Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session D38: Heavy Fermions |
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Sponsoring Units: DCMP Chair: Greg Stewart, University of Florida Room: LACC 513 |
Monday, March 21, 2005 2:30PM - 2:42PM |
D38.00001: High resolution photoemission study of the itinerant magnetism in 5f systems Tomasz Durakiewicz, Cristian D. Batista, Joe D. Thompson, Clifford Olson, John Joyce, Gerry H. Lander, James E. Gubernatis, Ela Guziewicz, Martin T. Butterfield, Al Arko, Janez Bonca, Kurt Mattenberger, Oscar Vogt Magnetic properties of 5f systems as seen by characteristic features in the valence band photoemission are discussed, with particular focus on ferromagnetic uranium compounds. As shown by the authors, electron photoemission experiments demonstrate that the magnetization of the ferromagnetic state of UTe is proportional to the binding energy of the hybridized band centered around 50meV below the Fermi Energy (EF). This proportionality is direct evidence that the ferromagnetism of UTe is itinerant, i.e., the 5f electrons are not fully localized close to the atomic core. A simple model for the observed proportionality between the temperature dependence of the magnetization and the binding energy of the hybridized band near EF is proposed. This model allows an estimate of the effective magnetic interaction and the possibility to identify signatures of itinerant ferromagetism in other materials. [Preview Abstract] |
Monday, March 21, 2005 2:42PM - 2:54PM |
D38.00002: Heavy fermion fluid in high magnetic fields: an infrared study of CeRu$_4$Sb$_{12}$ Sasa Dordevic, Kevin Beach, Naoya Takeda, Yong-Jie Wang, M. Brian Maple, Dimitri Basov We will report the first comprehensive infrared spectroscopy study of a heavy fermion state in high magnetic field. Detailed analysis of optical constants will be presented for CeRu$_4$Sb$_{12}$ in fields up to 17\,T. We find that the applied magnetic field strongly affects the low energy excitations by destroying coherence in the system. In particular, the quasiparticle effective mass m$^*$ is suppressed by as much as 25\,$\%$. This effect is in quantitative agreement with the mean-field solution of the periodic Anderson model augmented with a Zeeman term. [Preview Abstract] |
Monday, March 21, 2005 2:54PM - 3:06PM |
D38.00003: Evidence for molecular Kondo effect in rare-earth metallocenes from f-occupancy and magnetic susceptibility C.H. Booth, M. Daniel, W.W. Lukens, M.D. Walter, R.A. Andersen The Kondo effect describes a quasibound singlet state formed by the interaction between a local magnetic moment on a lattice site and states at the Fermi level. In theory, a similar interaction should occur in the single molecule cerium bis-cyclooctatetraene (cerocene), where the configuration interaction between the $f$-orbitals and the carbon p($\pi$)-orbitals create an intermediate valence state with a very high Kondo temperature, $T_K$ [Dolg et al., J. Chem. Phys. {\bf 94}, 3011 (1991)]. Very little experimental evidence exists for such a state, however. We report Ce $L_3$-edge x-ray absorption near-edge structure (XANES) measurements of the $f$-occupation that demonstrate intermediate valence, with an $f$-occupancy of $n_f\sim0.8$. Moreover, magnetic susceptibility $\chi(T)$ measurements demonstrate that the cerium in cerocene is paramagnetic, with a temperature-independent $\chi(T<300 K)=1.5\times10^{-4}$ emu/mol. These data are consistent with a $T_K$ of about 5000~K. A similar set of data on a series of ytterbium bis-cyclopentadienyl molecules supports this claim, except with a range of $T_K$'s from 800 K to greater than 1500 K. Taken together, these data are strong evidence of a molecular Kondo effect in these insulating systems and give the first indication of how to tune such Kondo interactions. [Preview Abstract] |
Monday, March 21, 2005 3:06PM - 3:18PM |
D38.00004: The electronic structure of CeNiSb3 probed with XAS and XES Per-Anders Glans, Kevin E. Smith, Jinghua Guo, Robin T. Macaluso, Evan L. Thomas, Julia Y. Chan Rare earth antimonides have drawn interest because of their important physical properties and bonding. A relatively new member of this family of materials is CeNiSb$_{3}$. Previous dependent resistivity measurements exhibit a behavior typical for magnetically Kondo lattices with a localized $f$ moment weakly coupled with the conduction band. X-ray absorption (XAS) and emission spectroscopy (XES) measurements of the Ce 3$d$ and Ce 4$d$ have been performed. These measurements probe the $p$ to $d$ and $f$ to $d$ transitions and the density of states from these measurements will be presented. The BU program is supported by the Department of Energy under DE-FG02-98ER45680 and the program is supported by the NSF (DMR-0237664). [Preview Abstract] |
Monday, March 21, 2005 3:18PM - 3:30PM |
D38.00005: Low-temperature properties of strongly correlated nanoclusters in the presence of magnetic field Yan Luo, Nicholas Kioussis Nano-sized particles and clusters exhibit different thermal and magnetic properties from both individual atoms and bulk properties in a material. We have used exact diagonalization calculations to study the specific heat, the susceptibility and short-range spin-spin correlations at low temperature in the present of an external magnetic field. The calculations reveal that the external magnetic field and the energy spacing $\Delta $ in the conduction band tune the interplay between the \textit{local} Kondo and \textit{non local} RKKY interactions. The field-induced level crossing of the low-lying many-body states gives rise to a rich magnetic behavior of the nanoclusters. We find a transition from antiferromagnetic to ferromagnetic state as the cluster size is reduced. This may be relevant to experimental realizations of small rings or isolated quantum dots with tunable magnetic properties. [Preview Abstract] |
Monday, March 21, 2005 3:30PM - 3:42PM |
D38.00006: Quantum critical behavior of heavy fermion Ce(Ru$_{1-x}$Rh$_{x}$)$_2$Si$_2$ ($x = 0, 0.03$) Hiroaki Kadowaki, Yoshikazu Tabata, Shuzo Kawarazaki, Masugu Sato, Naofumi Aso, Stephane Raymond A focus of recent experimental and theoretical studies on heavy fermion systems close to quantum critical points (QCP) is directed toward revealing the nature of the fixed point, i.e., whether it is the itinerant antiferromagnet (spin density wave) type or a locally critical QCP. The latter local QCP was supported by a neutron scattering study of the heavy fermion CeCu$_{6-x}$Au$_x$ showing the $E/T$ scaling. In this work, we have investigated another archetypal heavy- fermion Ce(Ru$_{1-x}$Rh$_{x}$)$_2$Si$_2$ [$x$ = 0, 0.03 (tuned to a QCP)] using single-crystalline neutron scattering. The dynamical susceptibility Im$\chi(Q,E)$ has been measured with high accuracy in a temperature range $1.5 < T < 20$ K. The quantum critical behavior of Ce(Ru$_{1- x}$Rh$_{x}$)$_2$Si$_2$ will be discussed based on the QCP of itinerant antiferromagnet ($E/T^ {3/2}$ scaling). [Preview Abstract] |
Monday, March 21, 2005 3:42PM - 3:54PM |
D38.00007: Anomalous f-electron Hall effect in the heavy-electron alloy Ce$_{1-x}$La$_{x}$CoIn$_{5}$ M.F. Hundley, J. Leonard, A. Malinowski, D.J. Mixson, E.D. Bauer, J.L. Sarrao We report the results of Hall effect measurements made on the heavy-electron alloy Ce$_{1-x}$La$_{x}$CoIn$_{5}$ in magnetic fields from 1 to 90 kOe and at temperatures from 2 to 300 K. $R_{H}(T)$ of CeCoIn$_{5}$ is negative, field-independent, and dominated by skew-scattering above $\sim$ 50 K. $R_{H}(H \rightarrow 0)$ becomes increasingly negative below 50 K and varies with temperature in a manner that is inconsistent with skew scattering. Field-dependent measurements show that the low-T anomaly is strongly suppressed when the applied field is increased to 90 kOe. Measurements on LaCoIn$_{5}$ indicate that the same anomalous temperature dependence is present in the Hall coefficient of this non-magnetic analog, albeit with a reduced amplitude and no field dependence. By measuring $R_{H}(T,H)$ in Ce$_{1-x}$La$_{x}$CoIn$_{5}$ alloys we can discriminate between the influence of many-body Kondo interactions and conventional band-structure effects on the Hall coefficient in the parent compound. The results are generally consistent with a two-fluid description of Kondo lattice systems proposed by Nakatsuji \textit{et al.}.\footnote{S. Nakatsuji \textit{et al.}, Phys. Rev. Lett. \textbf{92}, 016401 (2004)} [Preview Abstract] |
Monday, March 21, 2005 3:54PM - 4:06PM |
D38.00008: Magnetic field and Spin-dependence of Quasi-particle Mass Enhancements in $CeB_6$. Peter Riseborough The field and spin-dependence of the quasi-particle mass enhancements are examined in the paramagnetic and ferromagnetic states close to a quantum critical point. The down-spin quasi-particles are found to have heavier masses than the up-spin quasi-particles. It is also found that the spin-dependence of the quasi-particle mass enhancements is through a factor of the inverse (spin-dependent) Fermi wave vector. The mass enhancements drop to the spin-independent value of unity at sufficiently high fields, where the magnetization starts to saturate and spin-flip scattering is suppressed. The results are compared with experimental results on $CeB_6$. [Preview Abstract] |
Monday, March 21, 2005 4:06PM - 4:18PM |
D38.00009: Tunable Thermal Expansion Behavior in the Intermetallic YbGaGe Fivos Drymiotis, Yongjae Lee, Gavis Lawes, Jason Lashley, Tsuyoshi Kimura, Steven Shapiro, Albert Migliori, Victor Correa, Robert Fisher We investigate the effects of carbon and boron doping on the thermal expansion in the hexagonal (P6$_{3}$/mmc) intermetallic YbGaGe. While the pure YbGaGe samples exhibit positive thermal volume expansion- (V$_{300K}$-V$_{10K})$/V$_{300K}$ = 0.94{\%}, the volume expansion in the lightly C- and B-doped samples dropped in half. Such a strong response with such light doping suggests that the underlying mechanism for the reported zero volume expansion is substitutional disorder, not the proposed magnetic behavior. This research proceeded under the auspices of the National Science Foundation, the State of Florida, and the U. S. Department of Energy. Research carried out in part at the NSLS at BNL is supported by the U.S. DoE (DE-Ac02-98CH10886). [Preview Abstract] |
Monday, March 21, 2005 4:18PM - 4:30PM |
D38.00010: NQR and T1 studies of the high pressure phase in YbInCu4 Ben-Li Young, N. J. Curro, V. A. Sidorov, J. D. Thompson, J. L. Sarrao The pressure and temperature phase diagram of YbInCu$_{4}$ has been investigated by nuclear quadrupolar resonance (NQR) and spin- lattice relaxation rate (1/T$_{1})$ experiments. The pressure dependence of the $^{63}$Cu NQR frequency suggests that the 1st-order valence transition temperature, T$_{v}$, does not vanish at the critical pressure P$_{c}$ = 23.7 kbar and thus there is no quantum critical point (T$_{v}$ = 0) in YbInCu$_{4}$. This is consistent with the 1/T$_{1}$ data, which show no evidence for non-Fermi-liquid behavior near P$_{c}$. For pressures P $\ge $ P$_{c}$, 1/T$_{1}$ increases sharply near 2.4 K, which suggests the presence of ferromagnetic (FM) ordering associated with critical fluctuations, as suggested by the ac susceptibility. We analyzed the 1/T$_{1}$, resistivity, and the pressure-enhanced susceptibility data in the mixed- valent state of YbInCu$_{4}$ and found no evidence to indicate that the pressured-induced FM phase can be described by the Stoner theory for itinerant ferromagnetism. This may suggest that the pressure-induced FM order is due to pressure-stabilized Yb$^{3+}$ local moments rather than the itinerant electrons from the mixed-valent state. We also examined the possibility of the FM order induced by an external field near P$_{c}$, but found no evidence down to 1.5 K. [Preview Abstract] |
Monday, March 21, 2005 4:30PM - 4:42PM |
D38.00011: New heavy fermion compounds Yb$_4$Ni$_9$Al$_{24}$ and YbRh$_3$Si$_7$ Gerard Lapertot, Emilia Morosan, Sergey L. Bud'ko, Yurij Mozharivskyj, Paul C. Canfield Yb$_4$Ni$_9$Al$_{24}$ and YbRh$_3$Si$_7$ are newly discovered compounds, with triclinic (space group P $\overline{1}$) and rhombohedral (space group R $\overline{3}$c) crystal structure respectively, and two, and respectively one Yb site in the unit cell. Measurements on solution-grown single crystals of Yb$_4$Ni$_9$Al$_{24}$ and YbRh$_3$Si$_7$ indicate anisotropic susceptibility and field-dependent magnetization for both compounds. No apparent magnetic ordering was observed in Yb$_4$Ni$_9$Al$_{24}$ down to 1.8 K, whereas the YbRh$_3$Si$_7$ data are consistent with a ferromagnetic component of the ground state below $\sim~10$ K, for H $\parallel (ab)$. We are also presenting zero-field resistivity and specific heat data, based on which and YbRh$_3$Si$_7$ can be classified as new stoichiometric heavy fermion compounds. [Preview Abstract] |
Monday, March 21, 2005 4:42PM - 4:54PM |
D38.00012: Possible magnetic field-induced quantum critical phase transition in YbPtIn Emilia Morosan, Sergey L. Bud'ko, Yurij Mozharivskyj, Paul C. Canfield We are presenting detailed anisotropic resistivity and heat capacity measurements for temperatures down to $\sim~0.4$ K, and magnetic fields up to 140 kOe, on solution-grown YbPtIn single crystals. For fields applied within the basal plane, the magnetic ordering temperature ($\sim~2.1$ K for H $=~0$) is driven below our base temperature around 40 kOe, whereas for higher magnetic fields non-Fermi-liquid behavior is possible; a slower decrease of the ordering temperature with the applied field is observed for H $\parallel~c$. By analogy with the previously reported YbAgGe compound, we anticipate a field-induced quantum phase transition in YbPtIn. [Preview Abstract] |
Monday, March 21, 2005 4:54PM - 5:06PM |
D38.00013: Anisotropic Behavior in Intermediate Valence Yb2M3Ga9 (M = Rh, Ir) A.D. Christianson, J.M. Lawrence, N.O. Moreno, E.D. Bauer, J.L. Sarrao, J.D. Thompson, C.D. Batista, F.R. Trouw, M.P. Hehlen, E.A. Goremychkin, C.H. Booth, A. Lobos, A.A. Aligia Yb$_{2}$M$_{3}$Ga$_{9}$ (M = Rh, Ir) are intermediate valence systems which exhibit anisotropic magnetic susceptibilities. This anisotropy can be explained by crystal field level splitting that is similar in magnitude to the Kondo temperature. To examine this picture further, we have performed inelastic neutron scatting experiments on polycrystalline samples at 12 and 300 K for Yb$_{2}$Rh$_{3}$Ga$_{9}$ as well as measurements of the 4$f$ occupation number of both Yb$_{2}$Rh$_{3}$Ga$_{9}$ and Yb$_{2}$Ir$_{3}$Ga$_{9}$. The inelastic neutron scattering spectrum indicates an inelastic response at low temperature and a quasielastic response at high temperature. These data are consistent with theoretical calculations based on an approach within the non-crossing approximation including the effects of crystal field level splitting. [Preview Abstract] |
Monday, March 21, 2005 5:06PM - 5:18PM |
D38.00014: Tuning the Hall coefficient in single crystals of the heavy fermion compound YbNi$_2$B$_2$C by annealing. Paul Canfield, Sergey Bud'ko We present temperature-dependent magneto-transport measurements on as-grown and annealed YbNi$_2$B$_2$C single crystals. Annealing causes drastic changes in the Hall coefficient, $R_H(T)$. Whereas for as-grown samples the Hall coefficient is negative between room temperature and 2 K, with a pronounced {\it minimum} at $\approx 22$ K, for the samples annealed at $950^\circ$ C for 150 hours, $R_H(T)$ changes its sign twice in the same temperature range: from negative to positive on cooling below $\sim 100$ K and back to negative below $\sim 10$ K, and has a clear {\it maximum} at $\approx 45$ K. Intermediate temperature dependencies can be achieved by reducing the annealing time. These findings are discussed within the framework of an annealing dependence of the skew scattering in conjunction with the recent structural, thermodynamic and transport studies of the effects of annealing in YbNi$_2$B$_2$C. [Preview Abstract] |
Monday, March 21, 2005 5:18PM - 5:30PM |
D38.00015: Anomalous Pressure Dependence of Kadowaki-Woods ratio and Crystal Field Effects in Mixed-valence YbInCu$_4$ Tuson Park, Vladimir Sidorov, John Sarrao, Joe Thompson The Mixed-valence (MV) compound YbInCu$_{4}$ was investigated by electrical resistivity at low temperatures and high pressures. Scaling of the first derivative of the resistivity at different pressures reveals two characteristic temperatures, where the slope in $d\rho /dT$ changes abruptly: $T_{v}$ due to the first-order MV transition and $T_{CEF}$ due to crystal-field effects. The Kadowaki-Woods (KW) ratio, $A/\gamma ^{2}$, is anomalously small at $P=0$, but sharply increases to a value comparable to that of heavy fermion compounds at $P=25$~kbar. The dramatic pressure dependence is attributed to a change in the ground state degeneracy from an octet to a doublet at $P\approx 25$~kbar. [1] K. Kadowaki and S. B. Woods, Solid State Commun. 58, 507 (1986), [2] T. Park et al., cond-mat/0409243 (2004). [Preview Abstract] |
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