Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session S41: Correlated Electrons: Exotic Magnetism |
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Sponsoring Units: GMAG Chair: S.D. Mahanti, Michigan State Univ. Room: LACC 150A |
Wednesday, March 23, 2005 2:30PM - 2:42PM |
S41.00001: Properties and Detection of Spin Nematic Order in Strongly Correlated Electron Systems Daniel Podolsky, Eugene Demler A spin nematic is a state which breaks spin SU(2) symmetry while preserving translational and time reversal symmetries. Spin nematic order can arise naturally from charge fluctuations of a spin stripe state. Focusing on the possible existence of such a state in strongly correlated electron systems, we build a nematic wave function starting from a $t-J$ type model. The nematic is a spin-two operator, and therefore does not couple directly to neutrons. However, we show that neutron scattering and Knight shift experiments can detect the spin anisotropy of electrons moving in a nematic background. We find the mean field phase diagram for the nematic taking into account spin-orbit effects. [cond-mat/0411159]. [Preview Abstract] |
Wednesday, March 23, 2005 2:42PM - 2:54PM |
S41.00002: Can Frustration Preserve a quasi-two dimensional spin fluid? Marianna Maltseva, Piers Coleman One of the mechanisms recently proposed to account for non-Fermi liquid behavior in heavy fermion materials at a quantum critical point is based on the notion that the spins form a quasi-two-dimensional spin fluid. Using the Heisenberg antiferromagnet as a simple example to explore this line of reasoning, we show with the help of spin-wave theory that in general, geometric frustration fails to preserve a two-dimensional spin fluid. Even though one can eliminate the classical interlayer coupling by frustration, the layers always develop a quantum-mechanical coupling via tunneling. The magnon pair tunneling process responsible for this coupling is analogous to the pair tunneling process responsible for the Josephson effect generating a $\cos 2 \theta$ or biquadratic coupling between layers. To end our discussion we consider a special case of XY model in which decoupled "sliding phases" of spin fluid may exist in certain finely tuned conditions. In general these finely tuned situations are equally susceptible to the strong-coupling effects of quantum tunnelling, forcing us to conclude that in general, geometric frustration can not preserve a two dimensional spin fluid. [Preview Abstract] |
Wednesday, March 23, 2005 2:54PM - 3:06PM |
S41.00003: Geometric critical line and unconventional ordered phases in quantum kagome antiferromagnets Joel Moore, Cenke Xu We study the phase diagram of the XXZ antiferromagnet for spin$>$=1 on the kagome lattice for comparison with recent neutron scattering results. In addition to the usual geometric classical criticality that appears at zero temperature in the classical limit of the XY model, there is another zero-temperature geometrical critical line that separates two unconventional ordered phases. We also discuss numerical transfer-matrix results and similarities to plaquette phases proposed in the honeycomb lattice quantum dimer model. [Preview Abstract] |
Wednesday, March 23, 2005 3:06PM - 3:18PM |
S41.00004: Weak Chiral Magnetic Order in the Quantum Pyrochlore Antiferromagnet Valeri Kotov, Maged Elhajal, Michael Zhitomirsky, Frederic Mila Heisenberg (S=1/2) spins on the three-dimensional pyrochlore lattice do not order magnetically due to the strong frustration. However we show that the presence of antisymmetric, Dzyaloshinsky-Moriya (DM) interactions, can lead to weak antiferromagnetic order. This exotic state has chiral symmetry, dictated by the distribution of the DM vectors and is characterized by small magnetic moments induced by the DM interactions. An external magnetic field can also produce complex ordered states, and a quantum transition separates the field-induced and chiral ordered phases. [Preview Abstract] |
Wednesday, March 23, 2005 3:18PM - 3:30PM |
S41.00005: Pressure induced quantum phase transitions in Ca2RuO4 Patricia Lebre Alireza, Anne-Marie Cumberlidge, Gilbert Lonzarich, Stephen Julian, Fumihiko Nakamura, Yoshiteru Maeno Ca$_{2}$RuO$_{4 }$is a member of the family of ruthenates, which are strongly correlated systems that exhibit a wide range of interesting phenomena including metal-insulator transitions, orbital and magnetic ordering and unconventional superconductivity. Using a novel setup in a miniature anvil cell, we have been able to measure magnetic susceptibility under high hydrostatic pressure and have followed the transitions of Ca$_{2}$RuO$_{4}$ from an antiferromagnetic Mott insulator to a ferromagnetic metal. Additionally, we have investigated the evolution of this ferromagnetically ordered state as the pressure is increased, successfully suppressing this transition towards a quantum critical point. [Preview Abstract] |
Wednesday, March 23, 2005 3:30PM - 3:42PM |
S41.00006: Magnetic droplets in nearly ferromagnetic metals close to the quantum critical point Yen Lee Loh, Vikram Tripathi, Misha Turlakov Metallic palladium and platinum have anomalously high magnetic susceptibilities because of their proximity to quantum phase transitions, so that giant magnetic moments may form around impurities such as iron atoms, resulting in a magnetic susceptibility which varies sensitively with temperature, but sometimes shows deviations from the Curie law due to quantum fluctuations. We have studied the case of a magnetic droplet with XY anisotropy using perturbation theory and path-integral Monte Carlo simulation. We find that the susceptibility obeys a logarithmic law close to the quantum critical point that is distinct from the logarithms in the Kondo and Larkin-Mel'nikov theories. Our work provides a fuller understanding of the `phase diagram' of magnetic droplet systems and has implications for the design of magnetic thermometers based on giant-moment alloys. [Preview Abstract] |
Wednesday, March 23, 2005 3:42PM - 3:54PM |
S41.00007: BEC critical exponent near quantum critical point in BaCuSi$_2$O$_6$ Suchitra E. Sebastian, I.R. Fisher, P.A. Sharma, M. Jaime, N. Harrison, C.D. Batista, V. Correa, L. Balicas, N. Kawashima BaCuSi$_2$O$_6$ is a spin gap compound comprising coupled square bilayers of vertical dimers. The magnetic ordering transition in applied magnetic fields above the critical magnetic field (H$_{c1}$ = 23.5T) has been interpreted as a condensation of triplons. Proximity to the Quantum Critical point (QCP) can be tuned in this material by changing the particle density via the applied magnetic field (chemical potential.) We present a series of experiments that measure the critical exponent $\nu$ relating the proximity to the QCP, to the ordering temperature (T$_c$) by the power law $T_{c} \alpha (H-H_{c1})^\nu$. Experimental estimates of $\nu$ in this system agree with the theoretical mean field prediction of 2/3 for Bose Condensation of a dilute Bose gas. [Preview Abstract] |
Wednesday, March 23, 2005 3:54PM - 4:06PM |
S41.00008: Quantum Oscillations and Competing Ground States in triple layered Sr4Ru3O10 V. Durairaj, X.N. Lin, S. Chikara, E. Elhami, V.A. Bondarenko, J.W. Brill, G. Cao, S. Parkin, L. Balicas, Y. Xin The triple-layered Sr$_{4}$Ru$_{3}$O$_{10}$ is characterized by an unexpectedly strong quasi-two dimensional characteristic, and a sharp metamagnetic transition and ferromagnetic behavior occurring within the basal plane and along the c axis, respectively. The interplane resistivity at magnetic field B, up to 45 T, exhibits low-frequency quantum oscillations associated with the spin polarized state when B is parallel to the c axis, and a large magnetoresistivity accompanied by critical fluctuations governed by the metamagnetic transition when B is perpendicular to the c axis. The complex behavior evidenced in magnetization, specific heat, and resistivity presented is not characteristic of any obvious ground states, and points to an unusual state that shows a delicate balance between fluctuations and order. The results will be presented and discussed along with comparisons with data of impurity doped Sr$_{4}$Ru$_{3}$O$_{10}$. [Preview Abstract] |
Wednesday, March 23, 2005 4:06PM - 4:18PM |
S41.00009: Non-Fermi-liquid behavior in annealed UCu$_{4}$Pd Ryan Baumbach, Nicholas Butch, M. Brian Maple, Douglas MacLaughlin The effect of disorder in the polycrystalline UCu$_{4}$Pd system is addressed in an annealing study. Samples were annealed at 750$^{\circ}$C for 7, 14 and 56 days and compared to unannealed samples. X-ray diffraction data indicate that all samples are single phase UCu$_{4}$Pd. Magnetic susceptibility vs. temperature data and the Sommerfeld coefficient ($\gamma =C_{e}$/$T $where $C_{e}$ is the electronic specific heat) vs. temperature both show little variation with annealing and can be fit with either a logarithmic or weak power law function for 4.5K$\le T\le $50K and 0.6K$\le T\le $2K, respectively. In contrast, electrical resistivity vs. temperature data develop a Kondo-like minimum near 35K that strengthens with annealing. Additionally, at low temperatures (2K$\le T\le $10K), the resistivity is linearly proportional to temperature for all samples. These data indicate that the non-Fermi liquid behavior of UCu$_{4}$Pd is not suppressed by annealing and may resolve inconsistencies reported in previous studies. Data will be collected and presented for electrical resistivity at temperatures less than 2K. This work was supported by grants from the NSF and DOE. [Preview Abstract] |
Wednesday, March 23, 2005 4:18PM - 4:30PM |
S41.00010: Theory of Ferromagnetic Transition in One-Dimensional Itinerant Electron Systems Kun Yang Ferromagnetic transitions in itinerant electron systems are among the very first examples of quantum phase transitions studied theoretically. In the Hertz-Millis approach, one decouples the electron-electron interaction using Hubbard-Strotonovish transformation, integrates out the fermionic degrees of freedom, and arrives at a free energy functional that involves the ferromagnetic order parameter only. It has been pointed out recently that the procedure of integrating out gapless fermions may lead to subtle singularities in the bosonic free energy functional, which may complicate the analysis of the theory or even invalidate this approach. In this work we offer an alternative approach of obtaining a bosonic Ginsburg-Landau-Wilson theory that describes ferromagnetic transition in one-dimension. Our approach is based on Abelian bosonization, which allows for a derivation the effective field theory without integrating out fermions. The resultant theory is shown to have dynamical exponent z=2 at tree level and upper critical dimension 2. Thus one dimension is below the upper critical dimension of the theory, and the critical behavior of the transition is controlled by an interacting fixed point, which we study via epsilon expansion. Comparisons will be made with the Hertz-Millis theory, and possible generalizations to high dimensions will be discussed. [Preview Abstract] |
Wednesday, March 23, 2005 4:30PM - 4:42PM |
S41.00011: Orbitally driven behavior: Mott transition, quantum oscillations and colossal magnetoresistance in bilayered Ca$_3$Ru$_2$O$_7$ X.N. Lin, V. Durairaj, S. Chikara, E. Elhami, G. Cao, L. Balicas, P. Schlottmann, J.E. Crow We report recent transport and thermodynamic experiments over a wide range of temperatures for the Mott-like system Ca$_{3}$Ru$_{2}$O$_{7}$ at high magnetic fields, $B(\le $ 30 T). This work reveals a rich and highly anisotropic phase diagram, where applying $B$ along the $a$-, $b$-, and $c$-axis leads to vastly different behavior. A fully spin-polarized state via a first-order metamagnetic transition is obtained for $B \quad \ge $ 6 T and $B\vert \vert a$, and colossal magnetoresistance is seen for $B\vert \vert b$, and quantum oscillations in the resistivity are observed for $B\vert \vert c$, respectively. In addition, both magnetic and transport properties of the system are highly sensitive to oxygen content and other impurity doping. The orbital ordering is considered to be the driving force for the rich phase diagram. [Preview Abstract] |
Wednesday, March 23, 2005 4:42PM - 4:54PM |
S41.00012: Strongly-correlated crystal-field approach to heavy-fermion compounds and to 3d oxides Ryszard Radwanski, Zofia Ropka The description of electronic and magnetic properties of real compounds like LaMnO$_{3}$, LaCoO$_{3}$, Na$_{2}$V$_{3}$O$_{7}$, FeO, NdAl$_{2}$ and ErNi$_{5}$ as well as heavy-fermion superconductor UPd$_{2}$Al$_{3}$ and heavy-fermion metal YbRh$_{2}$Si$_{2}$, both zero-temperature ground state properties and thermodynamics, will be presented pointing out the existence of a discrete atomic-like low-energy, in the meV scale, electronic structure. This low-energy many-electron discrete atomic-like electronic structure is governed by very strong electron correlations, predominantly on-site, by the intra-atomic spin-orbit coupling and by details of the local surrounding (crystal-field interactions), but later is modified by inter-site interactions. Our studies indicate that there is the highest time to ``unquench'' the orbital moment in solid state physics in description of 3d-/4f-/5f-atom containing compounds and that heavy-fermion phenomena are of the relativistic origin. [Preview Abstract] |
Wednesday, March 23, 2005 4:54PM - 5:06PM |
S41.00013: High-temperature weak ferromagnetism on the verge of a metallic state: Impact of dilute Sr doping on BaIrO3 Esmat Elhami, Gang Cao, Xinu Lin, Shalinee Chikara, Vinobalan Durairaj The 5d-electron-based BaIrO$_{3 }$is a nonmetalic weak ferromagnet with a Curie temperature at T$_{C}$= 175 K. Its greatly extended orbitals generate strong electron-lattice coupling, and the magnetism and electronic structure are thus critically linked to the lattice degree of freedom. Here we report results of our transport and magnetic study on slightly Sr-doped BaIrO$_{3 }$. It is found that dilute Sr doping drastically suppresses T$_{C}$, and instantaneously leads to a nonmetal-metal transition at high temperatures. All results highlight the instability of the ground state and the subtle relation between magnetic ordering and electron mobility. It is clear that BaIrO$_{3}$ along with very few other systems represent a class of materials where the magnetic and transport properties can effectively be tuned by slight alterations in lattice parameters. [Preview Abstract] |
Wednesday, March 23, 2005 5:06PM - 5:18PM |
S41.00014: Role of Strong Correlations in Disproportionation of Aqueous Actinides Steven E. Horowitz, J.B. Marston We study the role of strong electronic correlations in the disproportionation of aqueous actinide complexes An(aq) and AnO$_2$(aq) where An = U, Np, and Pu. Correlations are expected to be important due to the localized nature of the actinide 5f orbitals. We first confirm that relativisitic DFT\footnote{ADF2004.01, \urllink{SCM}{http://www.scm.com}, Theoretical Chemistry, Vrije Universiteit.}, despite yielding reasonable geometries and bond lengths, fails to reproduce\footnote{P. J. Hay, R. L. Martin, and G. Schreckenbach, J. Phys. Chem. A {\bf 104}, 6259 (2000).} experimentally observed degeneracies of the redox potentials\footnote{D. L. Clark in {\it Los Alamos Science} No. 26 Vol. II (2000).}. By using a continuum model for the water beyond the first solvation sphere we are able to construct and diagonalize reduced Hubbard-like models of the actinide complexes, and incorporate the missing physics of strong intra-atomic Coulomb repulsion\footnote{M. X. LaBute {\it et al.}, J. Chem. Phys. {\bf 116}, 3681 (2002).} \footnote{D. V. Efremov {\it et al.}, \urllink{cond-mat/0303414}{http://arxiv.org/abs/cond-mat/?0303414}; E. Runge {\it et al.}, \urllink{cond-mat/0402124}{http://arxiv.org/abs/cond-mat/?0402124}.}. [Preview Abstract] |
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S41.00015: On the Mott Transition in Ca$_{2-x}$Sr$_x$RuO$_4$ Ansgar Liebsch The Mott transition in multi-band materials like Ca$_{2-x}$Sr$_x$RuO$_4$ involving subbands of different widths is studied within the dynamical mean field theory [1]. Using the multi-orbital Quantum Monte Carlo method and iterated perturbation theory for the quantum impurity problem it is shown that at low temperatures inter-orbital Coulomb interactions give rise to a single first-order transition rather than a sequence of orbital selective transitions. Recent photoemission data [2] seem to confirm these results. Nevertheless, at finite temperatures, the degree of metallic or insulating behavior of the subbands differs greatly. Thus, on the metallic side of the transition, the narrow band can exhibit quasi-insulating features, whereas on the insulating side the wide band exhibits pronounced bad-metal behavior. The transition is therefore partially incomplete for individual subbands. This complexity of the quasi-particle spectra, and the difficulty of clearly identifying metallic and insulating properties at finite temperatures, presumably is the origin of contradictions between several previous works. The role of Hund's rule exchange interactions will also be discussed. \\ {[1]} A. Liebsch, Phys. Rev. B {\bf 70}, 165103 (2004); Phys. Rev. Lett. {\bf 91}, 226401 (2003).\\ {[2]} S.-C. Wang {\it et al.}, Phys. Rev Lett. {\bf 93}, 117007 (2004). [Preview Abstract] |
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