Temperature, frequency, and rf field dependence of the surface resistance of polycrystallineYBa2Cu3

Abstract

The rf surface resistance of a single bulk polycrystalline YBa2Cu307 -sample was measured with TEM resonant cavities as a function of temperature from 4.2 to 100 K, rf field amplitude from 0 to 640 G, and frequency from 175 to 1050 MHz. The surface resistance increased monotonically with rf field amplitude, saturating at a value approximately 5% of the normal-state surface resistance. The surface resistance is strongly frequency and temperature dependent below the saturation region and weakly frequency and temperature dependent above. Low-field surface resistances as small as~1.1 pQ (at 175 MHz) were observed at T=4.2 K. The superconducting state did not break down, even at the highest field achieved ( -640 G).

Superconducting magnesium diboride coatings for radio frequency cavities fabricated by hybrid physical-chemical vapor deposition

“…According to Collings et al [5], MgB 2 -coated cavities can potentially exhibit a higher superheating critical field H sh than that of Nb, and as a result, a much higher E acc would be imaginable [10]. In addition, MgB 2 exhibits a low surface resistance (R S ) [11][12][13][14] and is free from the weak link behavior that is encountered in high T c superconductors [15][16][17][18][19][20], implying better power dependence of R S [21]. While the issue has been raised that H c1 could be a limiting factor for MgB 2 since its bulk H c1 value is lower than that of Nb, studies suggest that it can be enhanced through the employment of multilayer structures containing superconductive films thinner than the London penetration depth, placed between insulating layers [22].…”

Tunable coaxial cavity resonator for linear and nonlinear microwave characterization of superconducting wires

“…It has been experimentally shown that it is also valid in HTSC single crystals and high quality thin films. For bulk HTSC materials, it has been observed that R s ∝ f n with n ranging from 1 to 2, depending on the investigated sample [22,24,26,27]. Deviations from the f 2 law have been ascribed to normal material inclusion at the grain boundaries, poor surface quality, wide variation of crystal-axis orientation of the grains, etc [26,27].…”

“…The nonlinear behavior of the MW surface impedance in HTSC has been investigated by several authors especially in films [8,9]; only a few investigations concern bulk samples [22,24]. In spite of considerable effort, an universal model able to explain all the observed features has not yet been developed.…”

“…Prototypes of coaxial resonators have been built using normal metal as an outer conductor and HTSC as an inner conductor and used for measuring the MW surface resistance of the inner SC [22][23][24]. The use of this kind of resonator is particularly suitable for characterizing samples with dimensions too large for the cavity-perturbation method.…”

Analysis of superconducting microstrip resonator at various microwave power levels

“…[8][9][10] When the rf field increases, the current distribution in a superconducting sample becomes nonuniform. 3 The current distribution has been given by Oates et al 11 The critical current density is a function of the input rf field.…”