### Session V44: Kondo Physics and Luttinger liquids

 Thursday, March 16, 2006 11:15AM - 11:27AM V44.00001: Quantum Phase Transition in an Anisotropic Kondo Lattice M.T. Glossop , K. Ingersent The Kondo lattice model (KLM), which captures the competition between Kondo screening of localized moments by conduction electrons and their ordering due to the RKKY interaction, is of interest in the context of non-Fermi-liquid behavior in quantum critical heavy-fermions. An important issue concerns the possibility of a local quantum critical point (QCP) --- where Kondo screening is itself critical at the magnetic ordering transition --- recently invoked [1] to explain anomalous properties of, e.g., CeCu$_{5.9}$Au$_{0.1}$. We study the anisotropic KLM using the extended dynamical mean-field theory (EDMFT), which maps the KLM onto a self-consistent Bose-Fermi Kondo model (BFKM). Whether a local QCP arises as a self-consistent EDMFT solution of the KLM is a contentious issue that we seek to resolve. Separate studies [2,3], both employing Quantum Monte Carlo (QMC) to solve the BFKM, have reached opposite conclusions, but limitations of QMC at low temperatures $T$ obscures the picture at $T=0$. We address this matter, providing reliable $T=0$ solutions using our extension of [4] Wilson's numerical renormalization group method to solve the BFKM. We present results for both paramagnetic and antiferromagnetic phases, shedding light on the nature of the QPT. Supported by NSF Grant DMR-0312939. [1] Q. Si, S. Rabello, K. Ingersent, and J. L. Smith, Nature \textbf{413}, 804 (2001). [2] J-X Zhu, D. R. Grempel and Q. Si, Phys. Rev. Lett. 91, 156404 (2003). [3] P. Sun and G. Kotliar, Phys. Rev. Lett. 91, 037209 (2003). [4] M. T. Glossop and K. Ingersent, Phys. Rev. Lett. 95, 067202 (2005). Thursday, March 16, 2006 11:27AM - 11:39AM V44.00002: Zero temperature phase diagram of the periodic Anderson model Lorenzo De Leo , Marcello Civelli , Gabriel Kotliar We study the phase diagram of the periodic Anderson model using a cluster extension of DMFT to take into account non-local effects generated by the RKKY exchange. We employ exact diagonalization in order to access the zero temperature regime which was previously unexplored. In particular we focus our attention away from half filling where the competition between the localization of the heavy electrons and their magnetic ordering could result in a quantum critical point with unusual properties. We also consider the effect of a direct hopping between the $f$-electrons in order to understand if an indipendent tuning of the RKKY interaction influences the character of the transition. Thursday, March 16, 2006 11:39AM - 11:51AM V44.00003: Non-Fermi-liquid phase in a frustrated Kondo trimer Kevin Ingersent , Dohyung Seo , Andreas Ludwig , Ian Affleck The Kondo model for three antiferromagnetically coupled half-integer spins exhibits a non-Fermi-liquid phase that is stable against magnetic fields and against particle-hole symmetry breaking [1,2]. This phase has been argued [3] to describe the low-energy physics of equilateral Cr trimers on Au (111) surfaces [4]. It also has potential realizations in quantum-dot devices of triangular symmetry. We report properties of this phase obtained using the boundary conformal field-theory (CFT) technique, including characteristic signatures in the conductance, and apply CFT and renormalization-group methods to examine the phase's behavior under various perturbations. [1] B. C. Paul and K. Ingersent, cond-mat/9607190. [2] K. Ingersent, A. W. W. Ludwig, and I. Affleck, cond-mat/0505303 (Phys. Rev. Lett., in press). [3] B. Lazarovits et al., Phys. Rev. Lett. 95, 077202 (2005). [4] T. Jamneala, V. Madhavan, and M. F. Crommie, Phys. Rev. Lett. 87, 256804 (2001). Thursday, March 16, 2006 11:51AM - 12:03PM V44.00004: Egxact ground states for the periodic Anderson model at half filling in two dimensions Zsolt Gulacsi Recently, starting from a procedure based on the decomposition of the Hamiltonian in positive semidefinite operators, exact ground states have been deduced for the periodic Anderson model at finite value of the interaction at 1/4 and 3/4 filling even in three dimensions (PRL 91,186401,(2003); PRB 72,075130, (2005)), the method being so powerfull that its application for disordered systems, at the same values of the filling, and two dimensions, is also possible (PRB 69, 054204, (2004)). Herewith we extend the procedure such to be applicable at half filling as well, in the presence of finite on-site Hubbard interaction acting at the level of the correlated band. The extensions lead to a method which uses extended operators, (e.g. linear combinations of the starting fermionic operators acting along the whole system), and also sublattice operators, in constructing the ground state wave functions. The ground states describing conducting spin-singlet states, are presented in two dimensions. Thursday, March 16, 2006 12:03PM - 12:15PM V44.00005: Dynamic Magnetic Response of Heavy Fermion Semimetals Peter Riseborough We have calculated the dynamical magnetic response of a model of a heavy fermion semimetal, which is characterized by a narrow gap in the f density of states and a low conduction electron density of states at the Fermi energy. The model is used to fit optical absorbtion measurements on $CeRu_{4}Sb_{12}$ performed by Dordevic {\it et al.}, Phys. Rev. Lett. {\bf 86}, 684 (2001). The temperature dependence of the dissipative part of the magnetic response is compared with the experimentally determined inelastic neutron scattering cross-section of $CeRu_{4}Sb_{12}$ measured by Adroja {\it et al.} Phys. Rev. B {\bf 68}, 099426 (2003). Thursday, March 16, 2006 12:15PM - 12:27PM V44.00006: Magnetic Quantum Phase Transitions of a Kondo Lattice Model with Ising Anisotropy Jian-Xin Zhu , Stefan Kirchner , Qimiao Si , Daniel R. Grempel , Ralf Bulla We study the Kondo Lattice model with Ising anisotropy, within an extended dynamical mean field theory (EDMFT) in the presence or absence of antiferromagnetic ordering. The EDMFT equations are studied using both the Quantum Monte Carlo (QMC) and Numerical Renormalization Group (NRG) methods. We discuss the overall magnetic phase diagram by studying the evolution, as a function of the ratio of the RKKY interaction and bare Kondo scale, of the local spin susceptibility, magnetic order parameter, and the effective Curie constant of a nominally paramagnetic solution with a finite moment. We show that, within the numerical accuracy, the quantum magnetic transition is second order. The local quantum critical aspect of the transition is also discussed. Thursday, March 16, 2006 12:27PM - 12:39PM V44.00007: Coherence in the two-impurity Kondo problem Lijun Zhu , C.M. Varma We use the Wilson's renormalization group method to investigate the splitting of the even and odd Kondo resonances in the problem of two interacting Kondo impurities which presages the band-width or the coherence scale in the heavy-Fermion lattice. A finite splitting requires both potential scattering V which lifts particle-hole degeneracy and a difference between the exchange in the even and the odd parity channels(Je-Jo)[1]. We also investigate the elimination of the quantum critical point in the two-impurity Kondo problem[2] due to loss of particle-hole symmetry. [1] I. Affleck and A. W. W. Ludwig, Phys. Rev. Lett. 68, 1046(1992). [2] B. A. Jones, C. M. Varma, and J. W. Wilkins, Phys. Rev. Lett. 61, 125(1988). Thursday, March 16, 2006 12:39PM - 12:51PM V44.00008: Large temperature renormalization of anomalous Luttinger exponent in $Li_{0.9}Mo_{6}O_{17}$ Feng Wang , S.-K. Mo , J.W. Allen , J.V. Alvarez , G.-H. Gweon , J. He , R. Jin , R. Mandrus , H. H\"ochst $Li_{0.9}Mo_{6}O_{17}$ is unique as a quasi-1 dimensional metal for which both photoemission spectroscopy (PES) [1] and tunneling [2] find Luttinger liquid (LL) power law behaviors in spectra near the Fermi energy $E_{F}$, albeit with differing values of the anomalous exponent $\alpha$, $\approx0.9$ at temperature 300K and $\approx0.6$ below 50K, respectively. New T-dependent PES spectra from T = 300K down to 15K can be well fit by finite-T LL theory, with $\alpha$ varying continuously from $\approx0.9$ to $\approx0.6$, showing consistency of PES and tunneling. We find that its incommensurate Fermi wavevector would preclude such a large renormalization of $\alpha$ with T for $Li_{0.9}Mo_{6}O_{17}$ were it not for interband dynamics and residual interaction scattering that can occur only because there are two (nearly degenerate) bands crossing $E_{F}$. We also discuss implications of the theory for further experiments. [1] G.-H. Gweon et al, Phys. Rev. B $\bf {68}$, 195117 (2003). [2] J. Hager et al, Phys. Rev. Lett. $\bf {95}$, 186402 (2005). Thursday, March 16, 2006 12:51PM - 1:03PM V44.00009: Finite temperature ac conductivity of disordered Luttinger liquids Andreas Glatz , Bernd Rosenow , Thomas Nattermann Due to the strong effect of interactions in one spatial dimension, elementary charge excitations of a Luttinger liquid are plasmons. Backscattering of electrons from a random impurity potential creates single particle excitations, which strongly interact with these plasmons. In this way, backscattering from the impurity potential is modified by interactions and acquires a strong energy dependence first described in [1]. Based on a finite temperature renormalization group (RG) calculation [2], we determine the ac conductivity and include both the renormalization of the impurity strength and of the charge dynamics. The latter was neglected in [1], where the conductivity was calculated using the effective impurity strength obtained from the RG. We discuss the full frequency and temperature dependence of the conductivity and compare our results with those of [1]. \newline \newline [1] T. Giamarchi and H.J. Schulz, Phys. Rev. B 37, 325 (1988). \newline [2] A. Glatz and T. Nattermann, Phys. Rev. Lett. 88, 256401 (2002). Thursday, March 16, 2006 1:03PM - 1:15PM V44.00010: Dynamics of Strongly Correlated 1D Fermi Gases Razvan Teodorescu Dynamics of special collective modes in cold, degenerate Fermi gases are investigated through bosonization. The study applies to a variety of 1D or quasi-1D systems of fermions, including opticaly trapped cold gases and nanowires. Thursday, March 16, 2006 1:15PM - 1:27PM V44.00011: Tunneling, charge spreading, and the infrared catastrophe in conductors Kelly Patton , Michael Geller In many strongly correlated and low-dimensional electron systems the tunneling density of states (DOS) is suppressed near the Fermi energy; for example, the Luttinger-liquid characterization of one-dimensional conductors predicts that the DOS vanishes as a power law. Here we establish a connection between these DOS anomalies and the infrared catastrophe. The infrared catastrophe can occur during a tunneling event in systems where the relaxation of the newly introduced charge is inhibited by low dimensionality or other localizing effects. This catastrophe is known to be responsible for the x-ray edge spectra of metals, the Anderson orthogonality catastrophe, and the Kondo effect. By expressing the exact Green's function as a functional average of non-interacting Green's functions over of all space and time dependent potentials, we can appropriately treat the potentials responsible for the infrared catastrophe. The resulting interacting Green's function is the product of the noninteracting Green's function and $e^{-S}$, where $S$ is interpreted as a classical electrostatic action of a charge density spreading in time. These results give justification to other previously introduced phenomenological charge spreading theories. We apply this formalism to the Tomonaga-Luttinger, Calogero-Sutherland and other models. Thursday, March 16, 2006 1:27PM - 1:39PM V44.00012: Boundary Green's Function for Spin-incoherent Interacting Electrons in One Dimension Paata Kakashvili , Henrik Johannesson Recently the spin-incoherent regime of 1D strongly interacting, very low density electrons has attracted a lot of interest[1,2]. For sufficiently low densities the potential energy dominates the kinetic energy, driving the system towards a Wigner crystal and leading to an exponentially small spin exchange energy. One can then easily reach the spin-incoherent regime where the exchange energy is much less than the temperature. The physics of the spin-incoherent regime has been addressed using Bethe's Ansatz and a bosonized path integral approach, revealing that the spin incoherence dramatically influences the correlations of charge excitations. We have generalized the description to account for the presence of a boundary. By calculating the exact Green's function we find that the charge sector exponent is highly sensitive to the boundary, strongly modifying the tunneling of electrons close to it. Our approach also allows for a detailed description of the crossover between boundary and bulk regimes.\\ 1. V.V. Cheianov and M.B. Zvonarev, PRL 92, 176401 (2004)\\ 2. G.A. Fiete and L. Balents, PRL 93, 226401 (2004) Thursday, March 16, 2006 1:39PM - 1:51PM V44.00013: Phonon Effects on Spin-Charge Separation in One Dimension Chang-Qin Wu , Wen-Qiang Ning , Hui Zhao , Hai-Qing Lin Phonon effects on spin-charge separation in one dimension are investigated through the calculation of one-electron spectral functions in terms of the recently developed cluster perturbation theory together with an optimized phonon approach. It is found that the retardation effect due to the finiteness of phonon frequency suppresses the spin-charge separation and eventually makes it invisible in the spectral function. A signature of electrons pairing in weak interaction regimes was found to be consistent with the existence of a metallic phase proposed recently by Clay and Hardikar [Phys. Rev. Lett. \textbf{95}, 096401 (2005)]. By a comparison between our result and the experimental data of TTF-TCNQ, it is observed that electron-phonon interaction must be taken into account even in the strongly correlated system. Thursday, March 16, 2006 1:51PM - 2:03PM V44.00014: Dynamic Properties of 1-D Ising Chain in a Random Transverse Field Xun Jia , Sudip Chakravarty We considered a one dimensional spin-1/2 Ising chain in a random transverse magnetic field. Dynamic structure factor $S(k,\omega)$ at $T=0$ is numerically computed by mapping to Jordon-Weigner fermions. Two types of distributions of magnetic fields are introduced into our model. With rectangular distribution, single branch of dispersion relation is observed, and disorder tends to broaden the dispersion peak and close the excitation gap. With a binary distribution, a non-dispersing branch at almost zero energy is recovered. This is reminiscent of neutron scattering measurement in $LiHoF_4$, although this is a three-dimensional system with long-range dipolar coupling between the electronic spins, which are in turn coupled to the nuclear spins through the hyperfine interactions. The implications of this similarity will be discussed. Thursday, March 16, 2006 2:03PM - 2:15PM V44.00015: Stripe Glass from Competing Short and Long Range Interactions Gergely Zimanyi , Chris Pike , Richard Scalettar We investigate a film of dipoles oriented perpendicular to the film. The system's behavior is related to inhomogeneous non-Fermi liquid states, recently studied by Kivelson and Spivak and by Schmalian and Wolynes. The competition of short range ferromagnetic and long range antiferromagnetic interactions causes the formation of stripes. The system has an ordered stripe-crystal phase. However, this phase is avoided unless an extremely slow annealing protocol is utilized. Without any quenched disorder during normal annealing protocols the frustrated competing interactions self-generate a stripe-glass state. The stripe glass exhibits aging, manifesting itself in waiting-time dependent correlations. A scaling analysis of the aging is presented. The long time behavior shows stretched exponential behavior, the relaxation time surprisingly exhibiting a simple activated form. Dynamical inhomogeneities are identified, both frozen domains and instantaneous crystallites.