Frequency analysis of the dielectric constant ofYBa2Cu3O7Josephson junctions fabricated on bicrystalline substrates

Abstract

We have studied the electromagnetic parameters of YBa 2 Cu 3 O 7 Josephson junctions fabricated on bicrystalline substrates with different angles tilted around the ͓100͔ and ͓001͔ axis. Changing a technological parameter such as the junction width permits change to the resonant frequency of the barrier cavity. This change in the resonance frequency allows one to determine a frequency dependent dispersion relation of the dielectric constant ͑͒. We have explored the proximity to a resonance in the dielectric response and analyzed its resonance frequency and damping constant. In terms of a RLC circuital equivalence additional information on the inductive response is presented as a comparative study of junctions fabricated on substrates with different bicrystalline misorientations.

Amplitude sensitive experiment of pairing symmetry ind0–d0submicron Y–Ba–Cu–O bicrystal grain boundary junctions

“…Along the quasiparticle branch it is possible to observe current bumps or current steps, indicating the presence of resonances. We will not present data on such resonances in this paper, because we have already analyzed electromagnetic properties of micrometric [100] tilt YBCO grain boundary junctions elsewhere [29][30][31]. Moreover, resonances observed in submicron junctions and DC-SQUIDs made on the same chip will be presented in a separate paper [32].…”

Fiske steps and hysteresis in YBa2Cu3O7 grain boundary Josephson junctions: Structural information of the barrier by means of a nondestructive approach

“…Electrodes show critical temperatures in the range of 89.5-91 K, transition widths smaller than 0.2 K, and critical current densities higher than 10 6 A / cm 2 at 77 K. The accurate control of the film growth process in our sputtering system has been previously demonstrated. [10][11][12] 100 nm thick gold layers were deposited on the samples for making low contact resistance paths. Films were patterned obtaining junction widths ranging between 4 and 20 m by Ar ion milling, cooling the sample holder down to −50°C.…”

“…In this discussion, particular care has been taken in order to eliminate possible sources of error. 11,12 The dielectric response of the strontium titanate substrate is frequency dependent and at low frequencies the relative dielectric constant can be large ͑below 200 GHz at 4.2 K͒. 18 If such a frequency range is reached, the substrate may affect the capacitance determination of the barrier.…”

“…In that analysis, the values of NQ 2 / mt, t, and 0 are derived from the fitting of the experimental dispersion relation r ͑ ͒ to the theoretical expression for a resonance in the frequency response of a dielectric constant of a material. 11,12 An average mean value r = 28 has been obtained by means of expression ͑3͒ for our geometries. In several works published in the literature r Ј values ranging between 5 and 10 have been assumed as estimated for oxygen deficient YBCO.…”

“…8,9 We have previously published several works showing the power of the electromagnetic parameters to reveal interesting insights on the nature of the barrier and to corroborate the information deduced from the analysis of transport parameters. [10][11][12] The results deduced in Ref. 10 were based on the analysis of the capacitance ͑C͒ associated with the barrier determined from both Fiske steps resonances and hysteresis of the current-voltage ͑I-V͒ curves of the junctions.…”