摘要:

AbstractWe present a detailed analysis of high resolution measurements of the specific heat anomalies at theTcof three YBa2Cu3O7‐δ‐samples. The anomalies can be described by the sum of a mean field (MF) step and a contribution from gaussian fluctuations of the order parameter. These fluctuations are threedimensional (3D) nearTcand show a crossover to 2D‐behaviour some K away fromTc. By means of a Lawrence‐Doniach type description of the fluctuations we estimate the anisotropic coherence lengths ξ and ξ⊥. The values are consistent with data of the fluctuation contribution to the susceptibility aboveTc. We give data for ΔCMFand discuss the relevance of critical fluctuations. The influence of the oxygen content δ on the broadening and splitting of the trans

ISSN:0003-3804    

DOI:10.1002/andp.19935050202

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe specific heat of three polycristalline samples of La2‐xSrxCuO4+δ(x = 0.15, 0.15, 0.16) nearTcwas measured with a resolution better than 0.1%. The anomaly atTcis analysed for fluctuations for the first time. It is well described by a superposition of a mean field step and a contribution due to gaussian fluctuations. By a fit of a Lawrence‐Doniach type of model to the specific heat nearTcwe estimate ΔCMFand the anisotropic coherence lengths ξ and ξ⊥ of the super

ISSN:0003-3804    

DOI:10.1002/andp.19935050203

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractWe consider the problem of the rectified current induced by laser radiation in the STM junction when the tip is placed above a small molecule like CO or NO. This is calculated assuming a simple tight‐binding model for the tunneling junction including the adsorbate and using nonequilibrium Green's functions techniques. The coupling between tunneling electrons and the molecule vibrational modes is taken into account by a local electron‐phonon interaction term. In a second step we estimate the excitation rate of the molecule vibrations for a given laser power. This value is then used to obtain the relative change in the rectified current when the laser is in resonance with a molecule vibration. For a moderate laser power of 2 kW/cm2a relative change of 1 to 3% is predic

ISSN:0003-3804    

DOI:10.1002/andp.19935050204

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe pronounced variation of the intensity of photons emitted from the tunneling gap of an STM with respect to the applied bias voltageVtis studied experimentally using simultaneous measurements of tunneling characteristics and photon emission. We show that the structure in isochromat photon spectra are determined by the following: bias‐dependent changes in tunneling characteristics, density of initial and final states, and modifications of tip‐induced plasmon modes. It is demonstrated that isochromat spectra provide a conclusive test for the inelastic tunneling mechanism. Coupling between tunneling electrons and tip‐induced plasmon modes which gives rise to the intense photon emission observed is discussed within this

ISSN:0003-3804    

DOI:10.1002/andp.19935050205

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractIn the present study we use the Scanning Tunneling Microscope (STM) as an instrument to investigate the photovoltaic properties of semiconducting materials. The surfaces of the layered semiconductor WSe2were optically illuminated during the tunneling process. The resulting photo‐induced tunneling current (PITC) was measured as a function of the wavelength. Microscopic information on the energy dependent generation and recombination of the photo‐electrons in the vicinity of the tunneling tip was obtained by this method without the necessity of covering the surface with a conducting electrode. The analysis of the wavelength dependence of the PITC points at the existence of excitonic excitations. Compared to the spectral response of conventional photosensitive heterodiodes our PITC spectra exhibit a more structured response and an increase of the signal in the UV region. Finally, PITC studies on differently treated WSe2surfaces show an improved photoactivity for WSe2crystals treated with NaI/I2soluti

ISSN:0003-3804    

DOI:10.1002/andp.19935050206

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractBy exploring the surface of an illuminated object at a very short distance by means of a subwavelength detector, it is possible to reconstruct images whose resolution is beyond the diffraction limit. This opportunity due to the properties of near fields can be explained in terms of non radiating field detection. Such a detection is the basis of near field microscopy. In this communication emphasis will be put on some fundamental aspects of the new concept of non radiative optics such as the relation between Rayleigh criterion and Heisenberg principle and the notion of light confinement. Some proposals of non radiative transfers will be evoked.

ISSN:0003-3804    

DOI:10.1002/andp.19935050207

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractTheoretical investigations on the dynamics of the (001), (110) and (111) surfaces of some cubic metals (Ag, Cu, Ni) will be reviewed. Both, lattice dynamical and continuum theoretical results are obtained via a Green's function formalism. The main attitude of this paper is the comparison of our results with experiments and with results obtained via slab‐calculations. The calculation of elastic surface waves has been performed using a modified surface‐green‐function‐matching method. We have used two different approaches of calculation the bulk Green's function (a) using the spectral representation and (b) a method, what works on residues. The investigations are carried out using shortrange phenomenological potentials. The atomic force constants in the first surface layers are modified to describe surface phonon anomalies, observed by experiments. In the case of Ag (100) and Ag(110) we conclude that the detection of odd symmetry shear modes by Erskine et al. [1 a, b] was not very a

ISSN:0003-3804    

DOI:10.1002/andp.19935050208

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractWe investigate systematically the effect of the electronic Coulomb interaction on the stochastic fluctuations (from sample to sample) in the persistent currentsI(Φ) of mesoscopic rings threaded by a magnetic flux Φ. In contrast to our recent publication [Europhys. Lett.18(1992) 457], we avoid separation of impurity and interaction scattering events and we present here a comprehensive view. By this alternative procedure, we are able to confirm our earlier result, namely that 〈I2〉1/2∼evF/L, which is a much larger quantity than the average current 〈I

ISSN:0003-3804    

DOI:10.1002/andp.19935050209

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe low wavenumber collective diffusion coefficient of a semi‐dilute suspension of spherical Brownian particles interacting via square well potential and hydrodynamic pair interaction is considered. The first two nonvanishing terms of an expansion in powers of the wavenumber are calculated. Analytical expressions are found for extremely narrow wells and in the limit of large well diameter

ISSN:0003-3804    

DOI:10.1002/andp.19935050210

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19935050201

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY