Development and Application of Layer Structured Nitride Superconductors

我们报道了碱金属插层掺杂的层状氮化物β-MnX(M=Zr，Hf；X=Cl，BrI)成为超导体。特别是Li与四氢呋喃(THF)共插层化合物LiO_&lt；48&gt；(THF)_yHfNCl具有较高的临界温度T_c=25.5 K。在本研究中，我们与固体物理学家合作研究了超导机制，并开发了新型的层状结构氮化物。主要研究结果如下：1.以卤化铵为助熔剂，在高压条件下成功地合成了β-MnX单晶，并通过单晶X射线分析确定了其结构。提出了一种新的电子掺杂方法，即通过氯原子的部分脱嵌生成在空气中长期稳定的β-ZrNCl1-x和β-HfNCl1-x&gt；脱插层样品表现出与碱金属插层掺杂电子相似的超导电性。制备了同位素取代的β-Hf^&lt；15&gt；NCL，并通过电子掺杂得到了它的超导体。~lt；15&gt；N核磁共振研究表明，层状氮化物超导体为二维结构，载流子密度很低，声子增强很弱。新超导体的机制不能用传统的BCS理论来解释。用断开结方法成功地测量了超导带隙。采用分子束外延技术，在高真空室中以氮自由基源制备了层状结构的Sr2N取向薄膜。

We have reported that layer structured nitride halides β-MNX (M = Zr, Hf ; X = Cl, Br, I) electron-doped by intercalation of alkali metals became superconductors. In particular, the compound cointercalated with Li and THF (tetrahydrofuran), Lio_<48>(THF)_yHfNCl, showed a high critical temperature of Tc = 25.5 K. In this study, we have collaborated with solid state physicists to investigate the superconducting mechanism, and new types of layer structured nitrides have been developed. The main results obtained are the followings;1. Single crystals of β-MNX were successfully prepared using ammonium halides as fluxes under high-pressure conditions, and their structures were determined by the single crystal X-ray analysis.2. A new electron-doping method was developed by partial deintercalation of chlorine atoms to form β-ZrNCl_<1-x> and β-HfNCl_<1-x>, which were stable in air for pretty long time. The deintercalated samples showed similar superconductivity with those electron doped by alkali metal intercalation.3. Isotope substituted β-Hf^<15>NCl was prepared, and its superconductors were derived by electron doping.4. ^<15>N NMR study revealed that the layer structured nitride superconductors were two-dimensional ones with very low carrier densities and weak phonon enhancement. The mechanism of the new superconductors cannot be interpreted in the conventional BCS theory.5. The superconducting gap was successfully measured by a break-junction method.6. Layer structured Sr_2N oriented films were prepared by MBE method in a high vacuum chamber with a nitrogen radical source.