Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session L12: Heavy Fermion Theory and Strong Correlations |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Jiangping Hu, Purdue University Room: Morial Convention Center 203 |
Tuesday, March 11, 2008 2:30PM - 2:42PM |
L12.00001: Phonon Anomalies in $\alpha$-uranium Xiaodong Yang, Peter Riseborough The temperature-dependence of the phonon spectrum of $\alpha$- uranium has recently been measured by Manley {\it et} al. [1] using inelastic neutron scattering and x-ray scattering techniques. Although there is scant evidence of anharmonic interactions, the phonons were reported to show some softening of the optic modes at the zone boundary. The same group of authors later reported that an extra mode was oibserved to form at a temperature above 450 K [2]. The existence of the proposed new mode is inconsistent with the usual theory of harmonic phonons, as applied to a structure composed of a monoclinic Bravais lattice with a two-atom basis. We investigate the effect that the f electron-phonon interaction has on the phonon spectrum and its role on the possible formation of a breathing mode of mixed electronic and phonon character.\newline [1] Manley {\it et} al. {\it Phys. Rev. Lett.} {\bf 86}, 3076 (2001).\newline [2] Manley {\it et} al. {\it Phys. Rev. Lett.} {\bf 96}, 125501 (2006). [Preview Abstract] |
Tuesday, March 11, 2008 2:42PM - 2:54PM |
L12.00002: Phonon Spectra and Lattice Thermal Conductivity of UO2 and PuO2 Quan Yin, Sergey Savrasov Electronic structure, phonon spectrum and lattice thermal conductivity of UO2 and PuO2 are studied using a combination of Density Functional Theory within Local Density Approximation and Dynamical Mean Field Theory (LDA+DMFT). UO2 and PuO2 are mixed oxides fuel (MOX) used in modern thermal reactors. Both oxides are Mott-insulators with strongly correlated 5f electrons, showing very similar electronic structures and phonon dispersions. The calculated phonon dispersion for UO2 is generally consistent with experiment and we give prediction for PuO2. Thermal conductivity is calculated based on the phonon dispersion. The phonon relaxation times are estimated in form of the Gr\"uneisen constant derived from compressed volume phonon calculations. [Preview Abstract] |
Tuesday, March 11, 2008 2:54PM - 3:06PM |
L12.00003: Spectral Properties of Plutonium and its Compounds Jian-Xin Zhu, A.K. McMahan, M.D. Jones, T. Durakiewicz, J.J. Joyce, J.M. Wills, R.C. Albers By combining the local density approximation (LDA) with dynamical mean field theory (DMFT), we analyze the spectral properties of plutonium and its compounds. The LDA Hamiltonian is extracted either from a tight-binding fit to full-potential linearized augmented plane-wave calculations, or directly from the full-potential linearized muffin tin orbitals calculations. The DMFT equations are solved by the exact quantum Monte Carlo method complemented with the Hubbard-I approximation. We compare the 5f electron behaviors in Pu elemental solid and compounds. The theoretical results will also be discussed in the context of photoemission spectroscopy data. [Preview Abstract] |
Tuesday, March 11, 2008 3:06PM - 3:18PM |
L12.00004: Crossover from non-Fermi liquid to Fermi liquid behavior: Amplitude of de Haas-van Alphen oscillations Pedro Schlottmann Deviations from Landau's Fermi liquid behavior in numerous U, Ce and Yb based heavy fermion systems are known as non-Fermi liquid behavior and are frequently attributed to a quantum critical point (QCP). A nested Fermi surface together with the remaining interaction between carriers after the heavy bands are formed may give rise to itinerant antiferromagnetism. We consider an electron pocket and a hole pocket, with Fermi momenta $k_{F1}$ and $k_{F2}$, respectively. The order can be suppressed by increasing the mismatch of the Fermi momenta and a QCP is obtained as $T_N \to 0$. For the tuned QCP the specific heat over $T$ increases as the logarithm of the temperature as $T$ is lowered [1] and the linewidth of the quasi-particles is linear in $T$ and $\omega$. [2] With increasing nesting mismatch and decreasing temperature the specific heat and the linewidth display a crossover from non-Fermi liquid ($\sim T$) to Fermi liquid ($\sim T^2$) behavior. [2] Using the quasi-particle linewidth the temperature dependence of the amplitude of the de Haas-van Alphen oscillations (corresponding to the pocket frequencies) is computed. \par\noindent [1] P. Schlottmann, Phys. Rev. B {\bf 68}, 125105 (2003). \par\noindent [2] P. Schlottmann, Phys. Rev. B {\bf 73}, 085110 (2006). \par\noindent [Preview Abstract] |
Tuesday, March 11, 2008 3:18PM - 3:30PM |
L12.00005: Fermi Surface and Symmetry of Magnetic Quantum Phases in Heavy Fermion Metals Seiji Yamamoto, Qimiao Si Magnetic ordering in heavy fermion metals is typically antiferromagnetic, although ferromagnetic ordering does occur in some materials, such as CeRu2Ge2. Extending a previously developed framework [1] for the antiferromagnetic Kondo lattice, we now consider the case where the magnitude of the antiferromagnetic Kondo coupling is small compared to the ferromagnetic RKKY interactions. The coupling between spin waves and conduction electrons is relevant, resulting in a change in the form of the QNLsM in the appropriate energy and momentum range. At the lowest energies, a gap in the continuum of excitations renders the Kondo coupling irrelevant. We conclude that a ferromagnetic state with a ``small'' Fermi surface (where local moments are NOT included in the Fermi volume) is stable. Finally, we discuss how the lack of Kondo screening in magnetic metal phases is reflected in symmetry properties. We show that, in some cases, spin symmetry breaking does not lead to a reduction of spin symmetry, further emphasizing the need to go beyond the conventional order parameter to characterize these magnetic quantum phases. [1] S. J. Yamamoto and Q. Si, Phys. Rev. Lett. 99, 016401 (2007) [Preview Abstract] |
Tuesday, March 11, 2008 3:30PM - 3:42PM |
L12.00006: Anomalous Hall Effect in Heavy Fermion Semiconductors Peter Riseborough, Sukalpa Basu Using the Kubo formula, the off-diagonal components of the conductivity tensor can be written in terms of completely filled states. This is a restatement of the discovery by Luttinger and Karplus that a (dissipationelss) anomalous Hall conductivity can result from the filled Fermi-volume which is occupied according to the equilibrium Fermi-Dirac distribution function, and has been recently interprted in terms of a Berry Curvature. The condition that the net anomalous conductivity is non-zero, is that time-reversal invariance should be broken and that the system should have low spatial symmetry. The heavy fermion semiconductors, such as Ce$_3$Bi$_4$Pt$_3$, are extremely narrow gap semiconductors in which the band-gap is subjected to strong many-body renormalizations at low- temperatures. The electrons in the vicinity of the gap are of mixed f and conduction band character and, therefore are subject to strong spin-orbit scattering, as can also be inferred from the finite low-temperature susceptibility of these compounds. Therefore, when subjected to an external magnetic field, these materials are candidates for showing a finite (dissipationless) intrinsic Hall conductivity of the Luttinger-Karplus type. [Preview Abstract] |
Tuesday, March 11, 2008 3:42PM - 3:54PM |
L12.00007: Study of the gap formation in Kondo insulators M. A. Majidi, K. Mikelsons, A. Macridin, J. Moreno, M. Jarrell Motivated by recent experimental measurements of the temperature-dependent gap formation in the Kondo insulator SmB$_6$ (Matsunami et al.) we investigate the Periodic Anderson Model at half-filling and in the strong-coupling regime. We solve this model in three dimensions using the Dynamical Cluster Approximation to incorporate non-local correlations and the Maximum Entropy Method to derive the spectral functions. We calculate the temperature dependence of the insulating gap and the screened moment, and discuss how the appearance of the gap is related with the lattice Kondo screening. [Preview Abstract] |
Tuesday, March 11, 2008 3:54PM - 4:06PM |
L12.00008: Is FeSi a Kondo Insulator? Jan Kunes, Vladimir I. Anisimov Using combination of a simple model of local bandstructure and quantum Monte-Carlo technique we show that 3d 'Kondo insulators' such as FeSi and FeSb$_2$ differ in many respects from classical f-electron based Kondo insulators. In particular we show that hybridization between narrow f-band and a broad conduction band typical for f-electron compounds is not a necessary condition for observation of the typical Kondo insulator behavior of susceptibily and dc as well as ac conductivity. The difference between FeSi and f-electron Kondo insulators becomes apparent when doped, while the former exhibits enhanced susceptibility leading to a Stoner-like ferromagnetic instability the latter are usually characterized by competition between the Kondo screening and local moment magnetism with RKKY inter-site coupling. [Preview Abstract] |
Tuesday, March 11, 2008 4:06PM - 4:18PM |
L12.00009: A Phenomelogical Theory of Quantum Tricritical Point: Applications to a Heavy-Fermion Compound YbRh$_{2}$Si$_{2}$ Takahiro Misawa, Youhei Yamaji, Masatoshi Imada We construct a phenomelogical theory of quantum tricritical point (QTCP) of itinerant antiferromagnets by extending the self-consistent renormalization theory. We have shown that a novel non-Fermi liquid behavior comes out at the QTCP where a continuous phase transition changes into a first-order one at zero temperature. In contrast to the conventional quantum criticality proposed by Moriya, Hertz and Millis, a remarkable feature of the QTCP is the divergence of the ferromagnetic susceptibility at the antiferromagnetic phase transition under the magnetic field. In a heavy-fermion compound YbRh$_{2}$Si$_{2}$, enhancement of the ferromagnetic susceptibility near the antiferromagnetic quantum critical point has been an unsolved puzzle. We have shown that the quantum tricriticality naturally explains this puzzling enhancement. In particular, singularities of ferromagnetic susceptibility and the magnetization curve near the QTCP are well consistent with the experimental results. [Preview Abstract] |
Tuesday, March 11, 2008 4:18PM - 4:30PM |
L12.00010: Two Channel Kondo Effect and Superconductivity in Pu and Np compounds Rebecca Flint, Maxim Dzero, Piers Coleman Recently, superconductivity has been observed in two heavy fermion compounds, PuCoGa$_5$ and NpPd$_5$Al$_2$, which transition directly from unquenched spins into the superconducting state, without passing through an intermediate heavy fermi liquid. These two compounds can be modeled with the two channel Kondo model, where the two channels derive from virtual valence fluctuations of different crystal symmetries. The electron-spin scattering develops an Andreev component, creating a composite bound state of a spin-flip and a triplet pair of electrons. This process can be examined in a controlled fashion with symplectic N, with the maximum transition temperature occuring when the two channels have equal strengths. We will also discuss the effect of Pu doping on the superconducting transition temperature of NpPd$_5$Al$_2$. [Preview Abstract] |
Tuesday, March 11, 2008 4:30PM - 4:42PM |
L12.00011: Fermionic quantum criticality and the fractal nodal surface Frank Kruger, Jan Zaanen Normal metals are characterized by a degeneracy scale imposed by Fermi-Dirac statistics: the Fermi energy. This paradigm breaks down in the high-Tc and heavy-fermion compounds where one encounters metallic states with scale invariant quantum dynamics. A theoretical understanding of these quantum critical states is lacking because the fermionic minus signs render the path integral non-probablistic. We demonstrate that within the constraint-path-integral formalism scale invariance and Fermi-Dirac statistics can be reconciled. The latter is translated into a geometrical constraint structure. We prove that this ``nodal hypersurface'' encodes the scales of the Fermi liquid and turns fractal when the system becomes quantum critical. To illustrate this we calculate nodal surfaces and electron momentum distributions of Feynman backflow wave functions and indeed find that with increasing backflow strength the quasiparticle mass gradually increases, to diverge when the nodal structure becomes fractal. This explains precisely the puzzling behaviors observed in the heavy-fermion intermetallics. [Preview Abstract] |
Tuesday, March 11, 2008 4:42PM - 4:54PM |
L12.00012: Non-linear Sigma Model of Kondo Lattice in Antiferromagnetic Regime Tzen Ong, B. A. Jones We analyze the antiferromagnetic transition in heavy fermion compounds in two dimensions, which we study using the Kondo-Heisenberg model. The system is assumed to be in the antiferromagnetic regime, with a Heisenberg coupling (J$_{H})$ that is larger than the Kondo coupling (J$_{K})$. The Heisenberg terms are mapped onto a non-linear sigma model, and the fermions are then formally integrated out to obtain an effective theory for the Neel field. We then study the evolution of the Heisenberg and Kondo couplings under perturbative RG, and calculate the critical exponents at the phase transition. Preliminary results indicate the possibility of a quantum phase transition from an AFM to a helical phase with anisotropy in the time-like direction . [Preview Abstract] |
Tuesday, March 11, 2008 4:54PM - 5:06PM |
L12.00013: Derivation and study of the Fermi-Majorana bi-resonant level model C.J. Bolech, A. Iucci We review the mapping of the anisotropic two-channel Anderson impurity model to a Fermi-Majorana bi-resonant level model. The correspondence is rigorously proved by using bosonization and explicitly constructing the new fermionic fields and Klein factors in terms of the original ones. We also demonstrate that the fixed points associated to the solvable manifold of the new model are renormalization-group stable and generic, and therefore representative of the physics of the original isotropic model. The simplicity of the mapped model allows for the computation of the full set of thermodynamic quantities as well as the identification of the different physical energy scales. In the absence of external fields the impurity physics is of non-Fermi liquid type. As expected, an arbitrarily small external field breaks some of the symmetries and introduces an extra energy scale below which the system flows to a local Fermi-liquid fixed point. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700