Exfoliation of a layered high-T_c superconductor

本文研究了层状高T_c超导体Li_x(THF)_yHfNCl的剥离，其中使用了吡啶、二甲基亚砜、N，N-二甲基甲酰胺和N-甲基甲酰胺等有机溶剂来溶解层间距较大的Li_x(THF)_yHfNCl样品，即约1.87 nm。遗憾的是，我们的Li_x(THF)_yHfNCl(x~0.5)样品从未在这些溶剂中溶解。另一方面，我们还研究了相关的蜂窝晶格超导体，如Na_&lt；0.29&gt；HfNCl和Li_&lt；0.19&gt；ZrNBr的结构和物理性质。利用中子衍射数据进行Rietveld分析，成功地确定了相关超导体Na_&lt；0.29&gt；HfNCl和Li_&lt；0.19&gt；ZrNbr的结构。我们是唯一一个成功确定了这些在空气中不稳定的碱金属插层超导样品的结构的研究小组。对NaxHfNCl的非弹性中子散射研究表明，在远高于超导能隙的几个能量处的声子态密度(PDOS)显著增加，这与高T_c铜酸盐，如La_&lt；1.85&GT；SR_&lt；0.15&gt；CuO_4和YBa2Cu3O_7的行为相似。最近的中子散射研究表明，这些与声子色散异常有关的声子态密度的增加可能是由于动态电荷密度波(DCDW)的存在。这表明DCDW可能是具有一定电子不稳定性的高T_c超导体的共同特征，其中包括自旋涨落似乎有很大不同的Ba&lt；1-x&gt；K_xBiO_3。

In the present research, exfoliation of a layered high-T_c superconductor Li_x (THF)_yHfNCl has been studied, where organic solvents such as pyridine, dimethylsulfoxide, N,N-dimethylformamide, and N-methylformamide were used to solve the Li_x(THF)_yHfNCl sample with large interlayer distance, i.e., about 1.87 nm. Unfortunately, our Li_x(THF)_yHfNCl sample (x〜0.5) has never been dissolved in these solvents. On the other hand, structures and physical properties on related honeycomb lattice superconductors, such as Na_<0.29>HfNCl and Li_<0.19>ZrNBr, have also been studied. Structures of related superconductors, Na_<0.29>HfNCl and Li_<0.19>ZrNBr, have been determined successfully by Rietveld analysis using neutron diffraction data. We are the only research group that has succeeded in determining the structures of these alkali metal intercalated superconducting samples, which are unstable in air. Inelastic neutron scattering study of Na_xHfNCl revealed that the phonon density of states (PDOS) at several energies much higher than the superconducting energy gap increased remarkably, which was the similar behavior to high-T_c cuprates, e.g., La_<1.85>Sr_<0.15>CuO_4 and YBa_2Cu_3O_7. Recent neutron scattering studies indicate that these increases of PDOS relating to phonon dispersion anomaly would be due to the existence of dynamical charge density wave (DCDW). It suggests that DCDW might be a common characteristic among high-T_c superconductors with some electronic instability including Ba_<1-x>K_xBiO_3, which seems to be quite different with one another in terms of spin fluctuation.