudoped STO at the interface suppresses metallic conductivity with a surprisingly sharp metalinsulator transition. A similar metalinsulator transition is observed when a homoepitaxial STO film is grown before LAO deposition. Xray Magnetic Circular Dichroism indicated no magnetic ordering of Ti down to 10 K, and electric transport was indistinguishable from that of undoped LAO/STO interfaces. Together our results indicate that ferromagnetism is not intrinsic to the interface, magnetic Ru dopants are not significant sources of scattering, and that cation vacancy formation alone cannot explain the insulating behavior observed in thick homoepitaxial LAO/STO/STO trilayers. [Preview Abstract] 
Tuesday, March 15, 2016 10:48AM  11:00AM 
E30.00013: The Superconducting Phase Diagram of LaAlO$_3$/SrTiO$_3$ Interfaces Stefano Gariglio, Alexandre FĂȘte, Danfeng Li, Wei Liu, Margherita Boselli, Marc Gabay, JeanMarc Triscone The discovery of a twodimensional electron liquid (2DEL), formed at the interface between the two band insulators LaAlO$_3$ (LAO) and SrTiO$_3$ (STO), has generated significant interest. The 2DEL has indeed intriguing electronic properties including superconductivity and spinorbit interaction which can be tuned both by fieldeffect. In this talk I will discuss in detail the superconducting phase diagram revealed by fieldeffect experiments and the consequences of the electric field on the conducting layer extension. I will then compare the superconducting behaviour of this 2D system with the 3D one of doped STO crystals. [Preview Abstract] 
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