Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V43: Iridate HeterostructuresFocus

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Sponsoring Units: GMAG DMP DCOMP Chair: Eva Benckiser, Max Planck Institute for Solid State Research Room: 390 
Thursday, March 16, 2017 2:30PM  2:42PM 
V43.00001: Magnetotransport properties in AllinAllout magnetic ordered epitaxial Sm$_{2}$Ir$_{2}$O$_{7}$ and Nd$_{2}$Ir$_{2}$O$_{7}$ films. W. J. Kim, J. H. Gruenewald, O. B. Korneta, S. S. A. Seo, T. W. Noh Pyrochlore iridates R$_{2}$Ir$_{2}$O$_{7}$ (R$=$rare earth element) have been predicted to exhibit a variety of exotic physical phenomena, such as the Weyl semimetallic state and topologically insulating behavior with allinallout (AIAO) magnetic ordering. Here, we have observed a metalinsulator transition accompanied by the AIAOtype magnetic ordering in both Nd$_{2}$Ir$_{2}$O$_{7}$ and Sm$_{2}$Ir$_{2}$O$_{7}$ films below their respective ordering temperatures. Negative magnetoresistance (MR) is observed below 20 K and this gradually transitions into positive MR upon warming. We speculate that this characteristic negative MR is related to the $f$$d$ exchange coupling between the electrons at the Ir sites and localized moments at the R sites, which induces magnetic ordering on the R sublattice. Another remarkable feature is unconventional domain wall (DW) conductance. AIAOtype magnetic DW shows metallic behavior in Nd$_{2}$Ir$_{2}$O$_{7}$ while Sm$_{2}$Ir$_{2}$O$_{7}$ shows insulating behavior. This AIAOtype metallic (insulating) DW conductance is thought to be closely related to the existence of Weylsemimetallic state (Mott insulating state) which is consistent with a recent theoretical prediction. [Preview Abstract] 
Thursday, March 16, 2017 2:42PM  2:54PM 
V43.00002: Wide gap Chern Mott insulating phases achieved by design Hongli Guo, Shruba Gangopadhyay, Okan Koeksal, Rossitza Pentcheva, Warren E. Pickett Chern insulators are exciting both as a novel electronic phase and for their novel and potentially useful boundary transport properties. Honeycomb lattices occupied by heavy transition metal ions,have been proposed by Okamoto and coworkers as Chern insulators, but finding a concrete example has been challenging due to an assortment of broken symmetry phases that thwart the topological character. Building on accumulated knowledge of the behavior of the $3d$ series, we tune spinorbit and interaction strength together with strain to design two Chern insulator systems (one with Ru, one with Os) with bandgaps up to 130 meV and Chern numbers ${\cal C}=1$ and ${\cal C}=2$. We find, in this class, that a tradeoff between larger spinorbit coupling and strong interactions leads to a larger gap, whereas the stronger SOC correlates with the larger magnitude of the Hall conductivity. Symmetry lowering in the course of structural relaxation hampers retaining QAH character, as pointed out previously. Fortunately there is only mild structural symmetry breaking of the bilayer in these robust Chern phases.Recent (111) growth of insulating, magnetic phases in closely related materials with this orientation supports the likelihood that synthesis and exploitation will follow. [Preview Abstract] 
Thursday, March 16, 2017 2:54PM  3:06PM 
V43.00003: Topological magnon bands and unconventional superconductivity in pyrochlore iridate thin films Pontus Laurell, Gregory A. Fiete We theoretically study the magnetic properties of pyrochlore iridate bilayer and trilayer thin films grown along the $[111]$ direction using a strong coupling approach. We find the ground state magnetic configurations on a mean field level and carry out a spinwave analysis about them. In the trilayer case the ground state is found to be the allin/allout (AIAO) state, whereas the bilayer has a deformed AIAO state. For all parameters of the spinorbit coupled Hamiltonian we study, the lowest magnon band in the trilayer case has a nonzero Chern number. In the bilayer case we also find a parameter range with nonzero Chern numbers. We calculate the magnon Hall response for both geometries, finding a striking sign change as function of temperature. Using a slaveboson meanfield theory we study the doping of the trilayer system and discover an unconventional timereversal symmetry broken $d+id$ superconducting state. Our study complements prior work in the weak coupling limit and suggests that the $[111]$ grown thin film pyrochlore iridates are a promising candidate for topological properties and unconventional orders. [Preview Abstract] 
Thursday, March 16, 2017 3:06PM  3:18PM 
V43.00004: Strong anisotropy and electronic confinement in 1D quantumstripe superlattices of iridium oxides S. S. A. Seo, J. H. Gruenewald, J. W. Brill, G. Cao, J. Hwang, J. Kim, H. S. Kim, H. Y. Kee Onedimensional (1D) systems offer a platform for studying lowdimensional phenomena associated with the onset of critical quantum phase transitions. Here we present a new approach of synthesizing 1D quantum systems by creating dimensionallyconfined stripesuperlattices from \textit{inplane} oriented 2D layered crystals. We have synthesized 1D IrO$_{2}$ stripes using $a$axis oriented superlattices of Sr$_{2}$IrO$_{4}$ and the wide bandgap insulator LaSrGaO$_{4}$, both of which contain the K$_{2}$NiF$_{4}$ symmetry. The dimensional confinement of our 1D superlattices is confirmed experimentally. Linearly polarized optical spectroscopy shows anisotropic characteristics and onedimensional electronic confinement of the $J_{eff}_{\, }=$ 1/2 band. Spin and orbital excitations observed in resonant inelastic xray scattering suggest enhanced exchange interactions and deconfined orbital excitations in the 1D IrO$_{2}$ stripes. The observed electronic confinement is consistent with density functional theory calculations. The method of transforming layered materials into 1D striped structures is a viable technique for studying dimensionalcrossover phase transitions from two to onedimension. [Preview Abstract] 
Thursday, March 16, 2017 3:18PM  3:30PM 
V43.00005: Tuning intralayer and interlayer couplings in artificial layered structure of perovskite iridate Lin Hao, Derek Meyers, Clayton Frederick, Junyi Yang, Mark Dean, Jian Liu Layered RuddlesdenPopper series Srm$+$1IrmO3m$+$1 iridates have attracted great attention recently for their novel Mott insulating state, spinorbit Heisenberg magnetism, and latent superconductivity. While intense investigation has been devoted to the bulk crystals, their electric and magnetic properties may be mimicked and tailored by confining ultrathin SrIrO3 layers in artificial superlattices, which affords a versatile platform for tuning the competing interactions. In our present work, we have varied both intralayer and interlayer couplings by preparing [(SrIrO3)m, (SrTiO3)n] (m $=$ 1, 2, 3, 4, and $\infty $, while n $=$ 1, 2, 3) superlattices through layerbylayer epitaxial growth. Such a thorough dimensionalitymodulation is absent in the bulk but can provide unique insight into the spinorbitentangled Mott physics. The results from a combination of synchrotron xray diffraction, spectroscopy, electrical and magnetic measurements reveal the interplay between m and n, and a control over the structural, electronic, and magnetic degrees of freedom. [Preview Abstract] 
Thursday, March 16, 2017 3:30PM  3:42PM 
V43.00006: Interfacial charge transfer and magnetism in 5$d$3$d$ oxide heterostructures John Nichols, Xiang Gao, Erjia Guo, Changhee Sohn, John W. Freeland, Yongseong Choi, Daniel Haskel, Satoshi Okamoto, Timothy Charlton, Michael. R. Fitzsimmons, Ho Nyung Lee The existence of strong spinorbit coupling has brought the iridates to the forefront of materials research, whereas strong electronic correlation has proven to produce a plethora of novel properties within the manganites. Here, we investigate the physical properties of interfaces between such materials by synthesizing a series of artificial superlattices with 5$d$ paramagnetic metal SrIrO$_{\mathrm{3}}$ and 3$d$ antiferromagnetic insulators AMnO$_{\mathrm{3}}$, where A $=$ Sr or La. Through our investigations by xray diffraction, magnetometry, dctransport, xray circular dichroism, and polarized neutron reflectometry measurements, we observe both novel magnetic and transport properties, which drastically differ from those of the constituent materials and are highly sensitive to the degree of dimensional confinement within the superlattices. Here we will present these results and discuss the implications of these intriguing magnetic and electronic properties. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. [Preview Abstract] 
Thursday, March 16, 2017 3:42PM  3:54PM 
V43.00007: Manipulation of magnetic exchange in iridate heterostructures D. Meyers, G. Fabbris, Weiguo Yin, D. Casa, Yue Cao, Lin Hao, T. Schmitt, Jian Liu, M. P. M. Dean Artificial layering of disparate materials into superlattices is an emerging method that promises unparalleled versatility in accessing ground states unavailable to bulk synthesis. Heterostructures composed of paramagnetic, metallic SrIrO$_3$ interspaced with band insulating SrTiO$_3$ were found to host a canted antiferromagnetic ground state, mirroring the RuddlesenPopper series iridates with enhanced tunability. We investigate the magnetic excitation spectrum of these artificial systems using resonant inelastic xray scattering and directly infer the interlayer and intralayer magnetic exchange interactions. Understanding how interfacial effects modify magnetic interactions is a vital prerequisite for efforts to controllably target different ground states within complex oxideheterostructures. [Preview Abstract] 
Thursday, March 16, 2017 3:54PM  4:06PM 
V43.00008: Controlling transport of the SrIrO3 correlated semimetal by doping with an ionic liquid. Jacobo Santamaria, J. Tornos, A. PerezMuĂ±oz, M. Cabero, F Gallego, A. Rivera, Z. Sefrioui, M. Varela, C. Leon, J. Garcia Barriocanal, F. Mompean, M. GarciaHernandez 
Thursday, March 16, 2017 4:06PM  4:18PM 
V43.00009: Abstract Withdrawn We report on electrostatic gating of spinorbit coupled Mott insulator Sr$_{2}$IrO$_{4}$ (Sr214) via ferroelectric field effect doping. Field effect doping has been used to modulate electronic phenomena in emerging 2D systems and strongly correlated oxides, but $5d$ systems with large spinorbit coupling have yet to be explored. Upon switching the polarization field of ferroelectric Pb(Zr$_{20}$Ti$_{80}$)O$_{3}$ (PZT) to the downpoled (electronaccumulation) state, temperaturedependent resistivity measurements indicate extremely metallic behavior in the ultrathin Sr214 channel. This work successfully closes the Mott gap in Sr214 in a "clean" doping environment free of chemical disorder, thereby strengthening the link to the isostrucutral highT$_{c}$ cuprates, as Sr214 has been predicted to host $d$wave superconductivity upon electron doping the parent antiferromagnetic insulating phase. Furthermore, the metallic behavior in Sr214 persists for thickness beyond the expected screening length, suggestive of a collective carrier delocalization mechanism. Electrostatically doped carriers prove to be a useful method for tuning the competition between spinorbit and Coulomb interactions in order to trigger novel phase transitions, such as the Mottmetal crossover. 
Thursday, March 16, 2017 4:18PM  4:30PM 
V43.00010: Exploring interfacial ferromagnetism and modulation of magnetic anisotropy in IridateManganite superlattices Di Yi, Charles Flint, Purnima Balakrishnan, Alpha N'Diaye, Elke Arenholz, Yuri Suzuki Recently, research on 5d transition metal oxides (TMOs) with pronounced spinorbit coupling (SOC) has been flourishing due to the emergence of new topological states and potential application in spintronics. Interfaces between 3d and 5d TMOs, where both the Coulomb correlation (U) and SOC are comparably strong, promise emergent properties that differ from those of the bulk constituents. One intriguing example is the SrIrO$_{\mathrm{3}}$/La$_{\mathrm{1x}}$Sr$_{\mathrm{x}}$MnO$_{\mathrm{3}}$ superlattice system. In this series of superlattices, we have observed a metalinsulator transition (MIT) by tuning the hole doping ratio ($x)$. Charge transfer from Ir to Mn cations, as measured by xray absorption spectroscopy, depends on the density of Mn e$_{\mathrm{g}}$ electrons (\textit{1x}). The degree of charge transfer determines the transport properties ranging from metal to insulator. The entire series of superlattices is ferromagnetic despite the fact that La$_{\mathrm{1x}}$Sr$_{\mathrm{x}}$MnO$_{\mathrm{3}}$ is antiferromagnetic for x\textgreater 0.5. More interestingly, we found a systematic evolution of magnetic anisotropy that can be independently modulated by changing the hole doping (x), the thickness of the manganite layer or the thickness of the iridate layer. The evolution of magnetic anisotropy is likely correlated with the symmetry change of oxygen octahedra (BO$_{\mathrm{6}}$, where B $=$ Ir or Mn) at the interface, as revealed by xray dichroism and diffraction measurements. Our results demonstrate that the low dimensional spinorbit entangled 3d5d interfaces provide a new playground to uncover electronic/magnetic properties unattainable in the bulk. [Preview Abstract] 
Thursday, March 16, 2017 4:30PM  4:42PM 
V43.00011: Electronic Properties of SrIrO$_{\mathrm{3}}$ Heterostructures Neil Campbell, Trevor Anderson, ChangBeom Eom, Mark Rzchowski Stronglycorrelated oxide electronic materials have sparked significant interest due to their wideranging electronic properties, including 2dimensional electron gasses, superconductivity, and semimetallic behavior. Strong spinorbit interactions have been predicted to introduce additional behaviors due to their interplay with electronelectron interactions. Perovskite SrIrO$_{\mathrm{3}}$ exhibits strong spinorbit coupling from the heavy iridium atoms, and has been shown to exhibit metalinsulator transitions induced by temperature, thickness, and strain. We probe these states with magnetotransport measurements of ultrathin SrIrO$_{\mathrm{3}}$ films epitaxially layered with polar and nonpolar oxides. The SrIrO$_{\mathrm{3}}$ heterostructures show a lowtemperature transition to a state with enhanced magnetoconductivity, and their sheet resistances exhibit a strong dependence on the interfacing oxide. Understanding these observations will give further insights into the relationship between spinorbit and electron correlations at oxide interfaces, and lead to design rules for strong spinorbit coupled heterostructures. [Preview Abstract] 
Thursday, March 16, 2017 4:42PM  4:54PM 
V43.00012: SpinOrbit Electronic and Magnetic States in 5d Oxide Heterostructures Jian Liu Complex oxides are a class of quantum materials where the delectrons may selforganize into a variety of intriguing emergent electronic and magnetic phases. Recently, there are growing interests in systems where the strong spinorbit coupling (SOC) may add a new dimension to the energetic landscape. On one hand, the interplay of SOC with electronic correlation is believed to derive novel quantum phenomena. But SOC scales with atomic number and is rather small for 3d electrons. On the other hand, while hosting strong SOC, 5d electrons exhibit weaker correlation and often stabilize a nonmagnetic ground state. Establishing approaches to design systems that combine the merits of both fundamental interactions has been challenging. Our investigations on various iridatebased heterostructures, such as iridatemanganite interfaces, show possible routes to control and utilize spinorbitentangled 5d electronic states by epitaxial layering. The experimental findings and theoretical analysis demonstrate heteroepitaxial designs for harnessing the nonsymmorphic semimetallicity in orthoperovskite iridates as well as tailoring spinorbit magnetism and magnetic anisotropy when coupled with 3d magnetic oxides. [Preview Abstract] 
Thursday, March 16, 2017 4:54PM  5:06PM 
V43.00013: Examining the weak localization and weak antilocalization in correlated semimetallic SrIrO$_{\mathrm{3}}$ thin films Le Zhang, Xiaozhe Zhang, Xuanyuan Jiang, Xiaoshan Xu, Xia Hong We have studied the weak localization (WL) and weak antilocalization (WAL) effects in epitaxial SrIrO$_{\mathrm{3}}$ (SIO) thin films to probe the electron correlation and spinorbit coupling (SOC). We deposited 230 nm SIO thin films on SrTiO$_{\mathrm{3}}$ (001) substrates via offaxis RF magnetron sputtering, with caxis (pseudocubic) growth and atomically smooth surfaces achieved. Resistance of the films shows a moderate decrease with decreasing temperature. Modeling the Hall effect result with the twocarrier model and assuming equal electron and holedensities, we extracted a carrier density of \textasciitilde 10$^{\mathrm{20}}$ cm$^{\mathrm{3}}$ and comparable electron and hole mobility of \textasciitilde 50 cm$^{\mathrm{2}}$/Vs. For films below 5 nm, we observed a slight resistance upturn at low temperature, which can be attributed to WL. The low temperature magnetoconductance (MC) (215 K) shows a transition from WAL to WL. By fitting the MC with the MaekawaFukuyama model, we extracted the inelastic dephasing time and spin relaxation time. While the inelastic field shows linear temperature dependence, suggesting electronelectron interaction as the phase breaking mechanism, the spin relaxation field exhibits quadratic temperature dependence. We also explore the effect of carrier doping on the spin relaxation time using the electric field effect approach. [Preview Abstract] 
Thursday, March 16, 2017 5:06PM  5:18PM 
V43.00014: Dimensionalitystrain phase diagram of strontium iridates superlattices Bongjae Kim, Peitao Liu, Cesare Franchini Using {\it ab initio} approach, we study the electronic and magnetic behavior of strontium iridates as a function of dimensionality and epitaxial strain by employing a (SrIrO$_3$)$_m$/(SrTiO$_3$) superlattice structure. We quantitatively evaluate the dimensional and straindependent change of the interaction parameters $U$ and $J$ using the constraint random phase approximation and construct a comprehensive phase diagram describing the evolution of the electronic and magnetic ground state upon strain and dimensionality. We find that compressive strain and increasing the dimensionality perturb the insulating relativistic Mott $J_{eff}=1/2$ state, a characteristic of the $m=1$ system, and induce two distinct types of insulatortometal transition (IMT) that can be explained from the entanglement of $U$ and the bandwidth of the Ir$t_{2g}$ manifold. The IMTs are associated with distinctive changes of the spin ordering manifested by spinflop transitions, correlated with the modulation of the interlayer exchange interaction, and with a complete quenching of any spinordered state in the $m\rightarrow\infty$ limit. The fundamental origin of these electronic and magnetic transitions will be discussed and compared with the corresponding situation in the RuddlesdenPopper series. [Preview Abstract] 
Thursday, March 16, 2017 5:18PM  5:30PM 
V43.00015: SpinOrbital entangled 2DEG in the $\delta$doped interface La$_{\delta}$Sr$_2$IrO$_4$: DensityFunctional Studies and Transport Results from Boltzmann Equations Churna Bhandari, Zoran Popovic, Sashi Satpathy The strong spinorbit coupled iridates are of considerable interest because of the Mottminsulating state,which is produced by the combined effect of a strong spinorbit coupling (SOC) and Coulomb repulsion. In this work, using densityfunctional methods, we predict the existence of a spinorbital entangled two dimensional electron gas (2DEG) in the deltadoped structure, where a single SrO layer is replaced by an LaO layer. In the bulk Sr$_2$IrO$_4$, a strong SOC splits the $t_{2g}$ states into $J_{eff}=1/2$ and $3/2$ states. The Coulomb repulsion further splits the halffilled $J_{eff}=1/2$ bands into a lower and an upper Hubbard band (UHB) producing a Mott insulator. In the $\delta$doped structure, La dopes electrons into the UHB, and our results show that the doped electrons are strongly localized in one or two Ir layers at the interface, reminiscent of the 2DEG in the wellstudied LaAlO$_3$/SrTiO$_3$ interface. The UHB, consisting of spinorbit entangled states, is partially filled, resulting in a spinorbital entangled 2DEG. Transport properties of the 2DEG shows many interesting features, which we study by solving the semiclassical Boltzmann transport equation in the presence of the magnetic and electric fields. [Preview Abstract] 
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