Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session X31: Focus Session: Ruthenates |
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Sponsoring Units: DMP GMAG Chair: Igor Mazin, Naval Research Laboratory Room: Morial Convention Center 223 |
Friday, March 14, 2008 8:00AM - 8:36AM |
X31.00001: Metallic Spin Liquid Behavior and Unconventional Anomalous Hall Transport of the Geometrically Frustrated Kondo Lattice Pr$_2$Ir$_2$O$_7$ Invited Speaker: Among metallic magnets on geometrical frustrated lattices, the pyrochlore oxide Pr$_{2}$Ir$_{2}$O$_{7}$ is unique for its metallic spin liquid behavior \footnote{S. Nakatsuji, Y. Machida, Y. Maeno, T. Tayama, T. Sakakibara, J. v. Duijn, L. Balicas, J. N. Millican, R. T. Macaluso, and Julia Y. Chan, \textit{Phys. Rev. Lett.} \textbf{96}, 087204 (2006).}, and unconventional Hall transport phenomena \footnote{Y. Machida, S. Nakatsuji, Y. Maeno, T. Tayama, T. Sakakibara, and S. Onoda, \textit{Phys. Rev. Lett.} \textbf{98}, 057203 (2007).}. Despite the Weiss temperature $T^* = 20$ K deu to the RKKY interaction, Pr$_{2}$Ir$_{2}$O$_{7}$ exhibits no magnetic long range order, but spin freezing at a very low temperature $\sim 120$ mK. Instead, the Kondo effect, including ln$T$ dependence in the resistivity, emerges and leads to partial screening of the $4f$-moments below $T^*$. Moreover, the underscreened 4f- moments show spin-liquid behavior below a renormalized energy scale of $\theta_{\rm{w}}\sim 1.7$ K. Interestingly, in this spin-liquidlike paramagnetic regime, the Hall resistivity $\rho_ {xy}$ becomes largely enhanced, and shows behavior far different from anomalous Hall effects (AHE) due to the spin- orbit coupling observed in ordinary magnetic conductors. We discuss the origin of the metallic spin liquid behavior and unconventional AHE in terms of the spin chirality due to the non-coplanar texture of the $<111>$ Ising-like Pr moments. This work is based on the collaboration with Y. Machida, T. Tayama, T. Sakakibara (ISSP, Univ.of Tokyo), Y. Maeno (Kyoto Univ.), S. Onoda (RIKEN, Tokyo), C. Broholm (Johns Hopkins Univ.), C. Stock and J. van Duijn (ISIS), L. Balicas (NHMFL), Jung Young Cho, and Julia Y. Chan (Louisiana State Univ.). [Preview Abstract] |
Friday, March 14, 2008 8:36AM - 8:48AM |
X31.00002: Magnetic phase diagram of (Sr$_{1-x}$Ca$_{x})_{3}$Ru$_{2}$O$_{7 }$ (0$\le $x$\le $1.0) Z.Q. Mao, Z. Qu, L. Spinu, J. Peng, T.J. Liu, D. Fobes, V. Dobrosavljevic, H.Q. Yuan, W. Bao, J.W. Lynn The layered ruthenates (Sr,Ca)$_{n+1}$Ru$_{n}$O$_{3n+1}$ have received widespread attention in recent years since they display a remarkable range of unique superconducting and magnetic properties, such as spin triplet superconductivity and metamagnetic quantum criticality. We have recently studied properties of the double layered (Sr$_{1-x}$Ca$_{x})_{3}$Ru$_{2}$O$_{7}$ solid solution series and established the magnetic phase diagram of this system using the high-quality single crystals grown by floating-zone method. We have observed rich magnetic ground states in this system: (I) Itinerant metamagnetic state (0.08$>x\ge $0); (II) enhanced PM state accompanied by non-Fermi liquid behaviors near $x\sim $0.08; (III) ferromagnetic cluster glass (CG) phase featuring an extremely large Wilson ratio ($\sim $120) and enhanced electron correlation (0.40$>x>$0.08); (IV) long-range AFM state (1$\ge x\ge $0.40). Furthermore, we found a new phase which shows an unconventional anomalous Hall effect in a low temperature range immediately above the CG phase. The magnetization of this phase is found to follow a new scaling expression derived by phenomenologically extending the quantum Griffiths phase model. [Preview Abstract] |
Friday, March 14, 2008 8:48AM - 9:00AM |
X31.00003: ARPES Investigations of the Electronic Structure Evolution of the Doped Ruthenate (Sr$_{1-x}$Ca$_{x})_{3}$Ru$_{2}$O$_{7}$ William Dunkel, Felix Baumberger, Milan Allan, Worawat Meevasana, Zhiqiang Mao, Zhi-Xun Shen The bilayer ruthenate system (Sr$_{1-x}$Ca$_{x})_{3}$Ru$_{2}$O$_{7}$ can be grown in the full range of dopings with the end members being an antiferromagnetic ``bad metal'' (x=1) and a paramagnetic Fermi liquid displaying a metamagnetic transition under applied field (x=0). Recent transport and magnetization measurements have shown that the system displays disorder-induced unconventional quantum critical behavior near the doping level x$\sim $0.3. We present ARPES data for a range of dopings to investigate the associated electronic structure evolution. [Preview Abstract] |
Friday, March 14, 2008 9:00AM - 9:12AM |
X31.00004: Study of the Layered Perovskite $Sr_3Ru_2O_7$ by STS and ARPES. Milan Allan, J. Lee, M. Wang, A. Schmidt, F. Baumberger, A. Tamai, J. Farrell, J.C. Davis, A. Mackenzie The Ruddlesden-Popper series, $Sr_{n+1}Ru_nO_{3n+1}$ exhibits a variety of electronic phases, including triplet superconductivity (n=1) or metamagnetism (n=2). Here we report studies of the electronic structure of the bilayered perovskite $Sr_3Ru_2O_7$ (n=2) by means of scanning tunneling spectroscopy. Special attention is given to the influence of titanium impurity atoms on the local electronic structure. A comparison with angle resolved photoemission experiments on the same set of samples is drawn. [Preview Abstract] |
Friday, March 14, 2008 9:12AM - 9:24AM |
X31.00005: Quasi-3D ordered lattice modulations in a bilayer ruthenate with no long-range order Zahirul Islam, Zhe Qu, Yejun Feng, Jonathan Lang, Jin Peng, Zhiqiang Mao Bulk measurements reveal disorder-induced unconventional quantum critical behaviors in (Sr$_{1-x}$Ca$_x$)$_3$Ru$_2$O$_7$ (SCRO) compounds, in particular, near $x = 0.3$. Here we report X-ray scattering studies on SCRO with $x =0.3$, as well as those for the end members. We find that at $x = 0.3$ robust 2-unit-cell periodic lattice modulations exist that are characterized by $(\frac12,0,0)$ and $(0,\frac12,0)$, respectively, even at room temperature. These modulations are transversely polarized and quasi-3D ordered in that they are fully coherent in the basal plane with {\bf c} axis correlations at least one unit cell in extent. These modulations are due to correlated displacements of the O atoms. The displacement pattern is consistent with $t_{2g}$-modes of distortion of RuO$_6$ octahedra, signifying the presence of lattice and orbital correlations, although no long-range magnetic or orbital order is present. These modulations are absent in the end members. [Preview Abstract] |
Friday, March 14, 2008 9:24AM - 9:36AM |
X31.00006: Doping-Induced Structural and Physical Properties Changes in Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7}$ Single Crystals Biao Hu, Manuel Angst, Ovidiu Garlea, V.B. Nascimento, David Mandrus, E.W. Plummer, R. Jin In the homologous strontium ruthenate series Sr$_{n+1}$Ru$_{n}$O$_{3n+1}$, double-layered Sr$_{3}$Ru$_{2}$O$_{7}$ exhibits unique physical properties. However, the partial substitution of Ru by the smaller Mn was found to change its ground state from a paramagnetic metal to an antiferromagnetic insulator with less distorted crystal structure. Interestingly, our Hall effect measurements show no change in the carrier concentration (x $\le $ 0.2), suggesting that Mn is isovalent with Ru in Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7}$. This is further supported by the magnetization data, which yield effective spin S = 3/2 for Mn corresponding to Mn$^{4+}$. In addition to bulk physical properties, the doping dependence of the surface structure and lattice dynamics of Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7}$ single crystals will be discussed. [Preview Abstract] |
Friday, March 14, 2008 9:36AM - 9:48AM |
X31.00007: Relation between structure and magnetic properties in (Sr$_{1-x}$Ca$_{x})_{3}$Ru$_{2}$O$_{7}$ J. Peng, Z. Qu, L. Spinu, T.J. Liu, D. Fobes, Z.Q. Mao The (Sr$_{1-x}$Ca$_{x})_{3}$Ru$_{2}$O$_{7}$ solid solution series exhibits rich magnetic ground states, ranging from itinerant metamagnetism, ferromagnetic instability, ferromagnetic cluster glass, to antiferromagnet.$\left[1\right]$ In this talk, we report a study on the relation between structure and magnetic properties in (Sr$_{1-x}$Ca$_{x})_{3}$Ru$_{2}$O$_{7}$. Our Rietveld refinement of x-ray scattering data shows that the rotation angle of RuO$_{6}$ octahedra increases with increasing $x$, and approaches saturation for $x>$0.2. The orthorhombicity, which is caused by the tilting of RuO$_{6}$ octahedra, occurs for $x>$0.4 and enhances significantly for $x>$0.7. By comparing these structural characteristics with the magnetic properties, we conclude that the ferromagnetic instability originates from the RuO$_{6}$ octahedra rotation, and the tilting of RuO$_{6}$ octahedra causes a significant magnetic anisotropy.\\ $\left[1\right]$ Z. Qu \textit{et al.} arXiv:0708.1291 (2007). [Preview Abstract] |
Friday, March 14, 2008 9:48AM - 10:00AM |
X31.00008: QPI in $Sr_3Ru_2O_7$. Jinho Lee, M. Wang, M. Allan, A. Schmidt, F. Baumberger, A. Tamai, J. Farrell, J. C. Davis, A. Mackenzie $Sr_{n+1}Ru_nO_{3n+1}$ family drew substantial attention recently due to its plethora of electronic phases like triplet superconductivity or metamagnetism. $Sr_3Ru_2O_7$ (n=2) is very similar to the triplet superconductor $Sr_2RuO_4$ in 2D conductivity as well as in structure, but shows no superconductivity. Understanding of the underlying band structure is the first step to fathom this strongly correlated oxide. STM has proven to be a high precision tool to measure band dispersions in momentum space along with the atomically resolved real space spectroscopic properties. Here we report the first atomically resolved 2D spectroscopic maps in $Sr_3Ru_{2(1-x)}Ti_{2x}O_7$ where QPI patterns are observed and discuss the band landscape responsible for the QPI in this energy range. [Preview Abstract] |
Friday, March 14, 2008 10:00AM - 10:12AM |
X31.00009: Orbital Hierarchy Inversion and Magnetic Transition in Mn Doped Sr$_3$Ru$_2$O$_7$ Muhammed Hossain, M.W. Haverkort, Z.H. Hu, T. Burnus, C.F. Chang, S. Klein, J.D. Denlinger, H.-J. Lin, C.T. Chen, R. Mathieu, Y. Kaneko, Y. Tokura, S. Satow, Y. Yoshida, H. Takagi, A. Tanaka, I.S. Elfimov, G.A. Sawatzky, L.H. Tjeng, A. Damascelli Ruthenium oxides are a very important class of compounds that are extremely sensitive to impurities. Here we present a study of the Mn doped Sr$_3$Ru$_2$O$_7$ by X-ray Absorption Spectroscopy (XAS) and a combination of density functional theory (LSDA) and cluster calculations. We find that delocalized RuO matrix forces the Mn impurities to behave as a negative charge transfer system and donate a hole. As a result Mn impurities behave as Mn3+ acceptors. Our XAS data clearly shows that the occupied $e_g$ orbitals have an in-plane alignment: a very surprising result in a tetragonally distorted system elongated along the $c$-axis. LSDA calculations reveal very strong anisotropy in oxygen bandwidth leading to a reversal of the $e_g$ crystal field hierarchy. This work further establishes that the Mn atoms are sitting in a bath of a uniaxial exchange field that gradually goes out-of-plane to in-plane as the Mn doping level is increased. Overall, the behavior has some similarities with Mn doped GaAs and may be relevant to the physics of dilute magnetic semiconductors. [Preview Abstract] |
Friday, March 14, 2008 10:12AM - 10:24AM |
X31.00010: Temperature dependence of a zero bias anomaly in scanning tunnelling spectra of Sr(4)Ru(3)O(10) Bernhard Nansseu, Tatjana Novgorodov, Michael Waelsch, J\"urgen Hager, Jiandi Zhang, R. Moore, Ward Plummer, Zhiqiang Mao, Rene Matzdorf We have studied a zero bias anomaly in scanning tunnelling spectra of layered ruthenate Sr(4)Ru(3)O(10). This material shows a dip-like feature in the dI/dV spectra, which has previously observed in the single-layer Sr(2)RuO(4) and double- layer Sr(3)Ru(2)O(7) ruthenates. We have studied in particular the temperature dependence of the zero bias anomaly, which is in all three materials different. The triple-layer material shows intergrowth of single and double layers, which have been identified by their spectroscopic fingerprint. Finally, we discuss different effects as possible explanations for the zero bias anomaly. [Preview Abstract] |
Friday, March 14, 2008 10:24AM - 10:36AM |
X31.00011: Anisotropy of magnetoresistivity in trilayered ruthenate Sr$_{4}$Ru$_{3}$O$_{10}$: Evidence for orbital dependent metamagnetism D. Fobes, M. Zhou, T.J. Liu, Z. Qu, H.Q. Yuan, M. Salamon, Z.Q. Mao Trilayered ruthenate Sr$_{4}$Ru$_{3}$O$_{10}$ is ferromagnetic with T$_{c}$ $\approx $ 100K and moderate in-plane magnetic field (B$_{c }\approx $ 2T) induces an itinerant metamagnetic transition [1,2]. Such metamagnetism within a FM ground state cannot be understood with a single band model of a field-tuned Stoner transition. We have measured azimuthal angular dependence of in-plane and out-of-plane magnetoresistivity ($\rho _{ab}(\phi $,B) and $\rho _{c}(\phi $,B)). We found that for B$<$B$_{c}$, at fixed field $\rho _{ab}(\phi )$ exhibits a two-fold anisotropy attributable to anisotropic behavior of an Ising ferromagnet, while $\rho _{c}(\phi )$ does not show such a behavior. For B$>$B$_{c}$, both $\rho _{ab}(\phi )$ and $\rho _{c}(\phi )$ exhibit a four-fold symmetry anisotropy, but the minimum value in $\rho _{ab}(\phi )$ and $\rho _{c}(\phi )$ occurs along different directions, i.e., [100] and [010] for $\rho _{ab}$, and [110] and [1$\overline{1}$0] for $\rho _{c}$. Such a difference in anisotropic behavior between $\rho _{ab}(\phi )$ and $\rho _{c}(\phi )$ provides strong support that metamagnetism in Sr$_{4}$Ru$_{3}$O$_{10}$ is orbital dependent, i.e., ferromagnetic and metamagnetic bands coexist. \\ $\left[1\right]$ Cao et al., Phys. Rev. B 68, 174409 (2003)\\ $\left[2\right]$ Mao et al., Phys. Rev. Lett. 96, 077205 (2006)\\ Work at Tulane is supported by NSF, DOE and the Research Corporation. [Preview Abstract] |
Friday, March 14, 2008 10:36AM - 10:48AM |
X31.00012: Fermi Surface mapping of Sr$_4$Ru$_3$O$_{10}$ using Angle Resolved Photoemission R.S. Singh, F. Wang, J.W. Allen, J.D. Denlinger, X.N. Lin, Gang Cao Layered strontium ruthenates in the Ruddlesden-Popper series (Sr$_{n+1}$Ru$_n$O$_{3n+1}$) are scientifically interesting and technologically promising materials exhibiting various novel electronic and magnetic properties. We will show the effect of dimensionality on the electronic structure as one goes from two dimensional to three dimensional crystal structures by increasing $n$. In particular, we will present new results and analysis of photon energy dependent angle resolved photoemission spectroscopy measurements on Sr$_4$Ru$_3$O$_{10}$ and make detailed comparison of Fermi surface maps with recently measured Shubnikov-de Haas frequencies and available LDA band structure calculations corresponding to various layered strontium ruthenates. \vspace{.5cm} \\ Work supported by U.S. DOE (DE-AC03-76SF00098 at ALS, DE-FG02-07ER46379 at UM currently) and U.S. NSF (DMR-03-02825 at UM initially, DMR-02-40813 at UK). [Preview Abstract] |
Friday, March 14, 2008 10:48AM - 11:00AM |
X31.00013: Mid-infrared Hall conductivity in Ca$_x$Sr$_{1-x}$RuO$_3$ films M.-H. Kim, G. Acbas, M.-H. Yang, V. Kurz, M. Eginligil, J. Cerne, P. Khalifah, I. Ohkubo, H. Christen, D. Mandrus, Z. Fang We have studied the complex longitudinal ($\sigma_{xx}$) and transverse (Hall, $\sigma_{xy}$) conductivities in a series of Ca$_x$Sr$_{1-x}$RuO$_3$ films by measuring the magnetic field induced polarization changes of mid-infrared (100 - 1000 meV) radiation in the 10~K-300~K temperature range. The infrared $\sigma_{xy}$ shows strong energy dependence and sign changes. We compare the complex magneto-conductivities $\sigma_{xx}$ and $\sigma_{xy}$ [M.-H. Kim, PRB 2007] with dc measurements and with calculations [Z. Fang, Science 2003] of the intrinsic anomalous Hall effect. To test the accuracy of these measurements and to remove the background magneto-optical response of windows and substrates, the magnetic field induced changes in the polarization of transmitted light also were measured in GaAs, ZnSe, and BaF$_2$. This work was supported by the Research Corp. Cottrell Scholar Award (UB), NSF-CAREER-DMR0449899 (UB), and an instrumentation award from the CAS(UB). Oak Ridge Nat. Lab.is managed by UT- Battelle, LLC, for the U.S. DOE (contract DE-ACO5-00OR22725). [Preview Abstract] |
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