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1.
高温超导体赝隙态与超导态之间的关系一直是研究的焦点.交流电导和能斯特(Nernst)效应测量相继探测到超导转变温度Tc0以上温区一定范围内存在磁通涡旋激发,利用力矩技术的磁化率测量则探测到超导涨落引起的弱抗磁性.这些发现都支持了高温超导体赝隙相中存在有限的超导序参量振幅和强烈的位相涨落的图像,说明Tc0处的相变是由库珀对之间长程位相关联的消失所驱动的.文章首先简短地介绍高温超导体的电子态相图和赝隙态,以及能斯特效应的原理和测量方法,然后对能斯特效应的测量结果作一评述性介绍,还讨论了相关的理论模型. 相似文献
2.
高温超导体赝隙态与超导态之间的关系一直是研究的焦点.交流电导和能斯特(Nernst)效应测量相继探测到超导转变温度Tc0以上温区一定范围内存在磁通涡旋激发,利用力矩技术的磁化率测量则探测到超导涨落引起的弱抗磁性.这些发现都支持了高温超导体赝隙相中存在有限的超导序参量振幅和强烈的位相涨落的图像,说明Tc0处的相变是由库珀对之间长程位相关联的消失所驱动的.文章首先简短地介绍高温超导体的电子态相图和赝隙态,以及能斯特效应的原理和测量方法,然后对能斯特效应的测量结果作一评述性介绍,还讨论了相关的理论模型. 相似文献
3.
We have investigated theoretically the Nernst effect in unconventional (d-wave) charge and spin density waves (UDW). In the presence of magnetic field, Landau levels are formed, and the gapless behaviour of the low energy excitations change into gapped behaviour. When additional electric field is applied, the quasiparticles drift with a velocity of E × B/B2, and carry entropy. From this, the Nernst coefficient can be calculated using the Kelvin relation. The present results account very nicely for the measured Nernst signal in the pseudogap phase of high Tc superconductor La2−xSrxCuO4 and Bi2Sr2−yLayCuO6. This indicates that the large Nernst effect is a clear signiture of UDW. 相似文献
4.
He Jian-e 《Frontiers of Physics in China》2007,2(2):208-211
We derive from the Kaluza-Klein theory a formula for the gravity-induced phase shift around a circuit loop, which amounts
to the order of 10−6 We propose experiments to detect this phase shift by using the high-T
c d-wave Josephson junction, which is included in a cuprate superconductor circuit loop. By rotating the loop around the horizontal
axis, the gravity-induced phase shift can be detected as a frequency shift. These settings can also be used in turn to determine
the gravitational constant. This method will be sensitive and accurate.
相似文献
5.
The nature of the pseudogap state and its relation to the d-wave superconductivity in high-T c superconductors is still an open issue. The vortex-like excitations detected by the Nernst effect measurements exist in a certain temperature range above superconducting transition temperature T c, which strongly support that the pseudogap phase is characterized by finite pairing amplitude with strong phase fluctuations and imply that the phase transition at T c is driven by the loss of long-range phase coherence. We first briefly introduce the electronic phase diagram and pseudogap state of high-T c superconductors, and then review the results of Nernst effect for different high-T c superconductors. Related theoretical models are also discussed. 相似文献
6.
An extension of Bean's model, incorporating the observed exponential decay, with increasing field, of critical current density in the high-Tc superconductors, is developed. It is used for explaining the various features of the isothermal magnetisation curves. Using this model, a calculation is presented for the time-decay of magnetisation after the sample is exposed to a magnetic field, and also after this applied field is switched off. The field dependence of the decay rate in these two conditions is calculated, and then compared with available results on the 90 K and the 40 K class of oxide superconductors. The results, in the limit of field-independent current density, also agree qualitatively with experimental results for the heavy fermion superconductor CeCu2Si2. 相似文献
7.
It is argued, from the dependence of the critical current density and ofT
c on applied magnetic field, that the pairing interaction in highT
c superconductors must be strongly field-dependent. 相似文献
8.
V. Gasumyants N. Ageev E. Vladimirskaya V. Kaydanov 《Superlattices and Microstructures》1998,24(6):443-447
We report experimental data on the temperature and concentration dependences of the Nernst coefficient in the normal state for the YBa2Cu3 − xCoxOyceramic samples with increasing Co content up tox = 0.3. The Nernst coefficient is positive, and its value increases almost linearly withx. The temperature dependences ofQhave been analyzed on the basis of a narrow band model, together with data on other transport coefficients. Using a complex quantitative analysis of four transport coefficients, we were able to estimate the carrier mobility and to elucidate a character of the energy dependence of the relaxation time. 相似文献
9.
We have tried to understand the field dependence of magnetization of high temperature superconductors in the light of phenomenological
theory. Especially, the field dependence of dM/d lnB of polycrystalline Bi(2212) is understood by incorporating the overlap of vortices in the London theory. 相似文献
10.
11.
The present paper attempts to study the Neel temperature of bilayer antiferromagnetic cuprate YBa2Cu3O6.2 within anisotropic Heisenberg model. The double time Green’s function formalism within random phase approximation (RPA) has
been used to obtain various correlation functions. The magnetization and the Neel temperature (T
N) are evaluated. It is observed that the ratio of intrabilayer to inplane exchange coupling (r=J⊥/J‖) plays an important role in the magnetic dynamics of bilayer systems. The recent experimental data of bilayer system YBa2Cu3O6.2 have been used to estimate the ratio r from the expression for Neel temperature. The estimated values of spin gap and the ratio of hopping matrix elements t⊥/t‖ are found to be in fairly good agreement with the existing experimental results. 相似文献
12.
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
13.
We have studied the hysteresis loops of RBa2Cu3O7 (R=Gd, Ho and Y) and detected anomalies in some of them. The observed anomalies support a recent prediction by Ravi Kumar
and Chaddah based on an extension of Bean’s model. The anomalies indicate lowH
c1 values and we have confirmed this by studying the onset of low-field hysteresis in less than 10 Oe at 77 K for these highT
c superconductors. 相似文献
14.
Abstract An update is given of all published data on δTc/δp, extending our previous review. Implications of new data for the RVB model are discussed. Under particular assumptions a striking discrepancy is found. 相似文献
15.
Shigeki Onoda Masatoshi Imada 《Journal of Physics and Chemistry of Solids》2002,63(12):2225-2231
Metals approaching the Mott insulator generate a new hierarchy in the electronic structure accompanied by an electron differentiation with emergence of strongly momentum dependent structure, beyond the Mott-Hubbard, Brinkman-Rice and Slater pictures of the Mott transition. To consider such nonlinear phenomenon, we develop an analytic nonperturbative theory based on operator projections combined with a self-consistent treatment of the low-energy excitations. This reproduces the Hubbard bands, Mott gap, spin fluctuations, mass divergence, diverging charge compressibility, and strongly renormalized flat and damped dispersion similar to angle-resolved photoemission data in high-Tc cuprates. Electronic spectra show a remarkable similarity to numerical results. 相似文献
16.
The real (χ′
n) and imaginary (χ″
n) parts of even harmonic susceptibility (n⩽6) are measured as a function of external DC field (H
dc) in the field increasing (H↑) and decreasing (H↑) cycle. Hysteresis is observed betweenH↑ andH↓ cycles. In theH↓ cycle, at a field,H
comp=4·2G, bothχ′ andχ″ of all the even harmonics vanish indicating a true cancellation of fields in the intergrain region (H
eff≈0) caused by the balance betweenH
dc and the remanent magnetization of the grains. The position of the extrema and the zero of the various harmonics undergo a
shift proportional to the remanent magnetization of the grains at that particular field. 相似文献
17.
Abstract The effect of a hydrostatic pressure (up to 6GPa) on the Raman spectra of YBa2Cu3Ox(x = 6.5 and overdoped) single crystals is investigated in the temperature range 77-300 K in connection with all available data in the literature for the other oxygen concentrations. All five strong modes (4Ag+1B1g) are examined for both oxygen doping and compared with previously published results. From the systematic investigation of the phonon spectral characteristics with the application of pressure, the formation or disappearance of the phases is examined. The results provide a spectroscopic support for the changes induced by the hydrostatic pressure on the chain ordering and the corresponding phases. 相似文献
18.
The measurements of Mössbauer effect, magnetic susceptibility and muon spin relaxation have been carried out for the high-T c superconductor La2?x Ba x CuO4. The intensity of Mössbauer doublet spectrum of the sample of x~1/8 begins to decrease rapidly at a certain temperature T m, which we define as a magnetic transition temperature T Möss. This temperature almost agrees with T μSR determined from muon spin relaxation. The quadrupole doublet disappears at low temperature below T m but a clearly splitted spectrum is not observed even at 4.2 K, which indicates a peculiar magnetic state with a wide distribution of internal magnetic field. Around x~1/8, the superconducting critical temperature T c and T m are competed each other. In conclusion, superconductivity disappears around 1/8 hole concentration and a peculiar magnetic state such as spin density wave appears. 相似文献
19.
Shiro Kawabata Satoshi Kashiwaya Yasuhiro Asano Yukio Tanaka 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):669
We discuss how to make use of high-Tc d-wave Josephson junctions in the construction of a phase qubit. We especially focus on the effect of the quasiparticle dissipation and the zero energy bound state on the macroscopic quantum tunneling which corresponds to the final measurement process of the d-wave phase qubit. 相似文献
20.
C M Srivastava 《Pramana》1998,50(1):11-23
The analysis of photoemission and femtosecond optical absorption spectroscopy in oxide superconductors supports the view that
the charge carriers are polaronic in nature. These carriers are found to exist in the (Ba/Sr)-O planes and are coupled toB
1g
vibrations of the apical oxygen. 相似文献