Showing papers on "Fermi liquid theory published in 1998"

Luttinger Liquid Behavior in Carbon Nanotubes

Abstract: An interacting one-dimensional (1D) electron system is predicted to behave very differently than its higher-dimensional counterparts. Coulomb interactions strongly modify the properties away from those of a Fermi liquid, resulting in a Luttinger liquid (LL) characterized by a power-law vanishing of the density of states at the Fermi level. Experiments on one-dimensional semiconductor wires and fractional quantum Hall conductors have been interpreted using this picture, but questions remain about the connection between theory and experiment. Recently, single-walled carbon nanotubes (SWNTs) have emerged as a new type of 1D conductor that may exhibit LL behavior. Here we present measurements of the conductance of individual ropes of such SWNTs as a function of temperature and voltage. Power law behavior as a function of temperature or bias voltage is observed: G~ T^a and dI/dV ~ V^a. Both the power-law functional forms and the inferred exponents are in good agreement with theoretical predictions for tunneling into a LL.

Non-Fermi Liquid Behavior and Griffiths Phase in f-Electron Compounds

Abstract: We study the interplay among disorder, RKKY, and Kondo interactions in $f$-electron alloys. We argue that the non-Fermi liquid behavior observed in these systems is due to the existence of a Griffiths phase close to a quantum critical point. The existence of this phase provides a unified picture of a large class of materials. We also propose new experiments that can test these ideas.

Truncation of a Two-Dimensional Fermi Surface due to Quasiparticle Gap Formation at the Saddle Points

Abstract: We study a two-dimensional Fermi liquid with a Fermi surface containing the saddle points $(\ensuremath{\pi},0)$ and $(0,\ensuremath{\pi})$. Including Cooper and Peierls channel contributions leads to a one-loop renormalization group flow to strong coupling for short range repulsive interactions. In a certain parameter range the characteristics of the fixed point, opening of a spin and charge gap, and dominant pairing correlations are similar to those of a two-leg ladder at half-filling. We argue that an increase of the electron density leads to a truncation of the Fermi surface to only four disconnected arcs.

SU(2) formulation of the t−J model: Application to underdoped cuprates

Abstract: We develop a slave-boson theory for the $t\ensuremath{-}J$ model at finite doping that respects an SU(2) symmetry: a symmetry previously known to be important at half filling. The mean-field phase diagram is found to be consistent with the phases observed in the cuprate superconductors, which contain $d$-wave superconductor, spin-gap, strange metal, and Fermi-liquid phases. The spin-gap phase is best understood as the staggered flux phase, which is nevertheless translationally invariant for physical quantities. The physical electron spectral function shows small Fermi segments at low doping that continuously evolve into the large Fermi surface at high-doping concentrations. The close relation between the SU(2) and the U(1) slave-boson theory is discussed. The low-energy effective theory for the low-lying fluctuations is derived and additional lying modes [which were overlooked in the U(1) theory] are identified.

Correlated transport and non-Fermi-liquid behavior in single-wall carbon nanotubes

Abstract: We derive the effective low-energy theory for single-wall carbon nanotubes including the Coulomb interactions among electrons. The generic model found here consists of two spin- $${1 \over 2}$$ fermion chains which are coupled by the interaction. We analyze the theory using bosonization, renormalization-group techniques, and Majorana refermionization. Several experimentally relevant consequences of the breakdown of Fermi liquid theory observed here are discussed in detail, e.g., magnetic instabilities, anomalous conductance laws, and impurity screening profiles.

k-Dependent Electronic Structure, a Large "Ghost" Fermi Surface, and a Pseudogap in a Layered Magnetoresistive Oxide

Abstract: The k-dependent electronic structure of the low temperature ferromagnetic state of La 1.2Sr1.8Mn2O7 was measured using angle-resolved photoemission spectroscopy and calculated using the local spin density approximation (LSDA). The measured near-Fermi energy states display E vs k and symmetry relationships which agree relatively well with the LSDA prediction through much of the Brillouin zone, and the locus of lowest energy excitations matches the predicted large Fermi surface quite well. However, the spectral features are too broad to be well described as Fermi-liquid-like quasiparticles, and they are strongly suppressed from the Fermi energy, i.e., there is a pseudogap in the excitation spectrum. We discuss the spectral properties in terms of strong coupling to a local effect such as a lattice distortion. [S0031-9007(98)06522-3] PACS numbers: 71.30. + h, 71.20.Lp, 72.80.Ga, 79.60.Bm

Fermi systems with strong forward scattering

Abstract: We review the theory of interacting Fermi systems whose low-energy physics is dominated by forward scattering, that is scattering processes generated by effective interactions with small momentum transfers. These systems include Fermi liquids as well as several important non-Fermi-liquid phases: one-dimensional Luttinger liquids, systems with long-range interactions, and fermions coupled to a gauge field. We report results for the critical dimensions separating different 'universality classes' and discuss the behaviour of physical quantities such as the momentum distribution function, the single-particle propagator and low-energy response functions in each class. The renormalization group for Fermi systems will be reviewed and applied as a link between microscopic models and effective lowenergy theories. Particular attention is paid to conservation laws, which constrain any effective low-energy theory of interacting Fermi systems. In scattering processes with small momentum transfers the velocity of each ...

Transverse transport in (TM)2X organic conductors: possible evidence for a Luttinger liquid

Abstract: We present c-axis resistivity measurements performed on the organic conductors and under pressure. The aim is to probe the density of states of quasi-one dimensional compounds the high temperature properties of which are those of a Luttinger liquid. It is found that the 1-D Luttinger description breaks down below a specific pressure-dependent temperature, giving rise to a transient regime. The Fermi liquid behaviour is however restored at low temperature i.e. around 10 K, as evidenced by NMR measurements. Accordingly, two different energy scales 100 K and 10 K are required to get a fair understanding of all observed physical phenomena. Our interpretation supports the picture of a power law exponent for the correlation functions of the order of 0.25–0.30.

A local moment approach to the Anderson model

Abstract: A theory is developed for the single-particle spectra of the symmetric Anderson model, in which local moments are introduced explicitly from the outset. Dynamical coupling of single-particle processes to low-energy spin-flip excitations leads, within the framework of a two-self-energy description, to a theory in which both low- and high-energy spectral features are simultaneously captured, while correctly preserving Fermi liquid behaviour at low energies. The atomic limit, non-interacting limit and strong-coupling behaviour of the spectrum are each recovered. For strong coupling in particular, both the exponential asymptotics of the Kondo resonance and concomitant many-body broadening of the Hubbard satellite bands are shown to arise naturally within the present approach.

Some comments on Kondo lattices and the Mott transition

Abstract: The so called exhaustion problem occurs when few electrons have to screen many spins in a metal with magnetic impurities. A singlet Fermi liquid ground state is possible only if all impurities are “isotropized” in such a way as to suppress their entropy. That takes a time and the corresponding energy limits the Fermi liquid range. The present note explores that issue of time and energy scales, and it concludes that is much smaller than the single impurity Kondo temperature. Similarly the relevant energy scale is proportional to the number of electrons. Recent results on the Mott metal insulator transition in infinite dimension are reconsidered in the light of these results: controversies in that respect are shown to reduce to a simple physical question, with no firm answer as to now.

Continuous Renormalization for Fermions and Fermi Liquid Theory

Abstract: I derive a Wick ordered continuous renormalization group equation for fermion systems and show that a determinant bound applies directly to this equation. This removes factorials in the recursive equation for the Green functions, and thus improves the combinatorial behaviour. The form of the equation is also ideal for the investigation of many-fermion systems, where the propagator is singular on a surface. For these systems, I define a criterion for Fermi liquid behaviour which applies at positive temperatures. As a first step towards establishing such behaviour in d≥ 2, I prove basic regularity properties of the interacting Fermi surface to all orders in a skeleton expansion. The proof is a considerable simplification of previous ones.

Magnetic phase diagrams of Kondo compounds Ce0.75La0.25B6 and Ce0.6La0.4B6

Abstract: We measured the elastic and thermal properties to examine the competing effect between the intersite interactions and the Kondo coupling in Ce 0.75 La 0.25 B 6 and Ce 0.6 La 0.4 B 6 with the Γ 8 ground state. The huge softening of the transverse C 44 mode of both compounds at low temperatures indicates a remarkable fluctuation of the quadrupolar moments O y z , O z x and O x y with Γ 5 symmetry. In the magnetic phase diagram of Ce 0.75 La 0.25 B 6 , we found a new ordered phase IV in addition to the antiferroquadrupolar phase II and the antiferromagnetic phase III. The compound Ce 0.6 La 0.4 B 6 , however, shows the Fermi liquid state without the long-range order at low fields and transits into the ordered phase II or III in the magnetic field above 16 kOe.

Observation of quantum oscillations in the electrical resistivity of SrRuO3

Abstract: We report the observation of quantum oscillations in the electrical resistivity of a high-quality thin film of the itinerant ferromagnet ${\mathrm{SrRuO}}_{3}.$ Our study demonstrates the existence of long-lived fermion quasiparticles at low temperatures, and strongly suggests that the ground state of ${\mathrm{SrRuO}}_{3}$ is a Fermi liquid, even though ac and dc conductivity measurements at higher temperatures show anomalous metallic behavior. The implications of these results are discussed.

Inducement of non-Fermi-liquid behavior with a magnetic field

Abstract: Using Ag doping of the nearly magnetic heavy-fermion system ${\mathrm{CeCu}}_{6}$ to vary the onset of antiferromagnetism between ${T}_{N}=0$ and 0.8 K, we have found a large region of the phase diagram where magnetic field can reach the quantum critical point ${(T}_{N}\ensuremath{\rightarrow}0)$ with sufficiently strong antiferromagnetic correlations remaining to produce non-Fermi-liquid (NFL) behavior. In this field and composition regime, the ${\mathrm{CeCu}}_{6\ensuremath{-}x}{\mathrm{Ag}}_{x}$ samples exhibit the typical NFL temperature dependencies for the various measured parameters over a broad range of temperature down to 100 mK. Application of higher fields to these samples causes entry into the Fermi-liquid regime. Due to the ease of changing magnetic fields when establishing the phase diagram at low temperatures, the increased efficacy of field suppression of ${T}_{N}$ versus that achieved by pressure, and the fact that magnetic field does not change the volume as do both pressure and doping, magnetic field offers distinct advantages as a method for exploring the crossover between antiferromagnetic, non-Fermi-liquid, and Fermi-liquid behavior in the vicinity of the quantum critical point.

LDA++ approach to electronic structure of magnets: correlation effects in iron

Abstract: A novel approach to investigation of correlation effects in the electronic structure of magnetic crystals which takes into account a frequency dependence of the self energy (so called ``LDA++ approach'') is developed. The fluctuation exchange approximation is generalized to the spin-polarized multi-band case and its local version is proposed. As an example, we calculate the electronic quasiparticle spectrum of ferromagnetic iron. It is shown that the Fermi liquid description of the bands near the Fermi level is reasonable, while the quasiparticle states beyond approximately 1 eV range are strongly damped, in agreement with photoemission data. The result of the spin-polarized thermoemission experiment is explained satisfactory. The problem of satellite structure is discussed.

Transport Properties of Heavy Fermion Compounds

Abstract: A technique for measuring the electrical resistivity and absolute thermopower is presented for pressures up to 30 GPa, temperatures down to 25 mK and magnetic fields up to 10 T. With the examples of CeCu2Ge2 and CeCu2Si2 we focus on the interplay of normal phase and superconducting properties. With increasing pres- sure, the behaviour of CeCu2Ge2 evolves from that of an antiferromagnetically ordered Kondo system to that characteristic of an intermediate valence compound as the Kondo temperature increases by about two orders of magnitude. In the pressure window 8-10 < P < 20 GPa, a superconducting phase occurs which com- petes at low pressure with magnetic ordering. For CeCu2Si2 the effective mass of carriers is probed by both the coefficient of the Fermi liquid law and the ini- tial slope of the upper critical field. The magnetic instability is studied no- tably for CeRu2Ge2 and Yb-based compounds for which pressure-induced magnetic ordering tends to develop. Finally, contrary to conventional wisdom, we argue that in heavy fermions a large part of the residual resistivity is most likely not independent of temperature; tentatively ascribed to Kondo hole, it can be very pressure as well as sample dependent. [electrical resistivity, thermoelectric power, heavy fermion, magnetic order, superconductivity]

Magnetic correlations and quantum criticality in the insulating antiferromagnetic, insulating spin liquid, renormalized Fermi liquid, and metallic antiferromagnetic phases of the Mott system V2O3

Abstract: Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V_2O_3) have been examined by magnetic thermal-neutron scattering. Specifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V_(2-y)O_3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V_2O_3, and the antiferromagnetic and paramagnetic phases of insulating V_(1.944)Cr_(0.056)O_3. While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a "single lobe'' spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V_2O_3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for ħω

Pd/Cu Site Interchange and Non-Fermi-Liquid Behavior in UCu{sub 4}Pd

Abstract: X-ray-absorption fine-structure measurements of the local structure in UCu{sub 4}Pd are described which indicate a probable lattice-disorder origin for non-Fermi-liquid behavior in this material. Short Pd-Cu distances are observed, consistent with (24{plus_minus}3){percent} of the Pd atoms occupying nominally Cu sites. A {open_quotes}Kondo disorder{close_quotes} model, based on the effect on the local Kondo temperature T{sub K} of this interchange and some additional bond-length disorder, agrees quantitatively with previous experimental susceptibility data, and therefore also with specific heat and magnetic resonance experiments. {copyright} {ital 1998} {ital The American Physical Society }

Multiply connected Fermi sphere and fermion condensation

Abstract: We examine the structure of the ground state of a homogeneous Fermi liquid beyond the instability point of the Fermi-like quasiparticle momentum distribution in the effective-functional method with a strong repulsive effective interaction. A numerical study of the initial stage of rearrangement of the ground state, based on a simple effective functional, showed that there exists a temperature T 0, above which the behavior of the system is the same as in the theory of fermion condensation, and for T

Phonon-mediated unconventional superconductivity in strongly correlated systems

Abstract: We propose an adiabatic approach for Hubbard models in the Fermi-liquid regime coupled to phonons. The Hubbard parameters are associated with the bandwidth $W$ via an interpolation formula between the trivial for $W$ strong- and weak-coupling limits of Hubbard models. Phonons are introduced via an adiabatic random-phase approximation scheme. We obtain simple conditions for phonon-driven instabilities in a Fermi liquid with short-ranged interactions. We report phonon-driven instabilities without nesting and describe the elimination of the Peierls instability in a nested system by Coulomb correlations. We also report the possibility for a phonon-driven phase separation (PS) instability as well as the strong enhancement of forward processes in the effective electron-phonon scattering near the phase separation instability. We show that the proximity to PS induces momentum decoupling (MD) in superconductivity which implies a tendency for decorrelation between the physics in the different regions of the Fermi surface. MD could induce anisotropic superconductivity with unconventional gap symmetry such as $d$ wave. Whether anisotropy in the high-${T}_{c}$ oxides is driven by MD or by anisotropic scattering (for example with spin fluctuations) becomes a crucial question. We discuss some qualitative implications of MD that explain puzzling qualitative aspects of superconductivity in the oxides and could advocate that MD is at the origin of anisotropies. Such effects are the marginality of the superconducting gap symmetry for the condensation free energy and the resulting possibility of gap symmetry transitions with the doping, the temperature dependence of the shape of the anisotropy, and the behavior of the anomalous dip above the gap in the density of states. We also show that in the MD regime the orthorhombic distortion of the ${\mathrm{CuO}}_{2}$ planes in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ could be sufficient to explain the mixing of $s$-gap components in the dominantly $d$-wave gap. On the other hand, if spin fluctuations mediate the pairing in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7},$ at least 25% of the condensate must be located in the chains. Our analysis could rehabilitate phonons as potential mediators of the pairing in all ``unconventional'' superconductors including heavy-fermion and organic compounds.

Thermodynamic properties of an ideal Fermi gas in an external potential with U=br(t) in any dimensional space

Abstract: The properties of an ideal Fermi gas in an external potential in any dimensional space are studied, based on the semiclassical (Thomas-Fermi) approximation. The general analytical expressions of the total particle number $N,$ density of states $D(\ensuremath{\varepsilon}),$ Fermi energy ${E}_{F},$ total energy $E,$ and heat capacity $C$ have been derived, where $N,$ $E,$ and $C$ are expressed by the Fermi integration. Moreover, the analytical expressions of the total energy $E,$ chemical potential \ensuremath{\mu}, and heat capacity $C$ in the high- and low-temperature approximations are given. From these results, how the characteristics of the Fermi gas depend on an external potential and the dimension of space is discussed.

Ultra-Low Temperature Magnetic Properties of Liquid 3He Films

Abstract: We report measurements of the nuclear magnetization of submonolayer liquid 3 He films adsorbed on a graphite substrate (Papyex) preplated by a monolayer of 4 He. In the submilliKelvin temperature range we observe a substantial enhancement of the nuclear magnetization with respect to the degenerate Fermi Liquid value. The unusual temperature dependence of this new contribution to the liquid 3 He film magnetization agrees well with that expected from the theory of weak disorder in two-dimensional (2D) correlated Fermion systems. The effects of disorder and reduced dimensionality suppress the superfluid transition at least to below 180 μK.

Interactions and scaling in a disordered two-dimensional metal

Abstract: We show that a non-Fermi liquid state of interacting electrons in two dimensions is stable in the presence of disorder and is a perfect conductor, provided the interactions are sufficiently strong. Otherwise, the disorder leads to localization as in the case of non-interacting electrons. This conclusion is established by examining the replica field theory in the weak disorder limit, but in the presence of arbitrary electron-electron interaction. Thus, a disordered two-dimensional metal is a perfect metal, but not a Fermi liquid.

The quantum-classical metal

Abstract: In a normal Fermi liquid, Landau9s theory precludes the loss of single-fermion quantum coherence in the low-energy, low-temperature limit. For highly anisotropic, strongly correlated metals, there is no proof that this remains the case, and quantum coherence for transport in some directions may be lost intrinsically. This loss of coherence should stabilize an unusual, qualitatively anisotropic non-Fermi liquid, separated by a zero-temperature quantum phase transition from the Fermi liquid state and categorized by the unobservability of certain interference effects. There is compelling experimental evidence for this transition as a function of magnetic field in the metallic phase of the organic conductor (TMTSF) 2 PF 6 (where TMTSF is tetramethyltetraselenafulvalene).

Electrical Conductivity of Interacting Fermions. II. Effects of Normal Scattering Processes in the Presence of Umklapp Scattering Processes

Abstract: The electrical resistivity due only to mutual Coulomb interaction of the d -dimensional lattice electron systems ( d ≥2) in the presence of Umklapp scattering processes is studied on the basis of the Fermi liquid theory. It is shown that normal scattering processes generally contribute to the resistivity if Umklapp scattering processes are present. This fact gives a natural explanation of the resistivity of the d =∞ Hubbard model which is determined only by the damping rate of quasi-particles, γ. In the case of d =2, however, it is shown that the resistivity is proportional to T 2 , T being the temperature, even when normal scattering processes, which give T 2 log T -contribution to γ, contribute to the resistivity. In the special case of the square lattice, where the transfer integrals are only between the nearest neighbors, the coefficient of the T 2 -term in the second order of the interaction is shown to diverge as (1/δ) log (1 / δ) when δ→0, δ being the doping rate away from half-filling.

ARPES results on Sr 2 RuO 4 : Fermi surface revisited

Abstract: The electronic band structure of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ has attracted considerable attention recently. However, it has also become a subject of an important controversy. Results of de Haas--van Alphen experiments yielded a Fermi surface consisting of two electronlike and one holelike sheets, in good agreement with the theoretical predictions. At the same time, results of angle-resolved photoemission spectroscopy (ARPES) measurements yielded one electronlike and two holelike sheets suggesting an extended van Hove singularity (evHS) similar to that found in cuprate high-temperature superconductors. In an effort to resolve this controversy we performed an extensive ARPES study using various incident photon energies. We found no conclusive evidence for an evHS.

Pressure-induced magnetically ordered Kondo lattice state in

Abstract: The effect of pressure on the electrical resistivity of several YbCu2Si2 samples was investigated up to 25 GPa and for 30 mK < T < 300 K. With increasing pressure the compound crosses from an intermediate valence state to a magnetic Kondo lattice state at a critical pressure GPa. Below P C, i.e. in the non-magnetic phase, is found at very low temperature, indicating the validity of the Fermi liquid description. On approaching the magnetic instability, the A coefficient and the residual resistivity increase strongly. Close to shows a pronounced maximum due to scattering by lattice defects. The pressure variation of the magnetic resistivity at high temperature is interpreted in the terms of a pressure induced change of the crystal field splitting.