SPA-LEED studies of growth of Ag on Ag(111) at low temperatures

The surface morphology after deposition of Ag on Ag(111) at low temperatures (130–200 K) has been studied in detail with SPA-LEED (Spot-Profile Analysis of Low-Energy Electron Diffraction). The surface roughness and the mean terrace size have been quantitatively determined under various conditions. At 130 K the surface roughness increases with coverage exactly according to the relation = ^1/2, which indicates that the inter-layer diffusion can be neglected at 130 K. Although the mean terrace length decreases with increasing coverage (following an approximate power law of ^–2/3) for all studied coverages, it is much larger than expected for a pure random or Poisson-growth mode without any diffusion of the adatoms. Therefore, Ag grows on Ag(111) at this temperature without interlayer diffusion but with intra-layer diffusion. The intralayer diffusion barrierE _d has been determined by measuring the temperature dependence of the two-dimensional island density according to the nucleation theory (supposing a critical nucleus size of one). The obtained valueE _c=0.18 eV agrees with the theoretical calculations and previous measurements. Furthermore, from comparing measured and Monte-Carlo-simulated (MC) surface roughness at different deposition temperatures we obtain E=0.05 eV as a lower limit for the additional barrier at steps.     

Spannungsverläufe Nach Wechseln der Verformungsgeschwindigkeit an Metalleinkristallen

The theoretical relations between _v and measured stress changes are discussed and compared with experimental results. For instantaneous change in the strain rate, the first deviation of the stress increase from the linearity ( _C ) can be used as a measure of _v for small deformation only. The comparison of _C with the extrapolated value _A enables to reveal the presence of recovery. The comparison of stress changes measured after a given rate change at the same strain on unrecovering (low temperatures) and recovering (higher temperatures) samples enables to differentiate between various types of recovery.     

Spin-wave analysis of easy-axis quantum antiferromagnets on the triangular lattice

We perform the standard spin wave analysis of the triangular Heisenberg quantum antiferromagnet with nearest neighbour coupling. The exchange interaction is taken to be J _{z=J x=J y} (0<1). We give a simple explanation of the non-trivial classical degeneracy pointed out by Miyashita and Kawamura and show that it is removed by quantum fluctuations, but that the degeneracy manifests itself through the appearance of a second gapless spin-wave branch. The existence of a second gapless mode has a drastic influence on the quasiclassical behaviour near the Ising limit: the energy gain with respect to the Ising state energy is found to be linear in , and the reduction of the sublattice magnetization on two of the three sublattices remains finite as 0. These findings essentially invalidate the original qualitative arguments [14] in favour of a spin-liquid ground state of the anisotropic triangular antiferromagnet.     

Pressure sensitivity of the peak current of gallium arsenide tunnel diodes

The influence of hydrostatic pressure on the peak current of gallium arsenide tunnel diodes is studied in this paper. Analysis of the experimental pressure dependence of the peak current for diodes with different levels of doping in the n region and comparison with the theory served as the basis for finding the size of the energy gap between the absolute and secondary minima at the point X₁ and the velocity of travel of the energy gap with pressure: ⁰=(0.37±0.01) eV; d/dP = –(15±2)·10^–6 eV/bar.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 74–77, September, 1976.     

Anisotropy of the low temperature resistivity of hexagonal single crystalline spin glass systems

The impurity contribution to the resistivity in zero field (T) of dilute hexagonal single crystals of ZnMn, CdMn and MgMn has been studied in the mK range on samples cut parallel () and perpendicular () to thec-axis, using a SQUID technique for the measurements. Typical spin glass behavior is found in (T) as well as (T) for all alloys, with Kondo like logarithmic increases at higher temperatures and maxima atT _m at lower temperatures, indicating the influence of impurity interactions. The differences in the corresponding isotropic resistivity _poly(T) between the three systems can qualitatively be understood within the framework of a theoretical model by Larsen, describing (T) as a function of universal quantitiesT/T _K and _RKKY/T _K , where _RKKY is the RKKY-interaction strength andT _K the Kondo temperature. With respect to the two lattice directions studied, the behavior of (T and (T is anisotropic in the Kondo regime as well as in the range where ordering becomes important. While the anisotropy in the Kondo slope can be understood by an anisotropic unitarity limit, the understanding of the anisotropy in region where impurity interactions are important remains problematic.Dedicated to Prof. Dr. S. Methfessel on the occasion of his 60th birthday     

Analysis of intermediate structures of spectral emission in pre-equilibrium nuclear reactions in the microscopic approach

The quasi-particle-phonon model of pre-equilibrium decay (QP Ph M PED) is proposed. Within this model, intermediate states are specified by the number of quasi-particles, quasi-holes and phonons. In describing nuclear relaxation we consider two types of internuclear transitions with the change in exciton number byN _ex=0, ±2 and number of phononN _ph=±1. The mixed densities of intermediate states(N _ex,N _ph,E) have been determined. An analysis has been made of the structure of the hard part of the emission spectrum in the⁶⁰Ni(p,p) and¹²⁰Sn(p,p) reaction at _p=62 MeV. This analysis suggests the importance of taking into account the transitions withN _ph=+1, along with the transitions withN _ex= +2.     

Energy band structure of CdSnAs2 and CdGeAs2

The energy band structure of CdSnA₂ and CdGeAs₂2 is calculated by the empirical-pseudopotential method, taking account of spin-orbital interaction. The calculated parameters – E_g = 0.25, _cr = 0.05, _s.o = 0.44 for CdSnAs₂ and E_g = 0.55, _cr = 0.20, and _s.o = 0.33 for CdGeAs₂ (all in eV) — are in good agreement with experiment. The conclusion drawn in a series of experimental works that there are additional minima close to the bottom of the CdSnAs₂ conduction band is not confirmed in the calculation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 78–82, December, 1981.     

Wannier–Stark effect in strongly coupled three quantum well structures and superlattices

The Wannier–Stark effect has been investigated in strongly coupled three quantum well structures and 23.5 period superlattices consisting of 25Å wide GaAs wells separated by Al_0.25Ga_0.75As barriers of the same width. A blue shift associated with the Wannier–Stark localization of heavy holes states is observed for the first time, followed by a second blue shift at higher electric fields due to the electron localization. This is contrary to the widely reported single blue shift of the order of (e+hh)/2, where e and hh are the electron and heavy hole miniband widths respectively, produced by Wannier–Stark localization in superlattices.     

A long-time tail for random walk in random scenery

Consider a simple random walk on ^d whose sites are colored black or white independently with probabilityq, resp. 1–q. Walk and coloring are independent. Letn _k be the number of steps by the walk between itskth and (k+1) th visits to a black site (i.e., the length of itskth white run), and let _k =E(n _k )–q ^–1. Our main result is a proof that (*) lim _k k ^d/2 _k = (1 –q)q ^{d/2 – 2}(d/2) ^d/2. Since it is known thatq ^{– 1} _k =E(n ₁ n _{k + 1} B) –E(n ₁ B)E(n _{k + 1} B), withB the event that the origin is black, (*) exhibits a long-time tail in the run length autocorrelation function. Numerical calculations of _k (1k100) ind=1, 2, and 3 show that there is an oscillatory behavior of _k for smallk. This damps exponentially fast, following which the power law sets in fairly rapidly. We prove that if the coloring is not independent, but is convex in the sense of FKG, then the decay of _k cannot be faster than (*).     

Representations of state space transformations by Markov kernels

Every convex subset of a locally convex Hausdorff space (X, ) is equipped with the (-algebra generated by its-relatively open subsets. Within the set () of probability measures on two particular convex subsets are considered: (a) the set ^s () of probability measures with a separable support, and (b) the set ^c () of probability measures with a compact convex support. If is the base of a cone inX, then there exists an affine barycenter map from ^c () onto whose composition with the natural embedding of in ^c () yields the identity map on , and every-continuous affine transformation of can be represented by an affine transformation of ^c () that is induced by a Markov kernel. If (X, ) is a Banach space and is a closed, bounded, generating cone base inX that is contained in a hyperplane, then analogous results are obtained with respect to ^s (). Since the state spaces considered in noncommutative measure theory are cone bases and every change in time of an empirical system can be thought of as an affine transformation of the associated state space (Schrödinger picture), the existence of these representation theorems implies that the time evolution of general empirical systems can be described by dynamical concepts borrowed from classical probability theory.     

Mathematical properties of gap-functions in strongly coupled superconductors

We consider the Dyson equation associated with the BCS superconducting state from a mathematical point of view. The Dyson equation gives rise to a modified gap equation that is similar to the BCS gap equation, but with a different kernel. We first show that for strong coupling (such that the McMillan parameter ||1) both the real and imaginary parts of the solution (E) of the modified gap equation alternate in sign as function of the excitation energyE, the periods being 4₀ for positive and 4₀/3 for negative . (₀ is the frequency of an Einstein spectrum of phonons). A closed, algebraic approximation to (E) is 2||₀log[cotan(E/ )]. Finally, the poles of the kernel of the integral equation are located in the complex-E plane. For the new-type, oscillatory solution of the modified gap equation the analogue of the causal (zero-temperature) Green's function is shown to have different analytic properties from those of the smooth Eliashberg solution of BCS theory.     

Anisotropic fiber with cylindrical polar axes

The newly proposed anisotropic fiber structures with cylindrical polar principal axes appear to be an interesting novel class of special lightguides. In this paper, some interesting results relating to such fibers are derived which, to the knowledge of this author, have not yet been reported in the literature. It is found that, ifn _c0 ( )^1/2>n _zc0( _r )^1/2, TE₀₁ will be the fundament mode with a range of single-mode operation given by 2.61n _zc0 (2 _r )^1/2 /a<2.61n _c0(2 )^1/2. On the other hand, ifn _zc0 ( _r )^1/2>n _c0( )^1/2, then TM₀₁ becomes the fundamental mode whose single-mode operation range is 2.61n _c0 (2 )^1/2 /a<2.61n _zc0(2 _r )^1/2.     

Weak density of states

Let L be a quantum logic, here an orthoalgebra, and let be a convex set of states on L. Then generates a base-normed space, and the dual-order unit-normed space contains a canonically constructed homomorphic copy of L, denoted by e(L). A convex set of states on L is said to be ample provided that every state on L is obtained by restricting an element of the base of the bi-dual order unit-normed space to e(L). For a quantum logic L we show that a convex set of states is ample if and only if is weakly dense in the convex set of all states on L. The notion of ampleness is then discussed in the context of Gleason-type theorems for W^* algebras and JBW algebras and also in the context of classical logics.Dedicated to Prof. Peter Mittelstaedt on the occasion of his sixtieth birthday. Research supported by the Swiss National Science Foundation.     

On the failure of the time-energy uncertainty principle

We establish, for the quantum system made up of a single free particle, the formula E t(v/c) , where E is the precision to whichE can be ascertained in time t. The measurement can be carried out with zero disturbance inE itself.     

Temperature dependence of the effective work function for the BaO - W system

The temperature dependence of the work function has been examined for the BaO-W system for degrees of coating less than 1 and about 1 in the range 700–1400 °K; it is found that a monomolecular film gives a negative sign of this coefficient in this temperature range ( /T 10^–4 –10^–3 eV/deg). At 1000–1200 °K, the temperature coefficient is almost zero, while at 1200–1400 °K there is a positive value. If the covering is less than monomolecular, the sign is positive throughout the entire temperature range (/T 10^–4 eV/deg).Deceased.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 9, pp. 65–70, September, 1971.We are indebted to N. I. Éngovatova for direct assistance with the measurements, and to V. Rumyantsev for advice.     

Optical properties of ternary ZnS x Se1−x polycrystalline thin films

Ternary ZnS_xSe_1–x polycrystalline thin films were prepared by evaporation in vacuum of 10^–5 Torr. The molecular fractionx varied in the region ox1. The optical constants (the refractive indexn, the absorption indexk, and the absorption coefficient) were determined in the wavelength range 300–1600nm. A plot representing ₂=f(hv) shows that the ZnS_xSe_1–x polycrystalline thin films of different compositions have two direct transitions corresponding to the energy gapsE andE+. The variation in eitherE orE+ withx indicates that this system belongs to the amalgamation type. Such variation follows a quadratic equation. The bowing parameter was found to be 0.456 eV, roughly equal to the calculated value 0.60 eV using the empirical pseudopotential method based on the virtual-crystal approximation, in which the disorder effect has not been taken into account.     

The theory of neutron scattering from mixed harmonic solids

In the intermediate valent cerium alloys Ce_1–xY_xPd₃, Ce(Pd_1–xRh_x)₃ and Ce(Pd_1–xAg_x)₃ the Gd³⁺-ESR shows a non-linear increase of the linewidth H(T) in the temperature range 4.2KT300K. The deviation from the linear Korringa law can be described by a reduced conduction electron density of states at the Gd site (which is a Ce lattice site) in the energy range E _4f (=width of the Ce 4f states). This supposition allows a determination of E _4f from the H(T)-data. For CePd₃:Gd³⁺ we find E _4f=(650±100) K. E _4f increases with Y- and Rh-concentration and decreases with Ag-concentration.     

Periodic Thermodynamics

This paper develops the thermodynamics of quantum Floquet systems, i.e., quantum systems driven by an arbitrarily strong periodic perturbation, which are in weak interaction with a heat bath. The physics differs in an essential way from that of undriven systems, because the usual energy conservation law, for interactions between the system and heat bath, is changed to +E=0, ±, ±2,... where is the driving frequency, is the difference of the so-called quasi-energies of the Floquet states and E the excitation energy of the bath. That is, a transition between two given physical Floquet states will be accompanied by bath transitions with many different energy changes, E=–+m, where m is an arbitrary integer. This results in a breakdown of detailed balance. There is a steady state in which the system has periodic fluctuations of period T=2/. The steady state density matrix is diagonal in the Floquet states, with all Floquet states having finite weights, even at zero temperature. Experimentally favorable conditions for studying periodic thermodynamics are briefly discussed.     

Wavevector scaling,surface critical behavior,and wetting in the 2-d, 3-state chiral clock model

The controversial 2-d, 3-state chiral Potts model is studied using transfer matrix finite size scaling. at =0, we find dq _N/dN ^–4/5, whereq is the wavevector, the chiral field, andN the strip width (N=4–10). The result is consistent with den Nijs's crossover exponent =1/6. With surface fields on the infinite free boundaries, exponents associated with bulk magnetizationy _H, surface magnetizationy _H, and surface susceptibility are computed vs. ; results are similar for or to the infinite direction. Preliminary results are given for the bulk specific heat critical amplitudes, to test the universality of amplitude ratios. The interface wetting line is located for 01/4 using simple transfer matrix calculations of surface tensions in the solid-on-solid approximation. Overhangs or bubbles seem relatively unimportant at all temperatures.     

An Equilibrium Lattice Model of Wetting on Rough Substrates

We consider a semi-infinite 3-dimensional Ising system with a rough wall to describe the effect of the roughness r of the substrate on wetting. We show that the difference of wall free energies (r)= _AW(r)– _BW(r) of the two phases behaves like (r)r(1), where r=1 characterizes a purely flat surface, confirming at low enough temperature and small roughness the validity of Wenzel's law, cos (r)r cos (1), which relates the contact angle of a sessile droplet to the roughness of the substrate