Non-Fermi-liquid behavior in the periodic anderson model

We study the Mott metal-insulator transition in the periodic Anderson model with dynamical mean field theory (DMFT). Near the quantum transition, we find a non-Fermi-liquid metallic state down to a vanishing temperature scale. We identify the origin of the non-Fermi-liquid behavior as being due to magnetic scattering of the doped carriers by the localized moments. The non-Fermi-liquid state can be tuned by either doping or external magnetic field. Our results show that the coupling to spatial magnetic fluctuations (absent in DMFT) is not a prerequisite to realizing a non-Fermi-liquid scenario for heavy fermion systems.     

Topological crossovers near a quantum critical point

We study the temperature evolution of the single-particle spectrum ε-(p) and quasiparticle momentum distribution n(p) of homogeneous strongly correlated Fermi systems beyond a point where the necessary condition for stability of the Landau state is violated, and the Fermi surface becomes multi-connected by virtue of a topological crossover. Attention is focused on the different non-Fermi-liquid temperature regimes experienced by a phase exhibiting a single additional hole pocket compared with the conventional Landau state. A critical experiment is proposed to elucidate the origin of NFL behavior in dense films of liquid ³He.     

General properties of a magnetic-field-induced landau Fermi liquid in high-temperature superconductors and heavy fermion metals

It has been shown that the magnetic-field-induced transition from a non-Fermi-liquid state to a Fermi liquid state in the Tl₂Ba₂CuO_{6 + x} high-temperature superconductor is similar to a transition observed in heavy fermion metals. This behavior is explained in the theory of the Fermi condensate quantum-phase transition implying the existence of Landau quasiparticles. The Fermi condensate quantum-phase transition can be considered as a universal cause of the strongly correlated behavior observed in various metals and liquids such as high-temperature superconductors, heavy fermion metals, and two-dimensional Fermi systems.     

Non-Fermi-liquid effects in tunneling

Non-Fermi-liquid tunneling mechanisms in a quantum structure with its own two-dimensional continuum doped with transition metal impurities are considered. New physical realizations of the two-channel Kondo orbital model with mechanisms different from those previously described in literature occur in such quantum structures. The tunneling transparency is anomalously high owing to new channels generated by multiparticle Fermi-liquid resonances near the edge of the two-dimensional energy band in the process of tunneling. The widths of new edge resonances can be much smaller than the width of the “bare” non-Fermi-liquid resonance at the Fermi level in the banks. The additional scattering due to tunneling induces a transition from the non-Fermi-liquid to the Fermi-liquid state as the separation between the Fermi level in the banks and the two-dimensional band edge in the quantum well varies. Zh. éksp. Teor. Fiz. 114, 1466–1486 (October 1998)     

Instability of the non-Fermi-liquid state in a metal with d or f impurities

It is shown that the non-Fermi-liquid state is unstable with respect to scattering of multiparticle excitations with different quantum numbers by one another. As a result of the scattering, a multiparticle Fermi-liquid resonance forms at the Fermi level. An anomalous increase in the conductivity occurs as a result of a transition between the non-Fermi-liquid and Fermi-liquid states. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 10, 721–726 (25 May 1999)     

Transition in a Luttinger liquid with two-level impurities to the fermi-liquid state

The mechanisms leading to instability of the non-Fermi-liquid state of a Luttinger liquid with two-level impurities are proposed. Since exchange scattering in 1D systems is two-channel scattering in a certain range of parameters, several types of non-Fermi-liquid excitations with different quantum numbers exist in the vicinity of the Fermi level. These excitations include, first, charge density fluctuations in the Luttinger liquid and, second, many-particle excitations due to two-channel exchange interaction, which are associated with band-type as well as impurity fermion states. It is shown that mutual scattering of many-particle excitations of various types leads to the emergence of an additional Fermi-liquid singularity in the vicinity of the Fermi level. The conditions under which the Fermi-liquid state with a new energy scale (which is much smaller than the Kondo temperature) is the ground state of the system are formulated.     

Topological Scenario for High-Temperature Superconductivity in Cuprates

The structure of the joint phase diagram of high-temperature superconducting cuprates has been studied within the theory of fermion condensation. Prerequisites of the topological rearrangement of the Landau state with the formation of a flat band adjacent to the nominal Fermi surface have been established. The related non-Fermi-liquid behavior of cuprates in the normal phase has been studied with focus on the non-Fermi-liquid behavior of the resistivity ρ(T), including the observed crossover from the linear temperature behavior ρ(T, x) = A₁(x)T at doping levels x below the critical value x _c ^h corresponding to the boundary of the superconducting region to the quadratic temperature behavior at x > x _c ^h , which is incompatible with predictions of the conventional quantum-critical-point scenario. It has been demonstrated that the slope of the coefficient A₁(x) is universal and is the same on both boundaries of the joint phase diagram of cuprates in agreement with available experimental data. It has also been shown that the fermion condensate is responsible for pairing in the D-wave state in cuprates. The effective Coulomb repulsion in the Cooper channel, which prevents the existence of superconductivity in normal metals in the S channel, leads to high-temperature superconductivity in the D channel.     

Ferromagnetic Kondo lattice CeRuSi2 with non-Fermi-liquid behavior

The structure, electronic, thermodynamic, and magnetic properties of the CeRuSi₂ Kondo lattice with ferromagnetic ordering characterized by a small moment of the ground state are investigated. Anomalies in the temperature dependences of heat capacity and resistivity (unusual power or logarithmic behavior) observed in the low-temperature range indicate a non-Fermi-liquid behavior. The results are compared with those for other Ce_lRu _n X _m compounds and anomalous systems based on rare-earth elements and actinides that had been studied earlier.     

Solution of the two-channel Anderson impurity model: implications for the heavy fermion UBe13

We solve the two-channel Anderson impurity model using the Bethe-ansatz. We determine the ground state and derive the thermodynamics, obtaining the impurity entropy and specific heat over the full range of temperature. We show that the low-temperature physics is given by a line of fixed points describing a two-channel non-Fermi-liquid behavior in the integral valence regime associated with moment formation as well as in the mixed valence regime where no moment forms. We discuss the relevance for the theory of UBe13.     

Fate of the Wiedemann–Franz Law near Quantum Critical Points of Electron Systems in Solids

We introduce and analyze two different scenarios for violation of the Wiedemann–Franz law in strongly correlated electron systems of solids, close to a topological quantum critical point (TQCP) where the density of states N(0) diverges. The first, applicable to the Fermi-liquid (FL) side of the TQCP, involves a transverse zero-sound collective mode that opens a new channel for the thermal conductivity, thereby enhancing the Lorenz number L(0) relative to the value L0 =π² k _B ²/3e ² dictated by conventional FL theory. The second mechanism for violation of the WF law, relevant to the non-Fermi-liquid (NFL) side of the TQCP, involves the formation of a flat band and leads instead to a reduction of the Lorenz number.     

Magnetic ordering and non-Fermi-liquid behavior in the multichannel Kondo-lattice model

Scaling equations for the Kondo lattice in the paramagnetic and magnetically orderedphases are derived to next-leading order with account of spin dynamics. The results areapplied to describe various mechanisms of the non-Fermi-liquid (NFL) behavior in themultichannel Kondo-lattice model where a fixed point occurs in the weak-coupling region.The corresponding temperature dependences of electronic and magnetic properties arediscussed. The model describes naturally formation of a magnetic state with soft bosonmode and small moment value. An important role of Van Hove singularities in the magnonspectral function is demonstrated. The results are rather sensitive to the type ofmagnetic ordering and space dimensionality, the conditions for NFL behavior being morefavorable in the antiferromagnetic and 2D cases.     

Transition between non-Fermi-liquid and Fermi-liquid states as a result of tunneling

It is shown that additional scattering due to tunneling induces a transition of the system from a non-Fermi-liquid into a Fermi-liquid state as the distance between the Fermi level in the walls and the 2D-band edge is varied in a double-barrier quantum well, doped with transition-metal impurities and having an intrinsic two-dimensional continuum. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 12, 1009–1014 (25 June 1998)     

Orbital non-fermi-liquid behavior in cubic ruthenates

We peruse various anomalous physical responses of the cubic (ferromagnetic SrRuO3 and paramagnetic CaRuO3) ruthenates, such as fractional power-law conductivity, anomalous Raman line shapes, and Hall currents. We show how these exciting power-law observations are naturally described within a new, local (orbital) non-Fermi-liquid state arising from strong, multiorbital Coulomb interactions. Introducing a multiorbital, correlated model treated within the dynamical mean-field theory, we also find two distinct relaxation rates for relaxation of transport in complete agreement with experiment.     

Dynamical mean-field theory for pairing and spin gap in the attractive hubbard model

We solve the attractive Hubbard model for arbitrary interaction strengths within dynamical mean-field theory. We compute the transition temperature for superconductivity and analyze electron pairing in the normal phase. The normal state is a Fermi liquid at weak coupling and a non-Fermi-liquid state with a spin gap at strong coupling. Away from half filling, the quasiparticle weight vanishes discontinuously at the transition between the two normal states.     

Quantum limit in a quasi-one-dimensional conductor in a high tilted magnetic field

Recently, we have suggested Fermi-liquid–non-Fermi-liquid angular crossovers that may exist in quasi-one-dimensional (Q1D) conductors in high tilted magnetic fields (see A. G. Lebed, Phys. Rev. Lett. 115, 157001 (2015)). All calculations in the Letter were done by using the quasiclassical Peierls substitution method, whose applicability in high magnetic fields was questionable. Here, we solve a fully quantum mechanical problem and show that the main qualitative conclusions of the work cited above are correct. In particular, we show that in high magnetic fields, applied along one of the two main crystallographic axis, we have 2D electron spectrum, whereas, for directions of high magnetic fields far from the axes, we have 1D electron spectrum. The latter is known to promote non-Fermi-liquid properties. As a result, we expect the existence of Fermi-liquid–non-Fermi-liquid angular crossovers or phase transitions. Electronic parameters of Q1D conductor (Per)₂Pt(mnt)₂ show that such transitions can appear in feasible high magnetic fields of the order of H ? 20–25 T.     

One- and two-channel Kondo model with logarithmic Van Hove singularity: A numerical renormalization group solution

Simple scaling consideration and NRG solution of the one- and two-channel Kondo model in the presence of a logarithmic Van Hove singularity at the Fermi level is given. The temperature dependences of local and impurity magnetic susceptibility and impurity entropy are calculated. The low-temperature behavior of the impurity susceptibility and impurity entropy turns out to be non-universal in the Kondo sense and independent of the s–d coupling J. The resonant level model solution in the strong coupling regime confirms the NRG results. In the two-channel case the local susceptibility demonstrates a non-Fermi-liquid power-law behavior.     

Non-Fermi-liquid behavior in UCu4+xAl8−x compounds

We report on experimental studies of the Kondo physics and the development of non-Fermi-liquid scaling in UCu_4+xAl_8−x family. We studied 7 different compounds with compositions between x=0 and 2. We measured electrical transport (down to 65 mK) and thermoelectric power (down to 1.8 K) as a function of temperature, hydrostatic pressure, and/or magnetic field.Compounds with Cu content below x=1.25 exhibit long-range antiferromagnetic order at low temperatures. Magnetic order is suppressed with increasing Cu content and our data indicate a possible quantum critical point at x_cr≈1.15. For compounds with higher Cu content, non-Fermi-liquid behavior is observed. Non-Fermi-liquid scaling is inferred from electrical resistivity results for the x=1.25 and 1.5 compounds. For compounds with even higher Cu content, a sharp kink occurs in the resistivity data at low temperatures, and this may be indicative of another quantum critical point that occurs at higher Cu compositions.For the magnetically ordered compounds, hydrostatic pressure is found to increase the Néel temperature, which can be understood in terms of the Kondo physics. For the non-magnetic compounds, application of a magnetic field promotes a tendency toward Fermi-liquid behavior. Thermoelectric power was analyzed using a two-band Lorentzian model, and the results indicate one fairly narrow band (10 meV and below) and a second broad band (around hundred meV). The results imply that there are two relevant energy scales that need to be considered for the physics in this family of compounds.     

Non-fermi-liquid behavior of electron-spin fluctuations in an elemental paramagnet

We report for the first time, the observation of non-Fermi-liquid scaling behavior in an elemental paramagnetic metal. Both the dynamical susceptibility and the resistivity of beta-Mn are shown to display non-Fermi-liquid scaling over a relatively large temperature range at ambient pressure. The temperature dependence of the resistivity in beta-Mn is consistent with the existence of an antiferromagnetic zero-temperature phase transition or "quantum critical point." Since there is no site disorder in this pure element, we show that non-Fermi-liquid behavior observed in beta-Mn is not a consequence of summing over different local atomic environments, but a much more fundamental phenomenon.     

Quantum criticality in a double-quantum-dot system

We discuss the realization of the quantum-critical non-Fermi-liquid state, originally discovered within the two-impurity Kondo model, in double-quantum-dot systems. Contrary to common belief, the corresponding fixed point is robust against particle-hole and various other asymmetries and is unstable only to charge transfer between the two dots. We propose an experimental setup where such charge transfer processes are suppressed, allowing a controlled approach to the quantum-critical state. We also discuss transport and scaling properties in the vicinity of the critical point.