Junmin Yan

Wide bandwidth lasing randomly assembled ZnS/ZnO biaxial nanobelt heterostructures

Wide-bandwidth random lasing action is observed from the randomly assembled ZnS/ZnO biaxial nanobelt heterostructures under optical excitation. This is because optical gain at ultraviolet regime can be obtained from the near-band-edge radiative recombination of ZnS and ZnO. Surface defects related radiative recombination centers of ZnS and ZnO nanostructures also contribute to the visible optical gain. Hence, a broadband optical gain is obtained from the ZnS/ZnO biaxial nanobelt heterostructures. Moreover, a wide bandwidth coherent optical feedback can be achieved from the randomly assembled biaxial nanobelts due to high refractive index contrast between the nanobelts and air.Wide-bandwidth random lasing action is observed from the randomly assembled ZnS/ZnO biaxial nanobelt heterostructures under optical excitation. This is because optical gain at ultraviolet regime can be obtained from the near-band-edge radiative recombination of ZnS and ZnO. Surface defects related radiative recombination centers of ZnS and ZnO nanostructures also contribute to the visible optical gain. Hence, a broadband optical gain is obtained from the ZnS/ZnO biaxial nanobelt heterostructures. Moreover, a wide bandwidth coherent optical feedback can be achieved from the randomly assembled biaxial nanobelts due to high refractive index contrast between the nanobelts and air.

Observation of metallic indium clusters in thick InGaN layer grown by metal organic chemical vapor deposition

Pure metallic indium clusters of 10–50nm are identified in In0.37Ga0.63N film grown by metal organic chemical vapor deposition based on analysis of x-ray diffraction, transmission electron microscopy, selected area diffraction, and high resolution transmission electron microscopy (HRTEM). The in-plane orientation relationships are InGaN[11−20]‖metallic indium [0−10], InGaN [1−100]‖metallic indium [−101], and InGaN [0001]‖metallic indium [101] along the growth direction. The rocking curve of indium (101) diffraction shows a large full width at half maximum of 3060arcsec, which is consistent with the small size of the indium clusters observed in HRTEM.

Resistivity plateau and large magnetoresistance in the charge density wave system TaTe4

Due to the time reversal symmetry, the metallic surface of the topological insulator (TI) survives and results in the resistivity plateau at low temperature, which is the transport signature of the metallic surface state. Such a universal character has been observed in many materials, such as Bi2Te2Se, SmB6, and so on. Recently, a similar behavior has also been found in the possible topological semimetal LaSb/Bi and the metallic compounds Nb/TaAs2. Herein, we have mainly explored the resistivity plateau and the magnetoresistance (MR) of TaTe4 single crystal with the charge density wave (CDW) transition temperature TCDW = 475 K. There are some interesting observations: (i) The large MR (MR is about 1200% in a magnetic field 16 T at T = 2 K) is observed at low temperature; (ii) A field-induced universal TI resistivity with a plateau at roughly T = 10 K and high quantum mobility of carriers in the plateau region are present; (iii) Quantum oscillations with the angle dependence of a two-dimensional Fermi surf...

Critical behavior of two-dimensional intrinsically ferromagnetic semiconductor CrI3

CrI3, which belongs to a rare category of two-dimensional (2D) ferromagnetic semiconductors, is of great interest for spintronic device applications. Unlike CrCl3 whose magnetism presents a 2D-Heisenberg behavior, CrI3 exhibits a larger van der Waals gap, smaller cleavage energy, and stronger magnetic anisotropy which could lead to a 3D magnetic characteristic. Hence, we investigate the critical behavior of CrI3 in the vicinity of magnetic transition. We use the modified Arrott plot and Kouvel-Fisher method, and conduct critical isotherm analysis to estimate the critical exponents near the ferromagnetic phase transition. This shows that the magnetism of CrI3 follows the crossover behavior of a 3D-Ising model with mean field type interactions where the critical exponents \b{eta}, {\gamma}, and {\delta} are 0.323, 0.835, and 3.585, respectively, at the Curie temperature of 64 K. We propose the crossover behavior can be attributed to the strong uniaxial anisotropy and inevitable interlayer coupling. Our experiment demonstrates the applicability of crossover behavior to a 2D ferromagnetic semiconductor.

Anomalous Hall effect in two-dimensional non-collinear antiferromagnetic semiconductor Cr0.68Se

Cr0.68Se single crystals with two-dimensional (2D) character have been grown, and the detailed magnetization M(T), electrical transport properties (including longitudinal resistivity and Hall resistivity and thermal transport ones (including heat capacity Cp(T) and thermoelectric power (TEP) S(T)) have been measured. There are some interesting phenomena: (i) Cr0.68Se presents a non-collinear antiferromagnetic (AFM) semiconducting behavior with the Neel temperature TN = 42 K and the activated energy Eg=3.9 meV; (ii) It exhibits the anomalous Hall effect (AHE) below TN and large negative magnetoresistance (MR) about 83.7% (2 K, 8.5 T). The AHE coefficient RS is 0.385 cm-3/C at T=2 K and the AHE conductivity {\sigma}H is about 1 ohm-1cm-1 at T=40 K, respectively; (iii) The scaling behavior between the anomalous Hall resistivity and the longitudinal resistivity is linear and further analysis implies that the origin of the AHE in Cr0.68Se is dominated by the skew-scattering mechanism. Our results may be helpful for exploring the potential application of these kind of 2D AFM semiconductors.