Browsing by Author "Kao, RT"

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Room-temperature single-electron charging and surface polarization in tunneling spectroscopy of high-T-c superconducting thin films
(1998-11-01)
Kao, RT
;
Wang, SJ
;
Chen, SP
;
Juang, JY
;
Wu, KH
The tunneling spectroscopy of both YBa2Cu3O7-delta (YBCO) and TlBa2Ca2Cu3O9+/-delta (Tl-1223) superconducting thin films was studied using scanning tunneling microspectroscopy. The marked staircase structure in the current-voltage characteristics showed the manifestation of single-electron charging of two series-coupled mesoscopic tunnel junctions. For YBCO films, the step width across the zero-bias voltage (Delta V-0) was larger than that of other steps (Delta V-n), with Delta V(0)congruent to 1.5L Delta V-n, as the bias voltage exceeded a threshold value. Such a step-widening anomaly, however, was not seen in Tl-1223 films. Preliminary surface polarization measurements showed that the polarization is much more hysteretic for YBCO than for Tl-1223 films, suggesting that the anomalous widening of Delta V-0 may originate from the polarization-induced residual charging effect. [S0163-1829(98)09841-5].
Single electron tunneling and superconducting energy gap in YBa2Cu3O7+delta and TlBa2Ca2Cu3O9+/-delta films
(1997-08-01)
Kao, RT
;
Wang, SJ
;
Chen, SP
;
Juang, JY
;
Wu, KH
The granularity of the high-Tc cuprates, though has been considered to be obnoxious for many applications, appeared to giving rise to the exotic incremental charging effects. This paper further demonstrates that it can also serve as an alternative for extracting the superconducting gap parameters of these materials. The results of 2 Delta(0)/KBTc approximate to 6-8(YBCO) and approximate to 9-11(Tl-1223), though are consistent with those obtained by other methods, the Delta(T)'s, however, are not BCS-like.
Surface topography and tunneling spectroscopy in high-temperature superconducting thin films by scanning tunneling microscopy
(1996-04-01)
Kao, RT
;
Horng, JH
;
Wang, SJ
;
Juang, JY
;
Wu, KH
The surface morphology and tunneling spectroscopies of the YBa2Cu3O7-x (YBCO) and TlBa2Ca2Cu3O9+x (Tl-1223) high-T-c superconducting thin films deposited on LaAlO3(100) substrates were investigated by scanning tunneling microscopy (STM). The preliminary results show that although both systems have a common layer-like surface structure, the grain morphologies are quite different suggesting that they may follow different growth mechanisms probably due to the different preparation methods used. In addition, the tunneling current-voltage characteristics (IVCs) manifested features akin to that of charging effect-induced single electron tunneling in both systems. As a result, the gap-like structure observed in the dI/dV-V curves may not be reflecting the superconducting energy gaps as commonly conceived.
Zero-bias anomaly in the tunneling spectroscopy of high-Tc superconducting films
(1997-08-01)
Kao, RT
;
Wang, SJ
;
Juang, JY
;
Wu, KH
;
Uen, TM
The Coulomb staircase structure observed in the tunneling current-voltage characteristics (IVC's) of superconducting YBa2Cu3O7-delta(YBCO) films have been found to exhibit an extra feature of zero-bias anomaly (ZBA), with Delta V-0 approximate to 1.5 Delta V-n when the bias voltage exceeded a certain threshold value. Where Delta V-0 and Delta V-n (which remains essentially constant) are the widths of the voltage step across zero bias and other higher order steps, respectively. Comparisons made with TlBa2Ca2Cu3O9+/-delta (Tl-1223) films under similar conditions indicate that the effects of surface layer polarization might be the primary reason responsible for the ZBA observed in YBCO films.