Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V29: Correlated Electrons |
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Sponsoring Units: GMAG Chair: Meigan Aronson, Brookhaven National Laboratory Room: 333 |
Thursday, March 19, 2009 8:00AM - 8:12AM |
V29.00001: Emergence of spin structure in quantum wires under strong magnetic fields Gilad Barak, Georg Schusteritsch, Amir Yacoby, Loren Pfeiffer, Ken West We study the effects of a perpendicular magnetic field on the spin and charge structure of a quantum wire. Using momentum resolved tunneling between two parallel wires we measure the dispersion relation for different perpendicular magnetic fields. We find that as the magnetic field increases, charges with opposing spin separate in the cross section of the wire giving rise to strips of polarized and unpolarized electrons. We argue that this structure results from the exchange interaction between electrons in the wire. We discuss the applicability of these results to the structure of Quantum Hall edge states. [Preview Abstract] |
Thursday, March 19, 2009 8:12AM - 8:24AM |
V29.00002: Nonequilibrium transport in the Anderson model of a biased quantum dot Sung Chao, Guillaume Palacios, Andres Jerez, Carlos Bolech, Pankaj Mehta, Natan Andrei We derive the transport properties of a quantum dot subject to a source-drain bias by means of the Scattering Bethe Anstaz, a generalization of the traditional Thermodynamic Bethe Ansatz to open systems out of equilibrium, which allows a description of the the system in nonequilibrium steady state over the full range of its parameters. Solving the equations at zero temperature and magnetic field we present here the non-linear conductance against the bias voltage with arbitrary tunneling rate and with the gate voltage varying from the mixed valence to the Kondo regime. [Preview Abstract] |
Thursday, March 19, 2009 8:24AM - 8:36AM |
V29.00003: Imaging the Fano lattice in the heavy fermion material URu$_{2}$Si$_{2}$ by scanning tunneling spectroscopy Andrew Schmidt, Mohammad Hamidian, Peter Wahl, Focko Meier, Graeme Luke, J.C. Davis We present scanning tunneling spectroscopy measurements of the heavy fermion material URu$_{2}$Si$_{2}$. Two dimensional differential conductance maps of mechanically cleaved surfaces reveal a narrow Fano lineshape about the Fermi level that is pervasive across the field of view. Such a lineshape is expected whenever a discrete energy level is coupled to a continuum of levels. By fitting the spectra to a Fano function, we produce maps showing the variation of the Fano parameters across the surface. [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 8:48AM |
V29.00004: Theory of the Unusual Quasiparticle Excitations in USb$_2$ Peter Riseborough, Xiaodong Yang A band of long-lived quasiparticles with a renormalized dispersion relation that does not cross the Fermi surface has been observed in USb$_2$ by angle resolved photoemission measurements. The existence of a kink in the quasiparticle dispersion relation of a band that does not cross the Fermi energy is unprecedented. We show that the observed renormalization does not come from the standard theory of electron-phonon renormalizations. We consider the effect of the interband self-energy and vertex corrections as possible causes for the formation of the renormalized quasiparticles. The effect of temperature is also considered. [Preview Abstract] |
Thursday, March 19, 2009 8:48AM - 9:00AM |
V29.00005: Kink in the dispersion of f-electrons Tomasz Durakiewicz, Peter S. Riseborough, Clifford G. Olson, John J. Joyce, Peter M. Oppeneer, Saad Elgazzar, Eric D. Bauer, John L. Sarrao, Ela Guziewicz, David P. Moore, Martin T. Butterfield, Kevin S. Graham Many-body interactions may result in the formation of long- lived heavy quasi-particles that exhibit kinks in their energy dispersion. Kinks are often seen in d-electron correlated systems and are attributed to many different origins, such as coupling to phonons, extended spin-fluctuations, or electron- electron correlations. We have found that the renormalization of a 5f electron band in USb2 leads to the formation of a kink characterized by two distinct regions with different quasiparticle masses, peak asymmetries, lifetimes and a record- breaking small width of 3meV. The kink energy scale of 17meV originates from renormalization of a point-like Fermi surface, and is a factor of two smaller than previously measured in correlated materials. [Preview Abstract] |
Thursday, March 19, 2009 9:00AM - 9:12AM |
V29.00006: Localized $5f$ antiferromagnetism in cubic UIn$_{3}$: $^{115}$In-NMR/NQR Study H. Sakai, S. Kambe, Y. Tokunaga, H. Chudo, Y. Tokiwa, D. Aoki, Y. Haga, Y. \={O}nuki, H. Yasuoka $^{115}$In nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements have been performed on an antiferromagnet UIn$_3$ with the cubic AuCu$_3$-type structure. The NQR frequency ($\nu_{\rm Q}$) and Knight shift ($K$) of $^ {115}$In in UIn$_3$ have been estimated in the paramagnetic state from NMR experiments under applied field. The perpendicular component of transferred hyperfine coupling constant ($A_\perp$) has been deduced from scaled behavior of $K$ to the static susceptibility ($\chi$). Under zero field, the observation of the NQR spectrum has led to an estimated $\nu_ {\rm Q}$ of 11.8 MHz at 90 K. The temperature variation of the NQR relaxation rates ($1/T_1$) far above the N{\'e}el temperature $T_{\rm N}$=88 K approaches a constant value, which indicates a localized nature for the $5f$- electrons in this system. On the other hand, in the antiferromagnetically ordered state at 4 K (well below $T_ {\rm N}$), the $^{115}$In-NMR spectrum has been scanned over frequencies ranging from $\sim$20 to $\sim$70 MHz under zero applied field. From the analysis of the NMR spectrum, we propose that the direction of U moments in the AF state is neither $\langle 100 \rangle$ nor $\langle 111 \rangle$, but may be $\langle 110 \rangle$. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:24AM |
V29.00007: Studies of the Ferromagnetic Superconductors URhGe and UCoGe Travis Williams, Adam Aczel, Weiqiang Yu, Yasutomo Uemura, Jeremy Carlo, Tatsuo Goko, Jim Garrett, Graeme Luke Superconductivity (SC) cannot cooperatively exist with ferromagnetism (FM) in conventional superconductors, since ferromagnetism would act to destroy Cooper pairs. Thus, in FM superconductors such as URhGe and UCoGe, a more exotic pairing type must exist. I will outline the growth and characterization of URhGe and UCoGe crystals, and our measurements of the FM and SC properties. Our combined results from DC Resistivity, Bulk Magnetometry and Muon Spin Relaxation show FM properties in the samples, including a clear FM transition at 9.5K in the URhGe crystal. We will discuss our results and their implications for the nature of the SC state in these materials. [Preview Abstract] |
Thursday, March 19, 2009 9:24AM - 9:36AM |
V29.00008: Renormalization of electronic structure close to Fermi level of CeIrIn$_{5}$ at 20K Yinwan Li, Tomasz Durakiewicz, John J. Joyce, Kevin S. Graham, John L. Sarrao, Eric D. Bauer, Clifford G. Olson The electronic structure of heavy-fermion superconductor CeIrIn$_{5}$ is investigated at $\sim $20K by high-resolution angle-resolved photoemission (ARPES). The low energy ARPES spectra indicate a kink near the Fermi surface within the~energy scale of~the order of~20meV.~Existence of a kink may suggest~coupling of electron~to~a collective boson mode of unknown origin. [Preview Abstract] |
Thursday, March 19, 2009 9:36AM - 9:48AM |
V29.00009: Interplay of magnetism and screening in the Kondo Lattice Piers Coleman, Andriy Nevidomskyy An increasing body of experimental evidence suggests that frustration and the Kondo effect have complimentary roles that act together to either reduce, or completely eliminate magnetic order in heavy electron systems[1]. I will review our attempts to explore the joint effects of frustration and Kondo effect in the Kondo Heisenberg model, using the large N Schwinger boson approach[2]. These results will be discussed in the context of recent doping experiments on YbRh$_2$Si$_2$ [3], where an intermediate spin liquid appears to develop between the antiferromagnet and the large Fermi surface metal. \\ $\hbox{[1]}$ S. Nakatsuji, Y. Machida et al, Phys. Rev. Lett. 96, 087204 (2006).\\ $\hbox{[2]}$ J. Rech, P. Coleman, O. Parcollet and G. Zarand, Phys. Rev. Lett. 96, 016601 (2006).\\ $\hbox{[3]}$ T. Westerkamp, P. Gegenwart, C. Krellner et al., Physica B - Condens. Matter 403, 1236-1238 (2008). [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:00AM |
V29.00010: Electronic band structure of Pr-based filled skutterudite antimonides J.W. Allen, B.J. Kim, Ravi S. Singh, O. Krupin, J.D. Denlinger, R.E. Baumbach, M.B. Maple Filled skutterudites exhibit a wide range of strongly correlated electron phenomena including heavy fermion, superconductivity, non-Fermi liquid and quantum critical behaviors. Knowledge of the electronic structures of these materials is almost entirely from band calculations and dHvA studies. We present the first angle-resolved photoemission spectroscopy (ARPES) measurements of the filled skutterudites antimonides: PrOs$_{4}$Sb$_{12}$ and PrRu$_{4}$Sb$_{12}$. Band dispersions and Fermi surface maps of these three-dimensional materials will be discussed and compared to available LDA band structure calculations. [Preview Abstract] |
Thursday, March 19, 2009 10:00AM - 10:12AM |
V29.00011: High frequency thermal transport for the 2d Hubbard model Louis-Francois Arsenault, Syed Hassan, Andre-Marie Tremblay In order to calculate thermal transport coefficients of correlated systems when the Boltzmann equation is not applicable, Shastry [1] has developed a new theoretical approach. Although, in this theory, quantities such as the thermopower depend only upon the one particle Green's function, vertex corrections are included. The price to be paid is that only the high frequency limit is accessible. This may be adequate for aforementioned transport coefficients. Results for the triangular lattice t-J model and the 1d Hubbard model are already in the literature but there are no results for the 2d Hubbard model, the prototype of correlated electron systems. We thus applied the Shastry approach to the 2d Hubbard model using quantum cluster approaches that include CDMFT + exact diagonalization, Bethe's lattice DMFT + CTQMC and CDMFT + CTQMC. Results were obtained for the thermopower as a function of temperature (T), chemical potential (mu), and band structure. Since infinite frequency is reached differently in the t-J and in the Hubbard model, our results enable us to assess the degree to which infinite frequency is related to experimental results on DC transport. [1] B. Sriram Shastry, Phys. Rev.~ B 73, 085117 (2006)~ [Preview Abstract] |
Thursday, March 19, 2009 10:12AM - 10:24AM |
V29.00012: Time evolution of excited state in the system with first-order metal-insulator transition W. Koshibae, N. Furukawa, N. Nagaosa We have studied numerically the relaxation process
in the system with a first-order metal-insulator transition
using the double-exchange model:
$H=-t\sum_{ |
Thursday, March 19, 2009 10:24AM - 10:36AM |
V29.00013: Chiral spin states in the pyrochlore Heisenberg magnet: Fermionic mean-field theory and variational Monte Carlo calculations Junghoon Kim, Jung Hoon Han Fermionic mean-field theory and variational Monte Carlo calculations are employed to shed light on the possible uniform ground states of the Heisenberg model on the pyrochlore lattice. Among the various flux configurations, we find the chiral spin states carrying $\pm$ $\pi$/2 flux through each triangular face to be the most stable both within the mean-field theory and the projected wave- function studies. Properties of the spin-spin correlation function and the chirality order parameter are calculated for the projected wave functions. Meanfield band structures are examined. [Preview Abstract] |
Thursday, March 19, 2009 10:36AM - 10:48AM |
V29.00014: Spectral properties of orbital polarons in Mott insulators Krzysztof Wohlfeld, Maria Daghofer, Andrzej M. Ole\'s, Peter Horsch Since orbital symmetry is lower than SU(2), superexchange in Mott insulators with orbital degrees of freedom is typically not Heisenberg-like and hole propagation is highly nontrivial [1]. We investigate cases with Ising-like superexchange, where the hole cannot propagate by its coupling to spin fluctuations. We find that the usually neglected three-site hopping determines hole motion [2]. One realization of Ising superexchange is the Falicov-Kimball model, where only electrons with one orbital flavor can move, and the other ones are localized --- then a hole inserted into the Mott insulator either moves via three-site hopping processes, or remains trapped in a small polaron. In another case of Ising exchange, a class of $t_{2g}$ or $e_g$ orbital systems, renormalized three-site hopping leads to one-dimensional hole propagation, with its direction determined by the orbital flavor of the hole. \\[3pt] [1] J. van den Brink {\it et al.\/}, Phys. Rev. Lett. \textbf{85}, 5174 (2000). \\[0pt] [2] M. Daghofer {\it et al.\/}, Phys. Rev. Lett. \textbf{100}, 066403 (2008). [Preview Abstract] |
Thursday, March 19, 2009 10:48AM - 11:00AM |
V29.00015: Spin conservation and Fermi liquid near a Pomeranchuk transition Andrey Chubukov, Dmitrii Maslov We analyze system behavior near a Pomeranchuk instability in terms of Fermi liquid theory. We argue that the original assumption that a single Landau parameter approaches $-1$ at a Pomeranchuk transition, while others are non-critical is incorrect in $D \leq 3$. We show that, near the transition, a system enters into a novel regime in which all other Landau components increase and eventually diverge at the critical point. We demonstrate that in this novel regime the relation between the Landau function and the full vertex is different from that in a conventional Fermi liquid theory -- the proportionality factor no longer contains the running effective mass and has the same constant value as at the boundary between a conventional Fermi liquid and the novel Fermi liquid behavior. We show how to restore spin conservation near a Pomeranchuk transition and discuss extra features specific to Pomeranchuk instabilities in the spin channel. [Preview Abstract] |
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