Time ID Correlated-Electron Physics in Transition-Metal Oxides I

Correlated-Electron Physics in Transition-Metal Oxides This session has been organised by the NCCR MARVEL. Wednesday, 23.08.207, CICG: Room 3 Time ID Correlated-Electron Physics in Transition-Metal Oxides I Chair: Marisa Medarde, PSI Villigen 4:00 60 Resonant elastic x-ray scattering of oxide multilayers Eva Benckiser, Max Planck Institute for Solid State Research Transition-metal oxide heterostructures are attractive for functional device applications because electronic and magnetic phases that are inaccessible in the bulk can be stabilized by epitaxial strain, confinement, charge doping, or interface effects. We use resonant elastic x-ray scattering to investigate ordering phenomena of spin, charge and orbitals in nanoscale complex oxide multilayers. As a model system we have investigated perovskite-type RNiO 3 -based heterostructures (R = rare-earth ion) grown by molecular-beam epitaxy and pulsed-laser deposition on various substrates. In my talk I will present results of our studies of the layer-resolved orbital occupations, the unusual antiferromagnetic order observed in the ultra-thin limit, and the quantitative investigation of the bond-order parameter. 4:30 602 Breathing mode distortion and magnetic order in rare-earth nickelates RNiO 3 Alexander Hampel, Claude Ederer, ETH Zürich Perovskite rare-earth nickelates, RNiO 3, display a rich and only partially understood phase diagram, where all compounds with R from Pr to Lu undergo a metal-insulator transition (MIT) that is accompanied by a structural distortion. We use density functional theory (DFT) and its extensions (DFT+U, DFT+DMFT), combined with symmetry-based distortion mode analysis to explore the interplay between lattice distortions, magnetic order, and electronic correlation effects in rare-earth nickelates. Thereby, we want to explore the capabilities of the DFT+DMFT method to describe complex materials with coupled electronic and structural degrees of freedom. 4:45 603 Distortion mode analysis of the lattice anomalies across the metal-to-insulator transition in PrNiO 3 Dariusz Jakub Gawryluk, Juan Rodríguez-Carvajal 2, Maria Teresa Fernández-Díaz 2, Philippe Lacorre 3, Marisa Medarde Paul Scherrer Institut, 2 Institut Laue-Langevin, 3 UFR Sciences et Techniques, Université du Maine RNiO 3 perovskites (R = rare earth, Tl 3+, Pb 3+ or Bi 3+ ) display a metal to insulator transition (MIT) at temperatures T MIT than increase by decreasing the lanthanide ionic radius. The electronic localization is associated to a charge disproportionation of the type 2Ni 3+ = Ni 3+d + Ni 3 d and with subtle structural distortions related to the Ni 3+d /Ni 3 d charge order. Using neutron powder diffraction the lattice anomalies of PrNiO 3 have been re-investigated and interpreted in terms of frozen normal distortion modes. We identify a new breathing mode with non-zero amplitude below T MIT and associate it to the charge order responsible for the MIT. 98

5:00 604 New magnetic phase in the nickelate perovskite TlNiO 3 Lukas Korosec, Marek Pikulski, Toni Shiroka, Marisa Medarde 2, Hubertus Luetkens 2, Jose-Antonio Alonso 3, Hans Rudolf Ott,2, Joel Mesot,2 ETH Zürich, 2 Paul Scherrer Institut, 3 Instituto de Ciencia de Materiales de Madrid, CSIC The perovskite rare-earth nickelates RNiO 3 are a family of transition metal oxides with strong electron correlations. They exhibit antiferromagnetic order with four Ni spins per period below a composition-dependent Néel temperature T N. Despite its high relevance to theoretical claims of ferroelectricity in the magnetically ordered phase, the exact arrangement of moments is still not well established. Our recently obtained results of nuclear magnetic resonance and muon spin rotation experiments on the closely related compound TlNiO 3 reveal a second magnetic phase transition at T N * = 202 K, above T N = 04 K. The new phase is suppressed by magnetic fields on the order of at most T. 5:5 605 Interplay between the structural and metal-insulator transition in rare-earth nickelates Oleg Peil, Materials Center Leoben, AT-8700 Leoben Rare-earth nickelates, RNiO 3, represent an intriguing example of materials with a highly tunable metal-insulator transition (MIT) and high potential for heterostructure engineering. The T - dependent paramagnetic MIT observed both in the bulk and ultrathin films of RNiO 3 is almost always accompanied by a subtle crystal-structure transformation, resulting in disproportionation of Ni-O bonds. We employ recent advances in understanding the nature of the insulating phase in RNiO 3 to unravel the mechanism underlying the combined structural/metal-insulator transition. By explicitly including lattice degrees of freedom into the description we show how a peculiar electronic structure may result in stabilization of the bond-disproportionated phase and we identify two control parameters associated with the transition. 5:45 606 Optical probe of correlations in rare-earth nickelates films Jérémie Teyssier, Julien Ruppen, Ivan Ardizzone, Oleg Peil, Sara Catalano, Jennifer Fowlie, Marta Gibert, Jean-Marc Triscone, Antoine Georges, Dirk van der Marel, Université de Genève We used reflectometry and ellipsometry to investigate electronic properties of rare-earth nickelate films. We study the temperature dependence of the optical conductivity as chemical composition and strain varies close to charge and magnetic ordering temperatures. The optical spectra show a characteristic two-peak structure when the material switches from metal to insulator that DMFT associates with a combined effect of bond disproportionation and Mott physics. At magnetic ordering temperature, the spectral weight increases in these two peaks. Landau model with coupled charge and magnetic order parameters, indicates that charge order is required to the emergence of a long range magnetic order. Through a positive feedback, magnetic order stabilizes the charge order. 6:00 607 Electronic structure of buried LaNiO 3 layers in ()-oriented LaNiO 3 /LaMnO 3 superlattices probed by soft x-ray ARPES Flavio Bruno, Marta Gibert, Shiobhan McKeown Walker, Oleg Peil, A. de la Torre, Sara Ricco, Zhiming Wang 2, Sara Catalano, Anna Tamai, F. Bisti 2, Vladimir Strocov 2, Jean-Marc Triscone, Felix Baumberger University of Geneva, 2 Paul Scherrer Institute Taking advantage of the large electron escape depth of soft x-ray angle resolved photoemission spectroscopy we report measurements of the electronic structure of ()-oriented [LaNiO 3 / LaMnO 3 ] superlattices and LaNiO 3 epitaxial thin films. For thin films we observe a 3D Fermi surface with an electron pocket at the Brillouin zone center and hole pockets at the zone vertices. Superlattices with thick nickelate layers present a similar electronic structure. However, as the thickness of the LaNiO 3 is reduced to 7 monolayers the superlattices become insulating. These heterostructures do not show a marked redistribution of spectral weight in momentum space but exhibit a pseudogap of 50 mev. [APL Materials 5, 060 (207)] 6:5 6:30 Coffee Break 99

Time ID Correlated-Electron Physics in Transition-Metal Oxides II Chair: Claude Ederer, ETH Zürich 7:00 6 Ultrafast demagnetization dynamics in TbMnO 3 Elsa Abreu, Elisabeth Bothschafter 2, Laurenz Rettig 2, Teresa Kubacka, Sergii Parchenko 2, Michael Porer 2, Christian Dornes, Yoav William Windsor 2, Mahesh Ramakrishnan 2, Aurora Alberca 2, Sebastian Manz, Jonathan Saari, Seyed M. Koopayeh 3, Manfred Fiebig, Thomas Forrest 4, Sarnjeet S. Dhesi, Steven L. Johnson, Urs Staub 2 ETH Zürich, 2 Paul-Scherrer Institute, 3 John Hopkins University, 4 Diamond Light Source TbMnO 3 is a well-studied low-temperature multiferroic. Below 4 K the magnetic system orders antiferromagnetically into a spin density wave. Upon further cooling, below 27 K, the magnetic order changes to cycloidal and a ferroelectric polarization arises. We present our results on photoinduced demagnetization dynamics in TbMnO 3, following excitation at.55 ev and 3 ev photon energies. The magnetic and orbital orders are tracked via the (0 q 0) and (0 2q 0) reflections, respectively, using polarization dependent resonant X-ray diffraction at the Mn L 2 edge. The timescales and pathways of the transition between the multiferroic and the high temperature phase will be discussed. 62 cancelled, replaced by talk 67 7:5 67 Metal-insulator transition in CaVO 3 thin films from DFT+DMFT Sophie Beck, Gabriele Sclauzero, Claude Ederer, ETH Zürich Complex oxide thin films and heterostructures exhibit a wide variety of interesting functionalities that are generally determined by numerous factors. Here, we investigate the effects of epitaxial strain, dimensional confinement, as well as interface and surface effects on the electronic properties of the correlated metal CaVO 3, using a combination of density functional theory (DFT) and dynamical mean-field theory (DMFT). We show that tensile epitaxial strain can induce a metal-insulator transition in CaVO 3, and we demonstrate that this strain effect cooperates with a similar tendency originating from the finite thickness of the film, consistent with recent experimental observations. Furthermore, we also address the influence of the substrate-film interface in CaVO3/ LaAlO 3 heterostructures. 7:30 63 Oxygen-vacancy engineering in strained multiferroic SrMnO 3 thin films Laura Maurel, Eric Langenberg 2, Roger Guzmán 3, César Magén 3, Pedro Antonio Algarabel 4, Jose Angel Pardo 3 Paul Scherrer Institut & ETH Zürich 2 Instituto de Ciencias de Materiales de Aragon 3 Laboratorio de Microscopías Avanzadas - Instituto de Nanociencia de Aragón 4 Departamento de Física de la Materia Condensada The control of the oxygen vacancies content in magnetoelectric oxides opens new routes to induce unexpected properties in strained thin films. Here we show experimental evidence for the increase of the oxygen-vacancy content upon increasing tensile epitaxial strain in multiferroic SrMnO 3 thin films. Furthermore, a novel dependence of the oxygen stoichiometry on the film thickness has been found, allowing us to control the concentration of these defects by both the applied strain and film thickness. We analyze the effect of the oxygen-vacancy content on the ferroic properties of strained SrMnO 3 films focusing on the generation of a flexoelectric component that rotates the in-plane <0> ferroelectric polarization. 7:45 64 Magnetic spiral order and multiferroism through impurity-induced frustration Markus Müller, Andrea Scaramucci 2, Christopher Mudry, Maxim Mostovoy 3, Hiroshi Shinaoka 4, Matthias Troyer 2, Nicola Spaldin 2 Paul Scherrer Institut, 2 ETH Zürich, 3 Groningen, 4 Tokyo Multiferroism can originate from the breaking of inversion symmetry caused by magnetic-spiral order. It usually arises due to competing magnetic exchange interactions that differ by their range and sign, and thus occurs at low temperatures. I present a mechanism that works at much higher temperatures. It relies on frustrating bonds randomly introduced along a single crystallographic direction, as found in a realistic model of YBaCuFeO 5, where spiral order at high temperatures 00

was indeed reported. We predict a correlation between the ordering temperature and the spiral wavevector. We show that spin orbit coupling at impurities induces a tilting of the easy plane, which ensures that spiral order couples to electric polarization. 8:00 65 Effect of epitaxial strain on the spin and spin-orbital excitations of Sr 2 observed by Resonant Inelastic X-ray Scattering (RIXS) Eugenio Paris, Daniel McNally, Yi Tseng, Milan Radovic, Thorsten Schmitt, Paul Scherrer Institut The sensitivity of the J eff = /2 state of Sr 2 to local coordination and structural distortions suggests epitaxial strain as an ideal route for manipulating this exotic ground state. As recently demonstrated, oxygen K-edge RIXS is capable to capture magnetic excitations in 5d-oxides []. From O K-edge RIXS on roughly 20-nm thick Sr 2 films we observed the low-energy elementary excitations encompassing single magnons, bimagnons and spin-orbital excitations and their dispersion relations. In this talk, I will present a direct observation of the evolution of these low- energy quasiparticle excitations and spin dynamics upon epitaxial strain in the J eff = ½ Mott insulator Sr 2. [] X. Lu et al, manuscript submitted 8:5 66 Investigation of Metal-Insulator transition in NaOsO 3 using Resonant X-Ray Diffraction Namrata Gurung,2, Naëmi Leo 2, Laura Heyderman,2, Kazunari Yamaura 3, Urs Staub 2, Steve Collins 4, Yves Joly 5, Valerio Scagnoli,2 ETH Zürich, 2 Paul Scherrer Institute, 3 National Institute for Material Science, Japan, 4 Diamond Light Source, UK, 5 Institut Neel, France In 5-d transition metal oxides, spin-orbit coupling becomes sizable and its interplay with e.g. the Coulomb interaction has led to the observation of exciting novel ground states. We report here on NaOsO 3, which has been proposed to be the first realization of a Slater insulator i.e. a system in which a metal-insulator transition is driven only by antiferromagnetic correlation. We employed Resonant X-ray Diffraction to elucidate the nature of the metal-insulator transition. By a careful study of forbidden reflections, we can exclude the presence of a structural crystallographic change at the phase transition. In addition, we observe an anomaly below the Neel temperature that is indicative of the Slater scenario. 8:30 9:00 Transfer to Dinner 9:30 Conference Dinner Thursday, 24.08.207, CICG: Room 3 Time ID Correlated-Electron Physics in Transition-Metal Oxides III Chair: Oleg Peil, Materials Center Leoben 0:45 62 A Different Route to Unconventional Superconductivity: New Spectroscopy on Bismuth Oxides Nicholas Plumb, Swiss Light Source, Paul Scherrer Institut Like parent compounds of other unconventional and/or high-t c superconductor families, BaBiO 3 is an unexpected insulator that becomes superconducting (> 30 K) when doped. But bismuth oxides also offer an interesting contrast to other HTSCs, as they have no magnetic order and very weak electron correlations. I will summarize our efforts to revisit these decades-old materials with modern x-ray spectroscopies, ARPES and RIXS, performed in situ on thin films. The investigations give new insights into the nature of the parent state, as well as how the electronic structure and bosonic coupling evolve with doping. We also demonstrate tuning the atomic structure by thin film engineering, which opens new paths for exploration. 0

:5 622 Identifying detrimental effects for multiband superconductivity Application to Sr 2 Aline Ramires, Manfred Sigrist, ETH Zürich We propose a general scheme to probe the compatibility of arbitrary pairing states with a given normal state Hamiltonian by the introduction of a concept called superconducting fitness. This quantity gives a direct measure of the suppression of the superconducting critical temperature in the presence of key symmetry-breaking fields, even in complex multi-band systems. In the light of this new concept we analyze the multiband superconductor Sr 2 and propose a new mechanism for the suppression of superconductivity, which we call inter-orbital effect, as a possible explanation for the unusual limiting feature observed in the upper critical field in this system. :30 623 Hallmarks of Hund s coupling in the Mott insulator Ca 2 Denys Sutter, Claudia Fatuzzo 2, Simon Moser 3, Minjae Kim 4, Rosalba Fittipaldi 5, Antonio Vecchione 5, Veronica Granata 5, Yasmine Sassa 6, Fabio Cossalter, Gianmarco Gatti 2, Henrik Rønnow 2, Nicholas Plumb 7, Christian Matt, Ming Shi 7, Moritz Hoesch 8, Timur Kim 8, Tay-Rong Chang 9, Horng-Tay Jeng 9, Chris Jozwiak 3, Aaron Bostwick 3, Eli Rotenberg 3, Antoine Georges 4,0, Titus Neupert, Johan Chang University of Zurich, 2 EPFL, 3 Advanced Light Source, 4 CNRS, Univ Paris-Saclay, 5 CNR-SPIN, 6 Uppsala University, 7 PSI, 8 Diamond Light Source, 9 National Tsing Hua University, 0 University of Geneva Ca 2 is an archetypal example for multi-band Mott physics including spin-orbit and Hund s coupling. For decades, the mechanism underlying its Mott insulating state has remained elusive. This talk will present the complete low-energy ruthenium band structure as observed by ARPES in the paramagnetic insulating state of Ca 2. These results suggest that Ca 2 is a unique example of an orbital differentiated conventional band and Mott insulator. In the talk we make a strong effort to explain how this conclusion is reached independently from both DMFT calculations and a purely phenomenological DFT model. :45 624 Electronic Phase Separation and Dramatic Inverse Band Renormalization in the Mixed-Valence Cuprate LiCu 2 O 2 Gianmarco Gatti, EPFL, Simon Moser, Advanced Light Source We measured, by angle-resolved photoemission spectroscopy, the electronic structure of LiCu 2 O 2, a mixed-valence cuprate where planes of Cu(I) ions are sandwiched between layers containing one-dimensional edge-sharing Cu(II) chains. We find that the Cu(I)- and Cu(II)-derived electronic states form separate electronic subsystems. The valence band, of the Cu(I) character, disperses within the charge-transfer gap of the strongly correlated Cu(II) states, displaying a 250% broadening of the bandwidth with respect to the predictions of density functional theory. Our observation is contrasting the widely accepted tenet of many-body theory that correlation effects yield narrower bands and suggests that present-day electronic structure techniques provide an intrinsically inappropriate description in late transition metal oxides. 2:00 625 Hubbard interactions from density-functional perturbation theory Iurii Timrov, Matteo Cococcioni, Nicola Marzari, EPFL DFT+U is a simple and powerful tool to model systems containing partially-filled manifolds of localized states. Conceptual and practical methods to determine U ab initio have been introduced long ago, based either on the constrained random-phase approximation or on linear-response theory. However, these approaches are often overlooked due to their cost or complexity. Here, we introduce a computationally efficient approach to determine U, hitherto obtained from the difference between bare and self-consistent inverse electronic susceptibilities evaluated from supercell calculations. By recasting these calculations in the language of density-functional perturbation theory we remove the need of supercells, and allow for a fully automated determination of susceptibilities and Hubbard parameters. 2:5 END; Lunch 8:30 Postersession and Apéro 20:00 Public Lecture 02

ID Correlated-Electron Physics in Transition-Metal Oxides Poster 63 Charge localization and energetics of Li-ion batteries cathodes from extended Hubbard-corrected functionals Matteo Cococcioni, Nicola Marzari, Theory and Simulations of Materials (THEOS), National Centre for Computational Design and Discovery of Novel Materials (MARVEL), EPFL The accurate modeling of transition-metal compounds (TMC) is essential for their deployment as electrodes of Li-ion batteries. Allowing to capture the localization of electrons during charge/discharge, Hubbard-augmented DFT functionals (DFT+U) have become the standard choice for the modeling of TMC when computational efficiency is required. This work shows how an extended formulation of DFT+U, including on-site (U) and inter-site (V) interactions, improves the description of the equilibrium structure and the electronic properties of mixed valence cathode materials as Li x MP and Li x CoO 2. In particular, the use of computed interaction parameters is shown to be crucial to assess the stability of intermediate compositions and to evaluate the voltage of the battery. 632 Optical evidence for bad-metal behavior in the doped Mott-insulator Sr 2 Nimrod Bachar, Kai Wang, University of Geneva We measured the in-plane optical conductivity spectra between 0.0 and 4 ev of (Sr -x La x ) 2. Our data confirm that Sr 2 is a Mott insulator with a gap onset at about 0.eV. La substitution leads to a rapid collapse of the gap which is completed for x = 0.05, and the emergence of a narrow-mode associated to free charge carriers. The intensity of this mode as compared to the nominal carrier doping reveals a very rapid transfer of high energy spectral weight above the gap down to the free-carrier sector. The free-carrier optical conductivity displays bad metal-like behavior as a function of temperature and frequency,with indications of a partial gapping of the free-carrier response of about 30 mev. 633 Orbital characters of the band structure in a high-temperature cuprate superconductor Kevin Hauser, Christian Matt, Denys Sutter, Ashley Cook, Yasmine Sassa 2, Martin Mansson 3, Oscar Tjernberg 4, Lakshmi Das, Nicolas Plumb 5, Ming Shi 5, Vladimir Strocov 5, S. Pyon 6, T. Takayama 6, H. Takagi 6, O. J. Lipscombe 7, S. M. Hayden 7, T. Kurosawa 8, N. Momono 8, M. Oda 8, Titus Neupert, Johan Chang University of Zurich, 2 Uppsala University, 3 Royal Institute of Technology, Stockholm, Sweden, 4 KTH Royal Institut of Technology, Kista, 5 Paul Scherrer Institute, 6 Department of Advanced Materials, University of Tokyo, 7 H. H. Wills Physics Laboratory, University of Bristol, 8 Department of Physics, Hokkaido University We present an angle resolved photoemission spectroscopy study of the overdoped cuprate superconductor La 2 x Sr x Cu. Using the symmetry properties of the photoemission matrix element effect, we present on this poster the orbital character of the band structure. With the obtained information, consequences for superconductivity and pseudogap physics is discussed. 634 Doping evolution of the multi-band Mott insulator Ca 2 Sara Ricco, Minjae Kim 2, Anna Tamai, Siobhan McKeown Walker, Irene Cucchi, Flavio Y. Bruno, Antoine Georges,2, Robin Perry 3, Felix Baumberger University of Geneva, 2 CNRS, Univ Paris-Saclay 3 London Centre for Nanotechnology and UCL Centre for Materials Discovery, University College London High temperature superconductivity, colossal magneto-resistance and many other intriguing phenomena in correlated electron physics arise in doped Mott insulators. Here, we present the first angle-resolved photoemission (ARPES) study of electron-doped Ca 2. The undoped parent compound of our study has been investigated intensely as a model system of a multi-band Mott transition. Our ARPES data reveal a coherent Fermi surface at doping levels as low as 0.. In contrast to cuprates or iridates, the emergent metallic state is characterized by heavy quasiparticle bands devoid of a pseudogap. These results show that key-properties of doped cuprates and iridates, such as the momentum dependent pseudogap are not universal features of doped Mott insulators. 635 moved to talk 67, replaces talk 62 03

636 Tuning magnetic spirals beyond room temperature with chemical disorder Mickael Morin, Marisa Medarde, Emmanuel Canevet, Adrien Raynaud, Marek Bartkowiak, Denis Sheptyakov, Voraksmy Ban, Michel Kenzelmann, Ekaterina Pomjakushina, Kazimierz Conder Paul Scherrer Institut In the past years, magnetism-driven ferroelectricity has been reported in a number of frustrated magnets with spiral magnetic orders. Such materials are of high current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low magnetic order temperatures (typically < 00 K) restrict their fields of application. In this talk I will show that chemical disorder is a powerful tool that can be used to stabilize magnetic spiral phases at higher temperatures. As example of this novel mechanism I will present our recent investigations on YBaCuFeO 5, where a controlled manipulation of the Cu/Fe chemical disorder was successfully used to increase the spiral order temperature from 54 to 30 K. 637 Decisive electronic interactions in iron-based superconductors as seen by ARPES Daniil Evtushinsky, EPFL It is becoming clear that strong electron interactions with other electrons and with the magnetic excitations unify all iron-based materials, and probably, all unconventional superconductors in general. I will review the electronic self energy, determined from the angle-resolved photoemission spectroscopy (ARPES) for the,, 22, and families, and will compare it to the situation in the compounds of other transition metals. I will show how the spectral features at the energy scale of the whole 3d band match with the results of calculations for correlated systems and how the low-energy features correspond to the peculiarities found in the spin-fluctuation spectrum measured in neutron scattering. 638 Isotope effect in superconducting n-doped SrTiO 3 Adrien Stucky, Dorota Pulmannovà, Gernot Werner Schereer, Zhi Ren, Didier Jaccard, Jean-Marie Poumirol, Céline Barreteau, Enrico Giannini, Dirk van der Marel University of Geneva, Departement of Quantum Matter Physics The strength of the electron-phonon coupling in the superconducting mechanism of n-doped STO is still under debate. Interestingly, it has been proven that SrTiO 3 becomes ferroelectric at low temperature when 6 O atoms are substituted by their isotope 8 O. Using DC resistivity and AC susceptibly measurements we have determined the effect of 8 O/ 6 O isotope substitution on T c and H c. We observed a factor.5 increase of T c and H c2 at any doping levels. This isotope effect is opposite to BCS theory, but anticipated by models of polaronic band narrowing, as well as proximity to a ferroelectric quantum critical point. 639 Higgs and Goldstone dynamics in h-rmno 3 Adrien Stucky, Quintin Meier 2, Sinead Griffin 2, Frank Lichtenberg 2, Dirk van der Marel, Nicola Spaldin 2 University of Geneva, Departement of Quantum Matter Physics, 2 ETH Zürich, Department of Materials Making connections between various domains of modern physic is an exciting opportunity. The spontaneous symmetry breaking of the crystal structure of hexagonal manganite creates an almost perfect Mexican hat potential. We have performed polarization resolved Raman spectroscopy of ErMnO 3 and two types of InMnO 3. In ErMnO 3, the phonons that have a substantial overlap with the Higgs amplitude mode show an unusually strong red softening on warming. In contrast the frequencies of the corresponding modes in InMnO 3 are largely temperature-independent. These results are consistent both qualitatively and quantitatively with our combined Landau and ab initio model describing the coupling between the Higgs and the Goldstone-like mode in the hexagonal manganites. 04

640 Evidence of electron-phonon interaction in single crystal of (Ru 3+ /+ ) mixed-valence Na 2.7 and NaRu 2 Arvind Yogi, C. I. Satish, Hasung Sim, J. G. Park Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Korea and Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea We report a comprehensive investigation of the structural, electric transport, magnetic, and thermodynamic properties of Na 2.7 and NaRu 2 single crystals. The compounds are structurally different; Na 2.7 crystalize in monoclinic (C 2/m) structure while NaRu 2 crystalize in orthorhombic (P 2/ma) structure. We observed a first-order phase transition in the electrical resistivity at T c = 365 K and T c = 530 K for Na 2.7 and NaRu 2, respectively. Resistivity is influenced by electron phonon scattering and additionally inter-band electron scattering and the evidence for metal-like electronic contribution in heat capacity was also observed. The electronic contribution to the specific heat (gamma) for Na 2.7 and NaRu 2 was determined to be 26.9 and 3.93 mj/mol K2, respectively. 05