Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Z19: f-Electron System Properties - Theory & Experiment |
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Sponsoring Units: DCMP Chair: Ryan Baumbach, Los Alamos National Laboratory Room: 321 |
Friday, March 22, 2013 11:15AM - 11:27AM |
Z19.00001: Tuning thermoelectric power factor by crystal-field and spin-orbit couplings in Kondo lattice materials Seungmin Hong, Pouyan Ghaemi, Joel Moore, Philip Phillips We study thermoelectric transport at low temperatures in correlated electron materials, motivated by the recent observation of a high thermoelectric figure of merit(ZT) in $FeSb_2$ at $T \sim 10K$. Even at room temperature, correlations have the potential to lead to high ZT, as in $YbAl_3$, one of the most widely used thermoelectric metals. At low temperature correlation effects are especially worthy of study because fixed band structures are unlikely to give rise to the very small energy gaps $E_g \sim 5 K$ necessary for a weakly correlated material to function efficiently at low temperature. We explore the possibility of improving the thermoelectric properties of correlated Kondo insulators through tuning of crystal field and spin-orbit coupling and present a framework to design more efficient low-temperature thermoelectrics based on our results. [Preview Abstract] |
Friday, March 22, 2013 11:27AM - 11:39AM |
Z19.00002: Quantum Oscillations of Nitrogen Atoms in Uranium Nitride S.E. Nagler, A.A. Aczel, G.E. Granroth, D.L. Abernathy, W.J.L. Buyers, G.J. MacDougall, G.D. Samolyuk, G.M. Stocks The quantum harmonic oscillator is among the very few soluble fundamental models in quantum mechanics and the foundation for understanding phonons in crystalline solids. Inelastic neutron scattering typically reveals acoustic and optic one phonon modes at low energies, and as energy increases a complex continuum of many-phonon excitations. In contrast, measurements using chopper spectrometers at the SNS have shown that for the binary crystal uranium nitride, where the nitrogen atoms are very light compared to the uranium atoms, the response above the optic phonon modes exhibits a remarkable spectrum of well-defined local levels that are equally spaced by 50 meV intervals and that extend to the tenth order ~500 meV. The levels are attributed to nearly isotropic, quantum harmonic oscillator behavior of the nitrogen atoms vibrating within a largely static uranium cage. See Nature Communications 3, 1124 (2012). [Preview Abstract] |
Friday, March 22, 2013 11:39AM - 11:51AM |
Z19.00003: First-principles study of the Kondo physics of a Pu impurity in a Th host Jian-Xin Zhu, K. Haule, R.C. Albers, J.M. Wills From the viewpoint of condensed matter physics properties, crystal structure, and metallurgy, plutonium is the most complicated element in the Periodic Table, including a phase diagram with six allotropic phases. Its anomalous properties are related to the special position of Pu in the Periodic Table, which is at the boundary of the light actinides that have itinerant 5$f$ electrons and the heavy actinides with localized 5$f$ electrons, indicative of a very strongly correlated state. To reveal the role of electronic correlations in Pu, we investigate the electronic structure of a Pu atom embedded in a Th host by combining density functional theory within the local density approximation with the continuous-time quantum Monte Carlo simulation of a Pu impurity. As a hallmark of electronic correlations, the Kondo resonance peak around the Fermi energy is obtained in the local density of states on the Pu impurity. Furthermore, we show that the resonance peak width is narrower for Pu atoms that are at the surface of Th than when compared to those in the bulk, due to a weakened Pu 5$f$-ligand hybridization in the former geometry. [Preview Abstract] |
Friday, March 22, 2013 11:51AM - 12:03PM |
Z19.00004: Electron Spin Resonance in Antiferro-Quadrupolar Ordered CeB$_6$ Pedro Schlottmann CeB$_6$ is a {\it cubic} heavy fermion compound with a $\Gamma_8$ ground-quartet with antiferro-quadrupolar (AFQ) order below 4 K. An ESR signal was observed [1] in the AFQ phase. Single ions with a $\Gamma_8$ ground-multiplet should display four transitions, but only one resonance was observed. Several fundamental questions arise: (1) why is only one transition seen, (2) why was this transition observed if the Kondo temperature is larger than the linewidth of the resonance, and (3) can the resonance be explained with localized moments or is an itinerant picture of heavy electron spins necessary? The interplay of AFQ and ferromagnetic correlations on the phase diagram, the magnetization and the ESR linewidth are discussed [2]. In contrast to other Yb and Ce heavy fermion systems displaying an ESR signal, CeB$_6$ does not have strong magnetic anisotropy with ferromagnetic correlations, rendering an observable narrow resonance [3,4]. The AFQ state is necessary for an ESR signal in the present case [2].\\[4pt] [1] S.V. Demishev {\it et al}, Phys. Rev. B {\bf 80}, 245106 (2009);\\[0pt] [2] P. Schlottmann, Phys. Rev. B {\bf 86}, 075135 (2012);\\[0pt] [3] E. Abrahams and P. W\"olfle, Phys. Rev. {\bf 78}, 104423 (2008); {\bf 80}, 235112 (2009);\\[0pt] [4] P. Schlottmann, Phys. Rev. B {\bf 79}, 045104 (2009). [Preview Abstract] |
Friday, March 22, 2013 12:03PM - 12:15PM |
Z19.00005: Heavy antiferromagnetic phases in Kondo lattices Ilya Vekhter, Leonid Isaev We propose a microscopic physical mechanism that stabilizes coexistence of the Kondo effect and antiferromagnetism in heavy-fermion systems. We consider a two-dimensional quantum Kondo-Heisenberg lattice model and show that long-range electron hopping leads to a robust antiferromagnetic Kondo state. By using a modified slave-boson mean-field approach we analyze the stability of the heavy antiferromagnetic phase across a range or parameters, and discuss transitions between different phases. We also address connection to experiments on heavy fermion compounds. [Preview Abstract] |
Friday, March 22, 2013 12:15PM - 12:27PM |
Z19.00006: ABSTRACT WITHDRAWN |
Friday, March 22, 2013 12:27PM - 12:39PM |
Z19.00007: Possible Itinerant Moment Contributions to the Magnetic Excitations in Gd, Studied by Neutron Spectroscopy G.E. Granroth, A.A. Aczel, J.A. Fernandez-Baca, S.E. Nagler Many experimental features in magnetic superconductors are also present when these complex materials are in the normal state. Therefore studies of simpler itinerant magnets may help provide understanding of these phenomena. We chose to study Gd as it is has an $\sim 0.6\mu_B$ itinerant moment in addition to a $\sim 7.0 \mu_B$ localized moment. The SEQUOIA spectrometer, at the Spallation Neutron Source at Oak Ridge National Laboratory, was used in fine resolution mode with $E_i$=50 meV neutrons, to measure the magnetic excitations in a 12 gm $^{160}$Gd single crystal. The crystal was mounted with the $h0l$ plane horizontal and rotated around the vertical axis to map out the excitations. The measured magnetic structure factor for the acoustic modes in the $hh0$ direction has an intensity step at $h \sim 0.3$. Electronic band structure calculations (W. M. Temmerman and P. A. Sterne, J. Phys: Condes. Matter,{\bf 2}, 5529 (1990) ) show this $Q$ position to be near several band crossings of the Fermi surface. A detailed analysis, including instrumental resolution, is presented to clarify any relationship between the magnetic structure factor and the electronic band structure. [Preview Abstract] |
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