Anomalies in the microwave power-dependent surface impedance of YBa 2 Cu 3 O 7-x thin films
Anomalies in the microwave power-dependent surface impedance of YBa 2 Cu 3 O 7-x thin films
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YBa 2 Cu 3 O 7-x 薄膜的微波功率相关表面阻抗异常
DOI：
10.1103/physrevb.65.104522
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发表时间：
2002
影响因子：
3.7
通讯作者：
F. Wellhofer
中科院分区：
文献类型：
--
作者：
A. Velichko;M. Lancaster;R. Chakalov;F. Wellhofer
采用共面谐振器技术研究了MgO衬底上两种高质量YBaCuO薄膜在8和16 GHz零磁场和12 mT有限直流磁场下的非线性微波特性。发现两种样品的表面阻抗Z s = Rs + jXS随着微波磁场H r f的增加而异常降低。在一种薄膜中，只有Rs（Hrf）出现反常行为，且只在低温T≤15 K时出现反常行为;而在另一种薄膜中，只有Xs（Hrf）出现反常行为，且大多在中温T（40-45 K）时出现反常行为。阻抗平面分析的T，频率f，和H r f的r参数的依赖性表明，异常的行为是最肯定的准粒子，而不是涡的动力学。但在较高的Hrf（≥10 kA/m）下，涡旋运动机制明显偏离准粒子标度，这表明在高微波场中，涡旋动力学可能掩盖或干扰了Zs（Hrf）的反常效应.还提出了一些证据，在Z s（H r f）的异常的起源似乎是有关的薄膜的氧含量。
Nonlinear microwave properties of two high-quality YBaCuO thin films on MgO substrate have been studied in zero and finite dc magnetic lield (up to 12 mT) at 8 and 16 GHz using the coplanar resonator technique. Anomalous decrease in the surface impedance Z s =R s +jX s as a function of increasing microwave magnetic field H r f was found for both the samples. In one of the films anomalous behavior is only seen in R s (H r f ) and only at low temperatures T≤15 K, whereas in the other one only X s (H r f ) exhibits anomalies and mostly at intermediate T (40-45 K). Impedance plane analysis in terms of T, frequency f, and H r f dependences of the r parameter revealed that the anomalous behavior is most certainly governed by dynamics of quasiparticles, rather than vortices. At higher H r f (≥10 kA/m), however, a noticeable deviation from the quasiparticle scaling towards the vortex motion mechanisms was found. This indicates that in high microwave fields the anomalous affects in Z s (H r f ) may be masked by or interfered with the vortex dynamics. Also some evidence is presented that the origin of the anomalies in Z s (H r f ) is seemingly related to the oxygen content of the films.