Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session S39: Quantum Phase Transitions in Strongly Correlated Electron Systems |
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Sponsoring Units: DCMP Chair: Victor Galitski, UCSB Room: Los Angeles Convention Center 514 |
Wednesday, March 23, 2005 2:30PM - 2:42PM |
S39.00001: Magnetic properties of Ni$_3$Al and Ni$_3$Ga: Emergent states and the importance of a tri-critical point? Robert P. Smith, Gilbert G. Lonzarich, Siddharth S. Saxena, Mark Ellerby Ni$_{3}$Al and Ni$_{3}$Ga are itinerant d electron systems which lie close to a ferromagnetic quantum critical point. Ni$_{3}$Al is a ferromagnet with a transition temperature at ambient pressure of 41K and a critical pressure of 80kbar while Ni$_{3}$Ga is a paramagnet all the way to zero temperature. These materials are ideal systems in which to test spin fluctuation theory. We present magnetisation data of these two materials and test the results against spin fluctuation theory with no adjustable parameters. While Ni$_{3}$Al (at ambient pressure) is found to fit well with the theory, Ni$_{3}$Ga can be understood by assuming that this system lies close to a quantum tri-critical point. We suggest that such a quantum tri-critical point may be a key feature in the understanding of quantum critical systems more generally. [Preview Abstract] |
Wednesday, March 23, 2005 2:42PM - 2:54PM |
S39.00002: Quantum oscillations in non-Fermi-liquid metals Stephen Julian, Alix McCollam, Patrick Rourke, Jacques Flouquet, Dai Aoki The temperature dependence of de Haas van Alphen (dHvA) and other quantum oscillations is governed in a Fermi liquid by the Lifshitz-Kosevich (LK) equation\footnote{see e.g. D.\ Shoenberg, {\em Magnetic Oscillations in Metals}, CUP 1984}. Several authors \footnote{e.g. A.\ Wasserman and M.\ Springford, Adv.\ Phys.{\bf 45} (1996) 471, and references therein.} have extended the LK theory to non-Fermi-liquid metals, but these treatments tend to be very technical. We will give a simple interpretation of the non-Fermi-liquid effects that arise in these theories, and will briefly discuss the possible observation of non-Fermi-liquid temperature dependence in dHvA oscillations in CeCoIn$_5$. [Preview Abstract] |
Wednesday, March 23, 2005 2:54PM - 3:06PM |
S39.00003: Quantum criticality in the Itinerant Ferromagnets Zr$_{1-x}$Nb$_{x}$Zn$_{2}$ D. Sokolov, M.C. Aronson, Z. Fisk We report the results of magnetization measurements performed on the family itinerant ferromagnets Zr$_{1-x}$Nb$_{x}$Zn$_{2}$, (0 $\leq x \leq 0.14)$. Nb doping reduces the moment M$_{0}$ and also the Curie temperature T$_{c}$, which simultaneously disappear at the critical Nb concentration x$_{c}$=0.084. We find that T$_{c}$ $\propto$ (x-x$_{c}$)$^{3/4}$, as predicted for a 3d ferromagnet, while M$_{0}$ $\propto$ T$_{c}$ (x), as expected for a Stoner ferromagnet. For all Nb concentrations and for temperatures which approach 100 K, the extrapolated zero field susceptibility $\chi$ can be expressed with a modified Curie Weiss expression $\chi=C/(T^\gamma +\theta)$. $\theta$ is finite in the paramagnetic state (x$>$x$_{C}$), but vanishes as the system becomes critical at x=x$_{C}$, evidenced by the T=0 divergence of $\chi$ in this system. We find that $\gamma$ is near one in paramagnetic regimes for x$<$x$_{c}$ (T$>$T$_{c}$), and for x $\gg$ x$_{c}$. However, $\gamma$ is substantially enhanced in the vicinity of the quantum critical point (0.08$<$x$<$0.09), indicating the breakdown of the conventional Stoner theory. [Preview Abstract] |
Wednesday, March 23, 2005 3:06PM - 3:18PM |
S39.00004: Thermoelectrical Transport of Quantum Critical Metals Seiji Yamamoto, Eugene Pivovarov, Qimiao Si Motivated by recent experimental measurements of an anomalously enhanced Nernst coefficient in strongly correlated electron systems, we examine thermal and electrical transport in metals near quantum phase transitions. We consider an electronic topological transition (Lifshitz transition) to mimic exotic quantum critical points with a large Fermi-surface reconstruction, and compare it with the case of spin-density-wave (SDW) transition. In the former, we find a strong enhancement of the Nernst coefficient. Across an SDW transition, on the other hand, the Fermi surface change is too smooth to significantly affect the Nernst coefficient. [Preview Abstract] |
Wednesday, March 23, 2005 3:18PM - 3:30PM |
S39.00005: Magnetic fluctuations close to an antiferromagnetic quantum critical point as observed in CeNi2Ge2 Almut Schroeder, Bilal ElZoghbi, C.L. Broholm, Y. Qiu, D.F. McMorrow, N. Christensen, J. Mydosh, O. Tegus, G. Aeppli, M. Adams Neutron scattering spectra of the heavy fermion compound CeNi2Ge2 will be presented to characterize the magnetic correlations and dynamics close to an antiferromagnetic quantum critical point. [Preview Abstract] |
Wednesday, March 23, 2005 3:30PM - 3:42PM |
S39.00006: The strongly paramagnetic-to-spin polarized ferromagnetic transition in Fe$_{1-x}$Co$_x$S$_2$ Song Guo, John DiTusa, David Young, Julia Chan Carrier doping of “fool’s gold”, the paramagnetic insulator FeS$_2$, by way of Co substitution for Fe, results in a insulator-to-metal transition at $x\le 0.001$. Further Co substitution beyond $x~0.035$ produces an itinerant and fully spin polarized ferromagnet by way of either a crossover or quantum phase transition. In order to explore the thermodynamics of this magnetic semiconductor near the paramagnetic-to- ferromagnetic phase transition the specific heat of Fe$_{1-x} $Co$_x$S$_2$ (x=0.045,0.03,0.005) was measured for temperatures down to 0.1 K. Our $x=0.045$ sample displayed a logarithmic like divergence of $C/T =\gamma$ in zero field which saturates to a Fermi liquid like constant below 0.5 K. For $x$=0.03 at zero field, the enhancement of $\gamma$ is extended down to 0.3K while for x=0.005 the logarithmic-like divergence continues down to the lowest temperature measured. For this last sample, $\gamma$ can be enhanced by the application of small magnetic fields ($H<0.15$ T) while higher fields tend to suppress $\gamma$ in all of our samples. [Preview Abstract] |
Wednesday, March 23, 2005 3:42PM - 3:54PM |
S39.00007: Anisotropic Hall Effect in Single Crystal Heavy Fermion YbAgGe Sergey Bud'ko, Emilia Morosan, Paul Canfield Temperature- and field-dependent Hall effect measurements are reported for YbAgGe, a heavy fermion compound exhibiting a field-induced quantum phase transition. The low temperature, field-dependent measurements reveal well defined, sudden changes with applied field; in specific for $H \perp c$ a clear local maximum that sharpens as temperature is reduced below 2 K and that approaches a value of 45 kOe - a value that has been proposed as the $T = 0$ quantum critical point. Similar behavior was observed for $H \| c$ where a clear minimum in the field-dependent Hall resistivity was observed at low temperatures. Although at our base temperatures it is difficult to distinguish between the field-dependent behavior predicted for (i) diffraction off a critical spin density wave or (ii) breakdown in the composite nature of the heavy electron, for both field directions there is a distinct temperature dependence of a feature that can clearly be associated with a field-induced quantum critical point at $T = 0$ persisting up to at least 2 K. [Preview Abstract] |
Wednesday, March 23, 2005 3:54PM - 4:06PM |
S39.00008: Numerical renormalization group study of the Bose-Fermi Kondo model Matthew T. Glossop, Kevin Ingersent The Bose-Fermi Kondo model (BFKM) is of current interest in the
context of non-Fermi liquid behaviour in quantum critical heavy
fermion systems [1]. We study the Ising-symmetry BFKM, employing
a novel extension of Wilson's numerical renormalization group to
include coupling of a quantum impurity
to {\it both} a conduction electron band {\it and} a dissipative
bosonic bath described by the spectral function
$\eta(\omega)\propto \omega^s$ ($0<\omega<\omega_c$).
For sub-Ohmic bath exponents $0 |
Wednesday, March 23, 2005 4:06PM - 4:18PM |
S39.00009: Metamagnetism and Non Fermi Liquid behavior in CeIrIn5 C. Capan, F. Ronning, E.D. Bauer, R. Movshovich, M.F. Hundley, J.D. Thompson, J.L. Sarrao, L. Balicas, T. Murphy, E. Palm, D. Hall, H. Radovan, S. Tozer, R. Goodrich Investigations of transport and thermodynamic properties near a quantum phase transition have been subject of intense theoretical and experimental efforts in strongly correlated electron systems in recent years. The nature of low energy excitations near a quantum critical point is strikingly different from the Landau quasiparticles, resulting in strong deviations from Fermi Liquid theory in most properties at low temperatures. In this context, recent studies of Sr3Ru2O7 have raised the possibility of a quantum critical point associated with metamagnetism. CeIrIn5, a recently discovered heavy fermion superconductor, offers yet another playground for such investigations. Indeed, CeIrIn5 has peculiar properties at high magnetic fields, with a field induced Non Fermi Liquid behavior in both resistivity and specific heat up to 17T. A metamagnetic transition has also been reported for magnetic fields above 30T. Thus, it is natural to ask whether the Non Fermi Liquid behavior is a result of a quantum critical point associated with metamagnetism in CeIrIn5. We will present new results of resistivity and magnetization up to 33T in an attempt to address this issue. [Preview Abstract] |
Wednesday, March 23, 2005 4:18PM - 4:30PM |
S39.00010: Antiferromagnetic Quantum Critical Point in CeRh(In,Sn)$_5$ Eric Bauer, D. J. Mixson, F. Ronning, J. D. Thompson, J. L. Sarrao, R. Movshovich, M. F. Hundley, G. R. Stewart CeRhIn$_5$ belongs to the family of CeMIn$_5$ (M=Co, Rh, Ir) heavy fermion superconductors that have attracted attention in recent years due to the rich variety of strongly correlated electron phenomena observed in these materials. The CeRhIn$_5$ compound exhibits antiferromagnetism at $T_N$=3.8 K with a Sommerfeld coefficient $\gamma \sim 300$ mJ/mol K$^2$. The Neel temperature is suppressed at a critical pressure $P_c \sim$25 kbar, while superconductivity is found to coexist with antiferromagnetism above $\sim15$ kbar, reaching a maximum transition temperature $T_c=2.1$ K. de Haas van Alphen measurements reveal a divergence of the effective mass at $P_c$, but signatures of an antiferromagnetic (AFM) quantum critical point (QCP) from other measurements are masked by the occurrence of superconductivity in this pressure range. The substitution of Sn for In in CeRhIn$_5$ offers an alternative way to probe the possible AFM QCP in this system. Preliminary measurements suggest an AFM QCP in CeRhIn$_{5-x}$Sn$_x$ at $x \sim 0.75$ with robust non-Fermi liquid behavior occurring for $x >0.75$. The physical properties of the CeRh(In,Sn)$_5$ system will be discussed. [Preview Abstract] |
Wednesday, March 23, 2005 4:30PM - 4:42PM |
S39.00011: Evolution of Superconducting H$_{c2}$ Transition with La-Doping in Ce$_{1-x}$La$_x$CoIn$_5$ Johnpierre Paglione, M.A. Tanatar, E. Boaknin, D.G. Hawthorn, R.W. Hill, M. Sutherland, Louis Taillefer, C. Petrovic Recent measurements of the heavy-fermion superconductor CeCoIn$_5$ have revealed a field-tuned quantum critical point which coincides with a {\it first-order} superconducting transition H$_{c2}$ as $T \to 0$ [1], resulting in a completely unique and intriguing H-T phase diagram with no known magnetic phase. By substituting La for Ce, a gradual destruction of the superconducting phase allows an investigation of the correlation between the order of H$_{c2}$ and the field-tuned quantum critical behaviour. Here we report low temperature heat and charge transport measurements of Ce$_{1-x}$La$_x$CoIn$_5$ as a function of field and doping, revealing an intriguing evolution of the quantum critical behaviour in this system. \newline \newline [1] J. Paglione {\it et al.}, Phys. Rev. Lett. 91, 246405 (2003). [Preview Abstract] |
Wednesday, March 23, 2005 4:42PM - 4:54PM |
S39.00012: Quantum Critical Behavior of the Bose-Fermi Kondo Model with Ising Anisotropy Tae-Ho Park, Stefan Kirchner, Qimiao Si The existence of a continous quantum phase transition of the Bose-Fermi Kondo Model (BFKM) with a self-consistently determined bosonic bath has been demonstrated within the Extended Dynamical Mean Field Approach to the anisotropic Kondo lattice model and $\omega/T$-scaling near the quantum critical point(QCP)was found[1,2]. We study the quantum critical properties of the anisotropic BFKM with specified bath spectral function, where the spectrum of the bosonic bath vanishes in a power-law fashion with exponent $\gamma$ for small frequencies. Motivated by very recent results that the quantum to classical mapping for a related class of models fails[3,4]. We determine the critical local susceptibility using both the classical and quantum Monte Carlo approaches of Ref.5. Our results cover several values of $\gamma$ below and above the upper critical dimension of the classical model for temperatures down to 1\% of the bare Kondo scale. [1]D. Grempel and Q. Si, Phys. Rev. Lett. 91, 026402 (2003). [2]J.Zhu, D. Grempel, and Q. Si, Phys. Rev. Lett. 91, 156404 (2003). [3]L. Zhu, S. Kirchner, Q. Si nad A. Georges, Phys. Rev. Lett. in press (cond-mat/0406293). [4]M. Vojta, N. Tong, and R. Bulla, cond-mat/0410132. [5]D. Grempel and M. Rozenberg, Phys. Rev. B 60, 4702 (1999). [Preview Abstract] |
Wednesday, March 23, 2005 4:54PM - 5:06PM |
S39.00013: Two-Impurity Dynamical-Mean-Field-Theory Study of the Periodic Anderson Model Ping Sun, Gabriel Kotliar We solve the periodic Anderson model using a two impurity dynamical mean field theory via QMC. We obtain the temperature v.s. hybridization phase diagram. In the crossover region, we observe logarithmic temperature ($T$) dependence in energy. As the quantum critical point (QCP) is approached, both the Neel and the lattice Kondo temperatures decrease and the two lines do not tend to cross at a finite temperature. We observe strong ferromagnetic spin fluctuations near the QCP on the Kondo side. Our results indicate that the critical spin susceptibility is local in space at the QCP. [Preview Abstract] |
Wednesday, March 23, 2005 5:06PM - 5:18PM |
S39.00014: Finite Temperature Properties of Quantum Lifshitz Transitions between valence bond phases: An Example of `Local' Quantum Criticality Pouyan Ghaemi, Ashvin Vishwanath, Todadri Senthil We study finite temperature properties near quantum `Lifshitz' transitions between different valence bond solid states of two dimensional quantum magnets. They are the generic versions of phase transitions associated with the solvable Rokshar Kivelson points in quantum dimer models on bipartite lattices. This quantum critical point is described by a free theory that nevertheless has operators with non-trivial scaling dimension. We show that while correlators of such operators exhibit the expected scaling as a function of time, they do NOT show analogous scaling in space. In particular, in the scaling limit, all such correlators are purely LOCAL. In contrast, the zero temperature properties are conventional, and the correlators decay as a power law in both space and time. This provides a valuable microscopic example of how some kind of `local' criticality may arise at finite temperatures (in the scaling limit), although the underlying zero temperature critical point is itself not `local' in any sense. We examine the underlying reasons for this unusual behaviour, present the exact local dynamical correlation functions at finite T for these operators, and the effect of irrelevant operators on the scaling limit results described above. [Preview Abstract] |
Wednesday, March 23, 2005 5:18PM - 5:30PM |
S39.00015: Extended-DMFT Study of Quantum Phase Transitions in a Kondo Lattice: Dynamical Large-N limit Stefan Kirchner, Lijun Zhu, Qimiao Si In one approach to the quantum critical heavy fermion metals, Kondo lattice systems are studied through self-consistent Bose-Fermi Kondo Model (BFKM) within the extended dynamical mean field theory. In the case with spin-rotational invariance, this model is still difficult to study theoretically or numerically. Very recently, it has been shown[1,2] that a dynamical large-N generalization provides an access to the quantum critical behavior of the spin-rotationally-invariant BFKM with a sub-ohmic boson spectral function. Here, we carry out a self-consistent EDMFT study of the model in this large-N limit. We determine the extent to which a second-order quantum phase transition exists in this limit for two- and three-dimensional spin fluctuations, as well as the critical exponents of the magnetic dynamics. [1] L. Zhu, S. Kirchner, Q. Si, and A. Georges, Phys. Rev. Lett, in press (cond-mat/0406293). [2] S. Kirchner, L. Zhu, and Q. Si, Physica B, in press (cond-mat/0407307). [Preview Abstract] |
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S39.00016: Out-of-Equilibrium Transport near a Quantum Phase Transition Stefan Kirchner, Lijun Zhu, Qimiao Si Non-equilibrium properties are expected to be particularly rich at a second order quantum phase transition, given that statics and (imaginary time) dynamics are already mixed at the equilibrium level. The issue has so far received only limited study, partly because equilbrium methods are not readily generalizable to non-equilibrium situations. Here we consider the quantum critical point of a Bose-Fermi Kondo model, which we have recently shown[1] to model the magnetic quantum dot systems[2]. We extend the saddle-point equations in a dynamical large-N limit[3] to the Keldysh contours, and determine the linear and non-linear conductance in the quantum critical regime. [1] S. Kirchner, L. Zhu, Q. Si, and D. Natelson, to be published (2004). [2] A. N. Pasupathy et al., Science {\bf 306}, 86 (2004). [3] L. Zhu, S. Kirchner, Q. Si, and A. Georges, Phys. Rev. Lett, in press; cond-mat/0406293. [Preview Abstract] |
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S39.00017: Magnetic field-tuned quantum critical point in CeAuSb$_2$ Luis Balicas, Satoru Nakatsuji, Hannoh Lee, Pedro Schlottmann, Timothy P. Murphy, Zachary Fisk Here we report on the anomalous metallic properties of CeAuSb$_ {2}$. At $H$ = 0, CeAuSb$_{2}$ displays AF ordering at $T_{N}$ = 6.0 K. Above $T_{N}$, the resistivity \textit{$\rho $} displays a $T^{\alpha }$ dependence with $\alpha \quad <$ 1 and $C_{e}$/$T$ has the -\textit{lnT} dependence characteristic of NFL behavior. For $T \quad <$ $T_{N}$, $\rho $ has the \textit{AT}$^{2}$ FL-like dependence and the extrapolation of $C_{e}$/$T$ to $T$ = 0 yields a Sommerfeld coefficient of $\gamma \quad \sim $ 0.1 J/mol.K$^{2}$, so that CeAuSb$_{2}$ is to be considered a heavy- Fermion system. A magnetic field along the inter-plane direction leads to two subsequent metamagnetic transitions and the concomitant \textit {continuous} suppression of $T_{N}$ to $T$ = 0 at $H_{C}$ = 5.3 $\pm $ 0.2 T. As the AF phase boundary is approached from the paramagnetic (PM) phase, $\gamma $ is enhanced and the $A$ coefficient of the resistivity diverges as $H-H_{C}^{-1}$. As $T$ is lowered for $H \quad \sim \quad H_{C}$, the $T$-dependence of \textit {$\rho $} and $C_{e}$/$T$ is sub-linear and -\textit{ln} $T$, respectively. These observations suggest the existence of a field-induced QCP at $H_{C}$. At higher fields an unconventional $T^{3}$- dependence emerges and becomes more prominent as $H$ increases, suggesting that the FL state is \textit{not} recovered for $H \quad >> \quad H_{C}$. [Preview Abstract] |
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