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.     

Non-Fermi-liquid behavior of impurity spins in the anisotropic Heisenberg chain

We consider a U(1)-invariant model consisting of the integrable anisotropic Heisenberg chain of arbitrary spin S embedding an impurity of spin S′. The impurity is assumed located on the mth link of the chain and interacting only with both neighboring sites. The coupling of the impurity to the lattice can be tuned by the impurity rapidity. The model is then integrable as a function of two continuous parameters (the anisotropy and the impurity rapidity) and two discrete variables (the spins S and S′). The thermodynamic Bethe ansatz equations are derived and used to analyze the small field and low temperature properties. Three situations have to be distinguished: (i) If S′ = S the impurity just corresponds to one more site in the chain. (ii) If S′ > S the impurity spin is only partially compensated at T = 0 and the entropy has an essential singularity at T = H = 0. (iii) If S′ < S the impurity is overcompensated, and again the entropy has an essential singularity at T = H = 0. The essential singularity gives rise to a quantum critical point and hence non-Fermi-liquid-like behavior as H and T tend to zero. While cases (i) and (iii) are analogous to the n-channel Kondo problem, case (ii) differs considerably as a consequence of critical behavior induced by the anisotropy.     

Non-Fermi-liquid behavior and double-exchange physics in orbital-selective Mott systems

We study a multiband Hubbard model in its orbital-selective Mott phase, in which localized electrons in a narrow band coexist with itinerant electrons in a wide band. The low-energy physics of this phase is shown to be given by a generalized double-exchange model. The high-temperature disordered phase thus differs from a Fermi liquid, and displays a finite scattering rate of the conduction electrons at the Fermi level, which depends continuously on the spin anisotropy.     

Spin nematic state as a candidate of the hidden order phase of URu2Si2

Motivated by the recent discovery of broken fourfold symmetry in the hidden order phase of URu2Si2 [R. Okazaki et al., Science 331, 439 (2011)], we examine a scenario of a spin nematic state as a possible candidate of the hidden order phase. We demonstrate that the scenario naturally explains most of experimental observations, and furthermore, reproduces successfully the temperature dependence of the spin anisotropy detected by the above-mentioned experiment in a semiquantitative way. This result provides strong evidence for the realization of the spin nematic order.     

Non-Fermi-liquid behavior of compressible electron states on the lowest Landau level

Experiments show that at even denominator fractions (EDF) (7p = 1=2;3=4;3=2,...) the two-dimensional electron gas (2DEG) in a strong magnetic field becomes compressible, has no energy gap, and demonstrates the presence of an ostensible Fermi surface (FS). Since this phenomenon results from a minimization of the interaction, rather than the kinetic energy, the EDF states might well exhibit deviations from a conventional Fermi liquid (FL). We show that impurity scattering and its interference with electronelectron and electron-phonon interactions provide examples of intrinsically non-Fermi-liquid (NFL) transport at EDFs.     

Anomalous behavior of the electrical resistivity of MnSi near the ferromagnetic phase transition

The results of measuring the electrical resistivity of a MnSi single crystal near the ferromagnetic phase transition at atmospheric and high pressures are reported. In contrast to the previous works, compressed helium is used as a pressure-transferring medium. It is shown that the temperature derivative of the electrical resistivity has the form of sharp maximum on the phase-transition line over the entire its length. Moreover, the observed maxima have a fine structure exhibiting a pronounced shoulder at temperatures slightly higher (by approximately 0.5 K) than the peak temperature, which indicates the existence of nontrivial fluctuations in the paramagnetic phase of MnSi. This feature disappears at a pressure of about 0.35 GPa, which corresponds to the tricritical-point coordinate.     

Non-Fermi-liquid behavior and d-wave superconductivity near the charge-density-wave quantum critical point

A scenario is presented, in which the presence of a quantum critical point due to formation of incommensurate charge density waves accounts for the basic features of the high temperature superconducting cuprates, both in the normal and in the superconducting states. Specifically, the singular interaction arising close to this charge-driven quantum critical point gives rise to the non-Fermi liquid behavior universally found at optimal doping. This interaction is also responsible for d-wave Cooper pair formation with a superconducting critical temperature strongly dependent on doping in the overdoped region and with a plateau in the optimally doped region. In the underdoped region a temperature dependent pairing potential favors local pair formation without superconducting coherence, with a peculiar temperature dependence of the pseudogap and a non-trivial relation between the pairing temperature and the gap itself. This last property is in good qualitative agreement with so far unexplained features of the experiments.     

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)     

Magnetostriction of monocrystalline URu2Si2

We report magnetostriction measurements on a monocrystalline sample of the heavy-fermion compound URu₂Si₂, below (at 4.2 K) and above (at 20 K) the Néel temperature. For a field direction along the tetragonal axis the magnetostriction is strongly anisotropic; the volume effect amounts to 1.4 × 10^-6T^-1 at 8 T and 4.2 K. For a field direction in the tetragonal plane the magnetostriction is nearly two orders of magnitude smaller, and less anisotropic.     

Aging in the ferromagnetic phase of terbium

We report on aging, rejuvenation and memory effects in the ferromagnetic phase of pure terbium. We have applied an experimental method specifically for investigating slow dynamics of spin glasses, because these effects cannot be interpreted as conventional diffusion after-effects. Results show that relaxation times of the magnetic response are widely distributed, and isothermal aging shifted the distribution towards longer durations. If the sample was heated/cooled after such isothermal aging, the relaxation times shortened as if aging was starting anew; the behavior resembles that in spin glasses. Uniform magnetization experiments indicate that, unlike rejuvenation in spin glasses, ferromagnetic correlations are not returned to disorder by thermal perturbations. In contrast with memory effects in spin glasses, the effects of isothermal aging cannot be recovered once these disappear, even if the system is returned to its initial temperature. The observed results can be explained as collective pinning of the domain walls for which the potential is given by a rugged temperature-sensitive energy landscape.     

Thermal transport in the hidden-order state of URu2Si2

We present a study of thermal conductivity in the normal state of the heavy-fermion superconductor URu2Si2. Ordering at 18 K leads to a steep increase in thermal conductivity and (in contrast with all other cases of magnetic ordering in heavy-fermion compounds) to an enhancement of the Lorenz number. By linking this observation to several other previously reported features, we conclude that most of the carriers disappear in the ordered state and this leads to a drastic increase in both the phononic and electronic mean free path.