Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session T36: Focus Session: Bulk Properties of Complex Oxides -- Layered Manganites and Theory |
Hide Abstracts |
Sponsoring Units: DMP GMAG Chair: Feng Ye, Oak Ridge National Laboratory Room: E146 |
Wednesday, March 17, 2010 2:30PM - 3:06PM |
T36.00001: Signature of charge-order fluctuations in the phonon spectra of a polaronic metallic manganite Invited Speaker: The colossal magnetoresistive layered manganites show a transition from a high temperature charge-ordered/polaronic insulating phase to a low temperature ferromagnetic metallic phase. The polaronic character of the metallic phase remains controversial because broad charge order peaks observed in the insulating phase disappear when La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ becomes metallic. Here we report results of inelastic neutron scattering measurements of lattice vibrations in La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$, which show that polarons remain intact deep inside the ferromagnetic phase as fluctuations that strongly broaden and soften certain optic phonons. They appear near the wave vectors where the charge order peaks are observed above T$_c$. The insight that our findings offer is that polaronic signatures in metals may generally come from a competing insulating charge-ordered phase. It is highly relevant to cuprate superconductors where a similar giant phonon renormalization associated with a stripe phase has been reported. [Preview Abstract] |
Wednesday, March 17, 2010 3:06PM - 3:18PM |
T36.00002: Electron-lattice coupling and partial nesting as the origin of Fermi arcs in manganites Juan Salafranca, Gonzalo Alvarez, Elbio Dagotto We present a detailed Monte Carlo study of the one-particle spectral function using a double-exchange model for layered manganites, incorporating lattice distortions. Our results contribute to clarifying the physical origin of the Fermi arcs observed in ARPES experiments on bilayered manganites.\footnote{Manella {\it el al.} Nature 438, 474 (2005)} In a range of parameters where no broken symmetry phase exists, the nearly-nested Fermi surface favors particular correlations between the Jahn-Teller distortions. Due to these correlations, the spectral weight is surpresed near the Brillouin zone edge, while a quasiparticle peak survives in the zone diagonal. This regime manifests as a pseudogap in the density of states, and produces a Fermi-arc like Fermi surface.\footnote{Salafranca {\it el al.} Phys. Rev. B 80, 155133 (2009)} We also discuss the stability of the pseudogap varying the temperature and the electron-lattice coupling strength for different hole dopings. [Preview Abstract] |
Wednesday, March 17, 2010 3:18PM - 3:30PM |
T36.00003: Orbital order in La$_{0.5}$Sr$_{1.5}$MnO$_{4}$: a failure of the local Jahn-Teller physics Hua Wu, C.F. Chang, O. Schumann, Z. Hu, J.C. Cezar, T. Burnus, N. Hollmann, N.B. Brookes, A. Tanaka, M. Braden, D.I. Khomskii, L.H. Tjeng Orbital order (OO) occurs quite often in orbitally degenerate correlated transition-metal compounds. It has been generally accepted that there is one-to-one correspondence between a specific orbital order and a local Jahn-Teller distortion. Here we demonstrate that this is not always true, by demonstrating a failure of the local Jahn-Teller physics in the layered perovskite La$_{0.5}$Sr$_{1.5}$MnO$_{4}$ which is one of prototype OO materials. We studied both the site- and bond-centered charge orderings, crystal field levels, orbital states and their dependence on the varying local lattice distortions, through detailed $ab$ $initio$ electronic structure calculations. We conclude that this material has the site-centered charge ordering, and that the local Jahn-Teller physics fails and the type of occupied orbitals (3x$^{2}$-r$^{2}$/3y$^{2}$-r$^{2}$ ones) contradicts the local compression of Mn$^{3+}$O$_{6}$ octahedra which could require x$^{2}$-z$^{2}$/y$^{2}$-z$^{2}$ occupation. We explain this by the contribution of the long-range crystal-field in this anisotropic layered material and by the maximization of kinetic energy. Our theoretical results are confirmed by x-ray absorption linear dichroism. [Preview Abstract] |
Wednesday, March 17, 2010 3:30PM - 3:42PM |
T36.00004: Electronic dispersion in the CE charge/orbital-ordered phase of LaSr$_{2}$Mn$_{2}$O$_{7}$ revealed by ARPES Zhe Sun, Qiang Wang, Alexei V. Fedorov, Hong Zheng, John F. Mitchell, Dan S. Dessau Using angle-resolved photoemission spectroscopy, we investigated the E vs. $k$ dispersion of electrons in the CE charge/orbital-ordered phase of bi-layer manganite LaSr$_{2}$Mn$_{2}$O$_{7}$. We found that the Bloch band of hopping electrons is well maintained with a dispersion qualitatively different from various band calculations based on the zigzag chains in the CE phase. By comparing the dispersions and spectral weight in the CE-AFM, CE-PM and A-type AFM states, we~reveal the~strong influences of spin, charge, and orbital on electron hopping amplitudes. [Preview Abstract] |
Wednesday, March 17, 2010 3:42PM - 3:54PM |
T36.00005: Electronic Self-Organization in the Single-Layer Manganite Pr$_{1-x}$Ca$_{1+x}$MnO$_{4}$ Feng Ye, Songxue Chi, Jaime Fernandez-Baca, Adriana Moreo, Elbio Dagotto, Jeff Lynn, Roland Mathieu, Yoshio Kaneko, Yoshi Tokura, Pengcheng Dai Using neutron scattering technique, we have investigated the doping evolution of the magnetic correlations in the single-layer manganite Pr$_{1-x}$Ca$_{1+x}$MnO$_{4}$ away from x = 0.5, where the CE-type commensurate antiferromagnetic (AF) structure is stable. Short-range incommensurate spin correlations develop as the system is electron doped (x $<$ 0.5), which coexist with the CE-type AF order. This suggests that electron doping induces an inhomogeneous electronic self-organization, where commensurate AF patches with x = 0.5 are separated by electron-rich domain walls, a different scenario than in the perovksite Pr$_{1-x}$Ca$_{x}$MnO$_{3}$. Instead of forming novel charge or magnetic order state, textured electronic structures are established in the doped layered manganites. These structures are strikingly similar to the stripe order in the superconducting cuprates and this work establishes important connections between two families of the strongly correlated electron system in terms of electronic self-organization and spin incommensurability. [Preview Abstract] |
Wednesday, March 17, 2010 3:54PM - 4:06PM |
T36.00006: Competing Magnetic Ground States in A{\-}Site Layer Ordered Manganites B. Dabrowski, O. Chmaissem, Y. Ren, D. E. Brown, S. Kolesnik, J. Mais We report the discovery of competing ground states near a multicritical point in A-site layer ordered La$_{1-x}$Ba$_{1+x}$Mn$_{2}$O$_{6}$ materials. We demonstrate the dual effects of deliberately introduced disorder on the system's stability, the freezing of the competing states, and the drastic reduction in magnetic fields required for the suppression of charge and orbital ordered phases. Our work suggests that quenched disorder is not the primary reason for phase separation and magnetoresistance, and that increased doping leads to electronic phase separation. [Preview Abstract] |
Wednesday, March 17, 2010 4:06PM - 4:18PM |
T36.00007: Oxygen Motion and Electroresistance Observed in a Bilayer Manganite Benjamin Bryant, Gabriel Aeppli, Christoph Renner, Yusuke Tokunaga, Yoshinori Tokura Oxygen defects and migration are thought to play key roles in electroresistive oxide devices$^{1,2}$. Scanning Tunnelling Microscopy (STM) can be used to study the dynamics of individual oxygen adatoms and vacancies at the oxide surface. We have identified a material, PrSr$_2$Mn$_2$O$_7$ which is suitable for STM study and also displays room temperature electroresistance. We have observed surface oxygen adatoms and vacancies in atomic-resolution STM images and tunnelling spectra. Time dependent STM imaging shows the dynamics of adatoms and vacancies, including adatom hopping and vacancy-adatom recombination. Bistable current-voltage characteristics are found for single oxygen adatoms. We suggest that the bulk material may be modelled as a network of electroresistive junctions. \footnotetext[1]{Nian, Y. B. et. al., Physical Review Letters 98, 146403 (2007).} \footnotetext[2]{Shono, K. et. al., Applied Physics Express 1, 055002 (2008).} [Preview Abstract] |
Wednesday, March 17, 2010 4:18PM - 4:30PM |
T36.00008: Quantum Effect of Ring-Exchange Interaction in Orbital Degenerated System Joji Nasu, Sumio Ishihara Orbital degree of freedom is one of the recent attractive themes in transition-metal oxides. In contrast to the spin degree of freedom, orbital interaction explicitly depends on the bond direction, and a certain kind of frustration exists. The doubly degenerate $e_{g}$ orbitals are represented by the pseudo-spin (PS) operator, and the orbital interaction is described by the nearest neighbor (NN) interaction. This model in a cubic lattice shows a macroscopic degeneracy in the classical ground state. This degeneracy is lifted by the quantum fluctuation and the antiferro-type quadrupole (AFQ) order is realized. Beyond the NN interaction, we study the ring-exchange interaction (REI) in this system, and in particular, focus on its quantum effects. We derive the REI through the fourth-order perturbation with respect to the electron transfer $t$ under the on-site Coulomb repulsion $U$ in the two-orbital Hubbard model. This interaction includes the magnetic octupole operator which does not appear in the NN interaction. To examine the quantum effect of this interaction, we adopt the extended Bethe approximation, the spin-wave approximation and the exact diagonalization methods in a cluster. In small $t/U$ region, the AFQ order is realized by the quantum fluctuation. The canted quadrupole order and the ocutupole order are stabilized by the REI. Reduction of the PS moment due to the quantum fluctuation is seen in large $t/U$ region. [Preview Abstract] |
Wednesday, March 17, 2010 4:30PM - 4:42PM |
T36.00009: Possible role of (nearly) localised spin minority electrons in the CMR manganese oxides Denis I. Golosov A new minimal model is constructed for the doped manganese oxides which exhibit colossal magnetoresistance (CMR), involving broad spin-majority conduction band as well as nearly localised spin-minority electron states. A simple mean field analysis yields a temperature-dependent hybridised band structure with suppressed carrier weight at the Fermi level. Spin stiffness is complex, indicating unusually strong spin wave damping. Experimental and theoretical investigations are needed to further verify the relevance of the proposed model. Preprint arXiv:0907.5512 [Preview Abstract] |
Wednesday, March 17, 2010 4:42PM - 4:54PM |
T36.00010: Calculation of model Hamiltonian parameters for LaMnO$_3$ using maximally localized Wannier functions Roman Kovacik, Claude Ederer The theoretical description of transition metal oxides is often based on effective tight-binding (TB) models. A systematic way to obtain realistic TB models is the construction of maximally localized Wannier functions (MLWFs) [1]. The corresponding TB representation is given by the real space Hamiltonian matrix elements in the MLWF basis. Here, we construct MLWFs for the Mn $e_g$ bands in LaMnO$_3$, and we monitor changes in the MLWF matrix elements induced by different magnetic configurations and structural distortions. From this we obtain values for the local Jahn-Teller and Hund's rule coupling strength, the hopping amplitudes between all nearest and further neighbors, and the corresponding reduction due to the GdFeO$_3$-type distortion. By comparing our results with commonly used model Hamiltonians for manganites, where electrons can hop between two "$e_g$-like" orbitals located on each Mn site, we find that the most crucial limitation of such models stems from neglecting changes in the underlying Mn($d$)-O($p$) hybridization. [1] N. Marzari and D. Vanderbilt, Phys. Rev. B 56, 12847 (1997). [Preview Abstract] |
Wednesday, March 17, 2010 4:54PM - 5:06PM |
T36.00011: CMR effect observed in Monte Carlo simulations of double-exchange models with Jahn-Teller lattice distortions Cengiz Sen, Gonzalo Alvarez, Elbio Dagotto The two $e_g$-orbital model, including Jahn-Teller lattice distortions and the superexchange interaction, is studied using unbiased exact diagonalization Monte Carlo techniques at a doping value $x=0.25$. A canonical colossal magnetoresistance (CMR) resistivity vs. temperature shape is obtained with a resistivity peak of nearly two orders of magnitude. We investigate the Monte Carlo evolution and temperature dependence of the spin, lattice, and orbital degrees of freedom in order to further understand the origin of the CMR effect. Results including quenched disorder, which seems to play an important role in stabilizing the competing phases, will also be discussed, and a comparison with recent nano-scale transmission electron microscopy experiments will be made [1]. This very CPU-time demanding effort, which was made possible due to the use of the ORNL computer facilities, generalizes the previous study to two orbitals where the CMR effect was observed in a one-orbital model [2].\\[4pt] [1]. J. Tao {\it et al.}, Phys. Rev. Lett. 103, 097202 (2009).\\[0pt] [2]. C. S. {\it et al.}, Phys. Rev. Lett. 98, 127202 (2007), R. Yu {\it et al.}, Phys. Rev. B 77, 214434 (2008). [Preview Abstract] |
Wednesday, March 17, 2010 5:06PM - 5:18PM |
T36.00012: Charge, spin, orbital and lattice degrees of freedom in manganites: The CE phase Pedro Schlottmann The CE phase of La$_{1-x}$Ca$_x$MnO$_3$ (LCMO) is stable for $x \ge 0.5$ and displays long-range magnetic, charge and orbital order. The magnetic order of the Mn spins arises from the competition of the superexchange and double-exchange interactions and the checkerboard charge and the orbital order is the consequence of the Jahn-Teller coupling of the $e_g$ orbitals to the lattice. Using a mean-field slave-boson approach for the $e_g$ electrons in two orbitals per site with excluded multiple occupancy and Hund's rule coupling between the $e_g$ and $t_{2g}$ states, we obtain the tight-binding band structure of the CE phase. The unit cell of the CE phase consists of 16 sites. The 32 $e_g$ bands in the Brillouin zone are grouped into two sets of 16 bands separated by a charge order gap. The charge order gap does not directly affect the ground state and low-energy properties of the CE phase. A strong coupling to the $Q_2$ and $Q_3$ Jahn-Teller modes leads to a gap at the Fermi level for the half-filled case, yielding an orbitally ordered insulating ground state. The phase diagram is obtained by comparing the ground state energies of the A, B, C, CE and G phases. As a function of $x$ the experimental phase sequence of LCMO is reproduced. Work supported by the Department of Energy under grant DE-FG02-98ER45707. P. Schlottmann, Phys. Rev. B {\bf 62}, 439 (2000); {\bf 73}, 214428 (2006); {\bf 77}, 104446 (2008); {\bf 80}, 104428 (2009). [Preview Abstract] |
Wednesday, March 17, 2010 5:18PM - 5:30PM |
T36.00013: Unconventional metamagnetism and orbital ordering in transition metal oxides (II) Wei-Cheng Lee, Congjun Wu Unlike charge and spin, the orbital degree of freedom of electrons in transition metal oxides is difficult to detect. We present the theoretical study of a new detection method in metallic orbitally active systems by analyzing the quasiparticle scattering interference (QPI) pattern of the spectroscopic imaging scanning tunneling spectroscopy, which is sensitive to orbital structures and orbital ordering. The QPIs for the $d_{xz}$ and $d_{yz}$-orbital bands in the t$_{2g}$-orbital systems show a characteristic stripe-like feature as a consequence of their quasi-one-dimensional nature, which is robust against orbital hybridization. With the occurrence of orbital ordering proposed in Sr$_{3}$Ru$_{2}$O$_{7}$ and iron-pnictides, the stripe-like QPI patterns exhibit nematic distortion breaking the C$_{4}$-symmetry. 1. W.-C. Lee and C. Wu, Phys. Rev. B 80, 104438 (2009). 2. W.-C. Lee and C. Wu, Phys. Rev. Lett. 103, 176101. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700