A High-Performance Mid-infrared Optical Switch Enabled by Bulk Dirac   Fermions in Cd3As2
  Pulsed lasers operating in the 2-5 {\mu}m band are important for a wide range of applications in sensing, spectroscopy, imaging and communications. Despite recent advances with mid-infrared gain media, the lack of a capable pulse generation mechanism, i.e. a passive optical switch, remains a significant technological challenge. Here we show that mid-infrared optical response of Dirac states in crystalline Cd3As2, a three-dimensional topological Dirac semimetal (TDS), constitutes an ideal ultrafast optical switching mechanism for the 2-5 {\mu}m range. Significantly, fundamental aspects of the photocarrier processes, such as relaxation time scales, are found to be flexibly controlled through element doping, a feature crucial for the development of convenient mid-infrared ultrafast sources. Although various exotic physical phenomena have been uncovered in three-dimensional TDS systems, our findings show for the first time that this emerging class of quantum materials can be harnessed to fill a long known gap in the field of photonics. 
Chunhui Zhu, Fengqiu Wang, Yafei Meng, Xiang Yuan, Faxian Xiu, Hongyu   Luo, Yazhou Wang, Jianfeng Li, Xinjie Lv, Liang He, ...
cond-mat.mtrl-sci physics.optics