Showing papers in "Physica B-condensed Matter in 1990"
TL;DR: In this paper, the dc I-V curve and fluctuation spectrum of a Josephson junction shunted by an arbitrary frequency-dependent impedance for very small and very large Josephson coupling were calculated.
Abstract: We have calculated the dc I-V curve and fluctuation spectrum of a Josephson junction shunted by an arbitrary frequency-dependent impedance for very small and very large Josephson coupling. The junction dynamics can be interpreted as an incoherent tunneling of the Cooper pairs (in former case) and magnetic flux quanta (in the latter case).
91 citations
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TL;DR: In this paper, false indications of heavy fermion behavior can arise from non-magnetic atom disorder (NMAD) in a compound in which the Ce(U) atom occupies a periodic lattice.
Abstract: False indications of heavy fermion behavior can arise from non-magnetic atom disorder (NMAD) in a compound in which the Ce(U) atom occupies a periodic lattice. The NMAD introduces a varying electronic environment around the CE(U) ions which causes a spin glass behavior and leads to a large C/T peak near 1 K. The existence of low lying crystal field levels in Ce and U compounds can also lead to large heat capacities which can be interpreted, incorrectly, as heavy fermion behavior. Several examples of each kind of false heavy fermions are described.
88 citations
TL;DR: In this paper, a sapphire loaded superconducting cavity resonator was implemented in a phase stabilised loop oscillator at 10 Ghz and achieved a fractional frequency stability of 10−14 for 3 to 300 seconds integration time and a resonator Q of 3 x 108.
Abstract: We have implemented a sapphire loaded superconducting cavity resonator in a novel phase stabilised loop oscillator at 10 Ghz and achieved a fractional frequency stability of 10–14 for 3 to 300 seconds integration time and a resonator Q of 3 x 108. We present here an overview of the oscillator.
63 citations
TL;DR: In this article, the superconducting state specific heat was measured in the range 0.3 ⩽T⩽30 K for 0.7T and P=0, and for H=0 and 0.6.3 kbar.
Abstract: Specific heats were measured in the range 0.3 ⩽T⩽30 K for 0⩽H⩽7T and P=0, and for H=0 and 0⩽P⩽6.3 kbar. For H=0 and P=0, the measurements were extended to 0.15K. Above the superconducting transition the H=0 and 7T data can be superimposed. For the magnetic transition near T0 = 18K, T0 increased with increasing P accompanied by a broadening and attenuation of the specific heat anomally. The superconducting transition near Tc = 1.5 K was broadened, attenuated and shifted to lower temperatures for both increasing P and H. The superconducting transition is similar to that of UPt3, and both the temperature dependence of the superconducting state specific heat and the derived parameters are consistent with an unconventional polar-type pairing.
62 citations
TL;DR: In this article, the general formula for Do Josephson current was obtained by means of the probability amplitude of the Andreev reflection, and applied to a simple model to obtain the result which includes those of Ambegaokar-Baratoff, Kulik-Omel'yanchuk, and Ishii as a special case.
Abstract: The general formula for the do Josephson current is obtained, which is written by means of the probability amplitude of the Andreev reflection. Applying the formula to a simple model, we obtain the result which includes those of Ambegaokar-Baratoff, Kulik-Omel'yanchuk, and Ishii as a special case. It is found that the current carrying states appear in the energy gap, which are localized around the tunnel barrier, when the phases of two superconductors do not coincide with each other.
61 citations
TL;DR: The application of modest pressures p to rare-earth and actinide-based heavy-electron / Kondo-lattice materials produces significant changes in both their temperature dependent electrical resistivity ϱ and electronic specific heat γ as discussed by the authors.
Abstract: The application of modest pressures p to rare-earth and actinide-based heavy-electron / Kondo-lattice materials produces significant changes in both their temperature dependent electrical resistivity ϱ and electronic specific heat γ. For a given compound, γ( p , T =0) appears to scale inversely with a characteristic temperature associated with features in ϱ( p , T ). These changes can be understood as arising from the strongly volume-dependent competition of interactions giving rise to the heavy-mass ground state. Similar behavior also may be found in transition-metal compounds, e.g., MnSi.
59 citations
TL;DR: In this article, the saturation hyperfine-field of antiferromagnetic coherent γ-Fe precipitates in a Cu 100− x Al x matrix (0⩽ x ⩽14) was found to increase remarkably with increasing x, i.e., rising lattice expansion of the matrix.
Abstract: Experimental results from 57 Fe Mossbauer-effect investigations on epitaxial, γ-Fe ultrathin films and on γ-Fe precipitates are presented. Depending on the preparation conditions, low-moment anti-ferromagnetic Fe or high-moment ferromagnetic Fe is observed in fcc-Fe (0 0 1) films on Cu (0 0 1), and high-moment Fe in fcc-Fe (0 0 1) films on Cu 3 Au (0 0 1). Isomer-shift values suggest that this behavior is related to different lattice strains. The saturation hyperfine-field of antiferromagnetic coherent γ-Fe precipitates in a Cu 100− x Al x matrix (0⩽ x ⩽14) was found to increase remarkably with increasing x , i.e., rising lattice expansion of the matrix. For γ-Fe precipitates in Cu, the magnetic transition temperature and the saturation hyperfine-field show an anomalous increase above a critical particle size indicating a suggested structural phase transition. Very small precipitates show superparamagnetism.
54 citations
TL;DR: In this paper, the imaginary part of the dynamic susceptibility X ″ of YbInCu 4 above and below the transition was investigated and compared with spectra of the stable valent compound YbNi 4.
Abstract: In YbInCu 4 a valence transition occurs from an almost stable trivalent phase for T >45K to an intermediate-valence state below 45K. We have investigated the imaginary part of the dynamic susceptibility X ″ of YbInCu 4 above and below the transition and compared it with spectra of the stable valent compound YbInNi 4 . YbInNi 4 and YbInCu 4 in the trivalent phase exhibit crystal-field (CF) excitations, centered at about 4meV. Below the valence transition in YbInCu 4 the CF excitations disappear and instead we observe a broad magnetic signal centered at about 40meV, i.e., energy transfers ten times larger than the position of the CF lines of the stable valent phase.
51 citations
TL;DR: In this article, the experimental evidence for a temperature-dependent build up of antiferromagnetic correlations between Cu 2+ planar spins in the normal state of cuprate oxide superconductors is reviewed, and a phenomenological one-component model, developed in collaboration with A. Millis and H. Monien, appears capable of providing a quantitative account of existing experiments.
Abstract: The experimental evidence for a temperature-dependent build up of antiferromagnetic correlations between Cu 2+ planar spins in the normal state of cuprate oxide superconductors is reviewed, and a phenomenological one-component model, developed in collaboration with A. Millis and H. Monien, which appears capable of providing a quantitative account of existing experiments is described. A scaling law which relates the superconducting transaction temperature to the measurable spin-spin correlation length is proposed. The NMR experimental results in the superconducting state are shown to be consistent with d-wave pairing in a strong coupling superconductor. Comparison of the results of NMR experiments on the cuprate oxide and heavy electron superconductors reveals striking similarities. I conclude that the cuprate oxide superconductors are unconventional superconductors in which the superconductivity is of (primarily) electronic origin and results from an attractive interaction of antiferromagnetic character between itinerant quasiparticles in the spin antisymmetric channel, and discuss similarities and differences between cuprate oxide and heavy electron systems.
50 citations
TL;DR: In this paper, the alignment of organic molecules polymerized in magnetic fields was investigated theoretically and experimentally, and partial alignment was seen even at 1 T. Aggregation of a number of molecules with their axes along the same direction makes it possible to orient them along the applied magnetic field even at room temperature.
Abstract: The alignment of organic molecules polymerized in magnetic fields is investigated theoretically and experimentally. Aggregation of a number of molecules with their axes along the same direction makes it possible to orient them along the applied magnetic field even at room temperature. Polymerization of fibrin fibers with considerable alignment is observed in magnetic fields up to 8 T. Partial alignment is seen even at 1 T.
48 citations
TL;DR: In this paper, the low temperature specific heat of nearly ferromagnetic AFe 2 (A = Nb and Ta) and nearly antiferromagnetic Y 1− x Sc x Mn 2 has been studied.
Abstract: The low temperature specific heat of nearly ferromagnetic AFe 2 (A = Nb and Ta) and Y(Co 1− x Al x ) 2 , and nearly antiferromagnetic Y 1− x Sc x Mn 2 has been studied. A large enhancement of the electronic specific heat coefficient is obseved for these compounds. The results are discussed on the basis of the recently developed spin fluctuation theory.
TL;DR: In this paper, the validity of the empirical relation for 1/ƒ noise, S R /R 2 = α/Nƒ, has been studied and an alternative version with a factor 1/A instead of the factor 1 /N is considered.
Abstract: The validity of the empirical relation for 1/ƒ noise, S R /R 2 = α/Nƒ , is studied. An alternative version with a factor 1/A instead of the factor 1/N is considered. N is the number of electrons and A the number of atoms. Experimental and theoretical arguments for the relation in its original form are put forward.
TL;DR: In this paper, a fine structure of the I-V curve of a quantum well was found due to either quantization of the 2D electron motion in the well, or charging of the well by single electrons, or both.
Abstract: Decrease of the quantum well area should result in a fine structure of its do I-V curve due to either quantization of the 2-D electron motion in the well, or charging of the well by single electrons, or both. What effect dominates, is determined by a parameter α , the same which determines magnitude of the I-V curve hysteresis due to the multi-electron charging of large-area quantum wells.
TL;DR: In this article, the authors compared calculated Fermi surfaces and quasiparticle bands of heavy fermion compounds with measured dHvA data, and focused on the question: how do high effective masses and crystalline electric field splitting influence the FermI surface topology?
Abstract: Band structure effects play an important role in determining the low-energy excitations in heavy fermion systems. The influence of coherence is evidenced by the recent de Haas-van Alphen experiments where well-defined Fermi surfaces for the heavy quasiparticles are observed and determined. Quasiparticles states in highly correlated electron systems can be described within the renormalized band method which merges realistic ab initio band calculations with phenomenological Fermi liquid considerations. In the present paper we compare calculated Fermi surfaces and quasiparticle bands of heavy fermion compounds with measured dHvA data. Emphasis is placed on the question: how do high effective masses and crystalline electric field (CEF) splitting influence the Fermi surface topology? Under which conditions can one expect conventional band theory to predict the correct Fermi surface?
TL;DR: In this article, the induced magnetization density in a single crystal of UCoAl has been studied by polarized neutron diffraction in fields of 1.7 and 5.0 T along the c -axis.
Abstract: The induced magnetization density in a single crystal of UCoAl has been studied by polarized neutron diffraction in fields of 1.7 and 5.0 T along the c -axis. The field dependence of the moments on the U and Co sites, which has been extracted from an atomic multipole expansion of the magnetization density using 5f and 3d orbitals, show that the meta-magnetic transition seen in the bulk magnetization takes place on the U sublattice.
TL;DR: In this paper, the authors performed diffraction experiments on Er 3 Si 5 silicide on a single crystal and a thin epitaxial layer, in agreement with the neutron data.
Abstract: Neutron diffraction experiments have been performed on Er 3 Si 5 silicide. The crystallographic structure of this compound is orthorhombic, the magnetic structure is non-collinear. Magnetic measurements on a single crystal and a thin epitaxial layer give very similar results, in agreement with neutron data.
TL;DR: In this paper, the magnetic anisotropy observed in all studied materials is tentatively attributed mainly to the hybridization-mediated anisotropic two-ion interaction, and the observed systematics of ground-state properties are discussed with respect to the development of the electronic structure related to the expected variations of the 5f-ligand hybridization.
Abstract: Investigations of magnetic and related electronic properties of UTX compounds have revealed a variety of magnetic phenomena ranging from weak paramagnetism to various types of magnetic ordering. The observed systematics of ground-state properties is discussed with respect to the development of the electronic structure related to the expected variations of the 5f-ligand hybridization. The huge magnetic anisotropy observed in all studied materials is tentatively attributed mainly to the hybridization-mediated anisotropic two-ion interaction.
TL;DR: In this article, new Sn-based compounds belonging to the tetragonal CaBe2Ge2 (CA) structure were reported, and the results can be understood on the basis of the Doniach model, previously used for Si and Ge based materials.
Abstract: We report on new Sn-based compounds belonging to the tetragonal CaBe2Ge2 (CA) structure. In all the studied compounds, Ce is trivalent without magnetic order appearance at 4.2 K. Thesresults can be understood on the basis of the Doniach model, previously used for Si and Ge based materials.
TL;DR: In this paper, the specific heat, the magnetization and the susceptibility can be accounted for using the results for the J = 7 2 Coqblin-Schrieffer model with T 0 ≅ 150 K.
Abstract: Calorimetric and magnetic measurements characterize YbAgCu4 as a Kondo lattice system. The specific heat, the magnetization and the susceptibility can be accounted for using the results for the J = 7 2 Coqblin-Schrieffer model with T0 ≅ 150 K.
TL;DR: In this article, the cosmological term in 3He-B and corresponding modification of this term in the general relativity are discussed, where the modified cosmology term in general relativity equations contains both the general metric tensor and the equilibrium Minkowski metric tensors.
Abstract: The analogue of the gravitation field in superfluid 3He-B, where some combination of the order parameter components plays a part of the metric tensor, is considered. Broken relative spin-orbit symmetry and parity violation in 3He-B lead to the dirac equation for the fermionic quasiparticles in the presence of a Vielbein. The cosmological term in the 3He-B and corresponding modification of this term in the general relativity are discussed. The modified cosmological term in the general relativity equations contains both the general metric tensor and the equilibrium Minkowski metric tensor. This term becomes zero in equilibrium and therefore does not give the huge gravitational mass of the vacuum which is a plague to the conventional gravity theory due to vacuum fluctuations. The cosmological term nevertheless gives the mass for gravitons. Domain walls in gravity analogous to that in 3He-B are also discussed.
TL;DR: In this article, the authors measured single electron charging effects in serially coupled tunnel junctions and found that the tunneling time was much longer than the barrier traversal time, indicating the presence of offset charging of the junctions.
Abstract: Measurements of single electron charging effects in serially coupled tunnel junctions are presented. The results show that the tunneling time is much longer than the barrier traversal time. We find evidence for the presence of offset charging of the junctions.
TL;DR: The magnetic phase diagram of Ce1−xLaxRu2Si2 alloys (x = 0.20 and 0.30) has been determined by neutron diffraction as mentioned in this paper.
Abstract: The magnetic phase diagram of Ce1−xLaxRu2Si2 alloys (x = 0.20 and 0.30) has been determined by neutron diffraction. Besides the zero-field incommensurate modulated structure (k1 = [0.31, 0, 0]) and the polarized paramagnetic state, two additional phases are observed: another incommensurate structure and a commensurate one ( k 3 = [ 1 3 , 1 3 , 0] ). The magnetic modulation at H = 0 remains practically unaffected by La dilution up to x = 0.80.
TL;DR: In this paper, it was shown that high-T c superconductors develop a London moment of the same magnitude as the conventional supercondors and discussed the consequences of this for the interpretation of the London penetration depth.
Abstract: Inside a stationary superconductor the magnetic field is zero, as described by the London equations. These equations also describe the development of a magnetic field in a superconductor when it is set into rotation. The generated magnetic moment is called the London moment. We show that the high- T c superconductors develop a London moment of the same magnitude as the conventional superconductors and discuss the consequences of this for the interpretation of the London penetration depth.
TL;DR: Inelastic neutron scattering studies of YBa 2 Cu 3 O 6+ x single crystals are reported in this article, where the 2D character of the spin wave spectrum and the exchange parameters have been established.
Abstract: Inelastic neutron scattering studies of YBa 2 Cu 3 O 6+ x single crystals are reported. In the pure AF phase ( x = 0.15, T N = 410 K) the 2D-character of the spin wave spectrum and the exchange parameters have been established. A small amount of p holes in CuO 2 planes ( x = 0.37, T N = 180 K,m n h = 1.8%) strongly modifies the spin dynamics at low q : strong damping of in-plane spin excitations and renormalization of the spin wave velocity. In the superconducting state ( x = 0.45, T c = 34.8 K) we have found dynamical magnetic correlations and an anomalous decrease of the intensity at low energy in the vicinity of T c .
TL;DR: In this paper, the possibility of extending finite cluster calculations by setting up an intercluster Hamiltonian, in terms of Hubbard X -operators, and then using renormalization group or generalized mean field approximations is explored.
Abstract: The possibility of extending finite cluster calculations by setting up an intercluster Hamiltonian, in terms of Hubbard X -operators, and then using renormalization group or generalized mean field approximations is explored. The feasibility of this approach is tested by applying it to the calculation of the one particle Green's function and dynamic susceptibility for the non-degenerate impurity Anderson model.
IBM1
TL;DR: A theory of magnetic instabilities which qualitatively explains the anomalous thermal properties of invar is presented in this article, where fixed-spin-moment band calculations are used to show the existence of two spin states similar to Weiss's 2γ-state model.
Abstract: A theory of magnetic instabilities which qualitatively explains the anomalous thermal properties of invar is presented Fixed-spin-moment band calculations are used to show the existence of two-spin-states similar to Weiss's 2γ-state model The two spin-states are connected by magnetic instabilities which are shown to occur near the equilibrium volume in the Fe-Ni invar alloy with approximately 86 valence electrons/atom The consequences of lattice vibrations on the thermal occupation of the two states are examined and it is shown that the low temperature expansion is dominated by a high-spin state, while the high temperature expansion results from a composite occupation of a high-spin and a low-spin state The initial negative thermal expansion is shown to result from an antiferromagnetic state
TL;DR: In this article, a new calculation of the time dependent wave function resulting from the passage of a monoenergetic (plane wave) neutron beam through a chopper consisting of a slit with time dependent width, taking into account the spatial diffraction from the time-dependent slit was presented.
Abstract: We present a new calculation of the time dependent wave function resulting from the passage of a monoenergetic (plane wave) neutron beam through a chopper consisting of a slit with time dependent width, taking into account the spatial diffraction from the time-dependent slit The results are expected to have a greater range of validity than those obtained previously
TL;DR: A modified Hubbard alloy analogy leads to an equation for the proper self-energy of the Hubbard model at T = 0 which yields exact results in certain limits and has a series solution in powers of the interaction U satisfying Luttinger's requirements as mentioned in this paper.
Abstract: A modified Hubbard alloy analogy leads to an equation for the proper self-energy of the Hubbard model at T = 0 which yields exact results in certain limits and has a series solution in powers of the interaction U satisfying Luttinger's requirements However, Fermi liquid behaviour breaks down in a region of the phase diagram where the series diverges, although it persists for all U at sufficiently low electron density
TL;DR: In this article, thermal expansion measurements on single crystalline samples of the heavy fermion compounds CeCu6, CeRu2Si2, UBe13 and UPt3 were discussed.
Abstract: We discuss recent thermal expansion measurements on single crystalline samples of the heavy fermion compounds CeCu6, CeRu2Si2, URu2Si2, UBe13 and UPt3, and compare the results with existing specific heat data. The resulting Gruneisen parameters ( Г = α v V m / KC ) are anomalously large at low temperatures and vary rapidly with temperature. This implies that a single energy parameter can describe the electron-electron interaction only at very low temperatures.
TL;DR: A review of recent magneto-volume experiments, such as thermal expansion and magnetostriction, performed on good-quality single crystals of heavy-fermion systems, like CeCu 6, CeRu 2 Si 2, URu 2Si 2, UBe 13 and UPt 3, can be found in this article.
Abstract: We present a review of recent magneto-volume experiments, such as thermal expansion and magnetostriction, performed on good-quality single crystals of heavy-fermion systems, like CeCu 6 , CeRu 2 Si 2 , URu 2 Si 2 , UBe 13 and UPt 3 . All investigated compounds exhibit large magneto-volume effects at low temperatures, as is reflected by their huge Gruneisen parameters (at least two orders of magnitude larger than in ordinary metals). A combination of specific-heat and thermal-expansion data yields furthermore information on the pressure dependence of the characteristic temperatures, and allows, in particular cases, for a detailed separation of the Kondo, crystal-field, phonon or other contributions to the thermal properties. We also discuss the magneto-volume effect connected with the metamagnetic-like transitions observed at 20 and 8 T (at 4.2K) for UPt 3 and CeRu 2 Si 2 , respectively.