Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session P39: Fermi Liquid and Strong Correlations |
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Sponsoring Units: DCMP Chair: Kun Yang, Florida State University Room: LACC 514 |
Wednesday, March 23, 2005 11:15AM - 11:27AM |
P39.00001: Critical Behavior of the Pauli Spin Susceptibility in A Strongly Correlated 2d Electron Liquid S. Anissimova, A.A. Shashkin, S.V. Kravchenko, M.R. Sakr, V.T. Dolgopolov, T.M. Klapwijk We have performed measurements of the thermodynamic
magnetization and density of states in a low-disordered,
strongly correlated 2D electron system in silicon. We have
found that the spin susceptibility of band electrons (Pauli
spin susceptibility) grows by almost an order of magnitude as
the electron density ($n_s$) is reduced, behaving critically
near $n_s=n_\chi\approx8\times10^{10}$~cm$^{-2}$. This
provides thermodynamic evidence for the existence of a phase
transition. The density $n_\chi$ is coincident within the
experimental uncertainty with the critical density $n_c$ for
the metal-insulator transition in clean samples. The nature of
the low-density phase ($n_s |
Wednesday, March 23, 2005 11:27AM - 11:39AM |
P39.00002: Thermodynamic Magnetization of Strongly Correlated 2d Electrons in Perpendicular Magnetic Fields Ananth Venkatesan, S. Anissimova, S.V. Kravchenko, A.A. Shashkin, V.T. Dolgopolov, M.R. Sakr, T.M. Klapwijk We will report measurements of thermodynamic magnetization ($M$) of strongly correlated 2D electrons in silicon in perpendicular magnetic fields. We see sawtooth oscillations of the magnetization as a function of the electron density, $n_s$. Near the integer filling factors, the slope $\partial M/ \partial n_s$ exceeds the maximum possible non-interacting value pointing to the existence of the regions with the negative thermodynamic compressibility. Comparing $\partial M/ \partial n_s$ on both sides of the spin gaps, we deduce the $g$-factor. The latter is found to be close to its bare value $g=2$ even at low electron densities, where the critical behavior of the spin susceptibility has been observed in similar systems. This indicates that it is the effective mass, rather than the $g$-factor, that is responsible for the giant enhancement of the spin susceptibility near the metal-insulator transition. [Preview Abstract] |
Wednesday, March 23, 2005 11:39AM - 11:51AM |
P39.00003: Precursors of 1D behavior for $D>1$: evolution of the non-analytic correction to the Fermi-liquid behavior Ronojoy Saha, Dmitrii Maslov The Fermi-liquid forms of the specific heat ($C(T)$) and static spin susceptibility ($\chi_s$) acquire universal non-analytic corrections[1] and the degree of non-analyticity increase inversely with the dimensionality. This predicts that the strongest non-analyticity in the specific heat should be found in 1D, however bosonization shows that $C(T)$ is linear in $T$ in 1D. We resolve this paradox by showing that the general argument, for non-analyticity in $D>1$ at the second order in the interaction, breaks down in 1D due to a subtle cancellation and the non-analytic $T\ln T$ term in 1D occurs at the \emph{third} order for electrons with spin. We obtain the same result by considering the RG flow of the marginally irrelevant operator in the sine-Gordon theory. For spinless electrons, the non-analyticities in the particle-particle and particle-hole channels cancel out and the resulting $C(T)$ is linear in $T$. The singularity in the particle-hole channel causes non-analyticity in the spin susceptibility $\chi_s \propto \ln \max \{|Q|,|H|,T\}$ present at the second order[2]. [1]A.V. Chubukov and D.L. Maslov, Phys. Rev. B 68, 155113 (2003). [2]I.E. Dzyaloshinskii and A.I. Larkin, Sov. Phys. JETP 34, 422 (1972) [Preview Abstract] |
Wednesday, March 23, 2005 11:51AM - 12:03PM |
P39.00004: Quantum Correction to Conductivity Close to Ferromagnetic Quantum Critical Point in Two Dimensions: Ballistic Regime Indranil Paul, Catherine P\'{e}pin, Boris Narozhny, Dmitri Maslov We study a two-dimensional disordered itinerant electron system close to a ferromagnetic quantum critical point. In the ballistic regime we calculate the temperature dependence of longitudinal conductivity as correction to the classical Drude term. Near the quantum critical point this temperature dependence has an exponent one-third, which is distinct from the linear temperature dependence of Fermi liquids. Away from the quantum critical point the temperature dependence crosses over to the usual Fermi liquid type. The origin of this behaviour is due to the difference in the two regimes in the momentum transferred by the spin fluctuations to the electrons during elastic scattering. Away from the criticality the momentum transferred depends on the mass of the spin fluctuations, while close to the criticality it depends on the Landau damping which brings additional temperature dependence. [Preview Abstract] |
Wednesday, March 23, 2005 12:03PM - 12:15PM |
P39.00005: Corrections to Fermi Liquid theory in 2D in a magnetic field Andrey Chubukov, Joseph Betouras, Dmitri Efremov In this work, we consider a Fermi liquid in two dimensions in a magnetic field, and study the effects of the Zeeman splitting on thermodynamics. We derive the temperature dependence of the spin susceptibility $\chi_s (T)$ from the thermodynamic potential, and show explicitly how $2p_F$ scattering gives rise to a non- analytic temperature dependence of the susceptibility. We explain why small momentum scattering does not give rise to non-analytic $\chi_s (T)$. We discuss experimental implications of this result. [Preview Abstract] |
Wednesday, March 23, 2005 12:15PM - 12:27PM |
P39.00006: Non-perturbative behavior of the Pomeranchuk quantum phase transition of a nematic Fermi fluid Michael Lawler, Victoria Fernandez, Eduardo Fradkin A nematic phase of an electron gas was predicted by Oganesyan et. al.[1] using a mean field approach by tuning the quadrupolar Landau paremeter $F_2$ to the Pomeranchuk quantum critical point at $F_2\sim-1$. We will present a study of the behavior at this QCP beyond the perturbative results of [1] using non- perturbative methods of higher dimensional bosonization. We extend the results on the Fermion residue calculated by Castro Neto and Fradkin for the Landau fermi liquid phase[2] to this case and present a calculation of the Fermion Green's Function at the critical point. [1] Oganesyan, V., Kivelson, S. A., and Fradkin, E., Phys. Rev. B. {\bf 64} 195109 (2001) [2] Castro Neto, A. H., Fradkin, E. H., Phys. Rev. B. {\bf 51} 4084 (1995) [Preview Abstract] |
Wednesday, March 23, 2005 12:27PM - 12:39PM |
P39.00007: Magnetic impurity in an itinerant Anti-Ferromagnet: Undressing the Kondo effect Vivek Aji, Chandra Varma, Ilya Vekhter We study the undressing of the Kondo effect in the aniferromagnetic phase of an itinerant metal. Expressed in terms of the quasiparticles of the AF, the Kondo interaction induces a new relevant operator that leads to incomplete screening and the ground state is no longer a spin singlet. We show how this comes about by expressing the exchange Hamiltonian in terms of the irreducible representation of the square lattice antiferromagnet and performing a renormalisation group calculation to obtain the ground state properties. [Preview Abstract] |
Wednesday, March 23, 2005 12:39PM - 12:51PM |
P39.00008: Deconstruction of the Kondo Effect near the Antiferromagnetic Quantum Critical Point Hideyaki Maebashi, Kazumasa Miyake, Chandra Varma The problem of a spin-1/2 magnetic impurity in a lattice near an antiferromagnetic transition of the host lattice is considered. Asymptotically near the critical point, a multichannel degenerate Kondo problem is realized; the number of channels depends on the symmetry of the lattice and the symmetry of the antiferromagnetic ordering vector. Besides its intrinsic interest, the problem is an essential ingredient in the problem of quantum critical points in heavy- fermions. [Preview Abstract] |
Wednesday, March 23, 2005 12:51PM - 1:03PM |
P39.00009: Anomalous scaling at the quantum critical point in itinerant antiferromagnets Artem Abanov, Andrey Chubukov We show that Hertz $\phi^4$ theory of quantum criticality is incomplete as it misses anomalous non-local contributions to the interaction vertices. For antiferromagnetic quantum transitions, we found that the theory is renormalizable only if the dynamical exponent $z=2$. The upper critical dimension is still $d= 4-z =2$, however the number of marginal vertices at $d=2$ is infinite. As a result, the theory has a finite anomalous exponent already at the upper critical dimension. We show that for $d<2$ the Gaussian fixed point splits into two non-Gaussian fixed points. For both fixed points, the dynamical exponent remains $z=2$. [Preview Abstract] |
Wednesday, March 23, 2005 1:03PM - 1:15PM |
P39.00010: Interacting electrons in 2D in the presence of van Hove singularities and phonons Shan-Wen Tsai, Antonio H. Castro Neto, David K. Campbell We have recently extended the RG approach to interacting electrons\footnote{R. Shankar, Rev. Mod. Phys. {\bf 66} 129 (1994).} to include electron-phonon interactions\footnote{S.-W. Tsai, A. H. Castro Neto, R. Shankar, and D. K. Campbell, {\it ``Renormalization Group Approach to Strong-Coupled Superconductors''}, cond-mat/0406174}. We now apply this method to study van Hove singularities. We consider the 2D Hubbard model at half-filling and use the two-patch model. Without phonons, there is a spin-density wave instability due to ($\pi$,$\pi$) nesting. We first consider isotropic phonons, which suppress this instability channel. Angle-resolved photoemission spectroscopy data have suggested that electron-phonon interactions in the cuprates are highly anisotropic\footnote{T. P. Devereaux, T. Cuk, Z.-X. Shen, N. Nagaosa, Phys. Rev. Lett. {\bf 93}, 117004 (2004)}. There is an out-of-phase buckling mode of the oxygen atoms that couples strongly to electronic states in the anti-nodal direction and a breathing mode of the copper-oxygen bond that couples strongly to nodal electronic states. We study the effect of such phonons in our simplified model of interacting electrons. The retardation effects give important corrections to the imaginary-part of the electron self-energy. We also study the competition between the spin-density wave and the $s$- and $d$-wave superconducting instabilities. [Preview Abstract] |
Wednesday, March 23, 2005 1:15PM - 1:27PM |
P39.00011: Renormalization-group treatment of the large-$N$ $t$-$J$ model Antonio H. Castro Neto, Shan-Wen Tsai, Ziqiang Wang, David K. Campbell Renormalization-group techniques for interacting electrons \footnote{R. Shankar, Rev. Mod. Phys. {\bf 66} 129 (1994)} are applicable to systems where the interactions are small compared to the Fermi energy, $U < E_F$. This condition is not satisfied in some systems of interest, such as the cuprates. The limit of large $U$ has been studied by starting from the $t$-$J$ model and applying slave-boson techniques to project out double occupied states. The resulting action can then be solved by saddle point calculations. We start from the Fermi liquid solution\footnote{M. Grilli and G. Kotliar, Phys. Rev. Lett. {\bf 64}, 1170 (1990)} and employ the renormalization-group approach to treat the leading order fluctuations of the bosonic fields in the $1/N$ expansion. We use a recently developed method\footnote{S.-W. Tsai, A. H. Castro Neto, R. Shankar, and D. K. Campbell, ``{\it Renormalization Group Approach to Strong-Coupled Superconductors},'' cond-mat/0406174} that allows electron-electron and electron-boson interactions to be treated on an equal footing. With this starting point, the renormalization-group approach can be safely applied since the interaction terms involving the fluctuations are of order $1/N$, and therefore much smaller than the Fermi energy. We study the self-energy corrections and the instabilities of this system, including the energy scale for the transitions. [Preview Abstract] |
Wednesday, March 23, 2005 1:27PM - 1:39PM |
P39.00012: Superconductivity in charge Kondo systems Maxim Dzero, Joerg Schmalian I will present a theory of superconductivity in charge Kondo systems, materials with resonant quantum valence fluctuations, in the regime where the transition temperature is comparable to the charge Kondo resonance. I will discuss superconductivity induced by charge Kondo impurities, study how pairing of a superconducting host is enhanced due to charge Kondo centers and investigate the interplay between Kondo-scattering and inter-impurity Josephson coupling. I also will discuss the implications of above mentioned theory for Tl-doped PbTe, which has recently been identified as a candidate charge Kondo system. [Preview Abstract] |
Wednesday, March 23, 2005 1:39PM - 1:51PM |
P39.00013: Luttinger-Liquid signature in scanning tunneling spectra of Li0.9Mo6O17 R. Matzdorf, J. Hager, M.A. Cazalilla, R. Jin, J. He, D. Mandrus, E.W. Plummer We present low-temperature scanning tunneling spectroscopy data from the quasi one-dimensional purple bronze Li$_{0.9}$Mo$_{6}$O$_{17}$. Our spectra show clearly a power-law behavior in density of states around Fermi-energy (-50meV $<$ E $<$ +50meV) with an exponent of $\alpha $ = 0.6 . Temperature dependent spectra between T = 5K and 50K are well-described using a model that involves tunneling into a Luttinger-Liquid at finite temperature. We do not observe any signature in the density of states near T = 24K where a insulator-to-metal transition has been reported. Finally we will discuss our data within the model of a zero bias anomaly (ZBA). However, this model does not describe the experimental data as well as the Luttinger-model does. (Oak Ridge national Laboratory, managed by UT-Battelle, LLC, for the U.S. Dept. of Energy under contract DE-AC05-00OR22725) [Preview Abstract] |
Wednesday, March 23, 2005 1:51PM - 2:03PM |
P39.00014: Doping dependent isotope effects of the quasi-1D electron-phonon system: comparison with the high-temperature superconductors Ian Bindloss The weak-coupling quantum phase diagrams of the one-dimensional (1D) Holstein-Hubbard and Peierls-Hubbard models are computed near half-filling, using a multi-step renormalization group technique. If strong enough, the electron-phonon interaction induces a spin gap. The spin gap, which determines the superconducting pairing energy, depends strongly on the band filling and decreases monotonically as the system is doped away from half-filling. However, the superconducting susceptibility exhibits a different doping dependence; it can vary non- monotonically with doping and exhibit a maximum at an "optimal" value of the doping. For a quasi-1D array of weakly coupled, fluctuating 1D chains, the superconducting transition temperature $T_c$ exhibits a similar non-monotonic doping dependence. The effect of changing the ion mass (isotope effect) on $T_c$ is found to be largest near half-filling and to decrease rapidly upon doping away from half-filling. The isotope effect on the spin gap is the opposite sign as the isotope effect on $T_c$. We discuss qualitative similarities between these results and properties of the high-temperature superconductors. [Preview Abstract] |
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P39.00015: Non-equilibrium quantum phase transition in an itinerant electron system Dima Feldman Recently there was much interest in quantum ferromagnetic transitions in one-dimensional itinerant electron systems. In particular, it was argued that spontaneous magnetization of the electrons might explain the 0.7 anomaly in quantum wires. We investigate the effect of an applied voltage bias on the ferromagnetic transition for one-dimensional itinerant electrons, and determine the critical behavior near the phase transition point. [Preview Abstract] |
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