Cd3As2, as a three-dimensional(3D) topological Dirac semimetal, has attracted wide attention due to its unique physical properties originating from the 3D massless Dirac fermions. While many efforts have been devoted ...Cd3As2, as a three-dimensional(3D) topological Dirac semimetal, has attracted wide attention due to its unique physical properties originating from the 3D massless Dirac fermions. While many efforts have been devoted to the exploration of novel physical phenomena such as chiral anomaly and phase transitions by using bulk crystals, the development of high-quality and large-scale thin films becomes necessary for practical electronic and optical applications. Here, we report our recent progress in developing single-crystalline thin films with improved quality and their optical devices including Cd3As2-based heterojunctions and ultrafast optical switches. We find that a post-annealing process can significantly enhance the crystallinity of Cd3As2 in both intrinsic and Zn-doped thin films. With excellent characteristics of high mobility and linear band dispersion, Cd3As2 exhibits a good optical response in the visible-to-mid-infrared range due to an advantageous optical absorption, which is reminiscent of 3D graphene. It also behaves as an excellent saturable absorber in the mid-infrared regime. Through the delicate doping process in this material system, it may further open up the long-sought parameter space crucial for the development of compact and high-performance mid-infrared ultrafast sources.展开更多
Monocrystalline SrMnBi2 thin films were grown by molecular beam epitaxy （MBE）, and their transport properties were investigated. A high and unsaturated linear magnetoresistance （MR） was observed, which exhibited a...Monocrystalline SrMnBi2 thin films were grown by molecular beam epitaxy （MBE）, and their transport properties were investigated. A high and unsaturated linear magnetoresistance （MR） was observed, which exhibited a transition from a semi-classical weak-field B2 dependence to a high-field linear dependence. An unusual nonlinear Hall resistance was also observed because of the anisotropic Dirac fermions. The two-carrier model was adopted to analyze the unusual Hall resistance quantitatively. The fitting results yielded carrier densities and mobilities of 3.75×10^14 cm^-2 and 850 cm^2·V^-1·s^-1, respectively, for holes, and 1.468×10^13 cm^-2, 4118 cm^2·V^-1·s^-1, respectively, for electrons, with a hole-dominant conduction at 2.5 K. Hence, an effective mobility can be achieved, which is in reasonable agreement with the effective hole mobility of 1800 cm^2·V^-1·s^-1, extracted from the MR. Further, the angle-dependent MR, proportional to cos 0, where 0 is the angle between the external magnetic field and the perpendicular orientation of the sample plane, also implies a high anisotropy of the Fermi surface. Our results about SrMnBi2 thin films, as one of a new class of AEMnBi2 and AEMnSb2 （AE = Ca, Sr, Ba, Yb, Eu） materials, suggest that they have a lot of exotic transport properties to be investigated, and that their high mobility might facilitate electronic device applications.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0303302 and 2018YFA0305601)the National Natural Science Foundation of China(Grant Nos.61322407,11474058,61674040,and 11874116)
文摘Cd3As2, as a three-dimensional(3D) topological Dirac semimetal, has attracted wide attention due to its unique physical properties originating from the 3D massless Dirac fermions. While many efforts have been devoted to the exploration of novel physical phenomena such as chiral anomaly and phase transitions by using bulk crystals, the development of high-quality and large-scale thin films becomes necessary for practical electronic and optical applications. Here, we report our recent progress in developing single-crystalline thin films with improved quality and their optical devices including Cd3As2-based heterojunctions and ultrafast optical switches. We find that a post-annealing process can significantly enhance the crystallinity of Cd3As2 in both intrinsic and Zn-doped thin films. With excellent characteristics of high mobility and linear band dispersion, Cd3As2 exhibits a good optical response in the visible-to-mid-infrared range due to an advantageous optical absorption, which is reminiscent of 3D graphene. It also behaves as an excellent saturable absorber in the mid-infrared regime. Through the delicate doping process in this material system, it may further open up the long-sought parameter space crucial for the development of compact and high-performance mid-infrared ultrafast sources.
文摘Monocrystalline SrMnBi2 thin films were grown by molecular beam epitaxy （MBE）, and their transport properties were investigated. A high and unsaturated linear magnetoresistance （MR） was observed, which exhibited a transition from a semi-classical weak-field B2 dependence to a high-field linear dependence. An unusual nonlinear Hall resistance was also observed because of the anisotropic Dirac fermions. The two-carrier model was adopted to analyze the unusual Hall resistance quantitatively. The fitting results yielded carrier densities and mobilities of 3.75×10^14 cm^-2 and 850 cm^2·V^-1·s^-1, respectively, for holes, and 1.468×10^13 cm^-2, 4118 cm^2·V^-1·s^-1, respectively, for electrons, with a hole-dominant conduction at 2.5 K. Hence, an effective mobility can be achieved, which is in reasonable agreement with the effective hole mobility of 1800 cm^2·V^-1·s^-1, extracted from the MR. Further, the angle-dependent MR, proportional to cos 0, where 0 is the angle between the external magnetic field and the perpendicular orientation of the sample plane, also implies a high anisotropy of the Fermi surface. Our results about SrMnBi2 thin films, as one of a new class of AEMnBi2 and AEMnSb2 （AE = Ca, Sr, Ba, Yb, Eu） materials, suggest that they have a lot of exotic transport properties to be investigated, and that their high mobility might facilitate electronic device applications.
