Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session L46: Heavy Fermions and Non-Fermi Liquids: Theory |
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Sponsoring Units: DCMP Chair: Pallab Goswami, National High Magnetic Field Laboratory Room: Mile High Ballroom 4E |
Wednesday, March 5, 2014 8:00AM - 8:12AM |
L46.00001: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 8:12AM - 8:24AM |
L46.00002: Emergence of heavy quasiparticles from a massless Fermi sea: Optical conductivity Hyun-Yong Lee, Stefan Kettemann We study the density of states and the optical conductivity of a Kondo lattice which is immersed in a massless Dirac Fermi sea, as characterized by a linear dispersion relation. As a result of the hybridization $V$ with the $f$-electron levels, the pseudo-gap in the conduction band becomes duplicated and is shifted both into the upper and the lower quasiparticle band. Furthermore, we find that due to the linear dispersion of the Dirac fermions, the Kondo insulator gap is observable in the optical conductivity in contrast to the Kondo lattice system in a conventional conduction band, and the resulting gap[$\Delta_{\rm gap}(T)$] depends on temperature. The reason is that the Kondo insulator gap is an indirect gap in conventional Kondo lattices, while it becomes a direct gap in the Dirac Fermi Sea. We find that the optical conductivity attains two peaks and is vanishing exactly at $2bV$ where $b$ is a condensation of slave boson depending on temperature. [Preview Abstract] |
Wednesday, March 5, 2014 8:24AM - 8:36AM |
L46.00003: Topological defects of N\'eel order and Kondo singlet formation for Kondo-Heisenberg model on a honeycomb lattice Qimiao Si, Pallab Goswami Heavy fermion systems represent a prototypical setting to study magnetic quantum phase transitions. In this context, we study the spin one-half Kondo-Heisenberg model on a honeycomb lattice at half filling [1]. The problem is approached from the Kondo destroyed, antiferromagnetically ordered insulating phase. We describe the local moments in terms of a coarse grained quantum non-linear sigma model, and show that the skyrmion defects of the antiferromagnetic order parameter host a number of competing order parameters. In addition to the spin Peierls, charge and current density wave order parameters, we identify for the first time Kondo singlets as the competing dual orders of the antiferromagnetism, which can be related to each other via generalized chiral transformations of the underlying fermions. We also show that the conduction electrons acquire a Berry phase through their coupling to the hedgehog configurations of the N\'eel order, which cancels the Berry phase of the local moments. Our results demonstrate the competition between the Kondo-singlet formation and spin-Peierls order when the antiferromagnetic order is suppressed, thereby shedding new light on the global phase diagram of heavy fermion systems at zero temperature. \\[4pt] [1] P. Goswami and Q. Si, arXiv: 1309.0501 [Preview Abstract] |
Wednesday, March 5, 2014 8:36AM - 8:48AM |
L46.00004: Finite $f$-Electron Bandwidth in a Heavy Fermion Model Axel Euverte, Simone Chiesa, Richard Scalettar, George Batrouni Determinant Quantum Monte Carlo is used to study the effect of non-zero hopping $t_f$ in the localized $f$-band of the periodic Anderson model in two dimensions. We show that a remnant of the band insulator to metal line at $U_f$ = 0 persists in the interacting system, manifesting itself as a maximal tendency toward antiferromagnetic correlations at low temperature. In this optimal $t_f$ region, short- and long-range spin correlations develop at similar temperatures in stark contrast with the more common scenario where short range correlations are stronger and develop at higher temperature. The effect that finite $t_f$ has on Kondo screening is investigated by considering the evolution of the local density of states for selected $t_f$ as a function of $V$. [Preview Abstract] |
Wednesday, March 5, 2014 8:48AM - 9:00AM |
L46.00005: Global phase diagram of heavy fermion metals: Insights from an Ising-anisotropic Kondo lattice model tuned by a transverse magnetic field Emilian Marius Nica, Lili deng, Kevin Ingersent, Jian-Xin Zhu, Qimiao Si Quantum criticality in heavy fermion metals involves the interplay between quantum fluctuations within the local moments and those associated with the Kondo interaction. The resulting global phase diagram [1,2] has provided a means to categorize heavy-fermion quantum critical points [3] and motivated the study of materials with tunable quantum fluctuations [4]. It can be theoretically characterized within an Extended Dynamical Mean-Field Theory (EDMFT). Towards this goal, we studied an Ising-anisotropic Bose-Fermi Kondo model with a local transverse field [2]. We found a line of critical points separating a Kondo screened phase and a local moment phase. We present preliminary results for the EDMFT study of an Ising-anisotropic Kondo lattice model tuned by a transverse magnetic field. In addition, we discuss the implications of the line of critical points for the global phase diagram.\\[4pt] [1] Q. Si, Phys. Status Solidi B247, 476 (2010); Physica B378, 23 (2006) [2] E.M. Nica et al, PRB 88, 014414 (2013) [3] S. Friedemann et al, Nat. Phys. 5, 465 (2009). [4] J. Custers et al, Nat. Mater. 11, 189 (2012); M. S. Kim {\&} M. C. Aronson, PRL 110, 017201 (2013); V. Fritsch et al, arXiv:1301.6062. [Preview Abstract] |
Wednesday, March 5, 2014 9:00AM - 9:12AM |
L46.00006: Un-Fermi Liquids: Unparticles in Strongly Correlated Electron Matter Brandon Langley, Philip Phillips, Jimmy Hutasoit Since any non-trivial infrared dynamics in strongly correlated electron matter must be controlled by a critical fixed point, we argue that the form of the single-particle propagator can be deduced simply by imposing scale invariance. As a consequence, the unparticle picture proposed by Georgi[1] is the natural candidate to describe such dynamics. Unparticle stuff is scale-invariant matter with no particular mass. Scale invariance dictates that the propagator has an algebraic form which can admit zeros and hence is a candidate to explain the ubiquitous pseudogap state of the cuprates. The non-perturbative electronic state formed out of unparticles we refer to as an un-Fermi liquid. We show that the underlying action of the continuous mass formulation of unparticles can be recast as an action in anti de Sitter space which serves as the generating functional for the propagator. We find that this mapping fixes the scaling dimension of the unparticle to be $d_U=d/2+\sqrt{d^2+4}/2$ and ensures that the corresponding propagator has zeros with $d$ the spacetime dimension of the unparticle field. [1] H. Georgi, Phys. Rev. Lett. 98, 221601 (2007) [2] B.W. Langley, P.W. Phillips, J.A. Hutasoit, Phys. Rev. B 88, 115129 (2013) [Preview Abstract] |
Wednesday, March 5, 2014 9:12AM - 9:24AM |
L46.00007: Critical charge fluctuations in a pseudogap Anderson model Tathagata Chowdhury, Kevin Ingersent Experiments on heavy-fermion $\beta$-YbAlB$_4$ raise the possibility of critical destruction of the Kondo effect in a mixed-valence system. We consider a toy model of this phenomenon: the particle-hole asymmetric Anderson model with a pseudogapped density of states $\rho(\epsilon) \propto |\epsilon-\epsilon_F|^r$ where $\epsilon_F$ is the Fermi energy. The model exhibits a critical spin response at a quantum phase transition separating a Kondo phase from a non-Kondo (local-moment) phase, where the Kondo energy scale is driven continuously to zero on approach from the Kondo side [1]. This Kondo-destruction transition has recently been shown, for certain values of $r$, to be accompanied by a divergence of the charge susceptibility coming from either phase [2]. Here we present a systematic numerical renormalization-group study of the charge response as a function of $r$. The charge fluctuations are described by critical exponents that show nontrivial $r$ dependence. Over a range of $r$ values, these exponents satisfy hyperscaling equations consistent with a scaling anzatz for the critical free energy at an interacting quantum phase transition. [1] K. Ingersent and Q. Si, Phys. Rev. Lett. 89, 076403 (2002). [2] J. H. Pixley et al., Phys. Rev. Lett. 109, 086403 (2012). [Preview Abstract] |
Wednesday, March 5, 2014 9:24AM - 9:36AM |
L46.00008: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 9:36AM - 9:48AM |
L46.00009: Fermi energy and dispersion anomalies in a bad metal Wenhu Xu, Kristjan Haule, Gabriel Kotliar The transport measurements in strongly correlated metals often reveal a vanishing Fermi liquid temperature. It is unexpectedly smaller than the effective Fermi energy indicated by spectroscopic measurements. We attribute this dichotomy to the strong temperature dependence and asymmetry in quasiparticle renormalization near Fermi surface. The quasiparticles hold as well-defined excitations up to much higher energy than the Fermi liquid scale implied by transport. Furthermore, the asymmetry leads to incoherent spectral weight only for quasiparticles near Fermi surface, thus the discontinuity in dispersion rises as a natural consequence. [Preview Abstract] |
Wednesday, March 5, 2014 9:48AM - 10:00AM |
L46.00010: Ubiquity of Linear Resistivity at Intermediate Temperature in Strongly Correlated Metals Greg Boyd, V. Zlatic, Jim Freericks Correlated metals display transport behavior that differs from what is commonly seen in ordinary metals (Fermi-liquids). One of the most salient features is a resistivity that is linear in temperature over decades in temperature and rises to well above the Ioffe-Regel limit (where the mean-free path is less than a lattice spacing). Using an exact representation of the Kubo linear response, we show that a linear resistivity naturally occurs in a minimal model that includes only hopping and correlation. We expect this to be common to many systems at an incoherent intermediate-temperature state, above the Fermi coherence scale. We verify the analytic arguments with exact calculations for Falicov-Kimball model which is solved with dynamical mean-field theory. Similar features have also been seen in Hubbard models, which can be approximated by the Falicov-Kimball model. [Preview Abstract] |
Wednesday, March 5, 2014 10:00AM - 10:12AM |
L46.00011: ABSTRACT WITHDRAWN |
Wednesday, March 5, 2014 10:12AM - 10:24AM |
L46.00012: Quantum Monte Carlo investigation of Knight shift anomaly in Periodic Anderson model Mi Jiang, Nicholas Curro, Richard Scalettar We report a Determinant Quantum Monte Carlo investigation of the Knight shift anomaly observed in nuclear magnetic resonance (NMR) of heavy fermion materials. As opposed to normal Fermi liquids, the Knight shift in heavy fermion materials deviates from the total susceptibility $\chi$ below a crossover temperature $T^{\ast}$. This deviation is believed to originate in the different temperature dependence of the conduction electron and local moment components of the total susceptibility $\chi$. Here we quantify the behavior of $\chi_{cc}(T), \chi_{cf}(T),$ and $\chi_{ff}(T)$ in the framework of periodic Anderson model (PAM), focussing on the evolution with different degree of conduction electron-local moment hybridization. These results confirm several predictions of the two-fluid theory of the Knight shift anomaly, including the demonstration of a universal logarithmic divergence of the contribution of the heavy electrons to the Knight shift. This universal behavior, which occurs with decreasing temperature below $T^{\ast}$ in the paramagnetic state, agrees well with experimental findings, and indicates that different heavy fermion materials exhibit a common scaling, differing only in the coherence temperature scale, $T^{\ast}$. [Preview Abstract] |
Wednesday, March 5, 2014 10:24AM - 10:36AM |
L46.00013: Supersymmetric SP(N) spin representation for heavy fermion systems Aline Ramires, Piers Coleman In heavy fermion materials, the character of the spin correlations change radically between the antiferromagnetic and fermi liquid region of the phase diagram. In the latter, the spin behaves as a bosonic object, condensing into magnetic order, which we traditionally describe using a Holstein-Primakoff or Schwinger bosons, whereas in the the fermi liquid phase, the spin binds to the conduction electrons to form a composite heavy fermion, usually described by Abriskosov fermions. Past work [1] developed a supersymmetric representation of SU(N) spin operators. Here we analyze the supersymmetry of SP(N) symplectic spin operators, which provides us with the capability of studying antiferromagnetic and superconducting order. As a warm up problem, we show how this formalism can be applied to a two site Kondo model, coupled via a Heisenberg coupling. [1] P. Coleman, C. Pepin and A. Tsvelik, Phys. Rev. B 62, 3852 (2000). [Preview Abstract] |
Wednesday, March 5, 2014 10:36AM - 10:48AM |
L46.00014: Low temperature phases of periodic Anderson model with electron-phonon correlated conduction band Enzhi Li, Peng Zhang, Ka-Ming Tam, Juana Moreno, Mark Jarrell We study a periodic Anderson model with the conduction electrons coupled to phonons. It has been shown by using the dynamical mean field theory that the model contains two disordered phases, the Kondo singlet phase and the local moment phase. In the hybridization--temperature plane, they are separated by a first order phase transition line which terminates at a second order phase transition point. At low enough temperature the entropy in the Kondo singlet phase is quenched by Fermi liquid formation, while the local moment phase will have residual entropy unless it is quenched by ordering. In this talk, we discuss this ordering by constructing the lattice susceptibilities from dynamical mean field theory. [Preview Abstract] |
Wednesday, March 5, 2014 10:48AM - 11:00AM |
L46.00015: Charge Kondo effect in a triple quantum dot Gwangsu Yoo, Jinhong Park, S.S.-B. Lee, H.-S. Sim We predict that the charge Kondo effect appears in a triangular triple quantum dot. The system has two-fold degenerate ground-state charge configurations, interdot Coulomb interactions, lead-dot electron tunnelings, but no interdot electron tunneling. We show, using bosonization and refermionization, that the system is described by the {\em anisotropic} Kondo model. The anisotropy can be tuned by changing lead-dot electron tunneling strength, which allows one to experimentally explore the transition between the ferromagnetic non-Fermi liquid and antiferromagnetic Kondo phases in the Kondo phase diagram. Using numerical renormalization group method, we demonstrate that the transition is manifested in electron conductances through the dot. [Preview Abstract] |
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