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排序方式: 共有1073条查询结果,搜索用时 218 毫秒
41.
Renato S. Gonnelli Mauro Tortello Dario Daghero Giovanni Alberto Ummarino Valeri A. Stepanov Jun S. Kim 《Central European Journal of Physics》2009,7(2):251-256
Point-contact Andreev-reflection (PCAR) experiments were performed in the Fe-1111 layered superconductor LaFeAsO0.9F0.1 with resistive T
c
on
∼ 27 K. The observation of two pairs of peaks in the low-temperature Andreev-reflection spectra clearly indicates the presence
of two order parameters. The behavior of the two gaps as a function of temperature, obtained by fitting the conductance curves
by means of the generalized two-band Blonder-Tinkham-Klapwijk model, shows some anomalies. A theoretical analysis performed
within the two-band Eliashberg theory with a generic electron-boson coupling can reproduce the low-temperature value of the
two gaps but generally fails in giving a satisfactory fit of their overall temperature dependence, indicating the rich and
complex physics of these newly discovered superconductors.
相似文献
42.
S. Tomita M. Kato K. Maki 《Physica C: Superconductivity and its Applications》2009,469(15-20):1074-1076
For analyzing the checker-board like modulation of the local density of states (LDOS) around a vortex observed in the slightly overdoped Bi2Sr2CaCu2Ox, we examined the effect of pseudogap state of high-Tc superconductors to the LDOS around the vortex. We first derived the Bogoliubov-de Gennes equation for d-wave superconductivity (d-SC) in the presence of d-spin density wave (d-SDW). Using the Fourier–Bessel expansion, we solved this equation for a single vortex state, numerically. We found that the peak of the bound states around E = 0 becomes small and modulation of the LDOS is observed for larger d-SDW order parameter. 相似文献
43.
M. R. Koblischka S. L. Huang K. Fossheim T. H. Johansen H. Bratsberg 《Physica C: Superconductivity and its Applications》1998,300(3-4):207-211
Flux distributions of partial-melting processed Bi2Sr2CaCu2O8+δ ceramics are obtained using magneto-optic imaging. In remanent states (μ0Ha=0 T), large amounts of trapped flux are observed along (Sr,Ca)2CuOy particles embedded in the Bi2Sr2CaCu2O8+δ matrix. Despite the relatively large size of these particles (up to 30 μm), the pinning effect is similar to that of Y2BaCuO5 particles in melt-processed YBa2Cu3O7−δ. Furthermore, we discuss how the pinning capability of non-superconducting particles of different sizes and densities will show up in magneto-optic images. 相似文献
44.
T. Mimura I. Terasaki K. Tomimoto S. Tajima M. Nakamura Y. Shiohara 《Physica C: Superconductivity and its Applications》1998,300(3-4):212-216
In order to clarify the origin of a strong peak effect in the magnetization curve of NdBa2Cu3O7−δ crystals, we investigated the superconductivity transition behavior of the in-plane resistivity in static magnetic fields up to 8 T. Comparing the results for the samples exhibiting and not exhibiting the peak effect, we found that the former (peak effect sample) shows lower resistivity above the vortex melting temperature. This implies that the pinning force is effective in the vortex liquid state. We also found that the normal state resistivity behaviors of some samples were unusual, indicating inhomogeneous current flow. These results suggest an existence of sheet-like pinning centers perpendicular to the conduction planes. 相似文献
45.
It is demonstrated that horizontai sandwich tank with two cover plates can be used to preconcentrate sample solutions. Narrow sharply-defined starting zones are obtained just outside the smaller cover plate when the series of spots of the sample solution are applied on the thin layer and predeveloped with a volatile solvent. After evaporation of the solvent, the whole area of the TLC-plate is covered with two plates and developed with a suitable solvent. 相似文献
46.
R. Menegotto Costa L. Mendon?a Ferreira V. N. Vieira P. Pureur J. Schaf 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):107-113
We have studied experimentally the electrical magneto-conductivity near the
superconducting transition of YBa2Cu3O7-δ, YBa2
(Cu2.95Zn0.05)O7-δ and Y(Ba1.75Sr0.25)Cu3O7-δ polycrystalline samples. The measurements were performed in magnetic fields ranging from 0 to 400 Oe applied parallel to
the current orientation. The results show that the resistive transition of these systems proceeds in two stages. The pairing
transition occurs at the bulk critical temperature Tc, where superconductivity is stabilized within small and homogeneous regions of the
sample generically called grains. The regime of approach to the zero resistance state reveals the occurrence of a coherence
transition at a lower temperature Tc0. This transition is related to the connective nature of the granular samples and is controlled by fluctuations of the
order-parameter phase of individual grains. Our experiments show that the Zn-doping, besides depressing the pairing critical
temperature, strongly enlarges the temperature range dominated by effects related to the coherence transition. The substitution
of Ba by Sr causes only a small reduction of Tc, but also enhances significantly the effects related to the grain
coupling phenomenology. In general, our results indicate that these impurity substitutions in YBa2Cu3O7-δ produce or magnify the granularity at a microscopic level, enhancing the effects of phase fluctuations in the conductivity
near the transition. 相似文献
47.
M. M. Korshunov S. G. Ovchinnikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):271-278
In this paper a mean-field theory for the spin-liquid paramagnetic non-superconducting phase of the p- and n-type high-Tc cuprates is developed. This theory applied to the effective t-t'-t′′-J* model with the ab initio calculated parameters and with the three-site correlated hoppings. The static spin-spin and kinematic
correlation functions beyond Hubbard-I approximation are calculated self-consistently. The evolution of the Fermi surface
and band dispersion is obtained for the wide range of doping concentrations x. For p-type systems the three different types
of behavior are found and the transitions between these types are accompanied by the changes in the Fermi surface topology.
Thus a quantum phase transitions take place at x = 0.15 and at x = 0.23.Due to the different Fermi surface topology we found
for n-type cuprates only one quantum critical concentration, x = 0.2. The calculated doping dependence of the nodal Fermi
velocity and the effective mass are in good agreement with the experimental data. 相似文献
48.
U. Schwingenschlögl C. Schuster 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(1):43-47
The incommensurate composite systems M14Cu24O41 (M = Ca, Sr, La)
are based on two fundamental structural units: CuO2 chains and
Cu2O3 ladders. We present electronic structure calculations
within density functional theory in order to address the interrelations
between chains and ladders. The calculations account for the
details of the crystal structure by means of a unit cell comprising 10
chain and 7 ladder units. It turns out that chains and ladders can be treated
independently, which allows us to introduce a model system based on a
reduced unit cell. For the CuO2 chains, we find two characteristic
bands at the Fermi energy. Tight binding fits yield
nearest and next-nearest neighbour interactions of the same order of
magnitude. 相似文献
49.
Wolfgang Scherer Prof. Dr. Christoph Hauf Dipl.‐Phys. Manuel Presnitz Dipl.‐Phys. Ernst‐Wilhelm Scheidt Dr. Georg Eickerling Dr. Volker Eyert Dr. Rolf‐Dieter Hoffmann Dr. Ute C. Rodewald Dipl.‐Ing. Adrienne Hammerschmidt Dr. Christian Vogt Dr. Rainer Pöttgen Prof. Dr. 《Angewandte Chemie (International ed. in English)》2010,49(9):1578-1582
50.
R Srinivasan V Sankaranarayanan N P Raju S Natarajan U V Varadaraju G V Subba Rao 《Pramana》1987,29(2):L225-L230
The absolute thermopower of single phase YBa2Cu3O7 and Y0.8Er0.2Ba2Cu3O7 has been measured in the range 250 K to the superconducting transition temperature. It is found that these compounds show
a large enhancement of thermopower in the range 150 K down toT
c. This enhancement shows a steep exponential drop as the temperature increases from the transition temperature. The temperature
variation of the enhancement is too steep to be accounted for by electron-phonon or electron-local structural excitation mechanisms. 相似文献