高质量的干净极限与脏极限MgB2超导薄膜

High Quality MgB_2 Films in Clean and Dirty Limit

利用混合物理化学气相沉积法(hybrid physical-chemical vapor deposition),在0001取向的SiC和Al2O3上原位制备了高质量的c轴外延MgB2薄膜,样品具有高于41K的零转变温度,超导剩余电阻率ρ(42K)<0.5μΩcm,很好地吻合第一原理计算的干净极限行为。X射线相分析图谱上没有MgO的衍射峰出现说明这种方法极大程度上避免了MgB2制备过程最易出现的"氧污染"。较高的磁电阻和低温低场条件下不存在磁通跳跃都说明了样品非常干净。借助一种改进的双加热丝装置,我们在干净MgB2样品基础上实现了可控的碳掺杂,掺碳后的样品超导临界温度下降,剩余电阻率升高,电子平均自由程由于杂质散射作用的增强而得到显著抑制,为符合脏极限的超导样品。

Pure and carbon-doped MgB2 thin films are fabricated using the hybrid physical-chemical vapor deposition. Excellent properties are obtained in the pure samples, including Tc（0） above 41K, ρ （42 K） down to below 0.5 μΩcm, which indicates that films are in the clean limit. Large normal state magnetoresistance before the transition and absence of flux jump at low temperature and low field regions in the magnetization curves strongly support that the film is very clean. Based on a developed HPCVD setup with dual-heater, by controlling the carbon concentration, MgB2 films in dirty limit can be prepared.