Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session N44: Quantum Criticality and Nematic Ordering |
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Sponsoring Units: DCMP Chair: Q. Si, Rice University Room: Baltimore Convention Center 347 |
Wednesday, March 15, 2006 8:00AM - 8:12AM |
N44.00001: The Effect of the Berry Phase on the Quantum Critical Properties of the Bose-Fermi Kondo model Stefan Kirchner, Qimiao Si The theory of the quantum critical point of a $T=0$ transition is traditionally formulated in terms of a quantum-to-classical mapping, leading to a theory of its classical counterpart in elevated dimensions. Recently, it has been shown that this mapping breaks down in an SU(N)$\times$SU(N/2) Bose-Fermi Kondo model (BFKM) [1], a BFKM with Ising anisotropy [2] and the spin-boson model [3]. Here we report the Quantum Monte Carlo results for the scaling properties of the quantum critical point of the BFKM with Ising anisotropy. In addition, using the Lagrangian formulation of the BFKM, we study the critical properties in the presence and absence of the spin Berry phase term. The results of the two cases are compared with the numerical results.\newline [1] L. Zhu, S. Kirchner, Q. Si, and A. Georges, Phys. Rev. Lett. 93,267201 (2004). [2] M. Glossop and K. Ingersent, Phys. Rev. Lett. 95, 067202 (2005). [3] M. Vojta, N-H Tong, and R. Bulla, Phys. Rev. Lett. 94, 070604 (2005). [Preview Abstract] |
Wednesday, March 15, 2006 8:12AM - 8:24AM |
N44.00002: Quantum Critical Behaviour Near the Kondo Breakdown Fixed Point Indranil Paul, Catherine P\'{e}pin, Mike R. Norman We study the Kondo-Heisenberg model using a fermionic representation for the localized spins. In this model, the mean field Kondo hybridization at $T=0$ can be continuously tuned to zero as a function of the exchange interactions. We calculate the fluctuations of the hybridization and its associated gauge potential at the one loop level, and their contribution to the specific heat and spin susceptibility, near the quantum critical point. [Preview Abstract] |
Wednesday, March 15, 2006 8:24AM - 8:36AM |
N44.00003: Kondo Screening and Fermi Surface in the Antiferromagnetic Metal Phase Seiji Yamamoto, Qimiao Si We address the Kondo effect deep inside the antiferromagnetic metal phase of a Kondo lattice Hamiltonian with SU(2) invariance. The local- moment component is described in terms of a non-linear sigma model. The Fermi surface of the conduction electron component is taken to be sufficiently small, so that it is not spanned by the antiferromagnetic wavevector. The effective low energy form of the Kondo coupling simplifies drastically, corresponding to the uniform component of the magnetization that forward-scatters the conduction electrons on their own Fermi surface. We use a combined bosonic and fermionic (Shankar) renormalization group procedure to analyze this effective theory and study the Kondo screening and Fermi surface in the antiferromagnetic phase. The implications for the global magnetic phase diagram, as well as quantum critical points, of heavy fermion metals are discussed. [Preview Abstract] |
Wednesday, March 15, 2006 8:36AM - 8:48AM |
N44.00004: Sign change of the Gr\"uneisen parameter and magnetocaloric effect near quantum critical points Markus Garst, Achim Rosch Strong fluctuations near a quantum critical point lead to a singular entropy distribution in the phase diagram. This results in strong signatures of the Gr\"uneisen parameter and the magnetocaloric effect. In particular, a sign change of the Gr\"uneisen parameter coincides with the accumulation point of entropy in the phase diagram. If the quantum critical point is the endpoint of a line of finite temperature phase transitions the sign change generically occurs in the Ginzburg regime of the classical transition as observed in several heavy fermion compounds. In addition, we predict a sharp peak in the Gr\"uneisen parameter at the critical temperature due to the contribution of classical critical fluctuations. For magnetic field tuning these signatures are also reflected in the magnetocaloric effect. Moreover, we discuss the case of metamagnetic quantum criticality where the sign change is located at the critical magnetic field. [Preview Abstract] |
Wednesday, March 15, 2006 8:48AM - 9:00AM |
N44.00005: Towards a unification of local moment magnetism and the Kondo lattice Jerome Rech, Piers Coleman, Gergely Zarand, Olivier Parcollet We apply the Schwinger boson scheme to the fully screened Kondo model and generalize the method to include antiferromagnetic interactions between ions. Our approach unifies the Kondo impurity approach of Parcollet and Georges with the Schwinger boson description of antiferromagnetism of Arovas and Auerbach, enabling the formalism to describe magnetically correlated and magnetically ordered heavy electron phases. For the single impurity, our approach captures the Kondo crossover from local moment behavior to a Fermi liquid with a non-trivial Wilson ratio. When applied to the two impurity model, the mean-field theory describes the ``Varma Jones'' quantum phase transition between a valence bond state and a heavy Fermi liquid. We will extend the method to the Kondo lattice, and explore the nature of the phase diagram connecting the heavy electron phase, the magnetic phase and the spin-liquid phase. [Preview Abstract] |
Wednesday, March 15, 2006 9:00AM - 9:12AM |
N44.00006: Quasi-particle linewidth close to a quantum critical point: Crossover from non-Fermi liquid to Fermi liquid behavior Pedro Schlottmann Heavy fermion systems frequently display non-Fermi liquid behavior due to a nearby quantum critical point. A nested Fermi surface together with the remaining interaction between the carriers after the heavy particles are formed may give rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point is obtained as $T_N \to 0$. The quasi-particle linewidth is calculated in the paramagnetic phase following an approach outlined by Virosztek and Ruvalds (Phys. Rev. B {\bf 42}, 4064 (1990)). The linewidth shows a crossover from non-Fermi liquid ($\sim T$) to Fermi liquid ($\sim T^2$) behavior with increasing nesting mismatch and decreasing temperature. The quasi-particle linewidth is a quantity relevant to the electrical resistivity and the width of the inelastic neutron scattering quasi-elastic peak. [Preview Abstract] |
Wednesday, March 15, 2006 9:12AM - 9:24AM |
N44.00007: Curie law, entropy excess, and superconductivity in heavy fermion metals and other strongly interacting Fermi liquids V.A. Khodel, M.V. Zverev, Victor Yakovenko Low-temperature thermodynamic properties of strongly interacting, itinerant Fermi liquids with fermion condensate are investigated. We demonstrate that the spin susceptibility of these systems exhibits the Curie-Weiss law, and the entropy contains a temperature-independent term. The excessive entropy is released at the superconducting transition, enhancing the specific heat jump $\Delta C$ and rendering it proportional to the effective Curie constant. The theoretical results are favorably compared with the experimental data on the heavy fermion metal CeCoIn$_5$, as well as $^3$He films. \\ Reference: cond-mat/0508275, Phys. Rev. Lett. (December 2005). [Preview Abstract] |
Wednesday, March 15, 2006 9:24AM - 9:36AM |
N44.00008: Super-frustration for strongly-correlated fermions in two dimensions Paul Fendley, Kareljan Schoutens We prove that there exists an exotic ``super-frustrated'' state of strongly-correlated spinless fermions hopping on a two-dimensional lattice. This state is characterized by an extensive ground-state entropy, and very possibly is at a non-Fermi-liquid quantum critical point. We give explicit Hamiltonians which exhibit this behavior. Exploring various lattices and limits, we show how the ground states can be frustrated, quantum critical, or combine frustration with a Wigner crystal. [Preview Abstract] |
Wednesday, March 15, 2006 9:36AM - 9:48AM |
N44.00009: Domain formation in electronic nematic phase coupled to lattice deformation Hyeonjin Doh, Yong Baek Kim, Keun Hyuk Ahn Motivated by the experiments on Sr$_3$Ru$_2$O$_7$, we have investigated the possibility of domain formation in electronic nematic phase coupled to lattice deformations. It has been suggested that the formation of the nematic order may explain the two consecutive metamagnetic transitions observed in Sr$_3 $Ru$_2$O$_7$. Our study may serve as the explanation of the high residual resistivity observed in a range of magnetic fields. [Preview Abstract] |
Wednesday, March 15, 2006 9:48AM - 10:00AM |
N44.00010: Non-Fermi Liquid Behavior of Nematic Fermi Fluids Michael Lawler, Eduardo Fradkin Following the initial study of Ref. 1, we explore the behavior of physically relevant quantities in the vicinity of the quantum critical point between a nematic Fermi fluid and a Fermi liquid. As shown in Ref. 1, this strong coupling fixed point is completely accessible within the method of high dimensional bosonization and we continue the analysis presented therein focusing on quasiparticle properties, such as the fermion residue and the fermion spectral function. We show in particular, that the fermion residue vanishes according to the essential singularity $\exp\big(-1/\sqrt{\delta}\big)$ where $\delta$ is the dimensionless coupling constant measuring the distance to the critical point. Also, at low temperatures, we verify explicitly that the heat capacity obey's the non-Fermi liquid powerlaw of $T^{2/3}$. We conclude with a discussion of the signatures of the nematic phase that would appear in light scattering and angle resolved photo emission spectroscopy experiments. \newline \newline [1] Lawler, Barci, Fernandez, Fradkin and Oxman, unpublished; cond-mat/0508747. [Preview Abstract] |
Wednesday, March 15, 2006 10:00AM - 10:12AM |
N44.00011: Phase and amplitude fluctuations for the $l=2$ Pomeranchuk instability in two dimensions. Jorge Quintanilla, Masudul Haque For a two-dimensional fermionic system, we analyze models that produce shape-distortion instabilities of the Fermi surface in the $l=2$ channel, leading to a non-Fermi liquid with nematic order. The finite-temperature phase diagram contains a transition of the Kosterlitz-Thouless type and a crossover at higher temperatures, corresponding respectively to the disordering of phase and amplitude degrees of freedom. [Preview Abstract] |
Wednesday, March 15, 2006 10:12AM - 10:24AM |
N44.00012: Interplay between parallel and diagonal electronic nematic phases in interacting systems Hae-Young Kee, Hyeonjin Doh, Nir Friedman An electronic nematic phase is a spontaneous broken state of a discrete rotational symmetry of a given crystal. There exist two distinct electronic nematic phases in a square lattice. One is the parallel nematic order which breaks the symmetry in $x$- and $y$-direction, and the other is the diagonal nematic order which breaks the diagonal $(x+y)$ and the anti-diagonal $(x-y)$ symmetry. We investigate the different features and the mutual interaction between these two nematic orders. We also discuss the possible implication of our results in the context of neutron scattering and Raman spectroscopy measurements in high $T_C$ superconductors. [Preview Abstract] |
Wednesday, March 15, 2006 10:24AM - 10:36AM |
N44.00013: Interacting fermions in two dimensions: singularities in the perturbation theory and the role of collective modes. Suhas Gangadharaiah, Dmitrii Gutman, Dmitrii Maslov We consider a system of interacting fermions in two dimensions. It is shown that even for an infinitesimally weak interaction a straight-forward perturbation theory is ill defined near the mass shell. Starting from the second order, the perturbative expansion for the self-energy is singular at the mass shell. We show that this singularity is a manifestation of a non- perturbative effect: the interaction of fermions with the collective mode. The singularities in the perturbation series for the self-energy is treated by resumming the most divergent diagrams. A threshold for emission of zero-sound waves leads to a non-monotonic variation of the self-energy. Consequently, the spectral function acquires a non-Lorentzian kink-like feature. This feature is reminiscent to spin-charge separation in 1D, as the kink is absent in a spin-polarized system. We examine the possibility of detecting the kink in momentum-conserving tunneling between two parallel layers of a 2D electron gas. [Preview Abstract] |
Wednesday, March 15, 2006 10:36AM - 10:48AM |
N44.00014: Ferromagnetic quantum phase transition in an itinerant three-dimensional system Ronojoy Saha, Dmitrii Maslov, Andrey Chubukov The non-analytic behavior of the spin susceptibility both away and near the quantum critical point signals the breakdown of the Hertz-Millis scenario for a ferromagnetic quantum phase transition in itinerant systems. It is believed that in both 2D and 3D $\chi_{s}$ increases as a function of the magnetic field ($H)$ or momentum ($q),$ which indicates a tendency to either first order transition or ordering at finite $q$. We show that the 3D case is different from the 2D one. Away from the 3D critical point, the non-analytic part of $\chi _{s}$ can be of either sign, depending on microscopic parameters. The non-analyticity in 3D arises from two physically distinct processes: excitations of a single and three particle-hole pairs. Both processes contribute a max\{$H^{2},q^{2}\}\ln \max \{H^{2},q^{2}\}$ term to $\chi _{s}$, but the signs of these contributions are opposite. The single-pair process leads to an increase of $\chi _{s}$ with $H,q$ whereas the three pair one corresponds to a decrease. In the paramagnon model, the three pair contribution always wins sufficiently close to the Stoner instability. We also discuss the behavior of $\chi _{s}$ in the immediate vicinity of the quantum critical point within the spin-fermion model. [Preview Abstract] |
Wednesday, March 15, 2006 10:48AM - 11:00AM |
N44.00015: Metallic phase in a two-dimensional disordered Fermi system with singular interactions Victor Galitski We consider a two-dimensional disordered system of gapless fermions interacting with a singular transverse gauge-field. We study quantum corrections to fermion conductivity and show that they are very different from those in a usual Fermi liquid. In particular, the weak-localization effect is suppressed by magnetic field fluctuations. We argue that these fluctuations can be considered static at time scales of fermionic diffusion. By inducing fluxes through diffusive loops that contribute to weak localization, they dephase via the Aharonov-Bohm effect. It is shown that while the flux-flux correlator due to thermal fluctuations of magnetic field is proportional to the area enclosed by the loop, the correlator due to quantum fluctuations is proportional to the perimeter of the loop. The possibility of dephasing due to these quasistatic configurations is discussed. We also study interaction induced effects and show that perturbation theory contains infrared divergent terms originating from unscreened magnetic interactions. We show that due to singular small-angle scattering, the corresponding contributions to the density of states and conductivity are very large and positive indicating that the fermion-gauge system remains metallic at low temperatures. [Preview Abstract] |
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