Werdehausen Daniel, Takayama Tomohiro, Albrecht Gelon, Lu Yangfan, Takagi Hidenori, Kaiser Stefan
Max-Planck-Institute for Solid State Research, 70569 Stuttgart, Germany. 4th Physics Institute, University of Stuttgart, 70569 Stuttgart, Germany.
J Phys Condens Matter. 2018 Aug 1;30(30):305602. doi: 10.1088/1361-648X/aacd76. Epub 2018 Jun 19.
The excitonic insulator is an intriguing correlated electron phase formed of condensed excitons. A promising candidate is the small band gap semiconductor TaNiSe. Here we investigate the quasiparticle and coherent phonon dynamics in TaNiSe in a time resolved pump probe experiment. Using the models originally developed by Kabanov et al for superconductors (Kabanov et al 1999 Phys. Rev. B 59 1497), we show that the material's intrinsic gap can be described as almost temperature independent for temperatures up to about 250 K to 275 K. This behavior supports the existence of the excitonic insulator state in TaNiSe. The onset of an additional temperature dependent component to the gap above these temperatures suggests that the material is located in the BEC-BCS crossover regime. Furthermore, we show that this state is very stable against strong photoexcitation, which reveals that the free charge carriers are unable to effectively screen the attractive Coulomb interaction between electrons and holes, likely due to the quasi 1D structure of TaNiSe.
激子绝缘体是一种由凝聚激子形成的有趣的关联电子相。小带隙半导体TaNiSe是一个很有前景的候选材料。在此，我们通过时间分辨泵浦探测实验研究了TaNiSe中的准粒子和相干声子动力学。使用Kabanov等人最初为超导体开发的模型（Kabanov等人，1999年，《物理评论B》59卷，1497页），我们表明，对于高达约250 K至275 K的温度，该材料的本征能隙几乎与温度无关。这种行为支持了TaNiSe中激子绝缘体状态的存在。在这些温度以上，能隙出现额外的与温度相关的成分，这表明该材料处于玻色-爱因斯坦凝聚-巴丁-库珀-施里弗交叉区域。此外，我们表明这种状态对强光激发非常稳定，这表明自由电荷载流子无法有效屏蔽电子和空穴之间的吸引库仑相互作用，这可能是由于TaNiSe的准一维结构所致。
