Showing papers in "Annalen der Physik in 1992"
TL;DR: In this article, an approach for calculating the free energy as well as the correlation lengths of integrable quantum chains at arbitrary finite temperatures is presented, which is applied to critical Hamiltonians related to restricted solid-on-olid models comprising the hierarchy by Andrews, Baxter and Forrester, and generalizations hereof by the fusion procedure.
Abstract: An approach is presented for calculating the free energy as well as the correlation lengths of integrable quantum chains at arbitrary finite temperatures. The method is applied to critical Hamiltonians related to restricted solid-on-olid models comprising the hierarchy by Andrews, Baxter and Forrester, and generalizations hereof by the fusion procedure. The derived non-linear integral equations can be studied analytically in the low-temperature and high-temperature limits. The central charges and all primary conformal weights are obtained for the generalized minimal unitary series of conformal field theory and the Z N parafermion theories. Thus an extension of the thermodynamic Bethe Ansatz is realized which recently has been speculated on in the literature
167 citations
TL;DR: In this paper, a Ginzburg-Landau theory was proposed to describe the crossover from BCS-superconductivity to Bose-condensation, where the mean field transition temperature exhibits a maximum at coupling strength.
Abstract: Starting from a model of free Fermions in two dimensions with an arbitrary strong effective interaction, we derive a Ginzburg-Landau theory describing the crossover from BCS-superconductivity to Bose-condensation. We find a smooth crossover from the standard BCS-limit to a Gross-Pitaevski type equation for the order parameter in a Bose superfluid. The mean field transition temperature exhibits a maximum at a coupling strength, where the behaviour crosses over from BCS to Bose like with corres- ponding values of 2A,/Tc = 5 which are characteristic for high Tc superconductors.
131 citations
TL;DR: In this paper, the authors take up the flexible formulation of RPA in subspaces of coordinate-like and momentum-like 1 ph operators, and apply the newly developed scheme to comparative studies of a hierarchy of approaches for the RPA spectra of doubly magic nuclei described with Skyrme forces.
Abstract: We take up the flexible formulation of RPA in subspaces of coordinate-like and momentum-like 1 ph operators which was developed in the preceeding paper. We draw the connection to many of the known collective approximations to RPA by proper choice of the subspace of operators. We finally apply the newly developed scheme to comparative studies of a hierarchy of approaches for the RPA spectra of doubly magic nuclei described with Skyrme forces.
53 citations
TL;DR: In this article, the existence of the Feynman integral as a Hida distribution for a large class of Schrodinger problems has been shown to be true for general conditions.
Abstract: Recently general conditions have been given which imply the existence of the Feynman integral as a Hida distribution. Here we perform an explicit construction of these distributions for a large class of Schrodinger problems.
39 citations
TL;DR: In this paper, the concept of positons is extended to the modified Korteweg de Vries equation with new properties, and it is shown that the essential features of the positons carry over to this case; the collision of positons, the solitary-wavepositon interaction and simple generalizations are discussed in detail.
Abstract: The concept of positons, i e certain multiparametric solutions of the Korteweg de Vries equation with new properties, is extended to the modified Korteweg de Vries equation It is shown that the essential features of positons carry over to this case; the collision of positons, the solitary-wave-positon interaction and simple generalizations are discussed in detail Suggestions for future research and possible applications of the present work are sketched
38 citations
TL;DR: In this article, the RPA is formulated in subspaces of coordinate-like and momentum-like I ph operators, and a detailed formulation in terms of wavefunctions in coordinate space is given.
Abstract: The RPA is formulated in subspaces of coordinate-like and momentum-like I ph operators. This allows to embed a large class of approximative schemes into a generalized RPA treatment. We give a detailed formulation in terms of wavefunctions in coordinate space which is ideally suited to practical programming. In particular, we work out the reduction to spherical tensors in the case of spherical symmetry which is most often the starting point in finite Fermion systems.
36 citations
TL;DR: In this paper, an interesting T-x phase diagram consisting of two different antiferromagnetic phases for x 0.5 was presented, along with measurements of the magnetic susceptibility, high-field magnetization, heat capacity, thermal expansion, electrical resistivity and thermopower.
Abstract: Elastic and inelastic neutron-scattering studies on the system Ce(Cu1−xNix)2Ge2 are reported. These measurements are complemented by measurements of the magnetic susceptibility, high-field magnetization, heat capacity, thermal expansion, electrical resistivity and thermopower. The results reveal an interesting T-x phase diagram consisting of two different antiferromagnetic phases for x 0.5. Further experimental evidence for different types of antiferromagnetic ordering derives from a line-shape analysis of the quasielastic neutron-scattering intensity, from magnetization and thermopower experiments.
29 citations
TL;DR: In this paper, a linear response formalism is developed which is based on density functional theory within the local density approximation, but which is now corrected for its spurious selfinteraction errors, in the way originally proposed by Perdew and Zunger for ground state calculations.
Abstract: A linear response formalism is developed which is based on density functional theory within the local density approximation, but which is now corrected for its spurious self-interaction errors, in the way originally proposed by Perdew and Zunger for ground state calculations. The original formulation is extended to incorporate self-interaction corrections in the scrrening terms. The general formalism is then applied to the calculation of the static and dynamic response of the metal clusters {Na8, Na9+}, {Na20, Na} and {Na40 Na} within the jellium model. Comparison with experimental data and with other theoretical calculations indicates that the present formalism accounts for the overall (and most of the fine) features of the photoabsorption spectrum of these systems, providing a systematic improvement with respect to previous approaches. The remaining discrepancies are rationalized in terms of the effects to be expected by correctly accounting for the discrete structure of the ionic cores.
26 citations
TL;DR: In this paper, the spontaneous formation of a damage in thin superconducting YBa2Cu3O7−x films was observed, apparently induced by the applied magnetic field of 0.1 T. The damage developed within less than 40 ms and showed up in the magnetiooptically recorded image of the flux above the sample as a path for massive flux penetration.
Abstract: During investigations of the magnetic flux dynamics in thin superconducting YBa2Cu3O7−x films we have observed the spontaneous formation of a damage in the film, apparently induced by the applied magnetic field of 0.1 T. The damage developed within less than 40 ms (the time resolution of the experiment) and showed up in the magnetiooptically recorded image of the flux above the sample as a path for massive flux penetration. A subsequent analysis revealed a 1 μm wide gap in the YBa2Cu3O7−x film which had developed over a major portion of the 1 · 1 cm2 sample. It is suggested that the film locally melted as a result of an instability of the superconductor in the critical state.
21 citations
TL;DR: In this article, the eigenvalue problem for arbitrary linear combinations kα + μα† of a boson annihilation operator α and an arbitrary boson creation operator α† is solved, and it is shown that these operators possess nondegenerate eigenstates to arbitrary complex eigenvalues.
Abstract: The eigenvalue problem for arbitrary linear combinations kα + μα† of a boson annihilation operator α and a boson creation operator α† is solved. It is shown that these operators possess nondegenerate eigenstates to arbitrary complex eigenvalues. The expansion of these eigenstates into the basic set of number states | n >, (n = 0, 1, 2, …), is found. The eigenstates are normalizable and are therefore states of a Hilbert space for | ζ | < 1 with ζ μ/k and represent in this case squeezed coherent states of minimal uncertainty product. They can be considered as states of a rigged Hilbert space for | ζ | ⩾ 1. A completeness relation for these states is derived that generalizes the completeness relation for the coherent states | α 〉. Furthermore, it is shown that there exists a dual orthogonality in the entire set of these states and a connected dual completeness of the eigenstates on widely arbitrary paths over the complex plane of eigenvalues. This duality goes over into a selfduality of the eigenstates of the hermitian operators kα + k* α† to real eigenvalues. The usually as nonexistent considered eigenstates of the boson creation operator α† are obtained by a limiting procedure. They belong to the most singular case among the considered general class of eigenstates with ζ μ/k as a parameter.
21 citations
TL;DR: In this article, the time-differential perturbation of an angular correlation for 111 Cd nuclei has been measured after implantation into polycrystalline TiO 2, the observed perturbations functions are characterized by a well-defined electric field gradient with the quadrupole coupling constant ν Q =105(1) MHz and the asymmetry parameter η=0.18.
Abstract: The time-differential perturbed an angular correlation for 111 Cd nuclei has been measured after 111 In implantation into polycrystalline TiO 2 . The observed perturbation functions are characterized by a well-defined electric field gradient with the quadrupole coupling constant ν Q =105(1) MHz and the asymmetry parameter η=0.18. We attribute these hyperfine parameters to 111 Cd on the (distorted) substitutional cation site in rutile. The PAC results are compared with those in SnO 2 rutile as well with X-ray diffraction, RBS channeling experiments and point charge model calculations including relaxation of the probe atom surrounding
TL;DR: In this paper, the classical Lyapunov exponents from the time dependence of quantum mechanical expectation values are extracted from a periodically kicked top and revealed as a quantum transient with a liftetime ∼ ln ħ.
Abstract: We extract classical Lyapunov exponents from the time dependence of quantum mechanical expectation values. Classical chaos is revealed as a quantum transient with a liftetime ∼ ln ħ. Our strategy is shown to work for the example of a periodically kicked top.
TL;DR: In this article, the collision dynamics of 96Mo + 96Mo at 55 A MeV is simulated by solving numerically the Boltzmann-Uehling-Uhlenbeck (BUU) transport equation for the one-body phase-space distribution function of nucleons with and without Coulomb interaction.
Abstract: The collision dynamics of 96Mo + 96Mo at 55 A MeV is simulated by solving numerically the Boltzmann-Uehling-Uhlenbeck (BUU) transport equation for the one-body phase-space distribution-function of nucleons with and without Coulomb interaction A scatter-plot of the one-body density distribution shows an initial compression, subsequent homogeneous expansion, a breaking into “fragments”, a very slow creeping expansion up to a freeze-out and in the case of included Coulomb-interaction a Coulomb-explosion In the calculation which included Coulomb-interaction the overall shape of the ensemble of dense fragments is spherical The fragments are created over the entire volume of the dense part of the source and not at the surface only In the simulation without Coulomb interaction a doughnut-like shape may develop
TL;DR: In this article, the authors propose a dynamical learning method to derive the deterministic and stochastic forces underlying an observed process, even if this process contains strong multiplicative noise.
Abstract: Starting from appropriate short-time correlation function measurements, we propose a dynamical “learning” method to derive the deterministic and stochastic forces underlying an observed process, even if this process contains strong multiplicative noise. To do this we extend the ideas of our previous paper [1] to establish mathematical relationships in this more general case between the joint distribution function of the process and its corresponding Ito-Langevin equation. A numerical example for a simulated process containing strong multiplicative noise shows good agreement with the theory.
TL;DR: In this article, the authors used a scanning tunneling microscope with a positive tip to obtain high-resolution images of layered transition metal-dichalcogenide ReS2 single-crystals (n-type semiconductor).
Abstract: Atomic resolution images of layered transition metal-dichalcogenide ReS2 single-crystals (n-type semiconductor) were obtained using a scanning tunneling microscope with a positive tip. In most cases only unresolved clusters of four rhenium atoms could be seen. Occasional images with higher resolution showed that these bright structures consist of four separated atoms. The symmetry of the imaged atoms is identical to that of the rhenium sublattice but not to that of the sulfur atoms. We conclude therefore that the main contribution to the tunneling current is due to the rhenium atoms, although the sulfur atoms are placed by about 0.15 nm closer to the tip. Thus for our positive bias of the tip the tunneling electrons originate from occupied rhenium states in the valence band of the semiconductor.
TL;DR: In this paper, the observed resistance peak(s), which go above the normal state resistance R N and can be as high as ≃ 1.5 R N, can be explained by a ''mesoscopic'' effect: superconducting percolation aggregates of size ξ p, larger than the super-conducting coherence length ξ S, but smaller than the quasiparticle relaxation length λ Q *, have a superconding gap, but are not yet able to carry a supercurrent.
Abstract: Granular films prepared from well-defined In clusters embedded in Kr (≃ 10-40 at % Kr) show sharp resistance anomalies very close to the superconducting transition temperature. The observed resistance peak(s), which go(es) above the normal state resistance R N and which can be as high as ≃ 1.5 R N , can be explained by a «mesoscopic» effect: Superconducting percolation aggregates of size ξ p , larger than the superconducting coherence length ξ S , but smaller than the quasiparticle relaxation length λ Q *, have a superconducting gap, but are not yet able to carry a supercurrent
TL;DR: In this article, the Migdal-Kadanoff approximation is applied to a nonlinear σ model with fields taking values in a perfectly graded noncompact superspace G/K of rank one.
Abstract: The Migdal-Kadanoff approximation is applied to a nonlinear σ model with fields taking values in a perfectly graded noncompact superspace G/K of rank one. It is shown how to implement the spherical transform for this model space numerically in a controlled manner. The correlation length exponent ν, and the dimensions of a series of G-invariant scaling operators at the fixed point, are computed for 2 < d ⩽ 3. No perturbative instability of the type found by Kravtsov et al. and Wegner is observed.
TL;DR: In this paper, a planar Ising model with an extended defect described by couplings of the form K(r) = K·(1 + A/r) was considered and the spectrum of the corner transfer matrix was determined numerically and analytically.
Abstract: We consider a planar Ising model with an extended defect described by couplings of the form K(r) = K·(1 + A/r). We determine the spectrum of the corner transfer matrix numerically and analytically and use it to calculate the local magnetization at the defect and the corresponding, non-universal critical exponent.
TL;DR: In this article, the competition between fission and evaporation as fragmentation channels of excited doubly charged Sodium clusters was studied using an Extended Thomas-Fermi method and the jellium model.
Abstract: We have studied the competition between fission and evaporation as fragmentation channels of excited doubly charged Sodium clusters. We have used an Extended Thomas-Fermi method and the jellium model. A preliminary account of the influence of shell effects is also given.
TL;DR: In this article, electron-phonon matrix elements relevant for indirect optical absorption, intervalley matrix elements and intravalley deformation potentials as well as splitting parameters for the k = 0 states in silicon and germanium within the rigid quasi-ion model were calculated.
Abstract: We have calculated electron-phonon matrix elements relevant for indirect optical absorption, intervalley matrix elements and intravalley deformation potentials as well as splitting parameters for the k = 0 states in silicon and germanium within the rigid quasi-ion model. In contrast to the "atomic" potentials in conventional rigid-ion models the quasi-ion potentials are well-defined. The agreement with experiment and with other theoretical results is satisfactory in most cases. We have also studied the role of distortion corrections to the rigid quasi-ion approximation. We find that the influence of distortions is small, indicating that the rigid quasi-ion model is an adequate description - at least in case of these two materials.
TL;DR: In this paper, the in-plane and out-of-plane resistivities of Tl 2 Ba 2 Ca 2 Cu 3 O 10 single crystals were measured in magnetic fields up to 10 Tesla.
Abstract: We present measurements of the resistivity tensor components ρ a (T) and ρ c (T) of high-quality Tl 2 Ba 2 Ca 2 Cu 3 O 10 single crystals wit T c = 118... 121 K. The in-plane resistivity ρ a as well as the out-of-plane resistivity ρ c show a metal-like temperature dependence with an anisotropy ratio ρ c /ρ a of up to 10 3 . The coherence length ξ c (0) = O.15 nm could be determined from an analysis of the fluctuation conductivity above T c . From measurements of the ac-susceptibility in magnetic fields up to 10 Tesla the temperature dependence of the depinning line could be obtained. The diffusion coefficient of the flux lines obtained from the frequency dependence of the depinning temperature shows a thermally activated behaviour of the flux motion in the field range 0.1 T ≤ B ≤ 10 T
TL;DR: In this paper, the thermal and laser induced metastable phase formation in amorphous GeSb 2 Te 4 thin films prepared by RF-magnetron sputtering was investigated.
Abstract: Reported here are studies about the thermal and laser induced metastable phase formation in amorphous GeSb 2 Te 4 thin films prepared by RF-magnetron sputtering. The general structural properties of this most promising optical phase change recording material are discussed from the point of view of fast structural phase transformation
TL;DR: In this article, the authors observed large-scale superperiodicities by a scanning tunneling microscope at room temperature in air and obtained several hexagonal superstrucatures with periods of 30 nm, 4.2 nm, 2.4 nm, and 2.0 nm.
Abstract: On freshly cleaved highly oriented pyrolytic graphite we observed large-scale superperiodicities by a scanning tunneling microscope at room temperature in air. Several hexagonal superstrucatures with periods of 30 nm, 4.2 nm, 2.4 nm, and 2.0 nm, respectively, and a strip-like superstructure with a period of 1 nm were obtained. With exception of the largest hexagonal superperiodicity (30 nm spacing), all other superstructures are superimposed on the atomic corrugation of graphite. The origin of these superstructures is not clear yet. We assume that they arise from crystal defects in graphite. The hexagonal superstructure may be caused by the Moire effect due to the rotational misorientation of the two top layers or of two successive layers near the surface
TL;DR: In this paper, the desorption kinetics and surface diffusion of the alkalis potassium, rubidium and cesium were investigated on a Si(111)7 × 7-surface at extremely low alkali coverages.
Abstract: Using pulsed atomic beam technique and a surface ionization ion microscope, the desorption kinetics and the surface diffusion of the alkalis potassium, rubidium and cesium were investigated on a Si(111)7 × 7-surface at extremely low alkali coverages.
In the temperature range 1120 … 800 K, the mean adsorption lifetime τ(T) = τ0 · exp(Edesi/kT) and the mean diffusion length x(T) - defined in the equilibrium between adsorption, diffusion and desorption - were measured. From these data the diffusion constant D(T) = D0 · exp(-Ediff/kT) was obtained as D = x−2/τ. For temperatures T ⩽ 750 K, the diffusion constant was calculated from nonstationary alkali concentration profiles using the Boltzmann-Matano method.
From the temperature dependence of these quantities the parameters of desorption (Edes,i τ0) and surface diffusion (Ediff, D0) for K, Rb and Cs on Si(111) were obtained. The values of Ediff and D0 are comparably high and may be interpreted by non-localized diffusion according to a model proposed by Bonzel (Surf. Sci. 21 (1970) 45).
TL;DR: In this article, the authors considered a quasi-one-dimensional metal with a Peierls transition at about 180 K to a charge density wave (CDW) ground state, where the exact transition temperature depends on three-dimensional coupling effects and therefore on the size of the counterion X− = PF, AsF, SbF.
Abstract: Due to the high anisotropy of the dc conductivity (σ|/σ⊥ ≈ 104) the organic conductor (fluoranthene)2X can be regarded as a model system for studying the Peierls instability in quasi-one-dimensional systems. The temperature dependence of the dc conductivity σ| (T) along the highly conducting crystal axis exhibits the typical behaviour of a quasi-one-dimensional metal with a Peierls transition at about 180 K to a charge density wave (CDW) ground state. As expected for a highly one-dimensional conductor the exact transition temperature depends on three-dimensional coupling effects and therefore on the size of the counterion X− = PF, AsF, SbF. Above the Peierls transition σ| (T) can be described quantitatively within a model of CDW fluctuations leading to a pseudo gap in the electronic density of states. Below, the existence of a real energy gap at the Fermi level with a BCS-like temperature dependence determines the charge transport over more than eight orders of magnitude in the electrical resistance. For the intrinsic energy gaps 2 Δ (0), which characterize the ground state of the Peierls semiconductor, values of 120-180 meV have been found for different crystals.
TL;DR: In this paper, the analytical form of the Green's function of 2-dimensional electrons with lateral confinement in a perpendicular magnetic field was derived, where the confinement potentials were infinite barriers at radius R (quantum dot) and at r and R(quantum ring).
Abstract: We derive the analytical form of the Green's function of 2-dimensional electrons with lateral confinement in a perpendicular magnetic field. The confinement potentials considered are infinite barriers at radius R (quantum dot) and at r and R (quantum ring).
TL;DR: In this paper, the symmetric part of the fourth-rank tensor of the magneto-electrogyration was determined with the aid of a high-resolution computer-aided polarimetric device.
Abstract: The simultaneous application of electric and magnetic fields on single crystals of Sr-, Ba-and Pb-dinitrate yields an additional term to the pure electrogyration and Faraday effect. The symmetric part of the fourth-rank tensor of this magneto-electrogyration has been completely determined with the aid of a high-resolution computer-aided polarimetric device. In Pb(NO3)2 a maximum magneto-electrogyration of about 10% of the magnitude of electrogyration is observed when a magnetic field of 1000 kA/m (1.2 Tesla) is applied along [111]. The effects in Sr(NO3)2 and Ba(NO3)2 are much smaller. Index of refraction, electrogyration, Faraday effect, and the new magneto-electrogyration obey the same sequence: Pb(NO3)2 > Ba(NO3)2 > Sr(NO3)2.
TL;DR: For short times and small clusters as discussed by the authors check the validity of the 1935 Becker-Doring equation by Monte Carlo simulations in the square Ising model at and near its critical point; some discrepancies are found.
Abstract: For short times and small clusters we check the validity of the 1935 Becker-Doring equation by Monte Carlo simulations in the square Ising model at and near its critical point; some discrepancies are found.
TL;DR: In this article, the superconductivity of heavy-fermions is investigated microscopically on the basis of the LNCA-approximation for strongly correlated electrons in a Kondo lattice and of Eliashberg theory for anisotropic singlet and triplet superconducting order.
Abstract: Superconductivity of Heavy-Fermions, with an emphasis on hexagonal UPt3, is investigated microscopically on the basis of the LNCA-approximation for strongly correlated electrons in a Kondo lattice and of Eliashberg theory for anisotropic singlet and triplet superconducting order. The effective interaction kernel incorporates exchange of spin fluctuations carried by strongly renormalized particle-hole excitations as well as exchange of phonons generated by the breathing mechanism. Particular care is taken to include realistic anisotropies in band structure and couplings and to expand interaction kernel and order parameter in appropriate Fermi surface harmonics. Separate interactions and corresponding gap equations are used for pseudo-spin-singlet and -triplet channel, with a restriction to the case of weak spin-orbit coupling. Our main results include a detailed study of phonon- and spin-fluctuation mechanisms as a possible source for superconductivity and, in combination, their mutual influence and competition. Furthermore, the questions regarding singlet or triplet order, conventional or unconventional symmetry, order parameter zeros and phase transitions between different superconducting states are addressed. We propose a possible scenario of Heavy-Fermion superconductivity.
TL;DR: In this article, conformal invariance conditions on a sigma model of the open bosonic string including the tachyon, the abelian gauge field an the first excited massive mode are calculated up to order a′.
Abstract: Conformal invariance conditions on a sigma model of the open bosonic string including the tachyon, the abelian gauge field an the first excited massive mode are calculated up to order a′. Inner symmetries are used to compute conformal invariance conditions from renormalization group beta functions.