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近来超薄MgB2薄膜被认为在研制新型超导电子器件方面具有比较重要的应用前景,对其超导特性的研究同时对理解低维度情形下的多带超导电性也有重要意义.在(0001)Al_2O_3衬底上,我们利用混合物理化学气相沉积方法生长了一系列厚度在50 nm至10 nm的MgB2超导薄膜,测量了薄膜的电阻率—温度曲线及其在不同磁场下的超导转变,考察了薄膜的基本特性参数如超导转变温度T_c、剩余电阻比RRR及超导上临界磁场H_(c2)等随薄膜厚度d的变化.测量发现H_(c2)(T)随温度变化呈现出线性依赖关系,反映出MgB_2薄膜的两带超导特性.随着d的降低,发现薄膜的T_c及RRR值逐渐下降,0 K时的H_(c2)(0)逐渐升高.进一步地,我们发现薄膜的T_c与H_(c2)(0)都随RRR值呈现出比较单调的变化:T_c随RRR值降低而降低,H_(c2)(0)随RRR值降低而升高,表明RRR值是影响薄膜超导特性的比较重要的变量.依照两带超导理论对此现象的分析表明,与薄膜的RRR值降低相伴随的可能是MgB_2薄膜内σ带电子和π带电子的带间散射率的增强.
Recently, ultrathin MgB2 thin films have been considered as important applications in the development of new superconducting devices, and the research on their superconductivity is of great significance for the understanding of multiband superconductivity in the low dimension.At the same time, Al_2O_3 substrate, a series of superconducting MgB2 thin films with a thickness of 50 nm to 10 nm were grown by a hybrid physical-chemical vapor deposition method. The resistivity-temperature curves of the films and their superconducting transition under different magnetic fields were investigated. The basic parameters of the film, such as the superconducting transition temperature T_c, the residual resistivity ratio RRR and the superconducting upper critical magnetic field H_ (c2) with the thickness d of the film, were measured. It was found that the H_ (c2) (T) The dependence of the superconductivity on the MgB_2 thin films shows that with the decrease of d, the values of T_c and RRR decrease gradually and the value of H_ (c2) (0) gradually increases at 0 K. Further, we find that The T_c and H_ (c2) (0) of the films all showed monotonous changes with the RRR values: T_c decreased with decreasing RRR values and H_ (c2) (0) increased with decreasing RRR values. The more important variables in the superconductivity of thin films are the pairs of superconducting theories Analysis showed phenomena, and decreased RRR value of the film may be accompanied by π σ belt reinforcing band electrons and scattering of electrons between the band MgB_2 film.