共查询到20条相似文献,搜索用时 15 毫秒
1.
Detailed computer simulations have been made of the effect of intrinsic noise current on the I-V characteristic and voltage noise spectral density S
v
(f) of an ideal Josephson element shunted by a capacitor and resistor. The minimum value of the parameter
c
at which hysteresis appears in the quasistatic I-V characteristic is greater than the noise-free value of 1. Moreover, as
c
is increased, a region of large differential resistance R
d appears in the I-V characteristic that is associated with a large increase in S
V(0). In this regime the noise current is seen to cause random switching between the superconducting and nonzero voltage states. For all bias conditions, S
V(f) > R
d
2S I(f) where S
I(f) is the spectral density of the intrinsic current noise. A comparison is made between these results and previous calculations. The implications for low-noise superconducting devices are discussed. 相似文献
2.
AbstractA zero-gap state with a Dirac cone type energy dispersion was discovered in the organic conductor α-(BEDT-TTF) 2I 3 under high hydrostatic pressures. This is the first two-dimensional (2D) zero-gap state discovered in bulk crystals with a layered structure. In contrast to the case of graphene, the Dirac cone in this system is highly anisotropic. The present system, therefore, provides a new type of massless Dirac fermion system with anisotropic Fermi velocity. This system exhibits remarkable transport phenomena characteristic to electrons on the Dirac cone type energy structure. The carrier density, written as n∝ T2, is a characteristic feature of the 2D zero-gap structure. On the other hand, the resistivity per layer (sheet resistance RS) is given as RS= h/ e2 and is independent of temperature. The effect of a magnetic field on samples in the zero-gap system was examined. The difference between zero-gap conductors and conventional conductors is the appearance of a Landau level called the zero mode at the contact points when a magnetic field is applied normal to the conductive layer. Zero-mode Landau carriers give rise to strong negative out-of-plane magnetoresistance. 相似文献
3.
The effects of different electric fields (4.2, 8.3, 12.5, 16.7 and 20.8 Vcm –1) on the sheet resistance, R
s, and optical band gap, E
obg, of As 2Se 3 samples (1×10 5nm) that were photodoped by Ag (5×10 3nm) have been studied. The R
s and E
obg of samples subjected to an electric field of 12.5 Vcm –1 decrease linearly to a distance of 5 mm from both electrodes, and then saturate at larger distances. This result suggests that there is a critical value of the electric field which affects photodoping. The dependence of R
s and E
obg on the distance from the electrodes shows similar profiles for these electrodes. 相似文献
4.
We have developed a model for the resistive transition in a transition edge sensor (TES) based on the model of a resistively shunted junction, taking into account phase-slips of a superconducting system across the barriers of the tilted washing board potential. We obtained analytical expressions for the resistance of the TES, R( T, I), and its partial logarithmic derivatives α I and β I as functions of temperature and current. We have shown that all the major parameters describing the resistive state of the TES are determined by the dependence on temperature of the Josephson critical current, rather than by intrinsic properties of the S-N transition. The complex impedance of a pristine TES exhibits two-pole behaviour due to its own intrinsic reactance. 相似文献
5.
We have measured the millimeter-wave (100 GHz) surface resistance of high-quality laserdeposited YBa 2Cu 3O 7 films on SrTiO 3 and LaA10 3 substrates. Due to finite film thickness, radiation losses are important in the normal state and in the superconducting state near T
c. These effects are calculated and R
s characteristic of the ohmics losses in the film are extracted from the data. The surface resistance R
s drops rapidly at T
c, and a detailed comparison with calculations which include finite mean free path effects suggests a gap which exceeds the weak coupling BCS limit. 相似文献
6.
Microwave surface impedance, Z
s( T), of epitaxial YBCO thin films deposited on CeO 2-buffered sapphire substrates, was measured at several discrete frequencies within the range 5–134 GHz by use of coplanar
resonator and end-plate cavity resonator techniques. The main features of obtained experimental results are as follows: (i)
surface resistance R
s( T) at low temperatures obeys the exponential law: R
s( T) = R
res+ R
0⋅exp [−δ/ T] with a small gap δ value (δ≈ 0.7 T
c); (ii) the most perfect quasi-single-crystalline films reveal a distinct two-peak structure of R
s( T) dependence, which is not observable in films with a less ordered crystal structure. These features are believed to reveal
some intrinsic electron properties of such films, namely: (i) mixed (d+ is) type symmetry of electron pairing, and (ii) dominant role of extended c-oriented defects (e.g., edge dislocation arrays or twin planes) in quasiparticles scattering for the most perfect films,
which demonstrate the two-peak anomalous R
s( T) behavior. 相似文献
7.
The knowledge of the surface resistance R
s of superconducting thin film at microwave and terahertz (THz) regions is significant to design, make and assess superconducting
microwave and THz electronic devices. In this paper we reported the R
s of MgB 2 films at microwave and THz measured with sapphire resonator technique and the time-domain THz spectroscopy, respectively.
Some interesting results are revealed in the following: (1) A clear correlation is found between R
s and normal-state resistivity right above T
c, ρ 0, i.e., R
s decreases almost linearly with the decrease of ρ 0. (2) A low residual R
s, less than 50 μΩ at 18 GHz is achieved by different deposition techniques. In addition, between 10 and 14 K, MgB 2 has the lowest R
s compared with two other superconductors Nb 3Sn and the high-temperature superconductor YBa 2Cu 3O 7−δ(YBCO). (3) From THz measurement it is found that the R
s of MgB 2 up to around 1 THz is lower than that of copper and YBCO at the temperature below 25 K. (4) The frequency dependence of R
s follows ω
n
, where ω is angular frequency, and n is power index. However, n changes from 1.9 at microwave to 1.5 at THz. The above results clearly give the evidences that
MgB 2 thin film, compared with other superconductors, is of advantage to make superconducting circuits working in the microwave
and THz regions. 相似文献
8.
Chiral organic−inorganic hybrid metal halide materials have shown great potential for circularly polarized luminescence (CPL) related applications for their tunable structures and efficient emissions. Here, this work combines the highly emissive Cu 4I 4 cubane cluster with chiral organic ligand R/ S-3-quinuclidinol, to construct a new type of 1D Cu-I chains, namely Cu 4I 4( R/ S-3-quinuclidinol) 3, crystallizing in noncentrosymmetric monoclinic P2 1 space group. These enantiomorphic hybrids exhibit long-term stability and show bright yellow emission with a photoluminescence quantum yield (PLQY) close to 100%. Due to the successful chirality transfer from the chiral ligands to the inorganic backbone, the enantiomers show intriguing chiroptical properties, such as circular dichroism (CD) and CPL. The CPL dissymmetry factor ( glum) is measured to be ≈4 × 10 −3. Time-resolved photoluminescence (PL) measurements show long averaged decay lifetime up to 10 µs. The structural details within the Cu 4I 4 reveal the chiral nature of these basic building units, which are significantly different than in the achiral case. This discovery provides new structural insights for the design of high performance CPL materials and their applications in light emitting devices. 相似文献
9.
The temperature, microwave current, and dc magnetic field dependencies of the effective surface resistance R
s
of YBa 2Cu 3O 7–x
grain boundary Josephson junctions have been investigated at 6 GHz. The junctions were prepared on stepped LaAlO 3 substrates and incorporated into tapered linear half-wavelength microstrip resonators. The characteristic parameters of the heterogeneous resonator were analyzed theoretically considering the junction as a lumped element of complex impedance. The microwave properties of the junction could then be extracted and related to their characteristic dc transport properties. The critical current I
c of the junction was found to limit the linear power dissipation in the superconducting strip. At microwave currents above I
c
, highly nonlinear microwave losses occurred, which displayed a characteristic magnetic field modulation. At even higher currents, R
s
saturated at a level corresponding to the normal resistance R
n
of the junction. 相似文献
10.
Microwave surface resistance ( R
s
) measurements on large-area (11.4 cm 2) Tl-based films deposited onto Ag (Consil 995) substrates have been made at a frequency of 18 GHz as a function of temperature. Deposition onto unoriented Ag substrates yields unoriented films characterized by R
s
values of 8.2 and 33.6 m at 10.6 and 77 K, respectively. In contrast, similar deposition onto oriented Ag substrates yields oriented films with values of 12.6 and 14.6 m at 11.2 and 77 K, respectively; corresponding Cu values are 9 and 21 m. Additionally, it is found that the dependence of R
s
on microwave surface magnetic field H
s
is weaker for the oriented films. These results suggest that the effect of orienting the c-axis in Tl films is twofold: (1) the high-frequency superconducting transition is made considerably sharper, resulting in a lower R
s
value at 77 K, and (2) the rate of increase in R
s
with applied H
s
is reduced. Both effects have significant ramifications for the potential application of these materials to high-frequency accelerating cavities. 相似文献
11.
In the present study we report the measurements of microwave surface resistance ( Rs) of YBCO thin films on LaAlO 3 substrate as a function of temperature, thickness and magnetic field by microstrip resonator technique. The Tc( R = 0) of the films is 90 K and Jc > 10 6 A/cm 2 at 77 K. The microwave surface resistance has been measured for films of various thicknesses. The value of Rs has been found to be initially decreased with increasing film thickness due to increase in number of defects. A minimum microwave surface resistance has been obtained for film thickness of about 300 nm. The increase of Rs with film thickness above 300 nm is possibly due to degradation of the film microstructure as observed with Atomic Force Microscopy. Temperature dependence of surface resistance has been studied for best quality films. The field induced variations of surface resistance are also investigated by applying dc magnetic field perpendicular to stripline structure and surface of the film. A general linear and square field dependence of Rs at low and high value of fields has been observed with critical field value of 0.4 T which confirms the microwave dissipation induced by flux flow in these resonators at 10 GHz frequency. The hysteresis of Rs in dc field observed for field value above critical field shows the higher value of surface resistance in decreasing field than in increasing field which is in agreement with one state critical model and is a characteristic of homogeneous superconductors. 相似文献
12.
A new behavior of the field dependence of microwave surface resistance ( R
s), which was observed on a microstrip resonator and may be caused by the edge of the center strip, is reported in this paper for epitaxial high- T
c superconducting (HTSC) thin films. The exhibited behavior is that R
s remains almost unchanged below a certain rf magnetic field H
rf, and then increases abruptly at this field, after which it increases in proportion to H
rf. To explain the behavior, the morphology of the microstrip resonator was examined by atomic force microscopy (AFM), which showed that the edge of the resonator was damaged in some regions because of the acid etching. If the damaged edge is considered as a weakened granular superconductor, the observed R
s behavior could be explained well in terms of the high-frequency critical state model. This implies that the edge condition should be considered in studying the field dependence of R
s when the planar resonator technique is used. 相似文献
13.
We present a simple model to simulate small three-dimensional superconducting constrictions of variable thickness (VTBs) for which the cross-sectional dimensions are of the same order as the length, and both are less than ( T). We study the behavior of the modulus of the order parameter f and the supercurrent density J
s
as a function of the various dimensions. We find that the extent to which f is depressed in the banks depends on the ratio of width to length of the constriction. We show that even for very abrupt geometries, J
s
is not zero and f does not reach its equilibrium value immediately outside the constriction. On the basis of our results, we propose a more general expression for the effective length valid also when all dimensions are of the same order. The calculated values of dI
c
/ dT are consistent with experimental data from well-characterized VTBs. We suggest that the discrepancy between the calculated and experimental values of I
c
R
n
may be due to the nonuniformity of the normal current density in the constriction. 相似文献
14.
An intrinsic gap depression at the superconductor-insulator interface due to the very short value of the coherence length
in high- T
c
superconductors [HTS] is considered in the framework of a mixed ( s+id)-wave pair symmetry for the order parameter ranging from pure s to pure d-wave. This gap depression acts as the main physical agent causing the relevant reduction of I
c
(T)R
n
(T) values with respect to BCS expectations in HTS SIS Josephson junctions. Good agreement with various experimental data is
obtained with both pure s-wave and pure d-wave symmetries of the order parameter, but with amounts of gap depression depending on the pair symmetry adopted. Regardless
of the apir symmetry considered, these results prove the importance of the surface order-parameter depression in the correct
interpretation of the I
c
(T)R
n
(T) data in HTS SIS junctions. In the case of a planar YBCO-based junction the use of the de Gennes condition allowed us to tentatively
obtain an upper limit for the amount of d-wave present in the gap of YBCO. 相似文献
15.
A colorimetric multifunctional phototransmittance‐based structural durability monitoring system is developed. The system consists of an array with four indium gallium zinc oxide (IGZO)‐based phototransistors, a light source at a wavelength of 405 nm through a side‐emitting optical fiber, and pH‐ and Cl‐selective color‐variable membranes. Under illumination at the wavelength of 405 nm at corrosion status, the pH‐ and Cl‐responsive membrane, showing a change in their color, generates a change in the intensity of the transmitted light, which is received by the phototransistor array in the form of an electrical current. Ids and R ( Ids/ IpH 12) are inversely proportional to the pH, which ranges from 10 to 12. When the pH drops from 12 to 10, the magnitude of Ids and R increases to ≈10 3. In the case of Cl detection, Ids and R ( Ids/ ICl 0 wt%) increase nearly 50 times with an increase in Cl concentration of 0.05 wt%, and when the Cl concentration reaches 0.30 wt%, Ids and R increase to ≈10 3 times greater. This multifunctional colorimetric durability sensing system demonstrates considerable potential as a novel smart‐diagnostic tool of structural durability with high stability, high sensitivity, and multifunction. 相似文献
16.
We present direct measurements of the density of states by tunneling spectroscopy on slightly overdoped Bi 2Sr 2CaCu 2O 8+x
(Bi2212) single crystals at low temperature using break-junction and point-contact techniques. We find that (i) the variation of the gap magnitude, , between 20 and 36 meV is likely to be intrinsic to Bi2212, and (ii) there is a correlation between the maximum value of the Josephson I
c
R
n product and the gap magnitude: I
c
R
n decreases with the increase of . The maximum I
c
R
n value of 26 mV is observed at = 20.5 meV. For = 36.5 meV, the maximum measured value of I
c
R
n is 7.3 mV. We conclude that (i) the distribution of the Josephson I
c
R
n product as a function of gap magnitude cannot be explained by the presence of a single energy gap in Bi2212, and (ii) the coherence energy scale in Bi2212 has the maximum Josephson strength. 相似文献
17.
This paper investigates the low‐cycle fatigue resistance of BS 460B and BS B500B steel reinforcing bars and proposes models for predicting their fatigue life based on plastic‐strain ( ?ap) and total‐strain ( ?a) amplitudes. Constant‐amplitude, strain‐controlled low‐cycle fatigue tests were carried out on these bars under cyclic load with a frequency of 0.05 Hz. The maximum applied axial strain amplitude (? s,max) ranges from 3 to 10% with zero and non‐zero mean strains. The strain ratios ( R = ? s,min/? s,max) used are R =?1, ?0.5 and 0. Hysteresis loops were recorded and plastic and total strain amplitudes were related to the number of reversals (2 Nf) to fatigue failure and models for predicting the number of reversals to fatigue failure were proposed. It is concluded that the predicted fatigue life of these bars is very accurate when compared with the measured experimental fatigue life results for wide range of values of strain ratios. It is also observed that based on plastic‐strain amplitude, BS B500B consistently has a longer life (higher number of cycles to failure) than those of BS 460B for all R values; however, at low plastic‐strain amplitudes they tend to behave similarly, irrespective of R value. Other observations and conclusions were also drawn. 相似文献
18.
A real-time monitoring technique for local plasticity using Lamb waves was developed. Tensile test of a thin aluminum plate with a circular hole where high stress concentration was induced was conducted to verify this technique. During the tensile test, a series of wave signals passing through the local plastic region were collected using a directional actuator/sensor set to monitor plasticity evolution. A pulse compression technique was used to process the wave signals. With the increase of tensile stress in the specimen, the amplitude changes of S 0 and A 0 modes were obtained and the difference of Lamb wave signals was further evaluated using a proposed signal index I calculated by wavelet analysis. Combined with the numerical stress analysis of the tensile specimen, the influence of the plasticity on the amplitudes of S 0 and A 0 wave modes was analyzed. As the plastic zone grows gradually, the wave amplitudes and I of S 0 and A 0 wave modes show their different change tendencies compared with those in elastic stage. The amplitude change is more sensitive to mild plasticity than that of I, while the change of I caused by severe plasticity is more obvious than the amplitude change. 相似文献
19.
The admittance characterizations of the ferroelectric Perovskite Materials 1% Osmium (Os)-doped YMnO3 and p-Si contacts were conducted by capacitance–voltage (C–V) and conductance–voltage (G–V) curves at various frequencies. In measurements performed in this study, it was seen that the device behaves like a metal/oxide layer/semiconductor (MOS) or a metal/insulator layer/semiconductor (MIS) capacitor, just because of the ferroelectric thin film at the metal/Si substrate interface. Therefore, an accumulation region (saturation region) formed in the forward bias C–V and G–V curves at each frequency. The accumulation region series resistance value Rsc was determined from the C–V and G–V curves. The Rsc value ranged from 652 Ω at 20 kHz to 56 Ω at 1000 kHz. Furthermore, the series resistance Rs versus V curves with frequency as a parameter were plotted from the C–V and G–V data. A peak appeared around 0.0 V in the Rs vs V curve at each frequency. The peak position of the Rs shifted towards positive voltages from approximately ? 0.2 V at 20 kHz to about 0.10 V at 1000 kHz. The peak position in the corrected conductance vs voltage curves shifted towards positive voltages from approximately 0.0 V at 20 kHz to about 0.20 V at 1000 kHz. It was seen that the series resistance effect caused the highest error in the capacitance occurs in accumulation and in some part of the depletion region at C–V and G–V results depending on frequency. So to conclude, it is not possible to disregard the series resistance everytime. Therefore, the series resistance must be measured and must be considered at the measured admittance. 相似文献
20.
The step-wise technique is used to follow the possible changes in d.c. transport of three different glasses of the system
Ag-As 2S 3 isothermally annealed at T
g< T< T
m. The isothermal time-dependence of different characteristic electrical quantities (e.g. E
σ,σ 20°C, and σ
0) has been drawn and correlated with the microstructural changes recorded for samples annealed at the same conditions. The
effect of silver content (up to 25 at %) on the interplanar spacings ( d
hkl) and relative intensities ( I/I
0) of the diffraction lines of As 2S 3 illustrates that the structure of the three-component system Ag-As 2S 3 can be represented as a solid solution of an element (e.g. S), binary phases (e.g. AsS, As 2S 3), and/or ternary phases (e.g. AgAs 2S 3, Ag 6As 2S 3), depending on the concentration of silver in the composition. 相似文献
|