Microwave surface impedance of Y1Ba2Cu3O7 − δ crystals: Experiment and comparison to a d-wave model

Abstract

We present measurements of the microwave surface resistance R s and the penetration depth λ of Y 1 Ba 2 Cu 3 O 7−δ crystals. At low T , λ(T ) obeys a polynomial behavior, while R s displays a characteristic non-monotonic T −dependence. A detailed comparison of the experimental data is made to a model of d-wave superconductivity which includes both elastic and inelastic scattering. While the model reproduces the general features of the experimental data, three aspects of the parameters needed are worth noting. The elastic scattering rate required to fit the data is much smaller than measured from the normal state, the scattering phase shifts have to be close to π/2 and a strong coupling value of the gap parameter 2∆(0)/kT c ∼ 6 is needed. On the experimental side the uncertainties regarding the material parameters λ(0) and R s, res (0) further complicate a quantitative comparison. For one sample, R s, res (0) agrees with the intrinsic value which results from the d-wave model.Microwave measurements of the surface impedance Z s = R s + iX s of superconductors are in principle capable of yielding a wealth of precise information regarding the superconducting state, such as the gap parameter, quasiparticle density and nature of scattering. In low T c superconductors the BCS theory provides a remarkably accurate description of experimental data for R s and X s over several orders of magnitude variation, including detailed effects of impurity scattering [1].

Circulating power, RF magnetic field, and RF current density of shielded dielectric resonators for power handling analysis of high-temperature superconducting thin films of arbitrary thickness

“…10. It means that the real maximum current density is about two times smaller than predicted from (22). The error becomes 86% for films of thickness equal to 0.6 , and for films with of 1 the real RF current density is 30% smaller than when calculated using the relation.…”

“…The current density for a superconductor of thickness and the penetration depth is given in [24] as (20) Hence the maximum RF current density, , on the superconductor surface in Fig. 5(a) has the magnitude equal to (21) For thick films when (21) may be simplified to (22) as given in [8], and for very thin films to (23) Equations (20)- (23) are based on the assumption that only HTS material determines the surface current density. Also (20) implies that the magnetic field is zero inside the superconductor and has maxima on both surfaces.…”

“…Let us now define an error coefficient as the difference between the maximum current density in the dielectric resonator expressed by (21) and the thick-film approximation (22), namely as (27) To quantitatively illustrate the influence of HTS films' thickness on the maximum current density on HTS films the coefficient was calculated for varying HTS film thickness ( ratio) for the 10-GHz sapphire resonator of Fig. 1.…”

“…The application of dielectric resonators to measurements of surface resistance of high temperature superconducting (HTS) films has resulted from the possibility of achieving high-resolution, highsensitivity, and large dynamic ranges of test systems [14]. The minimum surface resistance that can be measured with errors not exceeding 25% can be as small as 22 . There is no practical limitation in terms of measurable maximum resistance as even normal metals at room temperature can be successfully characterized.…”

Influence of magnetic impurities on the microwave resistance of overdopedYBa2Cu3OProkhorov1, Kaminsky2, Lee3 2001Phys. Rev. B1000View full textAdd to dashboardCite

“…The difference in sample preparation hardly results in changes of the symmetry of the order parameter, since it does not influence drastically on the intrinsic electron structure of the compound. Moreover, the analysis of the temperature dependence of the surface resistance, performed for the YBa 2 Cu 3 O 7Ϫ␦ single crystal in the framework of the d-wave model, 29 was not consistent with the experimental data.…”