Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session F49: Focus Session: Electricity and Magnetism: Manganites |
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Sponsoring Units: DMP Room: Mile High Ballroom 1C |
Tuesday, March 4, 2014 8:00AM - 8:36AM |
F49.00001: Quantum Femtosecond Magnetism: Phase Transition in Step with Light in a Strongly Correlated Manganese Oxide Invited Speaker: Jigang Wang Research of non-equilibrium phase transitions of strongly correlated electrons is built around addressing an outstanding challenge: how to achieve ultrafast manipulation of competing magnetic/electronic phases and reveal thermodynamically hidden orders at highly non-thermal, femtosecond timescales? Recently we reveal a new paradigm called {\em quantum femtosecond magnetism}--photoinduced femtosecond magnetic phase transitions driven by quantum spin flip fluctuations correlated with laser-excited inter-atomic coherent bonding [1]. We demonstrate an antiferromagnetic (AFM) to ferromagnetic (FM) switching during about 100 fs laser pulses in a colossal magneto-resistive manganese oxide. Our results show a huge photoinduced femtosecond spin generation, measured by magnetic circular dichroism, with photo-excitation threshold behavior absent in the picosecond dynamics. This reveals an initial quantum coherent regime of magnetism, while the optical polarization/coherence still interacts with the spins to initiate local FM correlations that compete with the surrounding AFM matrix. Our results thus provide a framework that explores quantum non-equilibrium kinetics to drive phase transitions between exotic ground states in strongly correlated elecrons, and raise fundamental questions regarding some accepted rules, such as free energy and adiabatic potential surface. This work is in collaboration with Tianqi Li, Aaron Patz, Leonidas Mouchliadis, Jiaqiang Yan, Thomas A. Lograsso, Ilias E. Perakis.\\[4pt] [1] T. Li, {\em et al.}, Nature, 496, 69 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 8:36AM - 8:48AM |
F49.00002: Quantum Femtosecond Magnetism in Strongly Correlated Electrons induced by Femtosecond Far-Infrared Pulses Tianqi Li, Aaron Patz, Jiaqiang Yan, Ilias Perakis, Jigang Wang There is growing evidence that femtosecond laser-induced transient polarization can be used to manipulate magnetic and electronic orders during a laser pulse. Recently we reveal a new paradigm called \textit{quantum femtosecond magnetism}---photoinduced femtosecond magnetic phase transitions driven by quantum spin flip fluctuations correlated with laser-excited inter-atomic bonding coherence. It provides the opportunity to study the non-equilibrium quantum dynamics of phase competitions in strongly correlated materials. In addition, the scheme of photo modulation of the magnetic/electronic properties of materials also provides potential candidates for industrial application. In this talk, we show our results of using femtosecond far-infrared to tune the ground state of a strongly correlated manganese oxide. A transient photo-induced coherence is introduced far below the band gap without electronic heating and inter-band transition. Such photo-induced coherence affects the spin correlations and the resonant phonon vibrational modes, which thus leads to femtosecond spin and charge dynamics. Such non-equilibrium quantum control of the magnetic/electronic order goes beyond the scope of the conventional thermal dynamics and provides new insights into correlation mechanisms in the materials. [Preview Abstract] |
Tuesday, March 4, 2014 8:48AM - 9:00AM |
F49.00003: Charge confinement in manganite thin film on stepped substrate Hoyoung Jang, B. Kim, C. Bell, Y. Hikita, X.M. Chen, P. Abbamonte, H.Y. Hwang, J.-S. Lee Technologies of fabricating the oxide films enable not only reproducing bulk properties even in the film form, but also generating new functionalities via the intrinsic interface effect in heterostructures. Beyond such aspects, nowadays, controlling a step terrace of single crystalline substrate that has been regarded as another playground of thin film research. We demonstrated resonant soft x-ray scattering (RSXS) experiment of thin La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) film grown on TiO$_{2}$ terminated SrTiO$_{3}$ (001) substrates which have the topographical step terrace. In this talk, we will present the site selective (i.e., step-edge sensitive) the RSXS results on the LSMO, showing the enriched Mn$^{3+}$ state distribution along step-edge. We propose that this distribution is associated with the anisotropic conductivity in the plane of the LSMO film. The details will be touched in presentation. [Preview Abstract] |
Tuesday, March 4, 2014 9:00AM - 9:12AM |
F49.00004: Chemically-induced Jahn-Teller ordering on manganite surfaces Zheng Gai, Wenzhi Lin, J.D. Burton, Evgeny Y. Tsymbal, K. Fuchigami, Jian Shen, P.C. Snijders, T.Z. Ward, Stephen Jesse, Sergei V. Kalinin, A.P. Baddorf Physical and electrochemical phenomena at the surfaces of transition metal oxides and their coupling to local functionality remains one of the enigmas of condensed matter physics. Understanding the emergent physical phenomena at surfaces requires the capability to probe the local composition, map order parameter fields, and establish their coupling to electronic properties. Here we demonstrate that measuring the sub 30 pm displacements of atoms from high-symmetry positions in the atomically resolved scanning tunneling microscopy (STM) allows the physical order parameter fields to be visualized in real space on the single atom level. Here, this local crystallographic analysis is applied to the in-situ grown manganite surfaces. In particular, using direct bond-angle mapping we report direct observation of structural domains on manganite surfaces, and trace their origin to surface-chemistry-induced stabilization of ordered Jahn-Teller displacements. Density functional calculations provide insight into the intriguing interplay between the various degrees of freedom now resolved on the atomic level. Research was supported by MSED and CNMS, which are sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy. [Preview Abstract] |
Tuesday, March 4, 2014 9:12AM - 9:24AM |
F49.00005: Phase separation in complex oxides: RTiO3 Bo Shi, C. Schussler-Langeheine, J.B. Goedkoop, M.S. Golden, M. Buchholz, C. Trabant, C.F. Chang, A. Ricci, C. Gutt, M. Sprung, H.A. Durr, A. Robert, M. Sikorski, S. Song Complex oxides display an unparalleled richness of physical phenomena arising from the coupling of their charge, spin and orbital degrees of freedom, with cuprate high Tc superconductors and colossal magnetoresistive (CMR) manganites as flagship materials systems. For the CMR systems, phase separation is believed to play a crucial role in creating the hypersensitivity to external stimuli such as external field. In this contribution I will report our experiments on perovskite titanate systems, which are a t2g materials analogy to the CMR systems with which they share much underlying physics. In particular, I will deal with calcium-doped rare earth titanium oxides, which exhibit charge and orbital ordering during a temperature-driven metal-insulator transition (T-driven MIT). These systems are hypersensitive to the tuning of the hole-doping level, whereby the electrical transport then differs by several orders of magnitude, as occurs with external field in the CMR manganites. In this talk, I will present recently recorded data aimed at the investigation of the phase separation dynamics during T-driven MIT in titanates at LCLS. This is the first time that the single crystal coherent x-ray diffraction patterns have been recorded at 120Hz in the time domain. [Preview Abstract] |
Tuesday, March 4, 2014 9:24AM - 9:36AM |
F49.00006: Electrostatic phase control of half-doped manganites Takafumi Hatano, Yasushi Ogimoto, Zhigao Sheng, Naoki Ogawa, Masao Nakamura, Masaki Nakano, Masashi Kawasaki, Yoshihiro Iwasa, Kenjiro Miyano, Yoshinori Tokura In perovskite manganites as a strongly correlated electron system, the cross correlation among charge-spin-orbital degrees of freedom provides various electronic phases which have been controlled by external stimuli such as a magnetic field and light. Especially, the electric-field induced switching of electronic phases is of critical importance for the application toward future electronics. In this presentation, we demonstrate the gate control of the phase transition of manganites in the field effect transistor. From the variety of manganites, we chose the half-doped system of Pr$_{0.5}$Sr$_{0.5}$MnO$_3$, which is on the nearly vertical phase boundary between a ferromagnetic metallic phase and an anti-ferromagnetic insulating phase. By adopting the electric double layer transistor, we realized the phase switching accompanying with the huge resistance change by the slight modulation of the gate voltage, which may lead to beyond CMOS devices. [Preview Abstract] |
Tuesday, March 4, 2014 9:36AM - 9:48AM |
F49.00007: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 9:48AM - 10:00AM |
F49.00008: Ordered phase separation in low dimensional manganite thin films B. Kim, C. Bell, Y. Hikita, H.Y. Hwang Two central challenges in ultra-thin oxide films are to understand the fundamental properties of low dimensional materials, and to create novel electronic ground states. In this context, manganites are of interest due to their complex phase diagrams which depend on the electronic band width. Here, we study in detail ultra-thin La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$ films on TiO$_{\mathrm{2}}$ terminated SrTiO$_{\mathrm{3}}$ (001) substrates around the dead layer thickness. We find a strong anisotropy in the electronic transport properties depending on the current flow direction with respect to the step and terrace direction just above the dead layer thickness. Furthermore, the magnetoresistance showed significant differences when the bias current was parallel and perpendicular to the steps. This suggests the presence of an emergent insulating phase at the step edges and ordered phase separation in these low dimensional complex oxide films. [Preview Abstract] |
Tuesday, March 4, 2014 10:00AM - 10:12AM |
F49.00009: Screening of Strain Fields in Manganites Gian Guzman-Verri, Richard Brierley, Peter Littlewood It is well known that elastic couplings mediate long-range interactions between local degrees of freedom in colossal magnetoresistance manganites. Though the effects of elastic strain couplings on phase transitions have been extensively studied in the past [1], several important questions remain such as whether strain can induce inhomogeneous ordered states as those observed in manganites. In this talk, we address this question phenomenologically and propose that the observed scaling of the metal-to-insulator transition temperature on ionic radii in perovskite manganites [2] is the result of rotations of MnO$_6$ octahedra that screen the strain fields. \\[4pt] [1] D. J. Bergman and B. I. Halperin, Phys. Rev. B 13 2145 (1976). \\[0pt] [2] L. M. Rodriguez-Martinez and J. P. Attfield, Phys. Rev. B 54 R15622 (1996). [Preview Abstract] |
Tuesday, March 4, 2014 10:12AM - 10:24AM |
F49.00010: Hybrid-Improper Ferroelectricity in a Cation Ordered Ruddlesden-Popper Manganite Antonio Cammarata, James Rondinelli There is strong interest in uncovering new routes to design multiferroic compounds, which combine ordered magnetic states with electric polarizations, since they have great potential in novel multifunctional devices. Using first principles calculations based on density functional theory, we show the ground state of the the cation ordered (La,Sr)MnO$_4$ Ruddlesden-Popper oxide is polar. The electric polarization arises from an anharmonic coupling mechanism, which can be designed at the atomic scale. We find that in addition to cooperative polar cation displacements, two non-polar distortions of the oxygen lattice, \emph{i.e.}, an octahedral rotation mode and Jahn-Teller bond distortions, are present in the polar phase. The latter originates from the \emph{electronic} susceptibility of the Mn $e_g$ orbitals to polarize, while the former is due to the La and Sr cation size mismatch. We find that the Jahn-Teller mode and the octahedral rotation mode are coupled through an anharmonic interaction and cooperatively stabilize the polar structure and induce a net electric polarization. Our survey of multiple transition paths reveal that this material is classified as a \emph{hybrid-improper} ferroelectric, and the Mn $d^4$ configuration makes it a potential multiferroic oxide. [Preview Abstract] |
Tuesday, March 4, 2014 10:24AM - 10:36AM |
F49.00011: Electronic structural origin of spin-phonon coupling in multiferroic CaMnO$_3$ Hongwei Wang, Hong Jiang, Lixin He, Xifan Wu Spin-phonon coupling is a functionality discovered recently in multiferroics and defined by the shift of polar phonon frequency as a function of varying magnetic ordering. In order to elucidate the electronic structural origin of this effect,in this work, we developed a novel computational method based on Extended Kugel-Khomskii (EKK) model. The maximally localized Wannier functions (MLWFs) are generated from density functional theory (DFT) band structure calculations and used as the basis to calculate the hopping integrals in the EKK model. In addition,the screened Coulomb interactions between MLWFs are computed by the random phase approximation. This method not only reproduces accurately the direct first-principles results but gives us a microscopic explanation. It is found that the large spin-phonon coupling in CaMnO$_3$ originates from in a large distortion of MLWFs generated by the slater phonon mode,which drastically affects the anitiferromagnetic hopping integral in the EKK model. On the other hand, phonon instabilities such as oxygen octahedral rotation will only result in a rigid rotation of MLWFs and the effect of spin-phonon coupling is much weaker. [Preview Abstract] |
Tuesday, March 4, 2014 10:36AM - 10:48AM |
F49.00012: Self-doping and emergent conductance at Mott interfaces via internal charge transfer Hanghui Chen, Andrew Millis, Chris Marianetti We use $ab$ $initio$ calculations to show that internal charge transfer can induce spatially separated electron-hole pairs at interfaces between two Mott insulators. DFT+ $U$ studies of multilayer systems consisting of Sr$_2$VO$_4$ and Sr$_2$MnO$_4$ (both Mott insulators) reveal that conductance emerges at their interface with electrons residing dominantly on the Mn $d_{x^2-y^2}$ orbital and holes on the V $d_{xy}$ orbital. With the transferred electron coupled to the core spin on Mn sites, ferromagnetism is significantly favored in the Sr$_2$MnO$_4$ layer, although this material is antiferromagnetic in bulk. Our work establishes internal charge transfer as a powerful method of tailoring correlation effects and that superlattices composed of Ruddlesden-Popper type oxides provide new possibilities for materials design, complementary to perovskite oxide heterostructures. [Preview Abstract] |
Tuesday, March 4, 2014 10:48AM - 11:00AM |
F49.00013: Controlling spontaneous symmetry breaking and topological defect duality in multiferroic InMnO3 from ab initio Sinead Griffin, Nicola Spaldin The rare earth hexagonal manganites are of considerable current interest because of the unusual nature of their ferroelectric phase transition that results in the formation of topological defects exhibiting universal scaling laws[1,2].~ Here we use first-principles density functional calculations and symmetry analysis to show that the spontaneous symmetry breaking in the related material InMnO3 can be described using dual Mexican-hat-like potentials that in turn explain the nature of the two recently reported low-symmetry structures. Our analysis also allows us to identify the third, previously unobserved structure that is allowed by symmetry to emerge from the high-symmetry prototype, giving a unified picture of the phase transitions and ground states in the multiferroic hexagonal manganites. [1] S.C. Chae et al., Phys. Rev. Lett. 108, 167603 (2012) [2] S.M. Griffin et al., Phys. Rev. X, 2, 041022 (2012) [Preview Abstract] |
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