Showing papers in "Journal of Physics C: Solid State Physics in 1978"
TL;DR: In this article, it was shown that the surface barrier potential can confine electrons in surface states, which because of the coulombic tail on the potential form a Rydberg series.
Abstract: It is shown that the surface barrier potential can confine electrons in surface states, which because of the coulombic tail on the potential form a Rydberg series. This previously known result is made more rigorous by a discussion of lifetime broadening of the states. Observability of the states via LEED experiments is also investigated. The Rydberg series should give rise to structure in LEED curves which can in principle be resolved for all members of the series as n to infinity .
376 citations
TL;DR: A relativistic generalisation of the Hohenberg-Kohn-Sham theory of the inhomogeneous non-relativistic electron gas was presented in this article, where the results of the homogeneous electron gas are used as input, and a selfconsistent one-particle Dirac-like equation was derived.
Abstract: A relativistic generalisation of the Hohenberg-Kohn-Sham theory of the inhomogeneous non-relativistic electron gas is presented. In a local scheme, where the results of the homogeneous electron gas are used as input, a self-consistent one-particle Dirac-like equation is derived. When only 'exchange' energy is used as an approximation, the usual Slater's rho 1/3 theory is shown to need a relativistic correction.
202 citations
TL;DR: In this paper, the authors present a discussion on the thermodynamic properties of conducting liquids, and calculate measurable quantities such as the compressibility, specific heat, and melting curves of metals from knowledge of the fundamental interactions among the electrons and ions.
Abstract: Publisher Summary The chapter presents a discussion on the thermodynamic properties of conducting liquids. The chapter discusses calculating measurable quantities as the compressibility, specific heat, and melting curves of metals from knowledge of the fundamental interactions among the electrons and ions. To understand this problem, it is necessary to consider both the electronic structure and the “bonding” structure or ionic arrangement. These are closely interrelated. For example, any description of the ionic arrangement must take into account the presence of the conduction electrons. Conversely, the electronic structure must in turn be strongly affected by the physical arrangement of the ions. The interplay between these dual aspects of liquid metals is quite complex, which is discussed in this chapter. Liquid metals may be further divided into roughly nonoverlapping classes according to their electronic structure, the chapter defines these classes under normal condition. A central question regarding liquid metals is, of course, why they form simple liquids, or equivalently, why, structurally, they have two body-central forces. The answer, in the case of free-electron metals, lies in the predictions of perturbation theory as applied to an interacting electron gas. The perturbation arises from the metallic ions which carry with them, in an adiabatic way, the fundamental interaction between the electrons and ions—the pseudopotential. The response of the electrons to this perturbation is discussed in the chapter. Once the nature of the interatomic forces is known, the thermodynamics of the liquid metal can be determined by the methods of classical statistical mechanics. Some of the methods for so doing are discussed in this chapter.
180 citations
TL;DR: In this paper, a set of interionic potentials of the Born-Mayer form is derived for the alkali halides, which is completely in terms of parameters of two types, (a) parameters relating to the constituent ions and (b) parameters which apply to all crystals.
Abstract: For pt.I see ibid., vol.11, p.1523 (1978). A set of interionic potentials of the Born-Mayer form is derived for the alkali halides. The specification is completely in terms of parameters of two types, (a) parameters which relate to the constituent ions and (b) parameters which apply to all crystals. Thus the parametrisation scheme contains no crystal dependent terms and is of a form which may readily be applied to systems of mixed alkali halides. Each of the nine ions is described by five parameters, its polarisability, its shell charge and three parameters which relate to the ion size. The van der Waals coefficients are calculated consistently from the ion polarisabilities. The model system, which has 47 free parameters, reproduces the lattice constants, high and low frequency dielectric constants and transverse optic frequencies for the 20 crystals to high accuracy. Of crystal properties which are not included in the fitting procedure, the cohesive energies are given in most cases to better than 1%, the NaCl/CsCl structural relative stability is correctly described in all cases except CsF, and reasonable phonon dispersion relations and elastic constants are obtained.
179 citations
TL;DR: In this paper, a discussion on martensitic transformation as a typical phase transformation in solids is presented, and three general theoretical approaches of thermodynamics and kinetics of Martensitic transformations are presented.
Abstract: Publisher Summary The chapter presents a discussion on martensitic transformation as a typical phase transformation in solids. Martensitic transformation is a polymorphic phase transition in solids consisting of the regular rearrangement of the crystal lattice, the constituent atoms of which do not interchange places. The transformation usually proceeds by means of the nucleation of new phase crystals inside the initial phase. These crystals form a complex heterophase system with a characteristic structure—that is, morphology, an internal substructure, and mutual arrangement of the individual phase components of the system. For different solids and under different conditions, both the kinetics and the morphology of the products may differ essentially. Nevertheless, some structure-morphological, thermodynamic, and kinetic features do exist that may be considered as typical of the martensitic transformations. The chapter presents a figure on the concrete data on the transformation in the Fe (30%) Ni alloy and other ferrous alloys. Regarding crystal nucleation kinetics, two types of martensitic transformations are distinguished: athermal and isothermal transformations. The chapter also presents the three general theoretical approaches of thermodynamics and kinetics of martensitic transformations. The concept of this study is based on the idea that martensitic transformation may be considered as a special type of phase transition (the so-called strain transition).
163 citations
TL;DR: In this article, the authors studied the crystalline perfection of the basal plane of ice Ih in thermodynamic equilibrium with its own vapour, between -130 degrees C and -2 degrees C by means of 100 keV proton channelling.
Abstract: The crystalline perfection of the basal plane of ice Ih in thermodynamic equilibrium with its own vapour, is studied between -130 degrees C and -2 degrees C by means of 100 keV proton channelling. An intrinsically disordered surface region is found. The disorder extends into the bulk, and increases rapidly with temperature above -40 degrees C. A partial order is retained, however, at least up to -1.8 degrees C. The results are compatible with the postulated existence of large-amplitude surface vibrations. At -1.8 degrees C the square of the mean surface-vibration amplitude of oxygen is 3.3 times larger than the bulk value deduced from past x-ray measurements. The thickness t of an amorphous layer, which has the same dechannelling effect as the partially disordered region, increases with temperature as t(nm)=(94+or-17)-(54+or-14)lg(273-T). This is the functional dependence predicted by Fletcher's theory, and found experimentally by Volta effect and NMR measurements. The order of magnitude of the thickness near 0 degrees C agrees with the results of measurements of electrical and mechanical surface properties of ice, and with Weyl's original suggestion, but is ten times larger than the value estimated from NMR measurements and predicted by Fletcher.
144 citations
TL;DR: In this paper, a discussion on the collective behavior of electrons and holes at low temperatures and high densities in semiconductors is presented, and a comparison of theory and experiment is made.
Abstract: Publisher Summary The chapter presents a discussion on the theoretical aspects of the electron-hole liquid in semiconductors. In an intrinsic semiconductor such as germanium or silicon, there are essentially no free carriers at very low temperatures. However, high densities of positive (hole) and negative (electron) charge carriers can be generated in these crystals by photoexcitation with a photon energy greater than the forbidden gap. In recent years, experiments in Ge and Si have revealed that optically pumped electrons and holes at high densities can undergo a phase transition at liquid helium temperatures into a metallic, liquid state. This condensate represents a state of matter particularly unique in nature because the electrons and holes, by reason of their small masses, are simultaneously in the quantum limit. This chapter presents a discussion on the collective behavior of electrons and holes at low temperatures and high densities. The chapter presents an historical introduction, mentions a few of the important early experiments performed, and presents a comparison of theory and experiment. Semiconductors can be divided into two classes. Those in which the conduction band minimum and valence band maximum occur at the same value of the wavevector are known as direct gap semiconductors, while those in which they are separated in k space are known as indirect gap semiconductors. The chapter discusses the latter.
133 citations
TL;DR: The ferroelectric and dielectric properties of La, Sr, Zr, Fe and Mn doped BaTiO3 ceramic are measured within wide limits of the amplitude Eapproximately of the external electrical AC field.
Abstract: The ferroelectric and dielectric properties of La, Sr, Zr, Fe and Mn doped BaTiO3 ceramic are measured within wide limits of the amplitude Eapproximately of the external electrical AC field. At sufficiently low Eapproximately the losses are not ferroelectric in origin but are rather determined by the low frequency relaxational response of the material, which is influenced by doping. In the ferroelectric phases a well defined threshold Eapproximately 0 exists at any composition such that the permittivity and the loss factor are independent of Eapproximately for Eapproximately Eapproximately 0 due to domain wall motions and reversal of the spontaneous polarisation Ps.Eapproximately 0 is less than 20 V cm-1 in La doped BaTiO3 and is up to 5000 V cm-1 in Fe or Mn doped samples. Compositions with large Eapproximately 0 show constricted hysteresis loops which are described by an internal bias field Ei. In Mn doped BaTiO3 both Eapproximately 0 and Ei are increased by annealing at low partial pressures of oxygen, Ei and Eapproximately 0 are a measure of the stability of the domain configuration established during ageing below the temperature of the para-electric to ferro-electric phase transition.
132 citations
TL;DR: In this paper, the authors studied the behavior of systems undergoing structural transformations between commensurate and incommensurate ordered phases, and found the phase transition to be first order, in agreement with experiment.
Abstract: For pt.I see ibid., vol.11, no.17, p.3578 (1978). The authors studied the behaviour of systems undergoing structural transformations between commensurate and incommensurate ordered phases. They reviewed the theory developed by McMillan, and by Bak and Emery (1976) in which the order parameter for such phase transitions is visualised as a soliton density, and give a critique of this theory. They extended the analysis to those cases where the commensurate phase ordering is characterised by a wavevector of the Lifschitz type, such as the Brillouin zone corner. In both cases they found the phase transition to be first order, in agreement with experiment. They also briefly analysed an n=2 component model system which is shown to exhibit a continuous commensurate-incommensurate phase transition entirely analogous to one promoted by an acoustic phonon instability.
127 citations
TL;DR: In this article, the main features of the electronic structure of transition metal layered dichalcogenides can be calculated in a simple ab initio atomic orbital framework, based on the properties of groups IV, V and VI of the transition series.
Abstract: It is shown that the main features of the electronic structure of transition metal layered dichalcogenides can be calculated in a simple ab initio atomic orbital framework. Examples from Groups IV, V and VI of the transition series are considered.
119 citations
TL;DR: The crystal structure of NbSe3 has been refined from single crystal X-ray diffraction data as discussed by the authors, which shows that the 145K transition in the electrical resistivity is not accompanied by a structural distortion.
Abstract: The crystal structure of NbSe3 has been refined from single crystal X-ray diffraction data. It has a monoclinic symmetry with lattice parameters: a=10.009 AA, b=3.4805 AA, c=15.629 AA, beta =109.47 AA, space group P21/m and six formulae per unit cell. The crystal structure of NbSe3 as determined at 100K shows that the 145K transition in the electrical resistivity is not accompanied by a structural distortion. Except for the decrease due to thermal contraction all interatomic distances are found to be the same. This is compatible with the proposed model of the charge-density-waves formation which has been put forward in order to explain the physical properties of the 145K transition. Electron diffraction pictures taken above and below the transition give direct evidence of the charge-density-waves formation at the transition. At 120K in agreement with Tsutsumi et al. (1977) the pictures contain superstructure spots at the (h,k+or-0.243, l) positions. Contrary to what has been reported by the same authors, the authors have found that at 3K above the transition the electron diffraction pictures do not contain the diffuse scattering streaks corresponding to the planes at k'=k+or-0.243, which would indicate fluctuations of the CDW above the transition.
TL;DR: In this article, the authors discussed the nature of the excitation spectrum of a structurally incommensurate phase, both when the displacement field is describable by a single Fourier component and when it may be described in terms of an array of phase solitons.
Abstract: For pt.II see ibid., vol.11, no.17, p.3591 (1978). The authors discussed the nature of the excitation spectrum of a structurally incommensurate phase, both when the displacement field is describable by a single Fourier component and when it may be described in terms of an array of phase solitons. In each case they established the character of the Goldstone phase mode, and in the latter case they found an additional phase excitation whose properties merge into those of a phase mode in the commensurate structure as the 'lock-in' phase boundary is approached. They examined phase mode-acoustic mode interaction and give a brief discussion of phase mode pinning.
TL;DR: In this paper, the authors present a theory for how excited molecules, located above a metal surface, are damped due to excitation of electron-hole pairs and bulk plasmons in the metal.
Abstract: Presents a theory for how excited molecules, located above a metal surface, are damped due to excitation of electron-hole pairs and bulk plasmons in the metal A detailed study of how the excitation energy will be spread into the metal is also given The theory is compared with experiments for the special case of vibrationally excited molecules adsorbed directly on the metal surface The author shows the usefulness of a particular vector field decomposition in treating surface problems
TL;DR: In this paper, a consistent set of shell parameters for alkali halide crystals of both rocksalt and CsCl structures is reported, and the fitting procedure, values of the parameters and their sensitivity are discussed.
Abstract: A consistent set of shell parameters for alkali halide crystals of both rocksalt and CsCl structures is reported. The fitting procedure, values of the parameters and their sensitivity are discussed. Short range interionic potentials are determined and are shown to give a good description of both static and dynamic properties of the crystals.
TL;DR: In this paper, the authors examined the behavior of a wide variety of systems undergoing structural phase transitions to a phase incommensurate with the high-temperature structure and argued that either the critical behaviour is effectively that of the n=2 component Heisenberg model or the phase transition is first order.
Abstract: The authors examined the behaviour of a wide variety of systems undergoing structural phase transitions to a phase incommensurate with the high-temperature structure. With the aid of renormalisation group methods they argued that, in the cases examined, either the critical behaviour is effectively that of the n=2 component Heisenberg model or the phase transition is first order.
TL;DR: In this paper, the antiferromagnetic spin-flop critical field Hc(x) was calculated on the basis of known exchange and anisotropy parameters of the MnF2 system.
Abstract: The antiferromagnetic resonance in MnxZn1-xF2, measured recently by Wiltshire (1977), gives information about the antiferromagnetic-spin-flop critical field Hc(x). The authors calculate Hc(x) on the basis of known exchange and anisotropy parameters of the MnF2 system. The concentration dependence of the anisotropy is determined through a separation between short-range and long-range parts of the dipolar forces while the Mn-Mn exchange interactions are assumed to be unaffected by the zinc dilution. The theoretical treatment is based on an extension of the Izyumov type of perturbation theory (1966) to non-magnetic impurity problems. Coherent potential approximation (CPA) analyses are also carried out. Results are in reasonable agreement with experiment.
TL;DR: In this article, a method for an ab-initio calculation of transverse dynamical effective charges Z* in partially covalent semiconductors within the framework of pseudopotential theory is presented.
Abstract: A method for an ab-initio calculation of transverse dynamical effective charges Z* in partially covalent semiconductors within the framework of pseudopotential theory is presented. It is based on previously established expressions for Z* in terms of the inverse microscopic dielectric function of the crystal but circumvents the direct inversion of the latter. In contrast to earlier calculations the results are definitely boundary insensitive. Moreover, the acoustic sum rule expressing charge neutrality is inherently guaranteed. Within the local empirical pseudopotential method a simple analytical model calculation, which is compared with the bond orbital model, as well as a full numerical computation is performed. For III-V compounds the resulting Z* underestimate the experimental effective charges by approximately 30% while good agreement for II-VI materials is obtained. Reasons for these findings are discussed and the effects of several refinements are estimated.
TL;DR: In this paper, a quantum-mechanical calculation of the multiphonon, non-radiative transition rate for electrons in solids is carried out without assuming the Condon approximation.
Abstract: A quantum-mechanical calculation of the multiphonon, non-radiative transition rate for electrons in solids is carried out without assuming the Condon approximation. A relatively simple result is obtained by adopting a single-frequency model. An expression valid at low and intermediate temperatures (0
TL;DR: In this paper, the behavior of correlation functions of the one-dimensional Fermi system at large distances has been investigated by reducing it to the Sine-Gordon model, which is dual to the low-temperature phase of a plane xy model.
Abstract: The behaviour of correlation functions of the one-dimensional Fermi system at large distances has been investigated by reducing it to the Sine-Gordon model. The latter is dual to the low-temperature phase of a plane xy model. In this case the fermion operator is the product of the order and disorder parameters. The transitions to the coupling constants between different states of the Fermi system states of the Fermi system may be considered as phase transitions equivalent to xy models. The elasticity modulus and spin susceptibility serves as superfluid density. The question on the phase transition of the xy model is discussed.
TL;DR: In this paper, the authors used Brillouin scattering methods to show that the disorder at Tc results in a large decrease in the elastic constant C11 and a much smaller change in C44 and C12.
Abstract: Crystals with the fluorite structure show a specific heat anomaly at a temperature Tc well below the melting temperature. This premelting phenomenon is due to generation of extensive disorder in the anion sublattice. The present investigation shows, using Brillouin scattering methods, that the disorder at Tc results in a large decrease in the elastic constant C11 and a much smaller change in C44 and C12. Comparison of both lattice and lattice-defect energy calculations with experimental data suggests a molar defect concentration of interstitials of order 10% just above Tc. The calculations also provide a qualitative explanation of the limitation of the disorder giving rise to the specific heat anomaly.
TL;DR: In this article, the lifetime of liquid argon, krypton and xenon excited by energetic electrons has been studied with such a high electric field that all of the observed decay characteristics have to be attributed to the self-trapped exciton luminescence.
Abstract: The lifetimes of luminescence from liquid argon, krypton and xenon excited by energetic electrons have been studied with such a high electric field that all of the observed decay characteristics have to be attributed to the self-trapped exciton luminescence. In all cases the decay shows two exponential components. The lifetimes of the fast components are in the range from 2 to 5 ns, and major second components have lifetimes of 860+or-30 ns for argon, 80+or-3 ns for krypton and 27+or-1 ns for xenon. These lifetimes are interpreted in terms of two self-trapped exciton states, one predominantly singlet in character, the other triplet; this is the first strong evidence for the triplet assignment. The variation in triplet-state lifetimes is attributed to the different spin-orbit couplings.
TL;DR: In this article, the structure of monolayers adsorbed on solids is investigated and the consequences of particular force laws explored The dipole-dipole interaction is assumed to predominate and a model is developed which explains the experimentally observed commensurate and incommensurate monolayer structures and the behaviour of the Debye-Waller factor.
Abstract: The structure of monolayers adsorbed on solids is investigated and the consequences of particular force laws explored The dipole-dipole interaction is assumed to predominate and a model is developed which explains the experimentally observed commensurate and incommensurate monolayer structures and the behaviour of the Debye-Waller factor
TL;DR: In this article, the Schottky barrier heights have been measured for a range of metals on atomically clean and on etched indium phosphide surfaces and it is suggested that this result applies in general to interfaces between metals and compound semiconductors.
Abstract: Schottky barrier heights have been measured for a range of metals on atomically clean and on etched indium phosphide surfaces. The metal work function has little influence on the contact behaviour and the 'index of behaviour' S, often used to describe metal-semiconductor contacts, is not a meaningful parameter. It is suggested that this result applies in general to interfaces between metals and compound semiconductors. Chemical effects are shown to dominate the electrical properties of the contacts.
TL;DR: The ground state properties of several systems showing the Toulouse frustration effect are investigated analytically in this article, where the energy and entropy of the random-bond Ising chain are obtained for all concentrations of antiferromagnetic bonds using the transfer-matrix method.
Abstract: The ground-state properties of several systems showing the Toulouse frustration effect are investigated analytically. First, the energy and entropy of the random-bond Ising chain in a uniform field are obtained for all concentrations of antiferromagnetic bonds using the transfer-matrix method. The susceptibility has discontinuities for an infinite number of critical values of the field, where the entropy shows spikes in addition to discontinuities. These effects are related to the physics of frustration. The second system studied consists of frustrated strips, which it is argued are the proper one-dimensional limit of spin glasses. Two kinds of strips are considered and the results are compared with recent numerical works on two-dimensional spin glasses and with the exact results for random (3*3) squares.
TL;DR: In this article, the analysis of the magnetic structures of type-II antiferromagnets (a FCC lattice with k = 1 2, 1 2, 1 2 1/2, 1 3, 1 1/ 2 ) is presented.
Abstract: The authors deal with the analysis of the equivalent magnetic structures of type-II antiferromagnets (a FCC lattice with k=(1/2, 1/2, 1/2)). This analysis is essentially based on symmetry considerations taking into account the symmetry of the group G(k) corresponding to a particular set of k-vectors and the symmetry group Gm of the ordered phase, which results from the direction of the Fourier component associated with each k-vector. Only a few magnetic structures are possible if two physical restrictions are imposed: the angle between ki and mki, is the same for each ki and each magnetic moment has the same value. It is concluded that MnO, NiO and FeO have a collinear magnetic structure whereas in CoO the collinear structure and the multiaxis Van Laar model are consistent with previous experiments. From neutron diffraction experiments on single crystals of CoO, under uniaxial stresses applied out of a tetragonal axis one can conclude that CoO is also a collinear antiferromagnet.
TL;DR: In this paper, the so-called "infinitesimal" strain tensor is shown to be a valid finite tensor for all symmetric deformations (which involve no rotation).
Abstract: The so-called 'infinitesimal' strain tensor is shown to be a valid finite strain tensor for all symmetric deformations (which involve no rotation). Comparison with a similar result for the triangular matrix of the Voigt strain parameters shows that either description is valid for arbitrary six-parameter deformations of invariant algebraic form.
TL;DR: In this article, the equivalence between a disordered electronic system and the n to 0 limit of a Ginzburg-Landau field theory was considered, with special attention to the convergence of the relevant functional integrals.
Abstract: The author considers the equivalence between a disordered electronic system and the n to 0 limit of a Ginzburg-Landau field theory, with special attention to the convergence of the relevant functional integrals. It is shown that a non-zero density of states and a finite localisation distance are only possible if the loop expansion of the field theory diverges. This divergence is controlled by the existence of non-trivial solutions of the classical field equations which can be interpreted as the envelope of the localised wavefunction, at least at short distances. For the case of Gaussian randomness, a density of states is obtained in the tail of the band proportional to (-E)d(5-d)/4 exp(-constant(-E)2-d/2) in d<4 dimensions. For a finite band, the density vanishes near the band edge E0 like (E-E0)-(d+1)/2 exp (-constant/(E-E0)).
TL;DR: In this paper, the existence of tricritical points at the ferroelectric-paraelectric transition of PbZrxTi1-xO3 close to a value of x=0.94 is presented.
Abstract: Evidence is presented for the existence of a tricritical point at the ferroelectric-paraelectric transition of PbZrxTi1-xO3 close to a value of x=0.94. Details are given of measurements of dielectric constant, remanent polarisation and spontaneous strain. It is also observed that in single crystals of PbZrxTi1-xO3 there is a peak in the transition temperature versus composition diagram coinciding with the tricritical composition. This is not seen in ceramics of the same composition.
TL;DR: In this paper, a perturbation expansion about the atomic limit of the Anderson model is formulated in the limit of infinite conduction bandwidth, and terms up to second order in Delta are constructed in various temperature regimes; non-logarithmic terms are explicitly given.
Abstract: A perturbation expansion about the atomic limit of the Anderson model is formulated in the limit of infinite conduction bandwidth. Terms up to second order in Delta are constructed in various temperature regimes; non-logarithmic terms are explicitly given. Particular care is taken to expose the structure of perturbation theory in the valence fluctuation limit. An expression for the Kondo temperature is obtained and compared with numerical results. The structure of the expansion is commented on in the light of scaling theory.