论文标题
掺杂的拓扑结晶绝缘子中的电子音波耦合和超导性（pb $ _ {0.5} $ sn $ _ {0.5} $）$ _ {1-x} $ in $ _x $ _x $ te
Electron-phonon coupling and superconductivity in the doped topological-crystalline insulator (Pb$_{0.5}$Sn$_{0.5}$)$_{1-x}$In$_x$Te
论文作者
论文摘要
我们提出了（pb $ _ {0.5} $ sn $ _ {0.5} $）$ _ {1-x} $ in $ _x $ te的单晶中的中子散射研究，$ x = 0 $（金属，但不使用$ x = 0.2 $ x = 0.2 $（nonnonallallicallic commation umportcucting）。我们绘制了声子分散（更全面的$ x = 0 $），并找到与理论计算的一般一致性，除了布里群区域中心的横向和纵向光学（TO和LO）模式外。在低温下，这两种模式都被强烈抑制，但坐在有限的能量（两个样品中的$ \ sim4 $ MEV）上，在室温下转移到更高的能量。这些模式由于PB-TE和SN-TE $ P $ - 轨道杂交对金属原子的偏置位移的敏感性而驱动的近距离结构不稳定性。柔软的光学模式对低能量声学模式的影响是通过低导热性推断出的，尤其是在低温下。鉴于预测最强的电子 - 音波耦合是LO模式的，这对于两个研究的组合物应该相似，因此只有掺杂的晶体才能超导很有趣。此外，我们观察到弹性扩散（Huang）散射，这些散射是由随机分布的PB和SN位点的晶格中的PB-TE和SN-TE键长的差异解释的。我们还确认存在异常的弥漫性低能原子振动，我们推测地归因于中心位点之间各个PB原子的局部波动。
We present a neutron scattering study of phonons in single crystals of (Pb$_{0.5}$Sn$_{0.5}$)$_{1-x}$In$_x$Te with $x=0$ (metallic, but nonsuperconducting) and $x=0.2$ (nonmetallic normal state, but superconducting). We map the phonon dispersions (more completely for $x=0$) and find general consistency with theoretical calculations, except for the transverse and longitudinal optical (TO and LO) modes at the Brillouin zone center. At low temperature, both modes are strongly damped but sit at a finite energy ($\sim4$ meV in both samples), shifting to higher energy at room temperature. These modes are soft due to a proximate structural instability driven by the sensitivity of Pb-Te and Sn-Te $p$-orbital hybridization to off-center displacements of the metal atoms. The impact of the soft optical modes on the low-energy acoustic modes is inferred from the low thermal conductivity, especially at low temperature. Given that the strongest electron-phonon coupling is predicted for the LO mode, which should be similar for both studied compositions, it is intriguing that only the In-doped crystal is superconducting. In addition, we observe elastic diffuse (Huang) scattering that is qualitatively explained by the difference in Pb-Te and Sn-Te bond lengths within the lattice of randomly distributed Pb and Sn sites. We also confirm the presence of anomalous diffuse low-energy atomic vibrations that we speculatively attribute to local fluctuations of individual Pb atoms between off-center sites.
