Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session U16: Correlated Electrons: Heavy Fermions, Kondo Lattice, and f-electron Systems |
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Sponsoring Units: GMAG Chair: Wei Bao, Los Alamos National Laboratory Room: Colorado Convention Center Korbel 4F |
Thursday, March 8, 2007 8:00AM - 8:12AM |
U16.00001: Ultrast study of Kondo-lattice coupling in the d-electron Kenneth Burch, Diyar Talbayev, B.C. Sales, D. Mandrus, A.J. Taylor, R.D. Averitt We report our recent ultrafast optical measurements of the Zintl compound Yb$_{14}$MnSb$_{11}$, which was recently determined to be the first ferromagnetic Kondo lattice in the underscreened limit. The response at low temperatures to has two components, which we attribute to the underscreened nature of this Kondo system. In addition we measure the generation of coherent acoustic and optical phonons, that allow us to demonstrate a clear connection between the Kondo effect and lattice vibrations. [Preview Abstract] |
Thursday, March 8, 2007 8:12AM - 8:24AM |
U16.00002: Resonant Ultrasound Studies of Ferromagnetic Yb$_{14}$MnSb$_{11}$ Sriparna Bhattacharya, Veerle Keppens, Ivan A. Sergienko, Brian Sales, David Mandrus The compound Yb$_{14}$MnSb$_{11}$ is believed to be a rare example of an under-screened Kondo lattice. In this material the Yb ions are divalent and hence nonmagnetic. The magnetism comes from the Mn 3d electrons and the antiferromagnetic coupling of these electrons to holes in the Sb 5p bands. The antiferromagnetic coupling between a local magnetic moment and extended Bloch states can result in ferromagnetism due to the RKKY interaction, but can also give rise to Kondo physics. Here we report measurements of the elastic moduli (obtained using resonant ultrasound spectroscopy) as a function of temperature (2-300K) and magnetic field (0-2 T) for Yb$_{14}$MnSb$_{11}$. An unusual lattice stiffening is observed below Tc. Attempts to model this behavior using Landau theory will be discussed. [Preview Abstract] |
Thursday, March 8, 2007 8:24AM - 8:36AM |
U16.00003: Valence state and magnetism of Yb$_{7}$Co$_{4}$InGe$_{12}$. Zsolt Rak, Maria Chondroudi, S.D. Mahanti, M.G. Kanatzidis Ytterbium (Yb) compounds exhibit unusual physical properties due to the Yb f-electrons, which play an active role in bonding, giving rise to intermediate valence, heavy-fermion or Kondo behavior. Many physical characteristics of the Yb systems are related to the fact that Yb can have two valence states: nonmagnetic divalent Yb$^{2+}$ (f$^{14})$ and magnetic trivalent Yb$^{3+}$ (f$^{13})$. We have synthesized a new Yb containing quaternary Yb$_{7}$Co$_{4}$InGe$_{12}$. XPS and magnetic susceptibility measurements indicate that all Yb are all trivalent. To understand the Yb valency in this compound, we have carried out \textit{ab initio }electronic structure calculations within density functional theory using FP-LAPW method. The electronic structure is obtained using LSDA with on-site Coulomb correlation potential (LSDA+U) included for both 4f electrons of Yb and 3d electrons of Co. As a one ``f-hole'' analogue of many Ce compounds$^{1, 2}$, we find that all the Yb atoms are trivalent, in agreement with XPS and magnetic susceptibility measurements. $^{1}$A. I. Liechtenstein, V. P. Antropov, and B. N Harmon, Phys. Rev. B 49, 10770 (1994). $^{2}$E. Bauer, Adv. Phys. 40, 417 (1991). [Preview Abstract] |
Thursday, March 8, 2007 8:36AM - 8:48AM |
U16.00004: Crystal structure and magnetic behavior in CeAu2Si2 and CeAu4Si2 Andriy M. Palasyuk, John D. Corbett, Athena S. Sefat, Paul C. Canfield Interest in Ce-based compounds of systems like CeCu2Si2, CePd2Si2 and CeRu2Si2 has attracted much interest due to magnetic ordering, heavy Fermion behavior and superconductivity. This work is a comparative study of crystal structure and properties of CeAuxSi2 flux-grown crystals with x=2, 4. For CeAuxSi2 system, we have studied structure and anisotropic field- and temperature-dependent magnetization M(H, T). The single-crystal x-ray data indicate that CeAu4Si2 has CeRe4Si2-type structure and is orthorhombic (Cmmm) and CeAu2Si2 is tetragonal (I4/mmm). Although there is an extra layer of Au atoms in the CeAu4Si2 structure the magnetic ordering temperatures of CeAu2Si2and CeAu4Si2 are remarkably similar. In this work we will examine and discuss the similarities and differences between the thermodynamic, transport and structural properties of these related materials. [Preview Abstract] |
Thursday, March 8, 2007 8:48AM - 9:00AM |
U16.00005: Interplay of Magnetism and Superconductivity in CeCu$_{2}$Si$_{2}$ and RNi$_{2}$B$_{2}$C Probed by Neutron Scattering Michael Loewenhaupt, Oliver Stockert, Andreas Kreyssig We will discuss results of neutron scattering experiments performed on two systems that were investigated in close collaboration with other groups: the heavy fermion superconductor CeCu$_{2}$Si$_{2}$ and the borocarbides RNi$_{2}$B$_{2}$C (with R = rare earth). In both systems SC and magnetic ordering is observed. Due to minor changes in stoichiometry single crystals of A-, A/S and S-type CeCu$_{2}$Si$_{2}$ can be grown that show only long range magnetic order (LRO), both SC and LRO, and only SC. However, LRO is suppressed as soon as SC sets in (phase separation in A/S-type crystals). In S-type crystals only short range correlations are observed that develop an energy gap in the magnetic excitation spectrum below $T_{C}$ . In the borocarbides both LRO and SC coexist (e.g. for HoNi$_{2}$B$_{2}$C: $T_{C}$ = 8 K and $T_{N}$ = 6 K). However, there is no change in the diffuse neutron scattering (being a signature of the susceptibility of the conduction electrons) for temperatures above and below $T_{C}$ (but still above$ T_{N})$. The origin of SC in the borocarbides is manifested in a strong phonon softening intimately connected with the development of the SC gap. Conclusion: Magnetism and superconductivity in CeCu$_{2}$Si$_{2}$ is (phase) separated in real space while in the borocarbides both phenomena may be understood as being decoupled in momentum space. [Preview Abstract] |
Thursday, March 8, 2007 9:00AM - 9:12AM |
U16.00006: Muon spin resonance study on UCu$_{1.5}$Sn$_{2}$ S. El-Khatib, A. Llobet, G. Kalvius, D. Noakes, C. Stronach, E. Ansaldo, M. Torikachvili, H. Nakotte We report on muon spin relaxation measurements results on UCu$_{1.5}$Sn$_{2}$, which crystallizes in the CaBe$_{2}$Ge$_{2}$-type structure. Our analysis is consistent with collinear antiferromagnetic order that occurs below 108 K, in agreement with previous reports. The Brillouin-like behavior of the temperature dependence of the magnetic response is consistent with localized 5$f$ moments. In the paramagnetic regime a fast and a slowly relaxing signal is seen, the former reflecting disturbed local magnetic surroundings caused by the defect structure. [Preview Abstract] |
Thursday, March 8, 2007 9:12AM - 9:24AM |
U16.00007: Characteristic energy scales for field-tuned quantum criticality of CeCoIn$_5$ M.A. Tanatar, J. Paglione, Louis Taillefer, C. Petrovic The Phase diagram of field-tuned quantum criticality in CeCoIn$_5$ was characterized by comparative electrical and thermal conductivity measurements. Main two findings for $J \parallel a$ are: (1) finite characteristic temperature of spin fluctuations, $T_{SF}$, terminates linear in $T$ resistivity observed at high temperatures; (2) the Wiedemann-Franz law is obeyed in $T \to 0$ limit, so that the integrity of quasiparticles is preserved, even though the standard $T^2$ Fermi-liquid temperature dependence of resistivity fails. A comparison with inter-plane transport revealed pronounced anisotropy of the phenomenology. 1. J. Paglione, et al. PRL 97, 106606 (2006). [Preview Abstract] |
Thursday, March 8, 2007 9:24AM - 9:36AM |
U16.00008: Angular dependent magnetorestriction study of CeCoIn$_{5}$ Catalin Martin, Victor. F. Correa, Kenneth M. Purcell, Timothy P. Murphy, Eric C. Palm, Stanley W. Tozer, George M. Schmiedeshoff, J. C. Cooley Using a capacitive dilatometer designed to operate on the rotating stage of a top loading dilution refrigerator probe, we measured the magnetorestriction $\left( L(H)-L(0)\right)/L(0)$, of the Heavy Fermion Superconductor CeCoIn$_5$, along all three crystallographic direction, and with the magnetic field applied parallel both to the superconducting \textit{ab}-planes and to the \textit{c}-axis. When $B||\textit{ab}$, the \textit{c}-axis magnetorestriction features, besides a sharp jump at the upper critical field, a continuous, second-order like, transition at a lower field, which is consistent with previous observations from specific heat measurements. Our results are consistent with a field induced modulation of the superconducting order parameter (FFLO state), rather than with a field induced magnetic ordering. [Preview Abstract] |
Thursday, March 8, 2007 9:36AM - 9:48AM |
U16.00009: Metamagnetism in CeIrIn5: magnetoresistance and dHvA study C. Capan, R.G. Goodrich, J.F. DiTusa, L. Balicas, T.P. Murphy, E.C. Palm, S.W. Tozer, R. Movshovich, E.D. Bauer, M.F. Hundley, J.L. Sarrao, J.D. Thompson, D. Hall Quantum phase transitions correspond to a continuous ground state transformation at T=0 driven by quantum fluctuations. A Fermi Surface change might be expected at a quantum critical point. The metamagnetic transition, corresponding to a non-linear increase in magnetization of a paramagnet, has been focus of attention since strong deviations from Fermi Liquid theory reported in Sr$_{3}$Ru$_{2}$O$_{7}$ have raised the possibility of a metamagnetic quantum critical end-point. CeIrIn$_{5}$, a heavy fermion compound with a recently discovered metamagnetic transition at high fields, offers yet another playground for such investigations. We report a study of magnetoresistance and de-Haas-van-Alphen effect (dHvA) in CeIrIn5 for magnetic fields up to 45T and in the temperature range 0.03K-1K. We found that the metamagnetic transition is marked by a concomitant drop in the resistivity and in the amplitude of dHvA oscillations as the magnetic field is increased, while the Fermi Surface remains intact. Possible scenarios will be discussed. [Preview Abstract] |
Thursday, March 8, 2007 9:48AM - 10:00AM |
U16.00010: Photoemission in 5f systems - duality and final state effects Tomasz Durakiewicz, John Joyce, Clifford Olson, Eric Bauer, Elzbieta Guziewicz, Martin T. Butterfield, Kevin Graham, John Sarrao, Joe D. Thompson In recent years, the concept of 5f electron duality started to play important role in our understaning of the electronic structure of actinides. With respect to the photoemission spectra, duality may be seen through the existence of two distinct regions in the valence band. First region, usually in the form of one narrow peak, is located near the Fermi level and represents the itinerant part of the spectral function. Second region, comprising a broad peak of major spectral weight is located a few eV below the Fermi level and corresponds to the more localized part of 5f response. The role of 5f duality in establishing electronic structure will be discussed. Aspects of the relevant final-state effects will also be shown. [Preview Abstract] |
Thursday, March 8, 2007 10:00AM - 10:12AM |
U16.00011: Probing the Localization Boundary in 5f electron Systems J.J. Joyce, T. Durakiewicz, K.S. Graham, J.M. Wills, E.D. Bauer, J.L. Sarrao, D.P. Moore, L.A. Morales, C.G. Olson, E. Guziewicz, M.T. Butterfield The role of the 5f electrons in the bonding and hybridization for the light actinides is examined. Through use of various types of photoelectron spectroscopy including angle-resolved and resonance techniques, one may define the boundaries for periodic versus central potentials experienced by the outer electrons in actinide materials including UO$_{2}$, PuTe and Pu metal. A comparison with various computational approaches sheds light on the limits of actinide separation in the lattice and bonding to ligand components before one converges on magnetic configurations for materials. [Preview Abstract] |
Thursday, March 8, 2007 10:12AM - 10:24AM |
U16.00012: ARPES Study on Ca$_{1.8}$Sr$_{0.2}$RuO$_{4}$ Madhab Neupane, P. Richard, Y. Xu, A.K.P. Shekharan, Z. Wang, H. Ding, R. Jin, D. Mandrus, T. Valla, P.D. Johnson The phase diagram of Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ shows a rich variety of physical phenomena covering the unconventional superconductor Sr$_{2}$RuO$_{4}$ to antiferromagnetic Mott-insulator Ca$_{2}$RuO$_{4}$. In particular, the x = 0.2 compound is at the boundary between a magnetic metal and a canted antiferromagnetic insulator. It has been argued that the surprisingly large effective mass observed at low temperature in this compound may be due to the Kondo-like coupling between the localized and itinerant Ru 4d valence electrons which coexist in this system. We will report ARPES results on this material, which may shed light to the unusual heavy-fermion behavior in this d-electron system. [Preview Abstract] |
Thursday, March 8, 2007 10:24AM - 10:36AM |
U16.00013: Application of Projective QMC to LDA+DMFT calculations for LiV$_2$O$_4$ Ryotaro Arita, Karsten Held, Alexey Lukoyanov, Vladimir Anisimov By means of the LDA+DMFT method (the local density approximation combined with the dynamical mean field theory), we investigate the electronic structure of LiV$_2$O$_4$, for which various heavy-fermion-like behaviors have been observed experimentally. To obtain the spectral function at $T \rightarrow 0$, we employ the projective quantum Monte Carlo method as the solver of the effective impurity problem in DMFT. We show that a sharp peak appears just above the Fermi level at $T \rightarrow 0$, which is consistent with the recent photoemission experiment by Shimoyamada {\it et al.} [Phys. Rev. Lett. {\bf 96} 026403 (2006)] [Preview Abstract] |
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