Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session A26: Experimental Advances in Strongly Spin-orbit Coupled OxidesFocus
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Sponsoring Units: DMP Chair: Kyle Shen, Cornell Room: 325 |
Monday, March 14, 2016 8:00AM - 8:12AM |
A26.00001: Ultrafast Optical Reflectivity Study of Photo-Carrier Relaxation Dynamics in Perovskite Iridates Hao Chu, Liuyan Zhao, Tom Hogan, Stephen Wilson, David Hsieh The Ruddlesden-Popper series of perovskite iridates Sr$_{n+1}$Ir$_{n}$O$_{3n+1}$ lie close to a localization-delocalization boundary, evolving from a Mott-like magnetic insulator in the single layer (n=1) compound to a paramagnetic semi-metal in the infinite layer (n=$\infty$) compound. We will discuss the insulator-to-metal transition in perovskite iridates from the point of view of time-resolved optical reflectivity measurements. This technique probes the relaxation dynamics of photo-generated carriers, which are strongly affected by the presence of a charge gap. [Preview Abstract] |
Monday, March 14, 2016 8:12AM - 8:24AM |
A26.00002: Ionic liquid gating Sr$_{2}$IrO$_{4}$ single crystal Boyi Yang, Allen Goldman The 5d iridates have attracted much interest due to the prediction of novel electronic phases driven by the interplay of spin-orbit coupling with onsite Coulomb interaction. The compound Sr$_{2}$IrO$_{4}$, with a crystal structure similar to that of La$_{2}$CuO$_{4}$, was identified as a spin-orbital Mott insulator. It has been doped in various ways in search of a possible superconducting state considering its similarities to the cuprates. Unlike the common ionic liquid gated thin film field effect transistor (FET), here we have fabricated an ionic liquid (DEME-TFSI) gated FET based on the cleaved ab plane surface of a Sr$_{2}$IrO$_{4}$ single crystal. Due to the insulating behavior of the bulk, the sensitive surface gating effect can be characterized with transport property measurements. We find an insulator to metal transition around 75K upon hole doping, while a minimal gating effect is observed on electron accumulation at the cleaved single crystal surface. The low temperature metallic behavior will be further studied in detail and the latest experimental results will be reported. [Preview Abstract] |
Monday, March 14, 2016 8:24AM - 8:36AM |
A26.00003: Decoupling of the Antiferromagnetic and Insulating States in Tb doped Sr2IrO4 H. Zheng, J.C. Wang, F. Ye, S. Aswartham, J. Terzic, S.J. Yuan, D. Haskel, Y. Choi, S. Chikara, P. Schlottmann, R. Custelcean, G. Cao We report results of a comprehensive study of single-crystal Sr$_{\mathrm{2}}$Ir$_{\mathrm{1-x}}$Tb$_{\mathrm{x}}$O$_{\mathrm{4}}$ (0$\le $x$\le $0.03). This study found that mere 3{\%} (x$=$0.03) tetravalent Tb$^{\mathrm{4+}}$ substituting for Ir$^{\mathrm{4+}}$ (rather than Sr$^{\mathrm{2+}})$ completely suppresses the long-range collinear AFM transition but retains the insulating state. Tb doping effectively changes the relative strength of the SOI and the tetragonal CEF and enhances the Hund's rule coupling that competes with the SOI, and destabilizes the AFM state. We observe unconventional correlation between the AFM and insulating states in which the magnetic transition plays no critical role in the formation of the charge gap in the iridate. [Preview Abstract] |
Monday, March 14, 2016 8:36AM - 9:12AM |
A26.00004: Switching the d-wave gap in layered perovskite iridates via spin reorientation Invited Speaker: Bumjoon Kim We demonstrate switching of the $d$-wave charge gap in electron-doped Sr$_{\mathrm{3}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$ through changing the spin easy axis. The pristine, undoped Sr$_{\mathrm{3}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7\thinspace }}$has $c$-axis collinear antiferromagnetic structure with strong Ising anisotripy, which gaps out magnons with an unprecedentedly large energy scale of 90 meV. However, a metastable phase with \textit{ab} easy-plane anisotropy is found in some surfaces of Sr$_{\mathrm{3}}$Ir$_{\mathrm{2}}$O$_{\mathrm{7}}$, for which low-energy magnons are expected. Doping electrons to the latter leads to opening of a $d$-wave charge gap below \textasciitilde 30 K, which is not found in the former. Our results indicate the magnetic origin of the $d$-wave gap in electron-doped layered perovskite iridates, and suggest a mechanism to control the charge gap via the spin degrees of freedom. [Preview Abstract] |
Monday, March 14, 2016 9:12AM - 9:24AM |
A26.00005: Isotropic and anisotropic regimes of the spin-dynamics in Sr$_{2}$IrO$_{4}$ : Field-dependent Raman scattering study Y. Gim, A. Sethi, Q. Zhao, J.F. Mitchell, G. Cao, S.L. Cooper Experimental studies of the strong spin-orbit coupled material, Sr$_{2}$IrO$_{4}$, have provided evidence that the spin dynamics of this material can be described by an isotropic two-dimensional effective Heisenberg description. To study how well this description describes the spin-dynamics of Sr$_{2}$IrO$_{4}$ in different magnetic field regimes, in this talk, we present field-dependent Raman scattering studies of the low-energy spin-dynamics in Sr$_{2}$IrO$_{4}$. We find that for H\textgreater 1.5 T, the spin-dynamics of Sr$_{2}$IrO$_{4}$ are well described by an isotropic, 2D description. However, at low fields, H\textless 1.5 T, the spin dynamics show evidence for the effects of in-plane anisotropy and interlayer coupling. These effects must therefore be considered when modeling the low-field magnetic and dynamical properties of Sr$_{2}$IrO$_{4}$. [Preview Abstract] |
Monday, March 14, 2016 9:24AM - 9:36AM |
A26.00006: From J$_{\mathrm{eff}}=$1/2 insulator to p-wave superconductor in single-crystal Sr$_{\mathrm{2}}$Ir$_{\mathrm{1-}}_{x}$Ru$_{x}$O$_{\mathrm{4}}$ (0 $\le $ x $\le $ 1) Shujuan Yuan, Saicharan Aswartham, Jasminka Terzic, Hao Zheng, Hengdi Zhao, Pedro Schlottmann, Gang Cao Sr$_{\mathrm{2}}$IrO$_{\mathrm{4}}$ is a magnetic insulator assisted by strong spin-orbit coupling (SOC) whereas the Sr$_{\mathrm{2}}$RuO$_{\mathrm{4}}$ is a p-wave superconductor. Our investigation of structural, transport, and magnetic properties reveals that substituting 4d Ru$^{\mathrm{4+}}$ (4d$^{\mathrm{4}})$ ions for 5d Ir$^{\mathrm{4+}}$(5d$^{\mathrm{5}})$ ions in Sr$_{\mathrm{2}}$IrO$_{\mathrm{4}}$ directly adds holes to the t$_{\mathrm{2g}}$ bands, reduces the SOC and thus rebalances the competing energies in single-crystal Sr$_{\mathrm{2}}$Ir$_{\mathrm{1-x}}$Ru$_{\mathrm{x}}$O$_{\mathrm{4}}$. A profound effect of Ru doping driving a rich phase diagram is a structural phase transition from a distorted $I$4$_{\mathrm{1}}$/\textit{acd }to a more ideal $I$4/\textit{mmm }tetragonal structure near x$=$0.50 that accompanies a phase transition from an antiferromagnetic-insulating state to a paramagnetic-metal state. We also make a comparison drawn with Rh doped Sr$_{\mathrm{2}}$IrO$_{\mathrm{4}}$, highlighting important similarities and differences. [Preview Abstract] |
Monday, March 14, 2016 9:36AM - 9:48AM |
A26.00007: Probing Novel States of Iridates and Ruthenates under Extreme Conditions Jasminka Terzic, Hao Zheng, Panpan Kong, Chanqing Jin, Daniel Haskel, Oleksandr Korneta, Shujuan Yuan, Gang Cao The highly delicate balance between competing energies in materials of interest makes high-pressure and high-magnetic-field powerful probes for generating novel states. Our studies have uncovered a number of remarkable properties of iridates and ruthenates under extreme conditions: avoidance of metallization at high pressures, absent conventional correlations between magnetic and insulating states in iridates; coexistence of a bulk insulating state and quantum oscillations period in 1/B or B (depending on the orientation of B which is applied magnetic field), and colossal magnetoresistivity without spin polarization in ruthenates. We will present and discuss our results with comparison drawn with relevant systems. [Preview Abstract] |
Monday, March 14, 2016 9:48AM - 10:00AM |
A26.00008: Mott Physics in lightly doped (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$ Gregory Affeldt, Tom Hogan, Christopher Smallwood, Tanmoy Das, Jonathan Denlinger, Sung-Kwan Mo, Stephen Wilson, Alessandra Lanzara The layered perovskite iridates Sr$_2$IrO$_4$ and Sr$_3$Ir$_2$O$_7$ exhibit a spin-orbit Mott insulating state that becomes metallic upon sufficient carrier doping. While Sr$_2$IrO$_4$ presents striking similarities to cuprates upon electron doping, Sr$_3$Ir$_2$O$_7$ appears to be a correlated metal. We show a detailed doping and temperature-dependent ARPES study which reveals important similarities between (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$ and doped Sr$_2$IrO$_4$, as well as other doped Mott insulators. [Preview Abstract] |
Monday, March 14, 2016 10:00AM - 10:12AM |
A26.00009: Shubnikov-de Haas oscillation of KTaO$_{\mathrm{3}}$ based electron gases Ludi Miao, Renzhong Du, Qi Li Two-dimensional electron gases (2DEGs) at transition metal oxide (TMO) surfaces and interfaces have attracted much attention due to their exotic properties such as superconductivity, and ferromagnetism. Recently, 5$d$ TMOs are hotly investigated due to their strong spin-orbit coupling (SOC), an indispensable element for topolotical insulating states. Among them, KTaO$_{\mathrm{3}}$ not only hosts 2DEGs but also involves strong SOC. We have created KTaO$_{\mathrm{3}}$ based electron gases, with low temperature mobility as large as 8000cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}}$. Shubnikov de Haas oscillations in magnetoresistance have been observed at 1.8 K for field applied along various directions. Contributions from $d_{\mathrm{xy}}$ and $d_{\mathrm{xz/yz}}$ bands are both seen. These oscillation curves exhibit a field direction dependence with 4-fold symmetry, revealing the cubic symmetry of Fermi surface of KTaO$_{\mathrm{3}}$ based electon gases. Moreover, the intercept of oscillation indices is close to 0.5, a typical value for systems that involve strong SOC. Our results provide unique insights into the electronic structures of KTaO$_{\mathrm{3}}$ based electron gases via magnetotransport measurements. [Preview Abstract] |
Monday, March 14, 2016 10:12AM - 10:24AM |
A26.00010: Pulsed laser deposition and characterizations of pyrochlore iridate thin films Matthew Starr, Jaime Aviles-Acosta, Yuantao Xie, Wenka Zhu, Zhen Li, Aiping Chen, Nan Li, Chenggang Tao, Quanxi Jia, J. J. Heremans, S. X. Zhang Pyrochlore iridates have attracted growing interest in recent years because of their potential to realize novel topological phases. While most of the previous studies have focused on polycrystalline and single crystalline bulk samples, epitaxial thin films offer a unique platform for controllable tuning of material parameters such as oxygen stoichiometry and elastic strain to achieve new electronic states. In this talk, we will present the growth and characterizations of epitaxial thin films of pyrochlore Y2Ir2O7 and Bi2Ir2O7 that are predicted to host topologically non-trivial states. The iridate thin films were grown by pulsed laser deposition at different conditions, and a narrow window for epitaxial growth was determined. Characterizations of crystalline structures were performed using X-ray diffraction and transmission electron microscopy to establish a growth parameter-structure phase diagram. The compositions of thin films were determined by energy dispersive X-ray spectroscopy, and the surface morphologies were characterized using atomic force microscopy and scanning tunneling microscopy. Magneto-transport studies indicate a strong dependence of transport properties on the oxygen stoichiometry and the film thickness. [Preview Abstract] |
Monday, March 14, 2016 10:24AM - 10:36AM |
A26.00011: Strongly enhanced Rashba splitting in the perovskite tantalate-hafnate heterostructure Suk Bum Chung, Minsung Kim In addition to superconductivity and magnetism, one notable ingredient of the two-dimensional electron gas (2DEG) emerging at the transition metal oxide surface is the Rashba-Dresselhaus spin-orbit interaction, the momentum-dependent spin splitting due to the broken inversion symmetry and atomic spin-orbit coupling. However, it has not been understood how this splitting can be maximized in a physical system without applying external electric field. Here, we present a promising route to realize significant Rashba-type band splitting using thin film heterostructure. Based on a first-principles method and analytic model analysis, a tantalate layer on BaHfO$_3$ is shown to host a two-dimensional bands originating from Ta $t_{2g}$ orbitals with strongly enhanced Rashba-Dresselhaus spin splittings at both the band minima and saddle points. A significant $t_{2g}$-$e_g$ coupling that contributes to this enhanced splitting is likely to be a generic feature for the surface 2DEG of transition metal oxide with maximal inversion symmetry breaking. Our results could be important in realizing topological superconductivity and potentially useful for spintronics application. [Preview Abstract] |
Monday, March 14, 2016 10:36AM - 10:48AM |
A26.00012: Elastic and inelastic scattering in SrTiO$_{\mathrm{3-\delta }}$ Kamran Behnia, Xiao Lin, Benoit Fauqué Scattering among electrons generates a distinct contribution to electrical resistivity that follows a quadratic temperature dependence. We show that the prefactor of this T$^{\mathrm{2}}$ resistivity can be tuned by four orders of magnitude in metallic SrTiO$_{\mathrm{3}}$ by tuning the concentration of the carriers and consequently, the Fermi energy. The T$^{\mathrm{2}}$ behavior persists in the single-band dilute limit despite the absence of two known mechanisms for T$^{\mathrm{2}}$ behavior, distinct electron reservoirs and Umklapp processes. The ultimate origin of the small residual resistivity is the long Bohr radius, which, in a shallow Fermi sea caused by a random distribution of dopants, sets the zero-temperature mobility. [Preview Abstract] |
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