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1.
Current-voltage (I–V) characteristics are studied in the intrinsic Josephson junctions of Bi2Sr2CaCu2Oy single crystals. In order to examine the influence of self-heating, a current pulse (∼0.2 μsec) is applied to the mesas of 40 μmϕx0.15 μm patterned on the crystal. As a consequence, in contrast to small characteristic voltageV c in the continuous-current measurement, theV c data is found comparable to the BCS value. Moreover, theI–V curve is nearly ohmic forl>l c , implying that the nonlinearity under the continuous current is due to heating. The quasiparticle resistance forT<T c is also presented by an estimate from the characteristic voltage.  相似文献   

2.
The detailed investigation of the phase dynamics and the I–V curves in the system of coupled Josephson junctions have been carried out. The superconducting, quasiparticle, diffusion, and displacement currents have been calculated as functions of the total current through the system. The role of the diffusion current in the formation of the I–V curves has been studied and the influence of this quantity on the I–V curve branching and the magnitude of the return current has been revealed. The calculation results agree qualitatively with the experimental data.  相似文献   

3.
Summary The recent improvements in the fabrication technology have succeeded in obtaining high-quality Josephson tunnel junctions. TheI–V characteristics of these junctions exhibit now lesser and lesser differences from the theoretical predictions. The various figures of merit, so far introduced to qualify the junctions, appear now focused on too limited aspects and a direct comparison with the detailed prediction of the theory is in order. For this awaken interest in the detailed predictions of the BCS theory, we have revisited the relevant formulae for the quasi-particle tunnelling current. A detailed discussion of the analytical transformation necessary for a simple numerical evaluation of this current is reported. SeveralI–V curves are obtained using the parameter values corresponding to the case of Nb-based junctions, which is the actual running technology. Peculiar interesting aspects are outlined.  相似文献   

4.
Summary Preparation procedure and sample characterization of 112 BiSCCO pellets exhibiting high-T c superconductivity are discussed. TypicalI–V and dV/dI curves of Nb/BiSCCO point conctact junctions at various temperatures are presented.  相似文献   

5.
Nanostructures with well-defined shape and highly monodisperse size were fabricated from model stilbazolium-like dyes with specific molecular structural and conformational characteristics. With the help of absorption and fluorescence optical spectroscopy, the correlated spectroscopy (COSY) and two- dimensional nuclear Overhauser effect spectroscopy (2D NOESY) techniques, along with X-ray diffraction (XRD) measurement, distinctively different aggregation processes of the model molecules are demonstrated. For model dye molecule with linear donor–π system–acceptor (D–π–A) structure, strong D–A pair, and planar conformation, specific intermolecular interaction was identified and special crystal structures as well as spectral properties were observed. For model dye molecules bearing nonlinear D–π–A–π–D structure, weak D–A pair but actual amphiphilic characteristics, a special aggregation process was confirmed and a focused size distribution of the produced nanostructures was obtained.  相似文献   

6.
In terms of the adiabatic theory of interactions, we consider the results of the theoretical estimation of the rate constants K ST of the nonradiative intersystem crossing conversion S 1(ππ*) ⇝ T 1 S (ππ*) for nine aromatic molecules containing 10–14 carbon atoms and one or two heavy (many-electron) oxygen or chlorine atoms.  相似文献   

7.
Electrical conduction in the temperature range of 120–370 K has been studied in sandwiched structures of Al/Ta2O5/Si. The tantalum oxide films were prepared by evaporation of tantalum on a p-Si crystal substrate, followed by oxidation at a temperature of 600°C. The temperature-dependent current-voltage (I–V) characteristics are explained on the basis of a phonon-assisted tunnelling model. The same explanation is given for I–V data measured on Ta2O5 films by other investigators. From the comparison of experimental data with theory the density of states in the interface layer is derived and the electron-phonon interaction constant is assessed.   相似文献   

8.
Results of experimental investigations into current-voltage characteristics of n+-π-p+ structures based on high-purity silicon doped with boron are presented. It is shown that the I–V characteristic at high injection levels is described by Stafeev's theory, when the thickness d of the π-region is smaller than or close to three ambipolar diffusion lengths La. For a current density J above (3–50) A/cm2 at varying temperatures, the I–V characteristic obeys a relation usually occurring in the case where charge-carrier recombination in the n+ and p+-regions dominates that found in the π-region. The effect of mutual electron-hole scattering on the behavior of the I–V characteristic is evident at J>630 A/cm3. For d/La=9, the I–V characteristic at high injection levels is treated by the theory of double carrier injection into a semiconductor with consideration for diffusion corrections. In the temperature range below 200–276 K, the I–V curve for all samples studied exhibits a linear dependence on J followed by a portion corresponding to a maximum occupancy of recombination levels by injected electrons. Here the Fe or Au donor levels presumably act as recombination levels. The electron and hole capture areas (cross sections) by recombination centers are roughly estimated. Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 35–45, July 2000.  相似文献   

9.
Differential cross-sections for the elastic scattering of excited exotic hydrogen atoms by hydrogenic atoms are calculated for the first time. The calculations are performed for exotic atoms (μ a,π a; a=p,d,t) in the states with the principal quantum numbers n=2-10 at relative motion energies E=0.001-15 eV and at scattering angles ϑ =0–18000B0;. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

10.
Zero-field current-voltage (I–V) characteristics of various high-temperature superconductor samples are analyzed in the context of the current-temperature (I−T) phase diagram. After establishing the validity and relevance of the phase diagram to these materials, the anisotropy factor is extracted from the slope ofI c 1 (T) (the current defined by the onset of resistance). It is concluded that studying theI−V characteristics of amples in the context of theI−T phase diagram is a simple, useful tool for comparing samples. Work supported by the Office of Naval Research.  相似文献   

11.
The sensitivity of the VLEED I–V curves to the shape and the position of the barrier is shown for the image- type surface barriers. For demonstration and comparison with experimental data the intensities of specularly reflected electron beams from Cu(111) are computed by dynamical theory of electron diffraction. Image plane position changes and modifications of the saturation shape of the surface barrier induce pronounced changes in the I–V curves calculated with the image-type barrier. Presented at the X-th Symposium on Suface Physics, Prague, Czech Republic, July 11–15, 2005.  相似文献   

12.
We extend the recently presented formalism for Monte Carlo calculations of the partition function, for both even and odd particle number systems (Phys. Rev. C 59, 2500 (1999)), to the calculation of many-body matrix elements of the type <ψ| e - βℋ|ψ> where |ψ> is a many-body state with a definite angular momentum, parity, neutron and proton numbers. For large β such matrix elements are dominated by the lowest eigenstate of the many-body Hamiltonian ℋ, corresponding with a given angular momentum parity and particle number. Emphasis is placed on odd-mass nuclei. Negligible sign fluctuations in the Monte Carlo calculation are found provided the neutron and proton chemical potentials are properly adjusted. The formalism is applied to the J π = 0+ state in 166 Er and to the J π = 9/2-, 13/2+, 5/2- states in 165 Er using the pairing-plus-quadrupole model. Received: 28 April 2000 / Accepted: 20 September 2000  相似文献   

13.
Thep-Si/HF-electrolyte interface was characterized by capacitance–voltage (C–V) and current–voltage (I–V) studies. At low frequency, the measured capacitance exhibits two maxima: one in the weak accumulation regime (around 0.8 V [SCE]) and the other in the strong accumulation regime (around 2.6 V [SCE]), both of which disappear at high frequency. The disappearance of the two capacitance maxima is attributed to the slow response of interface traps to high frequencies. The flat-band potential, VFB, is found to be frequency dependent. The surface state densities corresponding to the two capacitance maxima are estimated to be 3.2×1011 cm-2 and 2.4×1011 cm-2, respectively. The in situ I–V characteristics distinguish pore formation, transition and electropolishing regions. Porous Si synthesized at 50 mA cm-2 gives a broad photoluminescence peak around 2.04 eV at 300 K. Received: 4 September 2000 / Accepted: 9 February 2001 / Published online: 26 April 2001  相似文献   

14.
The decay rates of the3 D 1 level of I–II and the 3s 2 level of neon have been measured by the magnetic-field power dip method. The decay rate at the zero-pressure limit is found to be 7.1 MHz/2π for the3 D 1 level. The collision cross-section for excited I ions with helium atoms equals 0.19×10−15 cm2. This work was supported by project MR-1.5-1.05.  相似文献   

15.
Self-assembled monolayers (SAMs) of 4-trifluoromethyl-azobenzene-4′-methyleneoxy-alkanethiols (CF3– C6H4–N=N–C6H4–O–(CH2) n –SH on (111)-oriented poly-crystalline gold films on mica were examined by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The spectra are analyzed with the help of density-functional-theory calculations of the isolated molecule. Only one doublet is detected in the sulphur 2p spectra of the investigated SAMs, consistent with a thiolate bond of the molecule to the gold surface. The C 1s XP spectra and the corresponding XAS π * resonance exhibit a rich structure which is assigned to the carbon atoms in the different chemical surroundings. Comparing XPS binding energies of the azobenzene moiety and calculated initial-state shifts reveals comparable screening of all C 1s core holes. While the carbon 1s XPS binding energy lies below the π *-resonance excitation-energy, the reversed order is found comparing core ionization and neutral core excitation of the nitrogen 1s core-hole of the azo group. This surprising difference in core-hole binding energies is interpreted as site-dependent polarization screening and charge transfer among the densely packed aromatic moieties. We propose that a quenching of the optical excitation within the molecular layer is thus one major reason for the low trans to cis photo-isomerization rate of azobenzene in aromatic-aliphatic SAMs.  相似文献   

16.
The phenomenological amplitude for the reaction πN→ππN fixed by fittings to the experimental data in the energy region 0.300 ≤P Lab≤ 500 MeV/c is used for modelling the Chew–Low extrapolation and Olsson–Turner threshold approach. It is shown that the uncritical application of the former results in enermous theoretical errors, the extracted values being in fact random numbers. The results of the Olsson–Turner method are characterized by significant systematic errors coming from unknown details of the isobar physics. Received: 10 December 1997  相似文献   

17.
A systematic study on the geometrical structures, electronic and magnetic properties of Au5H n (n=1–10) clusters has been performed by using the all-electron scalar relativistic density functional theory with generalized gradient approximation at the PW91 level. It is found that all Au5H n clusters prefer to keep the planar structures like pure Au5 cluster, the Au5 structures in Au5H4, Au5H5 and Au5H6 clusters are distorted obviously. The adsorption of a number of hydrogen atoms enhances the stability of Au5 cluster and all Au5H n clusters are more stable than pure Au5 cluster energetically. The odd-even alteration of magnetic moment is observed in Au5H n clusters and may be served as the material with tunable code capacity of “0” and “1” by adsorbing odd or even number of H atoms. It seems that the most favorable adsorption between Au5 cluster and a number of hydrogen atoms takes place in the case that the odd number of hydrogen atoms is adsorbed onto Au5 cluster and becomes Au5H n cluster with even number of valence electrons.  相似文献   

18.
Electron-beam diagnostics are used to study the radiation-induced conduction of supershallow p +-n silicon junctions obtained by nonequilibrium boron diffusion. Current-voltage (IV) characteristics of radiation-induced conduction of a both forward-and reverse-biased p +-n junction are demonstrated for the first time, which has been made possible by the presence of self-organized transverse quantum wells inside a supershallow p + diffusion profile. The variation of the dark-current IV characteristics with electron irradiation dose shows that formation of self-organized longitudinal quantum wells inside supershallow p + diffusion profiles favors an increase of the breakdown voltage in p +-n silicon junctions. Fiz. Tverd. Tela (St. Petersburg) 41, 1871–1874 (October 1999)  相似文献   

19.
A low energy electron accelerator has been constructed and tested. The electron beam can operate in low energy mode (100 eV to 10 keV) having a beam diameter of 8–10 mm. Thin films of CdS having thickness of 100 nm deposited on ITO-coated glass substrate by thermal evaporation method have been irradiated by electron beam in the above instrument. The I–V characteristic is found to be nonlinear before electron irradiation and linear after electron irradiation. The TEP measurement confirms the n-type nature of the material. The TEP and I–V measurements also confirm the modification of ITO/CdS interface with electron irradiation.   相似文献   

20.
Summary In this paper we report the in-plane fabrication and the characterization of artificially engineered biepitaxial grain boundaries (GB) obtained by partly interposing a MgO seed layer between a bare or even-buffered substrate and a CeO2 thin layer. The main peculiarity of this technique can be summarized by the capability to locate and engineer a single 45°-tilted GB at any stage of the device preparation. The junctions, realized by patterning the grain boundary occurring in the overhanging YBCO film, show Josephson current modulation in a large temperature range with anI c R n value of about 200 μV at 4.2K, theR n value being constant over the whole superconducting region. Under microwave irradiation, theI–V characteristics display several Shapiro steps while, according to the Resistively Shunted Junction (RSJ) behaviour, the step heights have the typical current biased junction dependence. Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994.  相似文献   

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