具有空隙釔鋇銅氧環形微波共振器之物理性質

Abstract

本論文分三部分：第一部份為具有不同空隙結構高溫超導環形共振器在微波共振現象的研究，第二部分為微波量測波阻抗，用以推導重要的物理參數如Q值、表面損耗、穿透深度與能隙等的研究，第三部份討論缺氧時YBCO薄膜物理特性。首先，我們研製具有空隙的環形共振器為基本結構的微波組件，探討它們頻率響應圖的變化，並用微波模擬軟件用良好導體模擬各個元件，發覺到兩者的頻率響應是一樣的，只是超導體具有Meissner效應，我們的結論是共振頻率取決於邊界條件。其次，由於我們的元件是兩面YBCO的環形共振器，利用微波量測分析超導機制，具有更高的靈敏度。我們算出在滿氧情況下，2Δ0/kBTc為8±0.2，並且費米液體修正因子 <1，YBCO超導機制為單一波色子凝結(single boson condensation)。最後，對YBCO樣品用控氧系統改變樣品的氧含量，我們得到結論為超導電子密度對縮減溫度關係和氧含量無關，反映YBCO超導的成對特性和銅氧鏈(Cu-O chain)是無關的，而只在銅氧面上。

The thesis can be divided into three parts. The first is to investigate the microwave properties of high-Tc superconductor ring resonators with various split gap structures. The second part is to use the microwave data of wave impedance, from which the important physical parameters such as Q values, surface impedance, penetration depth and energy gap, have been deduced. The third part attempts to delineate the physical properties of YBCO thin films with various oxygen contents. A detailed process of fabrication of the epitaxial YBCO thin films as well as the microwave ring resonators will be described at first. Using these resonators the generation of the frequency response can be justified by the computer simulation of Ansoft software, in which a perfect conductor, instead of the superconductor, has been taken. From the experimental observation, the case of the superconducting ring resonator appears the resonate frequency as same as that in the conductor. Although both of them have the behavior of the same frequency response, it has possessed the Meissner effect for the superconductor. Incidentally their resonate frequencies are determined by their own boundary conditions. Finally a number of salient results in the microwave measurement allow us to get several important parameters, with which the basic nature of the high-Tc superconductivity in the underdoped case can be elucidated. For instances, the energy gap 2Δ0/kBTc=8±0.2 and Fermi liquid correction factor <1, can be yielded. Moreover, the reduced temperature T/Tc dependence of the superfluid density is shown to be independent of doping concentration, which reflects a fact that the Cu-O chain in the YBCO material is irrelevant in the consideration of superconductor properties, and the pairing mechanism occurs on the CuO2 planes thoroughly.