title: A robust and tuneable mid-infrared optical switch enabled by bulk Dirac fermions.
abstract: Pulsed lasers operating in the mid-infrared (3-20 μm) are important for a wide range of applications in sensing, spectroscopy, imaging and communications. Despite recent advances with mid-infrared gain platforms, the lack of a capable pulse generation mechanism remains a significant technological challenge. Here we show that bulk Dirac fermions in molecular beam epitaxy grown crystalline Cd3As2, a three-dimensional topological Dirac semimetal, constitutes an exceptional ultrafast optical switching mechanism for the mid-infrared. Significantly, we show robust and effective tuning of the scattering channels of Dirac fermions via an element doping approach, where photocarrier relaxation times are found flexibly controlled over an order of magnitude (from 8 ps to 800 fs at 4.5 μm). Our findings reveal the strong impact of Cr doping on ultrafast optical properties in Cd3As2and open up the long sought parameter space crucial for the development of compact and high-performance mid-infrared ultrafast sources.
authors.affiliation: School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
authors.forename: Chunhui
authors.initials: C
authors.lastname: Zhu
authors.affiliation: School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
authors.forename: Fengqiu
authors.initials: F
authors.lastname: Wang
authors.affiliation: School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
authors.forename: Yafei
authors.initials: Y
authors.lastname: Meng
authors.affiliation: Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.|State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Yuan
authors.affiliation: Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.|State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.
authors.forename: Faxian
authors.initials: F
authors.lastname: Xiu
authors.affiliation: School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054, China.
authors.forename: Hongyu
authors.initials: H
authors.lastname: Luo
authors.affiliation: School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054, China.
authors.forename: Yazhou
authors.initials: Y
authors.lastname: Wang
authors.affiliation: School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054, China.
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Li
authors.affiliation: Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.|National Laboratory of Solid State Microstructures and School of Physics, Nanjing University, Nanjing 210093, China.
authors.forename: Xinjie
authors.initials: X
authors.lastname: Lv
authors.affiliation: School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
authors.forename: Liang
authors.initials: L
authors.lastname: He
authors.affiliation: School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
authors.forename: Yongbing
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China.
authors.forename: Junfeng
authors.initials: J
authors.lastname: Liu
authors.affiliation: School of Physics and Institute for Superconducting and Electronic Materials, University of Wollongong, New South Wales 2522, Australia.
authors.forename: Chao
authors.identifier: 0000-0002-2817-0488
authors.initials: C
authors.lastname: Zhang
authors.affiliation: School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Shi
authors.affiliation: School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China.|Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
authors.forename: Rong
authors.initials: R
authors.lastname: Zhang
authors.affiliation: Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.|National Laboratory of Solid State Microstructures and School of Physics, Nanjing University, Nanjing 210093, China.
authors.forename: Shining
authors.initials: S
authors.lastname: Zhu