Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session L41: Correlated Electrons: Hall Effect and Kondo Physics |
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Sponsoring Units: GMAG Chair: Michael Pustilink, Georgia Tech Room: LACC 150A |
Tuesday, March 22, 2005 2:30PM - 2:42PM |
L41.00001: Hall effect in CoO2 Layer with Hexagonal Structure Wataru Koshibae, Akira Oguri, Sadamichi Maekawa The Hall effect in layered cobalt oxides with hexagonal structure is examined. We have pointed out that the large thermopower in the cobalt oxides is caused by the degeneracy of $t_{2g}$ orbitals in Co ions. Here, we show that the orbital degeneracy brings about a Kagomé lattice electronic structure hidden in the CoO$_{2}$ triangular crystal lattice. This is because the electron hopping occurs between Co ions via neighboring oxygens by exchanging the orbitals in the triangular lattice. The importance of $t_{2g}$ orbital degeneracy on the transport properties of the cobalt oxides under the magnetic field at high temperatures is discussed in light of the theory. [Preview Abstract] |
Tuesday, March 22, 2005 2:42PM - 2:54PM |
L41.00002: The anomalous Hall heat current and Nernst effect in the ferromagnetic spinel $\rm CuCr_2Se_{4-x}Br_x$ Wei-Li Lee, Satoshi Watauchi, V.L. Miller, R.J. Cava, N.P. Ong In a ferromagnet, the anomalous Hall current has been demonstrated to be independent of the electron lifetime $\tau$ [1], which provides a strong support for Karplus and Luttinger's anomalous-velocity theory based on the intrinsic spin-orbit interaction. Inspired by the fact that a heat flow accompanies a charge current, we studied the anomalous Nernst effect (ANE) in the ferromagnetic spinel $\rm CuCr_2Se_{4-x}Br_x$ with x ranging from 0 to 1.0. Combining with other transport parameters measured on the same sample, at low temperatures, we uncovered a simple relation for the off-diagonal Peltier conductivity tensor $\rm \alpha_{xy}$, which is a quantity directly relating to the anomalous Hall heat current. We found that $\rm \alpha_{xy}=C {\it N}_F T$ [2], where C is a constant independent of $\tau$, ${\it N}_F$ is the D.O.S. at the Fermi energy, and T is the temperature. This simple relation turns out to be consistent with the prediction based on the anomalous-velocity theory. Therefore, our observation provides another strong support for the anomalous-velocity theory in a ferromagnet. The AHE and ANE can then be understood in a unified picture. * Supported by funds from the U.S. National Science Foundation under grant DMR 0213706. [1]Lee, {\it et al}., Science 303, 1647 (2004). [2]Lee, {\it et al}., PRL 93, 226601 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 2:54PM - 3:06PM |
L41.00003: Unusual magnetization and Hall effect in the spinel chalcogenide (Fe$_{0.5}$Cu$_{0.5}$)Cr$_2$S$_4$ M. Lee, Wei-Li Lee, N.P. Ong, Satoshi Watauchi, V.L. Miller, R.J. Cava We have measured the magnetization M and Hall resistivity $\rho_{xy}$ in single-crystal (Fe$_{0.5}$Cu$_{0.5}$)Cr$_2$S$_4$, a spinel chalcogenide compound. At the ferromagnetic transition (T$_c$ $\sim$ 280 K), M at weak field (at 100 gauss) displays an unusually abrupt onset vs. temperature T. Below $\sim$120 K, we observe the appearance of a second contribution to the magnetization, which appears as a kink in the field dependence of both $\rho_{xy}$ and M, characterized by a linearly rising segment and a final saturation in high field. We will discuss how these features relate to a possible second ordering arising from the two different sublattices (Fe,Cu) and Cr. [Preview Abstract] |
Tuesday, March 22, 2005 3:06PM - 3:18PM |
L41.00004: Hall effect in NdB$_6$ Jolanta Stankiewicz, Zachary Fisk We report results of electrical resistivity, Hall effect and magnetization measurements in a NdB$_6$ single crystal, in a temperature range from 2 to 300 K and in magnetic fields of up to 7 T. We took care to use low magnetic fields ($H_{appl} < 1$ T) in our Hall effect experiments in order to avoid magnetic field smearing out anomalies at the critical points. The Hall resistivity $\rho_H$, which is electronlike, shows a maximum at $T\simeq T_N$. In the paramagnetic (PM) region, we find a linear dependence of $\rho_H/H_{appl}$ on effective susceptibility. This enables us to separate two contributions to the Hall effect, an ordinary and an anomalous one. The estimated anomalous Hall coefficient $R_s$ (holelike) is much larger than the ordinary one in the PM state and is independent of temperature. As the antiferromagnetic (AF) order sets in below $\sim 8$ K, $R_s$ decreases sharply with decreasing temperature. In the AF state, $R_s\propto\rho$, where $\rho$ is the total resistivity. We do not find any significant variations of the anomalous Hall coefficient near the critical point. Both magnetization and Hall voltage show an amomaly in low magnetic fields, which may be related to domain rotations. [Preview Abstract] |
Tuesday, March 22, 2005 3:18PM - 3:30PM |
L41.00005: Studies on Single Crystals CePdGa$_{6}$ and Ce$_{2}$PdGa$_{12}$ Long Pham, Han-Oh Lee, Satoru Nakasuji, Nelson Moreno, Robin Macaluso, Brad Carter, Julia Chan, Peter Klavins, Zachary Fisk Single crystals of tetragonal CePdGa$_{6}$ and Ce$_{2}$PdGa$_{12}$ are found to be antiferromagnetic below a T$_{N}$ of 5 and 12 K respectively, with ordering along the $c$-axis. The electronic specific heat coefficients at T$_{N }$are approximately 350 and 140 (mJ/mole-Ce-K$^{2})$ for CePdGa$_{6}$ and Ce$_{2}$PdGa$_{12}$ respectively, suggesting strong Kondo competition. In addition, a metamagnetic transition can be driven by relatively small magnetic fields applied along the $c$-axis in both systems. Field dependent thermodynamic properties and magnetization data will be presented and the origin of the complex ground states will be discussed. This work was supported by NSF DMR-0433560. [Preview Abstract] |
Tuesday, March 22, 2005 3:30PM - 3:42PM |
L41.00006: A new mean field theory for the emergence of magnetism in the Kondo lattice Jerome Rech, Piers Coleman, Olivier Parcollet, Gergely Zarand We present a new mean-field theory of the Kondo lattice model, which is exact in the large $N$ limit, that is able to span the heavy magnetic quantum critical point of the Kondo lattice. Our approach unifies the Kondo impurity approach of Parcollet and Georges with the Schwinger boson description of antiferromagnetism of Arovas and Auerbach, enabling the formalism to describe magnetically correlated and magnetically ordered heavy electron phases. One of the interesting aspects of the phase diagram in this theory, is the appearance of a new paramagnetic region in which short-range magnetic correlations grow in response to a pairing of the of the Schwinger bosons. We will discuss the evolution of the specific heat and the quasiparticle effective mass in the approach to the heavy electron quantum critical point, and the fascinating possibility that the critical theory involves the interplay of gapless critical excitations both bosonic and fermionic in character. [Preview Abstract] |
Tuesday, March 22, 2005 3:42PM - 3:54PM |
L41.00007: Toulouse point of a non-fermi liquid impurity C.J. Bolech, Anibal Iucci We present a mapping between a two-channel mixed-valece impurity model and a resonant-level Hamiltonian, that for particular values of the parameters becomes non-interacting. This property is analogous to the Toulouse point of the single-channel Kondo problem or the Kotliar-Si point of the infinite-U Anderson model, but displaying characteristics of non-Fermi-liquid physics like in the Emery-Kivelson mapping for the two-channel Kondo problem. We will discuss briefly some of the quantities that can be calculated by exploiting our mapping. [Preview Abstract] |
Tuesday, March 22, 2005 3:54PM - 4:06PM |
L41.00008: Studies of the ferromagnetic Kondo lattice system of single crystal CeZnSb$_{2}$ Han-Oh Lee, Satoru Nakatsuji, Ying Chen, Wei Bao, Robin Macaluso, Julia Chan, Tuson Park, Brad Carter, Peter Klavins, Joe Thompson, Zachary Fisk We have grown single crystals of the ferromagnetic Kondo lattice system CeZnSb$_{2}$. The ferromagnetic ground state was confirmed by neutron scattering. In addition, a small hysterisis in magnetization data indicates soft ferromagnetism. The large heat capacity coefficient (350 mJ/mol-Ce K$^{2})$ below the transition temperature, on the other hand, suggests a heavy mass state even below the magnetically ordered state. Thermodynamic, magnetic, and transport properties along with pressure experiments will be presented. The origin of such unusual magnetism will be discussed. This work was supported by NSF DMR-0433560. [Preview Abstract] |
Tuesday, March 22, 2005 4:06PM - 4:18PM |
L41.00009: Two-fluid behavior of the Kondo lattice in the $1/N$ slave boson approach. Victor Barzykin, Lev P. Gor'kov It has been recently shown by Nakatsuji, Pines, and Fisk [S. Nakatsuji, D. Pines, and Z. Fisk, Phys. Rev. Lett. \textbf {92}, 016401 (2004)] from the phenomenological analysis of experiments in Ce$_{1-x}$La$_x$CoIn$_5$ and CeIrIn$_5$ that thermodynamic and transport properties of Kondo lattices below coherence temperature can be very successfully described in terms of a two-fluid model, with ``Kondo gas" (interacting magnetic moments) and ``Kondo liquid" (heavy electron Fermi liquid) contributions. We analyze thermodynamic properties of Kondo lattices using $1/N$ slave boson treatment of the periodic Anderson model and show that these two contributions indeed appear below the coherence temperature. We find that the ``Kondo gas" contribution to thermodynamics corresponds to thermal excitations into the flat portion of the energy spectrum. As a result, the relative fraction of ``Kondo gas" depends exponentially on temperature, rather than linearly in experiment. [Preview Abstract] |
Tuesday, March 22, 2005 4:18PM - 4:30PM |
L41.00010: Optical study of rival interactions in a d-electron ferromagnetic Kondo system Alex Schafgans, K.S. Burch, N.P. Butch, M.B. Maple, D. Mandrus, D.N. Basov We report on a combined optical, transport and thermodynamic study of the Zintl compound Yb$_{14}$MnSb$_{11}$, demonstrating that it is the first ferromagnetic Kondo lattice in the underscreened limit. We suggest a scenerio whereby the combination of Kondo and Jahn-Teller effects provides a consistent explanation of both transport and optical data. [Preview Abstract] |
Tuesday, March 22, 2005 4:30PM - 4:42PM |
L41.00011: The Exact Solution for the Physical Properties of a Heinsenberg-Kondo Spin Glass, Including the Superconductor Properties of this System Bernard Coqblin, Robert Schrieffer We have carried out an exact solution for many physical problems of a Heisenberg-Kondo spin glass. Results will be reported over a wide range of system parameters of 1) the tunneling density of states $N_T \left( {eV} \right)$, the arpes cross section $d\sigma /d\omega d\Omega $, the $I.R_\lambda $and optical conductivities, the susceptibility $X_{\alpha \beta } \left( {Q,\omega } \right)$ the Roman cross section $R_{\alpha \beta } \gamma \left( {\omega ,v} \right)$, the specific heat $C_v \left( t \right)$, thermal conductivity $K_{Th} \left( T \right)$, etc. The influence of phonons on the system will be discussed, including the structure of the spin-phonon-polaron and it's propagation. [Preview Abstract] |
Tuesday, March 22, 2005 4:42PM - 4:54PM |
L41.00012: Decoupling methods for the solution of the dynamical mean field theory impurity problem Harald Jeschke, Gabriel Kotliar The use of equation of motion decoupling methods as impurity solvers to be used in conjunction with the dynamical mean field self-consistency condition for the solution of lattice models is explored. By comparing the impurity solver to exact diagonalization results and applying it to lattice models like Hubbard model and Periodic Anderson model it is shown that the method could be a cheap alternative to computationally demanding methods like quantum Monte Carlo. The method works in a large range of parameters and promises to be useful in combination with density functional theory for the study of strongly correlated materials. [Preview Abstract] |
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L41.00013: Magnetic and Kondo Behavior of CeCoGe$_{2}$ Costel Rotundu, Bohdan Andraka There is great interest in exotic states among Ce-Kondo lattices. Recently, specific heat and magnetic susceptibility of CeCoGe$_2$ have been accounted by the S=5/2 Kondo model; i.e., no crystalline electric field (CEF) effects have been observed.$^1$ This result is surprising since related $^2$ CeNiGe$_2$, belonging to this crystal structure, exhibits strong anisotropy in magnetic and transport properties due to CEF’s. Our magnetic susceptibility and specific heat results on (Ce,La)CoGe$_2$ suggest that exotic properties of this system are due to magnetic interactions in a quasi-two-dimensional Ce-lattice. This work was supported by NSF, grant DMR-0104240. \\ \\ $^1$ E. D. Mun et al., Phys. Rev. B {\bf 69}, 85113 (2004).\\ $^2$ Y. Okada et al., J. Phys. Soc. Jpn. {\bf 72}, 2692 (2003). [Preview Abstract] |
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