Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session A41: Heavy Fermions |
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Sponsoring Units: DMP Chair: Rena Zieve, University of California, Davis Room: 413 |
Monday, March 16, 2009 8:00AM - 8:12AM |
A41.00001: Realistic simulation of Kondo lattice model: application to Cerium compounds Munehisa Matsumoto, Myung Joon Han, Junya Otsuki, Sergey Savrasov In order to do a good description of heavy fermion materials at very low temperatures, we simulate the Kondo lattice model with the continuous-time quantum Monte Carlo method recently developed by one of the authors [1] combined with the conduction-electron density of states given by first-principle calculations and performing self consistency using dynamical mean field theory. We discuss our results for Cerium compounds down to the temperature range of O(1) [K] using realistic values of crystal-field and spin-orbit level splitting. [1] J. Otsuki, H. Kusunose, P. Werner, Y. Kuramoto, J. Phys. Soc. Jpn. 76, 114707 (2007). [Preview Abstract] |
Monday, March 16, 2009 8:12AM - 8:24AM |
A41.00002: Layered Kondo lattice model for quantum critical superconductor $\beta$-YbAlB$_4$ Andriy Nevidomskyy, Piers Coleman We perform a theoretical analysis of the magnetic and electronic properties of the quantum critical heavy fermion superconductor $\beta$-YbAlB$_4$. Using a combination of the realistic material modelling and single-ion crystal field analysis, we propose a layered Kondo lattice model for this system, in which two dimensional boron layers are Kondo-coupled via interlayer Yb moments in a $J_{z} = \pm 5/2$ state. This model fits the measured single ion magnetic susceptibility and predicts a substantial change in the electronic anisotropy as the system is pressure-tuned through the quantum critical point. An interesting connection is made between this model and the Kondo effect in Coulomb-blockaded quantum dots. We also calculate the Fermi surface and the angular dependence of the extremal orbits relevant to the de Haas--van Alphen measurements. [Preview Abstract] |
Monday, March 16, 2009 8:24AM - 8:36AM |
A41.00003: Interplay of Composite Pairs and Magnetism in Heavy Fermion Superconductors Rebecca Flint, Piers Coleman Superconductivity in Pu{\emph M}Ga$_5$, {\emph M} = \{Co,Rh\} and NpPd$_5$Al$_2$ can be treated within a two channel Kondo lattice model, where the electron-spin scattering develops an Andreev component, creating a composite bound state of a spin-flip and a pair of electrons. We extend this model to Ce{\emph M}In$_5$, where magnetism and superconductivity exist in close proximity by including antiferromagnetic interactions. Different crystal symmetries lead to composite pairing with either a g-wave gap or d-wave gap, while antiferromagnetism leads to RVB superconductivity with a d-wave gap. Within a symplectic large $N$ limit, we examine the effects of antiferromagnetic interactions on the composite pairing. If both gaps are d-wave, they couple linearly, mutually enhancing the superconducting transition temperature. [Preview Abstract] |
Monday, March 16, 2009 8:36AM - 8:48AM |
A41.00004: Very low temperature specific heat and magnetoresistance of PrOs$_{4}$Sb$_{12}$. Bohdan Andraka Heavy fermion character of PrOs$_{4}$Sb$_{12}$ has been concluded based on its superconducting properties, such as large values of the discontinuity in C and upper critical field slope at T$_{c}$ (1.85 K). On the other hand, normal state properties do not provide any strong evidence of the heavy fermion behavior. In particular, m* enhancement measured by the de Haas van Alphen technique in overcritical fields and below 700 mK is typical of transition metals, suggesting that the heavy fermion state is either suppressed by magnetic fields or collapses at low temperatures. We reexamine these possible scenarios using new magnetoresistance and specific heat, down to 50 mK, data. [Preview Abstract] |
Monday, March 16, 2009 8:48AM - 9:00AM |
A41.00005: Effect of ferromagnetism on unconventional superconductivity in the Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ system P.-C. Ho, M. B. Maple, T. Yanagisawa, W. M. Yuhasz, N. P. Butch, A. A. Dooraghi, C. C. Robinson The filled skutterudite compound PrOs$_4$Sb$_{12}$ is a 1.85\,K heavy fermion superconductor (SC), which displays unconventional SC property, such as existence of multiple SC phases and point nodes in the SC energy gap and the appearance of internal magnetic field in its SC state. NdOs$_4$Sb$_{12}$ is a mean-field type magnet with a low Curie temperature $\sim 1$\,K. The Nd substitution in the Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ has been carried out in order to investigate the ferromagnetic (FM) effect on the unconventional SC of PrOs$_4$Sb$_{12}$ and the quantum critical behavior in this system. SC state in this system disappears near $x \sim$ 0.55 and FM extends into the SC region. The x dependence of the 0-K extrapolated upper critical field $H_{c2}(x,T=0)$ has curvature breaking at $x \sim 0.3$. The $H_{c2}(x,T=0)$ data can be analyzed by multiple pair breaking effect due to magnetic field, appearance of impurity, and the exchange field generated by magnetic ions. However, when $H_{c2}(x,T=0)$ of Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ is compared to that of a BCS SC La$_{3-x}$Gd$_x$In, the curvature in the regime where $x/x_{cr} < 0.5$ is significantly different. Detail analysis and comparison will be discussed. Research at CSU-Fresno supported by RC CCSA $\#$7669 and Fresno State start-up fund; at UCSD by US DOE and NSF; at Hokkaido U by MEXT, Japan. [Preview Abstract] |
Monday, March 16, 2009 9:00AM - 9:12AM |
A41.00006: The role of $f$-electrons at the Fermi surface of the heavy fermion superconductor $\beta$-YbAlB4 Eoin O'Farrell, D.A. Tompsett, S.E. Sebastian, N. Harrison, C. Capan, L. Balicas, K. Kuga, T. Matsuo, M. Tomonaga, S. Nakatsuji, G. Cs\'anyi, Z. Fisk, M.L. Sutherland We present a detailed quantum oscillation study of the fermi surface of the recently discovered Yb-based heavy fermion superconductor $\beta$-YbAlB4. We compare the data, obtained at fields from 10 to 45 Tesla, to band structure calculations performed using the local density approximation. Analysis of the data suggests that the $f$-electrons are delocalized and contribute to the fermi volume at all fields. We comment on the significance of these findings for the observed quantum critical and superconducting properties of this material. [Preview Abstract] |
Monday, March 16, 2009 9:12AM - 9:24AM |
A41.00007: Superconducting Properties of the Non-Fermi-Liquid System $\beta $-YbAlB$_{4}$. Kentaro Kuga, Yoshitomo Karaki, Yosuke Matsumoto, Yo Machida, Naoki Horie, Satoru Nakatsuji {\$}$\backslash $beta{\$}-YbAlB{\$}{\_}4{\$} is the first Yb-based heavy fermion superconductor with the transition temperature of {\$}T{\_}{\{}$\backslash $rm c{\}} = 80{\$} mK [1]. Our study using high-purity single crystals indicates that the clean limit superconductivity directly emerges from the pronounced non-Fermi-liquid state [2]. The critical fields are anisotropic and probably have a paramagnetic effect under field along the {\$}c{\$}-axis because of the divergent behavior of the Ising like {\$}c{\$}-axis susceptibility. The strong pair-breaking effect, most likely due to nonmagnetic impurities, suggests that {\$}$\backslash $beta{\$}-YbAlB{\$}{\_}4{\$} is an unconventional superconductor. We discuss the detailed properties of superconductivity and quantum criticality. [1] S. Nakatsuji, K.Kuga, Y. Machida, T. Tayama, T. Sakakibara, Y. Karaki, H. Ishimoto, S. Yonezawa, Y. Maeno, E. Pearson, G. G., Lonzarich, L.Balicas, H. Lee and Z. Fisk, \textit{Nature Physics}, \textbf{4}, 603 (2008). [2] K. Kuga, Y. Karaki, Y. Matsumoto, Y. Machida, and S. Nakatsuji,\textit{ Physical Review Letters},\textbf{ 101}, 137004 (2008). [Preview Abstract] |
Monday, March 16, 2009 9:24AM - 9:36AM |
A41.00008: Electronic Structure of PuCoGa$_{5}$ and PuSb$_{2}$ Using Angle-Resolved Photoemission J.J. Joyce, T. Durakiewicz, K.S. Graham, D.P. Moore, J.M. Wills, Jian-Xin Zhu, E.D. Bauer, J. Mitchell The Electronic structure of PuCoGa$_{5}$ and PuSb2 is investigated using angle-resolved photoemission (ARPES). Details of the sharp quasiparticle peak at the Fermi energy are presented giving insight into the details of the mechanisms which give rise to strongly correlated characteristics in these materials. Additionally, the details of the dual nature of the 5f electrons are explored via characterization of more localized 5f states well removed from the Fermi energy. The ARPES data is compared with electronic structure models which move beyond the density functional theory approach to address the strong electron correlations present in Pu compounds as well as the dual nature of the 5f electrons. [Preview Abstract] |
Monday, March 16, 2009 9:36AM - 9:48AM |
A41.00009: $^{7}$Li NMR Study of Yb$_{4}$LiGe$_{4}$: A Possible Kondo Insulator M. J. Graf, V. Lanio, P. Carretta, Yu. Grin, S. Peter We report on the temperature-dependent resistivity, magnetic susceptibility, and nuclear spin-lattice relaxation rate of polycrystalline Yb$_{4}$LiGe$_{4}$. The parent compound, Yb$_{5}$Ge$_{4}$, is known to be mixed valent. The increasing susceptibility and resistivity with decreasing temperature are consistent with a Kondo insulator. Measurements of the temperature dependent $^{7}$Li spin-lattice relaxation rate $1/T_{1}$ show an increasing rate for decreasing temperature ($T \quad >$ 50 K), followed by a broad maximum near 30 K. These results are discussed in light of the heavy-fermion like nature of the material. [Preview Abstract] |
Monday, March 16, 2009 9:48AM - 10:00AM |
A41.00010: Revealing the Ce gamma-alpha Isostructural Phase Transition Yi Wang, Louise Hector, Shunli Shang, Long-Qing Chen, Zi-Kui Liu Since its discovery eighty years ago, the gamma-alpha iso- structural phase transition in cerium has been the subject of numerous theoretical studies. Existing theories, however, yield inaccurate results. Nowhere is this more evident than with the 50-200\% disagreement between existing theoretical predictions of the critical point and experiment. We resolve this issue by explicitly incorporating finite temperature mixing of the Ce nonmagnetic and magnetic states into a novel partition function wherein all input quantities are computed with density functional theory. Unique to our approach is the calculation of vibrational properties from phonon theory. The critical behavior of the transition is shown to be controlled by the configurational mixing entropy between the magnetic and nonmagnetic states. Our theoretical framework leads to predicted values of the critical point and equation-of-state that are in remarkably close agreement with experiment and thereby places the Ce gamma-alpha phase transition on a firm theoretical foundation. [Preview Abstract] |
Monday, March 16, 2009 10:00AM - 10:12AM |
A41.00011: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 10:12AM - 10:24AM |
A41.00012: Pressure Effect on The Kondo Behavior of Layered YbB$_{2}$ Bora Kalkan, Sefik Suzer, Tayyar Gungor, Engin Ozdas The structural properties and the effect of pressure on the electrical properties of polycrystalline YbB$_{2}$ were investigated via x-ray diffraction and x-ray photoemission spectroscopy (XPS) under ambient pressure and resistivity measurements up to 6.2 GPa. Rietveld refinement confirmed the hexagonal layered structure of YbB$_{2}$ in P6/mmm space group with \textit{a=b=3.2522(2) {\AA} }and \textit{c=3.7297(4) {\AA} }lattice parameters. XPS and low temperature measurements proved the magnetically ordered ground state of YbB$_{2}$ in which Yb ion has already magnetic trivalent state under ambient pressure. $\rho $(T) measurements down to 3.5 K at various pressures exhibit a typical Kondo lattice behavior at low temperatures with a resistivity minimum around 23 K and a coherence maximum around 11 K, which define the depth of the Kondo effect. Moreover, resistivity results yield the gradual weakening of the contribution of Kondo effect and the pressure dependence of Debye temperature as (d$\theta _{D}$/dP)=(1.46$\pm $0.30) K/GPa which is calculated using Bloch-Gr\"{u}neisen approximation. These results suggest that pressure increasing causes the suppressing of Kondo effect in YbB$_{2}$. [Preview Abstract] |
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