Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session A30: Focus Session: Vanadates, Iridates and Other Oxides |
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Sponsoring Units: DMP GMAG Chair: Stephen Nagler, Oak Ridge National Laboratory Room: 334 |
Monday, March 16, 2009 8:00AM - 8:12AM |
A30.00001: Electronic band structure of metallic phase V$_{2}$O$_{3}$ O. Krupin, J. Denlinger, B.J. Kim, Ravi S. Singh, J.W. Allen V$_{2}$O$_{3}$ has an archetypal strongly correlated paramagnetic metallic (PM) phase which becomes insulating with alloying or decreasing temperature. Recent progress has been made experimentally to measure the true bulk V 3d density of states of PM phase V$_{2}$O$_{3}$ using high-energy angle-integrated photoemission, and theoretically to quantitatively describe the observed prominent quasiparticle peak near E$_{F}$ using LDA+DMFT. Theoretical predictions of the k-resolved electronic band structure of V$_{2}$O$_{3}$ have been made, but experimental measurement has proven to be very challenging and elusive. We present intermediate-energy soft x-ray angle-resolved photoemission measurements of the PM-phase V$_{2}$O$_{3}$ (0001) cleaved surface that reveal for the first time distinct k-resolved band dispersions within the coherent quasiparticle peak and a corresponding three-fold symmetric Fermi surface topology. The agreement of these measurements to theoretical calculations will be discussed. [Preview Abstract] |
Monday, March 16, 2009 8:12AM - 8:24AM |
A30.00002: Concurrent structural and magnetic phase transition in nanopowder V$_{2}$O$_{3}$ J. P. Carlo, Y. J. Uemura, V. Blagojevic, M. L. Steigerwald, L. E. Brus, S. J. L. Billinge, W. Zhou, G. M. Luke, A. A. Aczel, G. J. MacDougall, P. W. Stephens V$_{2}$O$_{3}$, which has been the subject of investigations for well over 30 years, is a classic example of a Mott-Hubbard transition system. This first-order metal-insulator transition, near 160K, is accompanied by a rhombohedral-monoclinic structural as well as a paramagnetic-antiferromagnetic magnetic transition. We report on structural synchrotron x-ray characterization of V$_{2}$O$_{3}$ nanopowder (dia $\approx $ 10-50 nm) at NSLS, and magnetic characterization via muon spin relaxation at TRIUMF. We find that, just as in bulk V$_{2}$O$_{3}$, the structural and magnetic transitions are concurrent, and that in contrast to the abrupt and hysteretic transition witnessed in the bulk, in the nanopowder sample the transition occurs with phase separation over a broad temperature range. [Preview Abstract] |
Monday, March 16, 2009 8:24AM - 8:36AM |
A30.00003: Metal-insulator transition in AV$_{10}$O$_{15}$ (A=Ba,Sr) T. Katsufuji, T. Suzuki, T. Kajita In AV$_{10}$O$_{15}$ (A=Ba, Sr), the V ions take a mixed- valence state, V$^{2.8+}$ ($3d^{2.2}$), and form a modified triangular lattice, in which V triangles are periodically missing from a normal triangular lattice. It is known that BaV$_ {10}$O$_{15}$ undergoes a structural phase transition at around 120 K. We have succeeded in growing large single crystals of AV$_{10}$O$_{15}$ (A=Ba, Sr) by a floating-zone method. We found a large jump of electrical resistivity by $\sim 10^{3}$ times at the structural transition temperature (123 K) of BaV$_ {10}$O$_{15}$, which can be regarded as a metal-insulator transition presumably dominated by a charge/orbital ordering of V. We also found an antiferromagnetic ordering at 43 K in the same compound. On the other hand, SrV$_{10}$O$_{15}$ did not show any structural anomaly down to the lowest temperature, and a spin-glass behavior was observed. These results indicate a strong correlation between the structural anomaly (charge/orbital ordering) and the magnetism in this series of compounds. We also measured the optical reflectivity of BaV$_ {10}$O$_{15}$ and found the opening of a charge gap in the optical conductivity spectrum at low temperatures. [Preview Abstract] |
Monday, March 16, 2009 8:36AM - 8:48AM |
A30.00004: Charge dynamics in thermally and doping induced insulator-metal transitions of (Ti$_{1-x}$V$_x$)$_2$O$_3$ Masaki Uchida, Jun Fujioka, Yoshinori Onose, Yoshinori Tokura Charge dynamics of (Ti$_{1-x}$V$_x$)$_2$O$_3$ with $x=0-0.06$ has been investigated by measurements of charge transport and optical conductivity spectra in a wide temperature range of $2-600$ K with the focus on the thermally and doping induced insulator-metal transitions (IMTs). The optical conductivity peaks for the interband transitions in the 3$d$ $t_{2g}$ manifold are observed in the both insulating and metallic states, while their large variation (by $\sim 0.4$ eV) with change of temperature and doping level scales with that of the Ti-Ti dimer bond length, indicating the weakened singlet bond in the course of IMTs. The thermally and V-doping induced IMTs are driven with the increase in carrier density by band-crossing and hole-doping, respectively, in contrast to the canonical IMT of correlated oxides accompanied by the whole collapse of the Mott gap. [Preview Abstract] |
Monday, March 16, 2009 8:48AM - 9:00AM |
A30.00005: Intersite correlations and the metal insulator in cluster dynamical mean field theory: cluster size, interaction strength, and the location of the transition line C. Lin, A. Millis To gain insight into the physics of the metal insulator transition and the effectiveness of cluster dynamical mean field theory we have used one, two and four site dynamical mean field theory (both CDMFT and DCA) to solve a model of electrons coupled to a classical phonon field. A partial density of states is defined encoding a generalized nesting property of the band structure; variations in this density of states account for differences between dynamical cluster approximation and cellular-DMFT implementation of cluster DMFT, and for differences in behavior between single band (cuprate-like) and multiband (manganite-like) models. The cluster size dependence of the metal to polaronic insulator phase boundary is determined along with electron spectral functions and cluster correlation functions. Over most of the interaction strength regime the single-site and multi-site approximations are found to yield similar results. Important cluster size effects occur only in the metal insulator transition region, where short-ranged orrelations are found to significantly reduce the critical interaction strength required to drive a metal polaron insulator transition. In the cluster approximations the physics of the metal-insulator transition is shown to be Slater-like (driven by band filling). The minimal cluster size required to capture the metal-polaron insulator transition is shown to depend sensitively on the carrier concentration. Implications for the theoretical treatment of doped manganites are discussed. [Preview Abstract] |
Monday, March 16, 2009 9:00AM - 9:12AM |
A30.00006: Study of phase separated manganites by DC transport and infrared spectroscopy A. Zimmers, T. Wolf, J. Lesueur, R.P.S.M. Lobo, A. Kushwaha, R.C. Budhani We present confined geometry measurements of manganites La$_{0.325}$Pr$_{0.3}$Ca$_{0.375}$MnO$_{3}$ (LPCMO) and La$_{2/3}$Sr$_{1/3}$MnO$_3$ (LSMO). As reported previously, due to electronic phase separation, LPCMO microwires show a step-like metal insulator transition as temperature is lowered and as magnetic field is sweped. We will show how this feature evolves as a function of the width and shape of the microwires. On the contrary, LSMO microwires are found to have a smooth transition in all wire sizes down to a width of 140$nm$. We have created extra disorder in the LSMO sample by irradiating it using 150keV oxygen ions with a dose of 2 x 10$^{14}$ ions/cm$^2$. As expected, the microwires T$_{MI}$ transitions are lowered by 120K but the transitions remain stepless. The fact that the electronic homogeneity in LSMO sample is robust, even when irradiated, enabled us start an optical study of artificially phase separated highly correlated materials. We will show preliminary results comparing reflectivity spectra of micropatterned samples to effective medium approximation models. [Preview Abstract] |
Monday, March 16, 2009 9:12AM - 9:24AM |
A30.00007: Spectral Function of Manganite Systems Juan Salafranca, Elbio Dagotto Using a double exchange model with Jahn Teller distortions, we calculate the one particle spectral function of manganite systems. The relative contribution of the different interactions is established by means of Monte Carlo and self consistent mean field calculations. In particular, we examine the effects of electron-electron and electron-phonon couplings. We discuss the relevance of our results in relation to recent Photoemission experiments on layered manganites [1], where similarities of manganites spectra with that of cuprates was observed.\\[3pt] [1] N. Mannella {\it et al.} Nature {\bf 438} 474 (2005) [Preview Abstract] |
Monday, March 16, 2009 9:24AM - 9:36AM |
A30.00008: Anomalous nuclear relaxation in the ferromagnetic phase of the bilayered manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$. Michael Hoch, Philip Kuhns, William Moulton, Arneil Reyes, Jun Lu, John Mitchell In contrast to ferromagnetic (FM) 3D manganites, $^{55}$Mn NMR spectra obtained for the FM phase of the colossal magnetoresistance bilayer manganite La$_{1.2 }$Sr$_{1.8 }$Mn$_{2}$O$_{7}$ show a broad distribution of hyperfine fields implying a large distribution of local environments at Mn sites. The hyperfine distribution may be linked to orbital ordering effects. $^{55}$Mn spin -- lattice relaxation rates have a surprisingly weak dependence both on temperature and applied magnetic field. Significant departures of the relaxation rate from Korringa temperature dependence below 20 K provide evidence for non-Fermi liquid behavior in this quasi-2D metal. At temperatures approaching $T_{C }$ from below, further anomalous behavior is found consistent with spin polaron formation in the range where colossal magnetoresistance starts to appear. [Preview Abstract] |
Monday, March 16, 2009 9:36AM - 9:48AM |
A30.00009: Anomalous metallic state: Decisive effect of dilute impurity doping on ferromagnetic BaIrO$_3$ single crystals O.B. Korneta, S. Chikara, T.F. Qi, S. Parkin, G. Cao, W.H. Song BaIrO$_3$ is a quasi one-dimensional system, where a {CDW} and a ferromagnetic state with T$_{C}$=183K coexist. The ground state of the system is critically linked to the lattice and orbital degrees of freedom due to extended $5d$-orbitals. The central findings of this study are: (1) An occurrence of a 2D-metallic state with a linear temperature dependence of resistivity at low temperatures in slightly oxygen-deficient samples; (2) Unusual temperature dependence of resistivity above the Curie temperature in the rare-earth doped BaIrO3; (3) High sensitivity of the resistivity to applied pressure ($<12$ Kbar), which results in changes in resistivity by a few orders of magnitude in these doped samples. The results of the resistivity, heat capacity, magnetization, thermoelectric power and structural measurements as a function of temperature, magnetic field, and pressure will be presented and discussed. [Preview Abstract] |
Monday, March 16, 2009 9:48AM - 10:00AM |
A30.00010: Non-Fermi-liquid behavior in nearly ferromagnetic SrIrO$_{3}$ single crystals T.F. Qi, S. Chikara, O.B. Korneta, S. Parkin, L.E. De Long, G. Cao, P. Schlottmann We report magnetic, electric transport, and calorimetric properties of
single-crystal SrIrO$_{3}$ as a function of temperature $T$ and applied
magnetic field $H$. We find that SrIrO$_{3 }$is a non-Fermi-liquid metal near a
ferromagnetic instability, as characterized by the following properties: (1)
small saturation moment and no evidence for long-range order down to 1.7 K,
(2) strongly enhanced magnetic susceptibility that diverges as $T^{\gamma }$
at low temperatures with 1/2$<\gamma <$1, depending on the applied
field, (3) heat capacity $C(T$,$H)\sim \quad -T $ln $T $that is readily enhanced in low
applied fields, and (4) $T^{3/2}$ dependence of electrical resistivity over
the range 1.7 K$ |
Monday, March 16, 2009 10:00AM - 10:12AM |
A30.00011: Magnetic Soft Mode Behavior of the Field-Dependent Specific Heat of SrIrO$_{3}$ Lance De Long, Daheng He, Vinayak Bhat, Gang Cao Previous work\footnote{Cao et al., Phys. Rev. B \textbf{76}, 100402(R),(2007)} indicates SrIrO$_{3}$ is a strongly exchange-enhanced paramagnet (Wilson ratio = 75) exhibiting non-Fermi liquid (NFL) behavior at low magnetic fields, and a cross-over to weak ferromagnetism (0.025 $\mu _{B}$/Ir at $\mu _{o}$H = 7.0 T and T = 1.7 K) at applied fields $\mu _{o}$H $\approx $ 3 T and temperatures T $<$ 4 K. Measurements of the specific heat performed in constant field for 1.8 $<$ T $<$ 4K have been used to extract the field dependence C$_{P}$(H,T$_{o})$(constant T$_{o})$, which exhibits a Schottky-like peak as a function field in the range 1.0 $< \quad \mu _{o}$H $<$ 1.5 T at increasing temperatures 1.8 $<$ T$_{o} \quad <$ 3.9 K, respectively. Fits of C$_{P}$(H,T$_{o})$ imply a nonmagnetic ground state is separated from magnetic excited states by an energy splitting $\Delta $(H,T)/k$_{B}$ = T* that decreases from 7.5 to 2 K as $\mu _{o}$H increases from 0 to 8 T. The Schottky peak field increases as $\mu _{o}$H* = 0.94 T + (0.03 T/K$^{3})$T$^{3.1}$. We discuss how a semi-classical two-level model reproduces the NFL-weak ferromagnet cross-over with applied field. [Preview Abstract] |
Monday, March 16, 2009 10:12AM - 10:24AM |
A30.00012: Temperature-dependent electronic structure evolution of spin-orbit coupling induced Mott insulator Sr$_{2}$IrO$_{4}$ S. J. Moon, W. S. Choi, T. W. Noh, H. Jin, Y. S. Lee, G. Cao Recently, the effect of spin-orbit coupling in 5$d$ transition metal oxides attracted lots of attention. It was found that the cooperative interaction of spin-orbit coupling and electron correlation could realize unique Mott insulating ground state of Sr$_{2}$IrO$_{4}$. We investigated temperature-dependent optical conductivity spectra of 5$d$ Mott insulator Sr$_{2}$IrO$_{4}$. We observed drastic changes of the optical conductivity spectra. As temperature increases, the Mott gap was significantly reduced and spectral weight redistribution between the Ir $t_{2g}$ bands occurred. The electronic structure changes accompanied the change of optical phonon modes. These experimental observations could be understood in terms of the effects of spin-orbit and electron-lattice coupling. [Preview Abstract] |
Monday, March 16, 2009 10:24AM - 10:36AM |
A30.00013: LS separation of J=1/2 Mott insulator observed by magnetic X-ray diffraction Shigeki Fujiyama, B.J. Kim, H. Ohsumi, T. Komesu, D. Hirai, K. Ohashi, S. Sakai, T. Arima, H. Takagi Spin-orbit coupling is a key concept to realize spin Hall effect in insulating materials. A perovskite iridate Sr$_2$IrO$_4$ is known to show insulating transport properties in spite of large spatial extent of 5d electrons. The origin of this unconventional behavior is argued to be a strong LS coupling which results in $J_{\mathrm{eff}}=1/2$ Mott insulator. We performed off-resonant magnetic X-ray scattering in the antiferromagnetically ordered state of this material and found that considerable contribution from orbital moment for the ordered moment. The estimated ratio, $\langle \psi | L_z | \psi | \rangle / \langle \psi | S_z | \rangle$ is 5. This is consistent with $J_{\mathrm{eff}}=1/2$ which expects the ratio as 4. This justifies unconventional $J_{\mathrm{eff}}=1/2$ Mott insulator for this transition metal oxides. [Preview Abstract] |
Monday, March 16, 2009 10:36AM - 10:48AM |
A30.00014: Magnetization reversal in Sr$_3$Ir$_2$O$_7$ : DM interactions vs. magnetic single-ion anisotropy Hosub Jin, Jaejun Yu Recently the unusual insulating ground state of Sr$_2$IrO$_4$ was shown to be a consequence of a novel quantum ground state of $j_{\mathrm{eff}}$=1/2. Another compound in its series Sr$_3$Ir$_2$O$_7$ with double layers of the IrO$_2$ planes exhibits anomalous magnetic responses such as magnetization reversal during field-cooling processes. We performed density-functional theory calculations to investigate the electronic and magnetic properties of Sr$_3$Ir$_2$O$_7$. Similarly to the case of Sr$_2$IrO$_4$, both spin-orbit (SO) and on-site Coulomb interactions are found to be responsible for the insulating ground state. Based on the analysis of our first-principle calculations for the various spin and lattice configurations, we found that the non-zero angular momentum state originating from large SO interactions with lattice distortions plays a crucial role in determination of both single-ion anisotropy and Dzyaloshinski-Moriya interactions, which explains anomalous magnetic responses in Sr$_3$Ir$_2$O$_7$. [Preview Abstract] |
Monday, March 16, 2009 10:48AM - 11:00AM |
A30.00015: Post-perovskite transition and magnetic and charge transport properties of the correlated 4$d$ post-perovskite CaRhO$_3$ K. Yamaura, Y. Shirako, H. Kojitani, M. Arai, D.P. Young, M. Akaogi, M. Nakashima, T. Katsumata, Y. Inaguma, E. Takayama-Muromachi A high-quality polycrystalline sample of the correlated 4$d$ post-perovskite CaRhO$_3$ (Rh$^{4+}$: 4$d^5$ $S = 1/2$) was attained under a moderate pressure of 6 GPa for the first time. It is obvious that the perovskite CaRhO$_3$ transforms into a layered phase, in which RhO$_6$ octahedra are connected by shearing the edge along a-axis and the corner along c-axis. The Rh-O layer stacks up alternatively with the Ca layer along b-axis. The characteristic structure suggests an electronic anisotropy toward 2D, which may be essential for unusual magnetism. The sample was subjected for measurements of charge transport and magnetic properties. The data clearly indicate it goes into an antiferromagnetically ordered state below $\sim90$ K in an unusual way, being a strikingly contrast to what was observed for the perovskite phase. [Preview Abstract] |
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