共查询到20条相似文献,搜索用时 15 毫秒
1.
Z.C. Dong 《Solid State Communications》2007,142(10):577-582
We solve a self-consistent equation for the d-wave superconducting gap and the magnetization in the mean-field approximation, study the Zeeman effects on the thermodynamic potential of d-wave superconductor (S) and coherent quantum transport in normal-metal (N)/d-wave S/N double tunnel junctions. Taking simultaneously into account the electron-injected current from one N electrode and the hole-injected current from the other N electrode, we derive a general formula for the differential conductance in a N/d-wave S/N system under a Zeeman magnetic field on the d-wave S. It is found that oscillations of all quasiparticle transport coefficients and differential conductance with the bias voltage and the thickness of the d-wave S depend to a great extent on the crystal orientation of the d-wave S. In the N/d-wave S/N junctions, the Zeeman magnetic field can lead to the Zeeman splitting of conductance peaks, and the temperature can reduce the coherent effect. 相似文献
2.
Starting from the free energy of a moving vortex, we obtain the extended power law form of longitudinal resistivity pxx and the analytical form of Hall resistivity pxy.Based on them, we obtain a scaling relation which agrees well with the experimental data of different kinds of high-temperature superconductors. Furthermore, the theoretical results well fit the scaling results. 相似文献
3.
In view of the question about the vortex glass theory of the freezing of disordered vortex matter raised by recent experimental observations, we reinvestigate the critical scaling of high Tc superconductors. It is found that the dc current-voltage characteristic of mixed state superconductors has a general form of extended power law which is based on the Ginzburg-Landau (GL) functional in the similar way as the vortex glass theory. Isotherms simulated from this nonlinear equation fit the experimental I- V data of Strachan et al. [Phys. Rev. Left. 87(2001) 067007]. The puzzling question of the derivative plot for the I - V curves and the controversy surrounding the values of critical exponents are discussed. 相似文献
4.
We solve a self-consistent equation for the d-wave superconducting gap and the effective exchange field in the mean-field approximation, study the Zeeman effects on the d-wave superconducting gap and thermodynamic potential. The Josephson currents in the d-wave superconductor (S)/insulating layer (I)/d-wave S junction are calculated as a function of the temperature, exchange field, and insulating barrier strength under a Zeeman magnetic field on the two d-wave Ss. It is found that the Josephson critical currents in d-wave S/d-wave S junction depend to a great extent on the relative orientation of the effective exchange field of the two S electrodes, and the crystal orientation of the d-wave S. The exchange field can under certain conditions enhance the Josephson critical current in a d-wave S/I/d-wave S junction. 相似文献
5.
A spectrum of transverse oscillations of a single vortex filament in a granular type-II superconductor has been investigated theoretically. The oscillation frequency is shown to be highly dependent on characteristics of the Josephson medium and on vortex filament location in a granule. When the Abrikosov vortex enters (leaves) the granule, the spectrum looks like a surface potential barrier. A variation of granulated-medium parameters results in changes of gap size in the excitation spectrum. 相似文献
6.
The effective surface resistance of nearly ferroelectric superconducting film in the dielectriclike response is theoretically investigated based on the electrodynamics of the nearly ferroelectric superconductors. We calculate the intrinsic film surface resistance for isolated thin film and the effective surface resistance for a superconductor/dielectric layered structure. It is found that the thickness-dependent surface resistance has two different behaviors separated by a critical film thickness being equal to the London penetration length. That is, a nonresonant dependence is seen when the film thickness is less than the London penetration length, and an anomalously resonant behavior is found when the film thickness is larger than the London penetration length. The nonresonant dependence is similar to that of a cuprate superconductor and it further is characterized by some other critical thicknesses. As for the anomalous resonant region it is seen only in a nearly ferroelectric superconductor. 相似文献
7.
The influence of a uniform external magnetic field on the dynamical spin response of cuprate superconductors in the superconducting state is studied based on the kinetic energy driven superconducting mechanism. It is shown that the magnetic scattering around low and intermediate energies is dramatically changed with a modest external magnetic field. With increasing the external magnetic field, although the incommensurate magnetic scattering from both low and high energies is rather robust, the commensurate magnetic resonance scattering peak is broadened. The part of the spin excitation dispersion seems to be an hourglass-like dispersion, which breaks down at the heavily low energy regime. The theory also predicts that the commensurate resonance scattering at zero external magnetic field is induced into the incommensurate resonance scattering by applying an external magnetic field large enough. 相似文献
8.
K. Takahashi T. Nojima A. Ochiai S-I. Lee 《Journal of Physics and Chemistry of Solids》2008,69(12):3163-3166
The vortex matter phase transitions and intrinsic pinning effect were investigated in an MgB2 single crystal using the torque magnetometry. For the field directions apart from the ab plane, we succeed in the observation of the vortex lattice melting transitions, which are transformed from the order-disorder transitions at low temperatures. Both transition fields with field directions can be describe by the GL effective mass model. For the field direction along the ab plane, these transitions become unobservable. Instead, the sudden increase in the hysteresis of magnetization curve occurs, indicating the existence of the intrinsic pinning coming from the layer structure. 相似文献
9.
M. Tajmar 《Physics letters. A》2008,372(18):3289-3291
A fully consistent model to study electrodynamics for superconductors in the stationary and non-stationary regimes has been developed based on Proca equations and a massive photon. In particular, this approach has been applied to study the electric field penetration depth in superconductors. The model shows a deviation from the charge contribution to an internal electric field compared to previous approaches. 相似文献
10.
Qiong-Gui Lin 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):27-36
The interaction between a general magnetic source and a
long type-II superconducting cylinder in the Meissner or mixed state
is studied within the London theory. We first study the Meissner
state and solve the Maxwell–London equations when the source is a
magnetic monopole located at an arbitrary position. Then the field
and supercurrent for a more complicated magnetic charge distribution
can be obtained by superposition. A magnetic point dipole with
arbitrary direction is studied in detail. It turns out that the
levitation force on the dipole contains in general an angular as well
as a radial component. By integration we obtain the field and
supercurrent when the source is a two-dimensional monopole (a
magnetically charged long thread along the axial direction), from
which the results for a two-dimensional point dipole easily follow.
In the latter case the levitation force points in the radial
direction regardless of the orientation of the dipole. The case for a
current carrying long straight wire parallel to the cylindrical axis
is solved separately. The limit of ideal Meissner state is discussed
in most cases. The case of mixed state is discussed briefly. It turns
out that vortex lines along the axial direction and vortex rings
concentric with the cylinder have no effect outside the cylinder and
the levitation forces remain the same as in the case of the Meissner
state. 相似文献
11.
Li Cheng 《Journal of Physics and Chemistry of Solids》2008,69(12):3139-3141
Within the kinetic energy driven superconducting mechanism, the evolution of the magnetic excitations of the electron-doped cuprates in the superconducting state is studied. It is shown that there is a broad commensurate low energy magnetic scattering peak, while the magnetic resonance energy is located among this broad commensurate low energy scattering range. This broad commensurate low energy magnetic scattering disperses outward into a continuous ring-like incommensurate magnetic scattering at high energy. 相似文献
12.
A general phenomenological theory is presented for the phase behavior of ferromagnetic superconductors with spin-triplet electron Cooper pairing. The theory accounts in detail for the temperature-pressure phase diagram of ZrZn2, while the main features of the diagram for UGe2 are also described. Quantitative criteria are deduced for the U-type (type I) and Zr-type (type II) unconventional ferromagnetic superconductors with spin-triplet Cooper electron pairing. Some basic properties of quantum phase transitions are also elucidated. 相似文献
13.
S. Yuan K. Kadowaki Z. Yang H. Takeya T. Kimura K. Kishio 《Applied Physics A: Materials Science & Processing》1994,58(6):623-627
It was recently suggested that the out-of-plane resistive dissipation in the high-T
c systems could be quantitatively described in terms of the extended Josephson coupling model that accounts for both effective thermal energy and unusual anisotropy. This model is further confirmed in the present work by scaling the c-axis resistive transition data for Hc observed in single crystalline La1.86Sr0.14CuO4 onto a single curve, in which only parameters extracted from experiments are used. We also argue the difficulty of the other dissipation models as a dominating origin of the field-induced broadening of c-axis resistive transition for Hc. 相似文献
14.
Yusuke Takara Koji FujiwaraYoshiyuki Ishihara Toshiyuki Todaka 《Journal of magnetism and magnetic materials》2008
A single sheet tester (SST) for audio frequency of 400 Hz–10 kHz was made experimentally and the magnetizing winding can get the nearly uniform distribution of flux density of a specimen in the longitudinal direction at the frequency up to 10 kHz. The flux densities at various positions of strips measured by the Epstein method were detected by search coils wound on strips at 400 Hz and 1.0 T. They have large discrepancy. However, the magnetic properties obtained from both methods have a little discrepancy. Although the uniformity of flux distribution in the Epstein frame is not sufficient, the average is fairly effective because the magnetic properties can be assumed to be locally linear within the small deviation of flux density. 相似文献
15.
S. Kalavathi J. Janaki Awadhesh Mani V. Sankara Sastry 《Solid State Communications》2006,139(7):334-338
Some new members of a ruthenocuprate(2212) series have been synthesized by Mn substitution for Ru in Gd1.4Ce0.6Sr2RuCu2O10. Characterization by x-ray diffraction (XRD) phase analysis has been carried out. Changes in structural features on substitution, including a significant change in lattice parameter for a very low substitution level, have been observed. Four-probe resistivity studies indicate the coexistence of superconductivity and magnetism for the pristine compound and a semiconductor-like upturn in resistivity and the absence of superconductivity even for very low levels of Mn substitution. AC susceptibility measurements show a progressive suppression of the magnetic transition temperature as well as a smearing of the magnetic transition as a function of Mn substitution. Possible reasons for the absence of superconductivity have been discussed. 相似文献
16.
In this work we study the ac dissipation of mesoscopic superconductors at microwave frequencies using the time dependent Ginzburg-Landau equations. Our numerical simulations show that the ac dissipation is strongly dependent on the orientation of the ac magnetic field (hac) relative to the dc magnetic field (Hdc). When hac is parallel to Hdc we observe that each vortex penetration event produces a significant suppression of the ac losses because the imaginary part of the ac susceptibility as a function of Hdc increases before the penetration of vortices, and then it decreases abruptly after vortices have entered into the sample. In the second case, when hac is perpendicular to Hdc, we observe that the jumps in dissipation occur at the same values of Hdc but are much smaller than in the parallel configuration. The behavior of the dissipation in the perpendicular configuration is similar to previous results obtained in recent microwave experiments using mesoscopic lithographed squares of Pb [A.D. Hernández, O. Arés, C. Hart, D. Domínguez, H. Pastoriza, A. Butera, J. Low Temp. Phys. 135 (2004) 119]. 相似文献
17.
S. L. Yuan Z. J. Yang K. Kimura K. Kadowaki 《Zeitschrift für Physik B Condensed Matter》1995,98(1):23-26
The magnetoresistivity, (T, B), of single crystalline La1.86SrO0.14CuO4 as a function of temperature (T) and magnetic field (B) is experimentally studied in a typical Lorentz force free configuration ofB//I//C-axis. It is shown that the extended Josephson coupling model recently developed can quantitatively account for the variation in (T, B) in a wide transition region (five orders) 相似文献
18.
By the first-principles calculations, we studied the structure, electronic and magnetic properties of LaOMnSe. The band structure and Fermi surface of LaOMnSe are very similar to those of LaOFeAs, where there are three hole-like Fermi surfaces around Γ-point and two electron-like Fermi surfaces around M-point. The hole-like Fermi surfaces will strongly overlap with electron-like Fermi surfaces if they are shifted by the q vector (π,π,0). Such Fermi surfaces nesting will induce magnetic instability and spin density wave (SDW), which is similar to LaOFeAs. Because of so much similarity to LaOFeAs, LaOMnSe is expected to become superconductor with electron or hole doping. 相似文献
19.
Fabian Jachmann 《Solid State Communications》2007,142(4):212-216
In a thin film of superconducting Y Ba2Cu3O7 the impact of surface acoustic waves (SAWs) traveling on the piezoelectric substrate is investigated. A pronounced interaction between the ultrasonic waves and the vortex system in the type II superconductor is observed. The occurrence of a SAW-induced dc voltage perpendicular to the sound path is interpreted as dragging of vortices by the piezoacoustic SAW, which acts as a conveyor for the flux quanta. The antisymmetry of this voltage with respect to the magnetic field directly evidences the induced, directed flux motion. This dynamic manipulation of vortices can be seen as an important step towards flux-based electronic devices. 相似文献
20.
J. Barba-Ortega J. Albino Aguiar 《Physica C: Superconductivity and its Applications》2009,469(13):754-755
The time dependent Ginzburg–Landau equations (TDGLE) are used to study the properties of a mesoscopic superconducting square surrounded by different metallic materials. The properties of the metallic environment are taken into account by De Gennes boundary conditions, via the extrapolation length b. The external magnetic field is applied perpendicularly to the square surface. The TDGLE are used upon taking the magnetic field and the order parameter invariant along z-direction. It is determined the b-limit for the occurrence of a single vortex in a mesoscopic square of area d2, d varies discretely from 4ξ(0) to 10ξ(0). We can show a logarithmical dependence of the sample size as a function on b parameter. 相似文献