Browsing by Author "Zeng, HK"

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Determination of the doping dependence of the penetration depth using YBCO microstrip ring resonators
(2001-11-01)
Gou, YS
;
Zeng, HK
;
Juang, JY
;
Lin, JY
;
Wu, KH
We present a method to determine the temperature dependent London penetration depth measured by a microstrip ring resonator for YBCO thin films with various oxygen contents. It allows us to get the following important results of the superconducting properties in the underdoped cuprate superconductors. With increasing delta (e.g. delta = 0.05, 0.2, and 0.4), the superfluid density, lambda (2)(5 K) /lambda (2)(T), is linear in the low temperature range (T < T-c/3), and the slope changes with increasing oxygen deficiency. After the temperature normalization with respect to the critical temperature, the temperature dependence of the superfluid density is shown to be independent of doping concentration. Moreover the maximum energy gap can be estimated from the model of the d-wave pairing. We found that the ratio Delta /T-c is nearly fixed value, 3.0 +/- 0.4. (C) 2001 Elsevier Science B.V. All rights reserved.
Effects of split gap on the microwave properties of YBCO microstrip ring resonator
(2000-11-01)
Zeng, HK
;
Gou, YS
;
Juang, JY
;
Wu, KH
;
Uen, TM
Recently, we have succeeded in fabricating HTS ring resonators by using the double-side YBCO films deposited on LaAlO3 (LAO) substrates. Quality factor (Q) over 10(4) at 5 K with resonating frequency of 3.61 GHz has been demonstrated. Furthermore, by creating a narrow gap in the same ring structure, we found that the resonating frequency splits into two, one occurred at half and three halves of the original one (i.e. at 1.80 GHz and 5.33 GHz, respectively). The temperature dependence of the resonating frequency and Q-value were studied in detail. We found that although the resonating frequency changes by introducing the gap, the Q-value remains essentially unchanged.
High-Q YBa2Cu3O7-delta microwave ring oscillators
(2000-07-01)
Zeng, HK
;
Wu, KH
;
Juang, JY
;
Uen, TM
;
Gou, YS
YBa2Cu3O7-delta(YBCO) superconducting ring resonators with YBCO ground plane were fabricated. The resonators exhibit a high quality (Q > 10(4)) at 16 It, indicating high potential for applications. In addition, from the analyses of the surface resistance R-s(T) and reactance X-s(T), it was found that the derived London penetration depth lambda(T) - lambda(5 K) displays a linear behavior over a wide range of temperatures. The results suggest that a distinct line node feature in the gap function of a d-wave pairing superconductor may extend to temperatures higher than previously reported. (C) 2000 Elsevier Science B.V. All rights reserved.
HTS surface wave resonators
(2000-02-01)
Melkov, GA
;
Egorov, YV
;
Ivanjuta, OM
;
Malyshev, VY
;
Zeng, HK
A novel class of surface wave high-temperature superconductivity (HTS) resonators was investigated. The resonator consists of HTS film and one or two dielectric plates. One of the dielectric plates may be the HTS film substrate. Theoretical analysis of the resonator structure was carried out using the partial region method, with the 20 lowest waves being considered in every region. The resonant frequencies, quality of oscillations, and the field and current distributions were calculated. It was shown that there is a high-density and homogeneous microwave current flowing on the film surfaces. Experimental measurements carried out in the 3-cm wavelength range demonstrate good agreement with simulated data.
Miniaturized 3 GHz cross-coupled planar microwave filters
(2004-03-01)
Zeng, HK
;
Hsiao, AT
;
Hsu, WH
;
Wu, SW
;
Lin, JY
Cross-coupled planar microwave filters were fabricated using YB2Cu3O7-delta superconducting thin films deposited on both sides of a LaAlO3 single crystal substrate by pulsed laser deposition. The hairpin resonator geometry allows one to miniaturize the 3-GHz filters by compacting the entire filter onto a substrate with dimensions 0.5 cm x 1 cm. By adjusting the relative spacing among the resonators to establish adequate couplings, filters with very sharp rejection skirt and extremely small insertion loss in passband were obtained.
Temperature dependence of the penetration depth and effective dielectric constant measured by YBa2Cu3O7-delta microstrip ring resonators
(2001-03-15)
Zeng, HK
;
Juang, JY
;
Lin, JY
;
Wu, KH
;
Uen, TM
YBa2Cu3O7-delta(YBCO) superconducting ring resonators with a YBCO ground plane were successfully fabricated using double-side YBCO films deposited on LaAlO3 (LAO) substrates. The temperature dependent London penetration depth, Delta lambda = lambda (T) - lambda (5 K), was systematically studied by varying the oxygen content of the same resonator structure. For fully oxygenated case (delta = 0.05), the resonator exhibits a quality factor Q > 10(4) at 16 K, and Delta lambda (T) displays a linear behavior over a wide range of temperatures. With increasing delta (e.g. delta = 0.2, 0.4), although Delta lambda is still linear in temperature, the slope changes with increasing oxygen deficiency. The results suggest that, in the underdoped regime, the inelastic scattering of charged carriers may become increasingly prominent. From the effective dielectric constant obtained from the ring resonator the dielectric constant of the LAO substrate was estimated to be epsilon (r) congruent to 25.5 at 5 K and a frequency of about 3.6 GHz. (C) 2001 Elsevier Science B.V. All rights reserved.
Temperature dependence of the penetration depth in YBa2Cu3O7-delta measured by microwave ring resonators
(2000-11-01)
Zeng, HK
;
Juang, JY
;
Wu, KH
;
Uen, TM
;
Gou, YS
YBa2Cu3O7-(TM) (YBCO)) superconducting ring resonators with a YBCO ground plane were fabricated using double-side YBCO films deposited on LaAlO3 (LAO) substrates. The temperature dependent London penetration depth, Delta lambda = lambda (T)-lambda (5K), was systematically studied by varying the oxygen content of the same resonator structure. For fully oxygenated condition (delta = 0.05), the resonator exhibits a quality factor Q > 10(4) at 16K, and Delta lambda (T) displays a linear behavior over a wide range of temperatures. With increasing delta (e.g. delta = 0.2), although Delta lambda is still linear in temperature, the slope changes by more than a factor of 2. As delta is further increased, Delta lambda (T) changes fi om T- to T-2-dependence. The results suggest that in the underdoped regime, the incoherent scattering of charged carriers may become increasingly prominent.