Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Y17: Focus Session: Magnetic Metal Insulator Transitions |
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Sponsoring Units: DMP GMAG Chair: Eduardo Granado, Universidade Estadual de Campinas (Brazil) Room: 319 |
Friday, March 22, 2013 8:00AM - 8:36AM |
Y17.00001: Magnetically driven metal-insulator transition in NaOsO3 Invited Speaker: Stuart Calder The metal-insulator transition (MIT) is one of the most dramatic manifestations of electron correlations in materials, enjoying interest both for its fundamental nature and technological application. Various mechanisms producing MITs have been extensively considered over the years, including the Mott (electron localization via Coulomb repulsion), Anderson (localization via disorder) and Peierls (localization via distortion of a periodic one-dimensional lattice). One additional route to a MIT proposed by Slater in 1951, in which long-range magnetic order in a three dimensional system drives the MIT, has received relatively little attention, particularly from an experimental viewpoint. Using neutron and x-ray scattering we have shown that the MIT in NaOsO$_3$ is coincident with the onset of long-range commensurate magnetic order at 410 K. Whilst candidate materials have been suggested, our experimental methodology allows the first definitive demonstration of the long predicted Slater MIT. We discuss our results in light of recent work on other 5d systems that contrastingly have been predicted to host a Mott spin-orbit insulating state. [Preview Abstract] |
Friday, March 22, 2013 8:36AM - 8:48AM |
Y17.00002: Metal-insulator transition in pyrochlore Eu2Ir2O7 studied by infrared spectroscopy Andrei Sushkov, Dennis Drew, Jun Ishikawa, Satoru Nakatsuji, Xuan Luo, Sang-Wook Cheong The large family of pyrochlores with formula A$_2$B$_2$C$_7$ attracted a lot of early attention due to strong geometric magnetic frustration. Recent band structure calculations predict that the iridate pyrochlores A$_2$Ir$_2$O$_7$ may have nontrivial topological states. We will report the results of an infrared spectroscopic study of the metal-insulator transition in Eu$_2$Ir$_2$O$_7$ single crystal and Y$_2$Ir$_2$O$_7$ polycrystal. We will report the broad band IR reflection as a function of temperature for an overview of the M-I transition and the low frequency transmission which is more sensitive for detection of a 10 meV gap[1] and other possible excitations. We will discuss possible implications of the semimetal Weyl states. [1] J.J. Ishikawa et al., Phys. Rev. B 85, 245109 (2012). [Preview Abstract] |
Friday, March 22, 2013 8:48AM - 9:00AM |
Y17.00003: Tuning J$_{eff}$ = 1/2 Insulating State via Electron Doping and Pressure in Double-Layered Iridates L. Li, P.P. Kong, C.Q. Jin, T.F. Qi, O.B. Korneta, S.J. Yuan, G. Cao Sr$_3$Ir$_2$O$_7$ exhibits a novel J$_{eff}$=1/2 insulating state featuring a splitting between J$_{eff}$=1/2 and 3/2 bands due to spin-orbit interaction. We report that a metal-insulator transition can be induced by either dilute electron (La$^{3+}$) doping for Sr$^{2+}$ ions in Sr$_3$Ir$_2$O$_7$ or via application of high pressure. The following constitutes the central findings of our recent study of single-crystal Sr$_3$Ir$_2$O$_7$ and (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$: (1) application of high hydrostatic pressure P results in a drastic drop in the electrical resistivity by four orders of magnitude at a critical pressure, P$_C$ = 13.2 GPa, suggesting a significantly reduced splitting between J$_{eff}$=1/2 and 3/2 bands, but further increasing P up to 35 GPa produces no fully metallic state at low temperatures; (2) however, slight doping of La$^{3+}$ ions for Sr$^{2+}$ ions in Sr$_3$Ir$_2$O$_7$ readily induces a robust metallic state that follows no Fermi liquid behavior; and (3) the magnetic ordering temperature is significantly suppressed from 285 K for x=0 but remains finite for (Sr$_{0.94}$La$_{0.06}$)$_3$Ir$_2$O$_7$ where the metallic state occurs. The results will be discussed along with comparisons drawn with Sr$_2$IrO$_4$, a prototype of the J$_{eff}$ = 1/2 insulator. [Preview Abstract] |
Friday, March 22, 2013 9:00AM - 9:12AM |
Y17.00004: Exploring the Unusual Physical Properties near the Metal-Insulator Transition of RNiO$_3$ Luke G. Marshall, Jinguang Cheng, Jianshi Zhou, Mar\'Ia Jes\'us Mart\'Inez-Lope, Jos\'e Antonio Alonso, John B. Goodenough Understanding the physical properties at the crossover from localized to itinerant electronic behavior in the transition-metal perovskite-related oxides remains a challenging problem of solid-state physics. This problem can manifest in mixed-valent compounds at this crossover to produce unusual properties such as high-T$_c$ superconductivity in the cuprates and colossal magnetoresistance in the manganites. RNiO$_3$ (R=lanthanide) perovskites are single-valent compounds where the $\pi$-band is filled and the $\sigma$-band is $\frac{1}{4}$ filled. The electron bandwidth can be tuned by substituting different rare earth cations at the A site, so that the system provides a unique opportunity to study this crossover more simply. While the phase diagram for this compound is well known, magnetic rare earth ions prevent the study of the evolution from Pauli to Curie-Weiss paramagnetism. To account for this, we have used high-pressure synthesis to create a series of RNiO$_3$ samples (R=La, Y, Lu) and studied their magnetic and transport properties. We have also shown that the localized to itinerant crossover can also be explored by substituting Ga$^{3+}$ for Ni$^{3+}$ in LaNi$_{1-x}$Ga$_x$O$_3$. [Preview Abstract] |
Friday, March 22, 2013 9:12AM - 9:24AM |
Y17.00005: ABSTRACT WITHDRAWN |
Friday, March 22, 2013 9:24AM - 9:36AM |
Y17.00006: Multi-orbital Mott Transition and High $T_c$ Ferromagnetism in Strongly Correlated Oxides Mohit Randeria, Onur Erten, O. Nganba Meetei, Nandini Trivedi, Patrick Woodward Amongst all perovskites with a net magnetic moment, Sr$_2$CrOsO$_6$ (SCOO) [1] has the highest $T_c = 725$K. We model this as a multi-orbital Hubbard model with different Coulomb $U$'s and Hund's coupling $J_H$'s on the Cr and Os sites along with spin-orbit coupling (SOC) $\lambda_{so}$ on Os. Using a slave-rotor approach, we find a new Mott criterion [2] $\left(\tilde{U}_{\rm Cr}\tilde{U}_{\rm Os}\right)^{1/2} > 2.5W$, where $W$ is the bandwidth and $\tilde{U}$'s are the effective charge gaps including the effects of $U$, $J_H$ and $\lambda_{so}$. Using this result, we argue that SCCO is a Mott insulator. Next, we show that the orbital moment on Os is quenched. The effective spin Hamiltonian for $S=3/2$ moments has Cr-Os and Os-Os antiferromagnetic superexchange interactions that are frustrated. Using a variational approach and Monte Carlo simulations, we show that the system has a canted ground state with a net moment at $T=0$, a non-monotonic magnetization $M(T)$ and a high $T_c$. Our results [2] are in excellent agreement with available data [1] and we predict the magnetic $S({\bf q})$ that will test our theory. [1] Y. Krockenberger {\it et al.}, Phys Rev. B {\bf 75} 020404 (2007). [2] O. N. Meetei, O. Erten, M. Randeria, N. Trivedi, and P. Woodward, arXiv:1205.1811 [Preview Abstract] |
Friday, March 22, 2013 9:36AM - 9:48AM |
Y17.00007: Resonant Ultrasound studies of spin- and orbital ordering transitions in RVO$_{3}$ M. Koehler, J.-Q. Yan, Y. Ren, B.C. Sales, D. Mandrus, V. Keppens RVO$_{3}$ perovskites (R = rare earth) have been shown to undergo multiple spin and orbital transitions due to the Jahn-Teller active V$^{3+}$ electrons. We have initiated a study of the elastic response of RVO$_{3}$, ( R = Dy, Gd, Ce) as well as Y$_{1-x}$La$_{x}$VO$_{3}$ (x = 0.05, 0.3, 1) using resonant ultrasound spectroscopy. The temperature-dependence of the elastic response is dominated by the ordering transitions, with transition temperatures that change with the size of the rare earth. For CeVO$_{3}$ and LaVO$_{3}$, two transitions are observed, separated by 17K and 2K, respectively. DyVO$_{3}$ and Y$_{0.95}$La$_{0.05}$VO$_{3}$ show three transitions below 220K while GdVO$_{3}$ only shows one. The full elastic tensor of Y${_0.7}$La$_{0.3}$VO$_{3}$ has also been determined from 300K to 50K, yielding the temperature dependence of the 9 orthorhombic elastic moduli. [Preview Abstract] |
Friday, March 22, 2013 9:48AM - 10:00AM |
Y17.00008: Strong electronic correlations and spin-orbit coupling in layered ruthenates Frank Lechermann, Malte Behrmann, Christoph Piefke The combination of the local-density approximation to density functional theory with explicit many-body approaches has proven to be a powerful tool to investigate the problem of strong electronic correlations on a realistic level. Notably in quasi-twodimensional materials the interaction between the effective dimensionality and the symmetry of the underlying crystal structure with the competition between the localized and the itinerant character of electrons is indeed giving rise to highly interesting physical phenomena, especially within the family of transition-metal oxides. Here we want to focus on the intriguing interplay between rotational-invariant local Coulomb interactions and spin-orbit coupling for the case of the layered strontium ruthenates within the Sr$_{n+1}$Ru$_n$O$_{3n+1}$ Ruddlesden-Popper series. Novel results based on a generic realistic modelling of the correlated electronic structure for the n=1,2 members of this family of compounds will be discussed [1]. In this respect, also the intriguing metamagnetic behavior of Sr$_3$Ru$_2$O$_7$ will be addressed.\\[4pt] [1] M. Behrmann, C. Piefke and F. Lechermann, Phys. Rev. B 86, 045130 (2012) [Preview Abstract] |
Friday, March 22, 2013 10:00AM - 10:12AM |
Y17.00009: Pressure study of nematicity and quantum criticality in Sr$_3$Ru$_2$O$_7$ for a in-plane field Dan Sun, Wenlong Wu, Santiago A. Grigera, Robin S. Perry, Andy P. Mackenzie, Stephen R. Julian We study the relationship between the nematic phase of Sr$_3$Ru$_2$O$_7$ and quantum criticality. At ambient pressure, the nematic phase appears to be associated with a metamagnetic quantum critical end point (QCEP) when the applied magnetic field is near the c-axis. We show, however, that this metamagnetic transition does not produce the same nematic signatures when the QCEP is reached by hydrostatic pressure with the field applied in the ab-plane. Moreover, a distinct nematic phase, that is seen for field applied in the ab-plane close to, but not right at, a metamagnetic anomaly, persists with minimal change to the highest applied pressure, 16.55 kbar. Taken together our results suggest that quantum criticality may not be necessary for the formation of a nematic phase. [Preview Abstract] |
Friday, March 22, 2013 10:12AM - 10:24AM |
Y17.00010: Far-infrared optical properties and the metal-insulator transition in Ti-doped Ca$_3$(Ru$_{\mathrm{1-x}}$Ti$_{\mathrm{x}})_2$O$_7$ (x$=$0.03) D. Talbayev, T. Stanislavchuk, A. Sirenko, Jin Peng, Z.Q. Mao The discovery of the intriguing phase diagram of Ca$_3$(Ru$_{\mathrm{1-x}}$Ti$_{\mathrm{x}})_2$O$_7$ is the new and exciting development in correlated electron ruthenates, as Ti doping drastically changes the material's ground state properties. The undoped Ca$_3$Ru$_2$O$_7$ is metallic at high temperature and undergoes an antiferromagnetic transition at 56 K that is followed by a metal-insulator transition at 48 K driven by the opening of a charge density wave gap. A quasi-2D metallic state develops below 30 K. At 5{\%} Ti doping, the metal-insulator transition temperature is T$_{\mathrm{MI}}=$80 K, below which the material is a Mott insulator. By contrast, a weakly localized electronic state is observed at intermediate dopings (2-4{\%} Ti) together with antiferromagnetic long range order. In the undoped Ca$_3$Ru$_2$O$_{\mathrm{7}}$, the metal-insulator transition at 48 K is accompanied by the development of a charge gap below 200 cm$^{-1}$. At low temperatures, a small Drude peak develops below 50 cm-1, resulting from small non-nested metallic pockets of the Fermi surface. We report a far-infrared spectroscopic ellipsometry study of Ca$_3$(Ru$_{\mathrm{1-x}}$Ti$_{\mathrm{x}})_2$O$_{\mathrm{7}}$ (x$=$0.03) at U4IR beamline of NSLS-BNL. Our data indicate that the low-temperature gap in optical conductivity opens at 1000 cm$^{-1}$, a dramatically different value from the one in the undoped compound. We relate our observations to the effects of Ti doping - the induced changes in carrier itinerancy and the modified double-exchange and superexchange interactions in the material. [Preview Abstract] |
Friday, March 22, 2013 10:24AM - 10:36AM |
Y17.00011: Optical Polarization Microscopy of the Electron Nematic Phase in Sr$_3$Ru$_2$O$_7$ Colin Heikes, S. Ghosh, D. MacNeill, R. Perry, J.F. Mercure, E.A. Kim, A. Mackenzie, D.C. Ralph We report the implementation of a fiber-based optical microscope, capable of operating at temperatures below 100 mK and in magnetic fields in excess of 9 Tesla, with sub-micron spatial resolution. This microscope is integrated into the bore of a dilution refrigerator with an optical fiber coupling light to an external optical table. Bench-top optical elements allow for polarization analysis of the reflected light from a surface and thus the detection of magnetic or other polarization-sensitive properties of matter at low temperature and high fields. As a first application of the instrument, we are studying the proposed electron nematic phase of the n=2 Ruddlesden-Popper material Sr$_3$Ru$_2$O$_7$, which exhibits a low-temperature phase transition in the form of an in-plane conduction anisotropy. We report initial results from polarization analysis and polarization microscopy with sample temperatures below 150 mK and applied magnetic fields from 0 T to 9 T. [Preview Abstract] |
Friday, March 22, 2013 10:36AM - 10:48AM |
Y17.00012: Effect of disorder on quantum phase transition in (Sr$_{1-x}$Ca$_x$)$_3$Ru$_2$O$_7$ Z. Qu, J. Peng, T.J. Liu, D. Fobes, V. Dobrosavljevic, L. Spinu, Z.Q. Mao (Sr$_{1-x}$Ca$_{x}$)$_{3}$Ru$_{2}$O$_{7}$ is characterized by complex magnetic states, spanning from anantiferromagnetic state over an unusual heavy-mass nearly ferromagnetic (NFM) state to an itinerant metamagnetic state. The NFM state, which occurs in the 0.4 \textgreater\ $x$ \textgreater\ 0.08 range, freezes into a cluster spin glass phase at low temperatures [1]. A quantum phase transition (QPT) occurs as the spin freezing temperature $T_{f}$ is suppressed to zero K near $x=$0.08. In this talk, we will report a novel quantum phase observed near the QPT [2]. The isothermal magnetization $M(H)$ and the temperature dependence of electronic specific heat \textit{Ce}($T )$ of this phaseexhibit anomalous power-law singularities and are controlled by a single exponent. Moreover, the magnetization $M(T,H)$ of this phase is found to follow a phenomenological scaling law of $M(H,T)\propto H^{\alpha}f(H$/$T^{\delta})$. These observations indicate the slow dynamics in rare regions arising from the effect of disorder on the QPT.\\[4pt] [1] Z. Qu et al., Phys. Rev. B 78, 180407(R) (2008)\\[0pt] [2] Z. Qu et al., Phys. Rev. B 86, 014434 (2012). [Preview Abstract] |
Friday, March 22, 2013 10:48AM - 11:00AM |
Y17.00013: Field-induced magnetic phase transitions in Ti-doped Ca3Ru2O7 bilayer ruthenates M. Zhu, J. Peng, Z.Q. Mao, K. Prokes, S. Matas, T. Hong, X. Ke Bilayer ruthenate Ca$_{\mathrm{3}}$Ru$_{\mathrm{2}}$O$_{\mathrm{7}}$ shows strong magnetic instability that depends sensitively on chemical doping and magnetic fields. Previously we have shown that [1] Ti doping induces Mott insulating ground state with a G-type antiferromagnetic (AFM) structure where nearest-neighbor spins align antiferromagnetically, a feature dramatically distinct from the metallic ground state with an AFM-b structure where the ferromagnetically aligned spins (pointing along the $b$-axis) within the bilayer are coupled antiferromagnetically along the $c$-axis. Here we report magnetic phases of the Ti-doped Ca$_{\mathrm{3}}$Ru$_{\mathrm{2}}$O$_{\mathrm{7}}$ in a magnetic field revealed via neutron diffraction study. In sharp contrast to pure Ca$_{\mathrm{3}}$Ru$_{\mathrm{2}}$O$_{\mathrm{7}}$ [2], below the metal-insulator transition we find a field-induced magnetic phase transition from G-type AFM to AFM-a with spins projected along the $a$-axis. Concomitantly, a sharp change in lattice parameters is observed, suggesting strong magnetoelastic coupling. The effect of such a field-induced phase transition on the magnetotransport property in the Ti-doped Ca$_{\mathrm{3}}$Ru$_{\mathrm{2}}$O$_{\mathrm{7}}$ will be discussed as well. [1] X. Ke et al., Phys. Rev. B \textbf{84}, 201102 (R) (2011). [2] W. Bao et al., Phys. Rev. Lett. \textbf{100}, 247203 (2008). [Preview Abstract] |
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