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IEEE Transactions on Applied Superconductivity

Heavy-Ion Patterned Micro-Channels in YBCO Microwave Resonators

G. Ghigo, Roberto Gerbaldo, L. Gozzelino, F. Laviano

Published Feb 26, 2013• 5 citations
Publisher

Abstract

Microcollimated swift heavy-ion irradiation has been employed to carve channels with micron-sized width in YBa2Cu3O7-x(YBCO) superconducting coplanar microwave resonators. Comparative analysis of the first two resonant modes as a function of temperature, magnetic field, and input power was used to characterize the properties of the microchannels. As expected, due to the high fluence, increase of penetration depth and microwave resistivity have been found in the irradiated channels. It is shown that the microchannels can be driven into a highly dissipative and nonlinear regime while the rest of the resonator still persists in a low-dissipation and linear state. Thus, an external control signal (e.g., a small dc magnetic field) can tune the response of the resonator, in the modes coupled to the microchannel, when properly biased. This study is preliminary to the employment of such approach in the design of novel YBCO sensors operating above 77 K.

DOI
10.1109/tasc.2013.2239332

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Microcollimated swift heavy-ion irradiation has been employed to carve channels with micron-sized width in YBa2Cu3O7-x(YBCO) superconducting coplanar microwave resonators. Comparative analysis of the first two resonant modes as a function of temperature, magnetic field, and input power was used to characterize the properties of the microchannels. As expected, due to the high fluence, increase of penetration depth and microwave resistivity have been found in the irradiated channels. It is shown that the microchannels can be driven into a highly dissipative and nonlinear regime while the rest of the resonator still persists in a low-dissipation and linear state. Thus, an external control signal (e.g., a small dc magnetic field) can tune the response of the resonator, in the modes coupled to the microchannel, when properly biased. This study is preliminary to the employment of such approach in the design of novel YBCO sensors operating above 77 K.
Micro-channels of nanosized columnar tracks were planted by heavy-ion irradiation into superconducting microwave microstrip resonators that were patterned from YBa2Cu3O7-x thin films on LaAlO3 substrates. Three different ion fluences were used, producing different column densities, with each fluence having a successively greater impact on the nonlinearity of the device, as compared to a control sample. Photoresponse images made with a 638 nm rastered laser beam revealed that the channel is a location of enhanced photoresponse and a hot spot for the generation of intermodulation distortion. The microwave photoresponse technique was also advanced in this work by investigating the role of coupling strength on the distribution of photoresponse between inductive and resistive components.
Superconducting microwave circuits with and without Josephson inductances are the Swiss Army knife for many experiments and technologies from quantum information science to astrophysical particle detectors. Despite a large variety of existing circuit types, thin film materials and Josephson junction technologies, a flexible and reliable platform for high-magnetic-field and high-temperature applications is yet to be found. In this manuscript, we investigate coplanar waveguide cavities made of the high-temperature cuprate superconductor YBa2_22​Cu3_33​O7_77​ (YBCO), integrated with Josephson inductances and quantum interferometers that are generated by the controlled local irradiation of the YBCO with a focused helium ion beam. We obtain strongly flux-tunable microwave resonators, which not only display periodic interferometer oscillations of resonance frequency and decay rate, but also a superimposed Fraunhofer-like modulation pattern. The latter originates from the magnetic field tuning of the individual Josephson junction critical currents due to the out-of-plane junction barriers. It allows adjusting resonance frequency and flux responsivity independently of each other, potentially enabling tunable microwave circuits with low sensitivity to external magnetic-field noise over a broad range of frequencies. Finally, we investigate the temperature dependence of the cavities, show that they have promising characteristics up to 14 \,K, and present a model for the junction-induced cavity losses.
We have investigated the temperature dependence of microwave losses in the low-power limit and millikelvin temperature range of a thin-film YBa2Cu3O7-x(YBCO) λ/2 coplanar waveguide resonator patterned on a (La0.3Sr0.7) (Al0.65Ta0.35)O3(LSAT) substrate covered by a CeO2seed layer. The unloaded quality factor is mainly governed by the surface resistance of the YBCO film and the dielectric losses caused by resonant absorption due to a bath of two-level fluctuators in the dielectrics. The value of the unloaded quality factor at 20 mK and low power, i.e., Q0≃2000, allows for the realization of YBCO microwave quantum circuits implementing biepitaxial grain-boundary Josephson junctions.
This experiment is designed to compare the feedback from an altered superconductor resonator with a conventional, unaltered superconductor resonator. Superconducting transmission lines are patterned on a lanthanum aluminium substrate chip with a geometry that resonates within the microwave range. Nonlinearities, distortion of the signals in the superconductor, can be engineered into the transmission line using an ion beam or other artificial source of radiation. The sample in this experiment, thin-film yttrium barium copper oxide: YBCO was sent to a facility in Italy to be engineered with a nonlinearity and then characterized in a low temperature (77 K) cryostat. This means that the power dependence of a traditional resonator will differ greatly from this sample. Two key figures of merit of superconducting resonators are their critical power, where the power input to the resonator is most absorbed, and critical frequency of the sample, the frequency at which the critical power occurs. Both were found to vary with temperature, and at high incident power the frequency response of the resonator begins to experience deformation. The change of the power response as frequency is swept through (bending) and the hysteresis in the curve (bifurcation) form the core disparities between traditional superconducting resonators and those with engineered nonlinearities.
Coplanar microwave resonators made of 330 nm-thick superconducting YBa2Cu3O7 have been realized and characterized in a wide temperature (T, 2–100 K) and magnetic field (B, 0–7 T) range. The quality factor (QL) exceeds 104 below 55 K and it slightly decreases for increasing fields, remaining 90% of QL(B=0) for B = 7 T and T = 2 K. These features allow the coherent coupling of resonant photons with a spin ensemble at finite temperature and magnetic field. To demonstrate this, collective strong coupling was achieved by using di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium organic radical placed at the magnetic antinode of the fundamental mode: the in-plane magnetic field is used to tune the spin frequency gap splitting across the single-mode cavity resonance at 7.75 GHz, where clear anticrossings are observed with a splitting as large as ∼82 MHz at T = 2 K. The spin-cavity collective coupling rate is shown to scale as the square root of the number of active spins in the ensemble.
We report the microwave response of coplanar-waveguide (CPW) resonators fabricated from YBa2Cu3O7−δ\mathrm{YBa_2Cu_3O_{7-δ}}YBa2​Cu3​O7−δ​ (YBCO) thin films over temperatures from approximately 70 mK70~\mathrm{mK}70 mK to 40 K40~\mathrm{K}40 K. The resonators exhibit internal quality factors QiQ_\mathrm{i}Qi​ in the range of 4×1034\times10^34×103 to 10410^4104 at 70 mK, which increase to a maximum of approximately 8×1038\times10^38×103 to 1.2×1041.2\times10^41.2×104 near 6 K6~\mathrm{K}6 K. At low temperatures, both QiQ_\mathrm{i}Qi​ and the fractional shift of the resonance frequency Δfr/frΔf_\mathrm{r}/f_\mathrm{r}Δfr​/fr​ increases with temperature, qualitatively resembling behavior commonly associated with two-level-system (TLS) defects. However, neither response saturates on the temperature scale set by the resonator frequency, and the loss exhibits no observable microwave-power dependence. We show that low-temperature frequency upturn may be better described by an additional paramagnetic response associated with defect-induced local moments or Andreev bound states, while the low-temperature loss follows an approximately logarithmic temperature dependence whose microscopic origin remains unresolved. These measurements establish the millikelvin performance of patterned YBCO resonators and show that their low-temperature response cannot be understood within the conventional TLS framework alone.