T. Honma

Bio: T. Honma is an academic researcher from Yamagata University. The author has contributed to research in topics: Sheet resistance & Thin film. The author has an hindex of 5, co-authored 6 publications receiving 49 citations.

Microwave surface resistance of YBCO superconducting thin films under high DC magnetic field

Abstract: We investigated the dc magnetic field and temperature dependences of the microwave surface resistance ( R s ) of YBa 2 Cu 3 O y (YBCO) superconducting thin films with various thicknesses. We used YBCO thin films with 300, 500, and 700 nm deposited on a MgO (1 0 0) substrate by the thermal co-evaporation method. The R s was measured using the dielectric resonator method at 21.8 GHz, and a high dc magnetic field of up to 12 T was applied parallel to the c -axis of the YBCO thin films during R s measurements. The R s value of YBCO thin films increased when dc magnetic field was applied. These relationships could be explained by using the two-fluid model for high frequency and low magnetic field limits. We defined the viscous drag coefficient η under the low magnetic limit and the high magnetic field limit as the η low ( B , T , d ) and η high ( B , T , d ), respectively. The η low values were approximately two orders of magnitude greater than η high values. Also, all η low and η high value decreased or saturated as the temperature and film thickness increased. These results show that η under the low and high magnetic field limit depended on the temperature and film thickness.

Introducing Artificial Pinning Centers Into YBCO Thin Films to Improve Surface Resistance in a DC Magnetic Field

Abstract: We investigated the effect of introducing artificial pinning centers (APCs) into YBa2Cu3O7-δ (YBCO) thin films to reduce the microwave surface resistance (Rs) in a high dc magnetic field for high-performance microwave devices with high-quality factor (Q). YBCO thin films with and without APCs were deposited on MgO(100) substrates by using the pulsed laser deposition technique. We used commercial 0, 1.5, 3.0 wt% BaMO3 (BMO, M = Zr, Hf) doped YBCO targets. The δω and δφ of the YBCO thin films increased as BMO doping increased, and the rate of increase appeared to be smaller for BHO doping than for BZO doping. The Rs of these thin films was measured at 21.8 GHz with the dielectric resonator method and a dc magnetic field of up to 5.0 T was applied parallel to the c-axis of the YBCO thin films during the Rs measurements. The Rs of the BMO doped films in the magnetic field was smaller than that of the pure YBCO films. In particular the Rs of the 1.5 wt% BHO doped films was the smallest among all of the films, about half compared with that of the Rs of the pure YBCO films at 4 T and 20 K. As a result, we found that introducing APCs into YBCO thin films is effective for decreasing Rs under a dc magnetic field.

The dc magnetic field, temperature and film thickness dependence of microwave surface resistance of YBCO and DyBCO thin films

Abstract: We investigated the dc magnetic field and temperature dependences of the microwave surface resistance ( R s ) of YBa 2 Cu 3 O y (YBCO) and DyBa 2 Cu 3 O y (DyBCO) superconducting thin films. The YBCO and DyBCO thin films, each with a thickness of 300, 500, or 700 nm, were deposited on MgO (1 0 0) substrates by the thermal co-evaporation method. The R s was measured using the dielectric resonator method. A dc magnetic field of up to 5.0 T was applied parallel to the c -axis of the superconducting thin films. The results showed that the R s value had almost the same temperature dependence at various thicknesses in a zero-external field. The R s of the YBCO and DyBCO thin films increased with the applied dc magnetic field. The DyBCO thin films showed weaker magnetic field dependence of R s than the YBCO thin films. The R s ratio (defined as R s (5 T)/ R s (0 T)) linearly increased with the film thickness. These results show that pinning strength decreased with an increasing film thickness.

Intrinsic Surface Resistance of YBCO Thin Films Under DC Magnetic Field

Abstract: We investigated the dc magnetic field and temperature dependences of the microwave intrinsic surface resistance (Rsint) of YBa2Cu3Oy (YBCO) superconducting thin films with various thicknesses. We used YBCO films from 100, 200, and 300 nm thick YBCO films deposited on CeO2/Al2O3 substrates. The Rsint is means the surface resistance of YBCO film without the dielectric loss of the substrates. The Rsint was obtained from measured surface resistance (Rs) by using a phenomenological equation. The Rs was measured using the dielectric resonator method at 21.8 GHz. A dc magnetic field of up to 5.0 T was applied parallel to the c-axis of the superconducting thin films during the Rs measurements. The Rsint of the YBCO thin films increased when the dc magnetic field was applied. These relations could be explained with the two-fluid model for high-frequency and high-magnetic field limits. The Rsint ratio (defined as Rsint (5T)/Rsint (0T)) slightly decreased with the film thickness. These results indicate that the Rsint of HTS films depends on the film thickness in the dc magnetic field and the Rsint in a dc magnetic field may be related to the pinning center in the HTS films.

Relationship between intrinsic surface resistance and critical current density of YBCO thin films with various thickness

Abstract: We investigated the relationship between the intrinsic surface resistance ( R s int ) and critical current density (Jc) of YBa2Cu3Oy (YBCO) film thinner than the penetration depth (λL). The measured YBCO films were deposited on CeO2-buffered r-cut Al2O3 substrates by the pulsed laser deposition method. The thicknesses of these films were 300, 200, and 100 nm, respectively. The R s int means the surface resistance of YBCO film removing the loss by the impedance of the substrates. The effective surface resistance ( R s eff ) including the impedance of the substrate and the Jc of each YBCO film were measured using the dielectric resonator method at 21.8 GHz and the inductive method. We calculated R s int by using phenomenological expressions and the R s eff value. The R s int values of each YBCO film were almost the same in the measured temperature region. As a result, we found that R s int was in inverse proportion to the Jc of YBCO film thinner than λL.

YBa2Cu3O7 microwave resonators for strong collective coupling with spin ensembles

Abstract: 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.

YBCO microwave resonators for strong collective coupling with spin ensembles

Abstract: Coplanar microwave resonators made of 330 nm-thick superconducting YBCO have been realized and characterized in a wide temperature ($T$, 2-100 K) and magnetic field ($B$, 0-7 T) range. The quality factor $Q_L$ exceeds 10$^4$ below 55 K and it slightly decreases for increasing fields, remaining 90$\%$ of $Q_L(B=0)$ 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 DPPH 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 $\sim 82$ 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.

Materials process and applications of single grain (RE)–Ba–Cu–O bulk high-temperature superconductors

Abstract: This paper reviews recent advances in the melt process of (RE)–Ba–Cu–O [(RE)BCO, where RE represents a rare earth element] single grain high-temperature superconductors (HTSs), bulks and its applications. The efforts on the improvement of the magnetic flux pinning with employing the top-seeded melt-growth process technique and using a seeded infiltration and growth process are discussed. Which including various chemical doping strategies and controlled pushing effect based on the peritectic reaction of (RE)BCO. The typical experiment results, such as the largest single domain bulk, the clear TEM observations and the significant critical current density, are summarized together with the magnetization techniques. Finally, we highlight the recent prominent progress of HTS bulk applications, including Maglev, flywheel, power device, magnetic drug delivery system and magnetic resonance devices.