Tianxiang Xu

Strong anisotropy of magnetization and sign reversion of ordinary Hall coefficient in single crystal Ge1−xMnx magnetic semiconductor films

Epitaxial single-crystal Ge1−xMnx ferromagnetic-semiconductor films were fabricated on Ge(001) substrates by molecular beam epitaxy. All the samples are ferromagnetic and have strong magnetic anisotropy indicated by different magnetization in plane and out of plane. The electrical transport of the films obeys Efros variable range hopping law in the low temperature range. Interestingly, a negative coefficient of the ordinary Hall effect of p-type carriers was found in the variable range hopping at low temperature. Anomalous Hall effect in Ge0.949Mn0.051 film was observed below the Curie temperature, indicating the carrier-mediated intrinsic ferromagnetism.

Growth and property characterization of CaNdGa3O7 and SrNdGa3O7 melilite single crystals

Piezoelectric CaNdGa3O7 and SrNdGa3O7 single crystals with the melilite structure were successfully grown by the Czochralski technique. The thermal properties of these crystals have been systematically investigated. A full matrix of electromechanical material constants was measured by the IEEE resonance method, with k′12 and d14 being on the order of 12.5–14.0% and 9.3–9.4 pC N−1, respectively. A relationship between the physical properties and microstructures was established to explain the anisotropic properties of melilite crystals. In addition, the GaO4 tetrahedral layers, acting as barriers against charge transport, account for the high electrical resistivity along the Z-axis. The high thermal stability of the elastic constants and piezoelectric coefficients of SrNdGa3O7 over the temperature range of 25–600 °C together with its high resistivity on the order of 9.2 × 106 ohm cm at 600 °C make it a promising candidate for piezoelectric sensing applications at high temperatures.

Magnetoresistance and electron-hole exchange interaction in (Co1-xInx)2O3-v concentrated ferromagnetic semiconductors

Systematic studies of electrical transport properties of (Co1-xInx)2O3-v concentrated ferromagnetic semiconductors were performed. Quantitative analysis demonstrated that spin dependent variable range hopping dominated the low temperature transport behavior. Moreover, it was found that ferromagnetic or antiferromagnetic coupling of electron-hole pair generated during the variable range hopping process is responsible for the negative or positive magnetoresistance, respectively. Our results not only illustrate the connection between magnetoresistance and electron-hole exchange interaction but also provide a unique method to detect the exchange interaction of electron-hole pair.

Passively Q-switched ytterbium-doped ScBO3 laser with black phosphorus saturable absorber

Abstract. We demonstrate a passively Q-switched Yb3+-doped ScBO3 bulk laser using a black phosphorous (BP) saturable absorber, a two-dimensional semiconductor. The response spectra of BP show that it is suitable as a universal switcher in the spectral range from the visible to midinfrared band. Considering the saturable absorption properties of BP and emission properties of Yb3+-doped crystals, the passively Q-switched bulk laser pulses were realized with the Yb3+:ScBO3 crystal as a gain material and a fabricated BP sample as a Q-switcher. Because of the large energy storage capacity of Yb3+:ScBO3, the maximum output energy is obtained to be 1.4  μJ, which is comparable with the previous reported maximum energy of graphene Q-switched lasers. The obtained results identify the potential capability of BP as a pulse modulator in bulk lasers, and BP plays an increasingly important role in a wide range of its applications, including photonics and optoelectronics.

A naturally grown three-dimensional nonlinear photonic crystal

Nonlinear frequency conversion via three-dimensional(3D) quasi-phase matching (QPM) process is experimentally realized based on a Ba0.77Ca0.23TiO3 (BCT) crystal. The ferroelectric domains in BCT crystal are observed, and the results reveal that the antiparallel domains distribute in three dimensions and can provide 3D reciprocal lattice vectors for QPM processes. Broadband petal-like second-harmonic patterns are achieved, which are well consistent with the theoretical quasi-cubic model of 3Dnonlinearphotonic crystals. Our work not only promotes the development of QPM technique but also builds a platform for 3Dnonlinear optics and quantum optics.

Acentric langanite La 3 Ga 5.5 Nb 0.5 O 14 crystal: a new nonlinear crystal for the generation of mid-infrared parametric light

The mid-infrared spectral range extending from 2 to 6 μm is significant for scientific and technological applications. A promising nonlinear oxide crystal La3Ga5.5Nb0.5O14 (LGN) is proposed and fully characterized for the first time to our knowledge. The transparency range extends between 0.28 and 7.4 μm. The two principal refractive indices were measured and we found that the nonlinear coefficient d11 = 3.0 ± 0.1 pm/V at 0.532 μm. The simultaneous fit of data allowed us to refine the Sellmeier equations of LGN and to calculate the tuning curves for optical parametric generation (OPG) pumped at 1.064 μm. Calculations are consistent with recorded data and also show the generation of a supercontinuum between 1.5 and 3.5 μm when pumped at 0.98 μm by a Ti:Sapphire laser.

Studies about relationships between the symmetries of ferroelectric crystal and frequency-doubled patterns

The broadband quasi-phase-matching process in Ca0.28Ba0.72Nb2O6 was demonstrated and the relationships between crystal symmetries and second-harmonic patterns were studied. Considering the light-matter interaction, the frequency-doubled photons were found to be trapped by a centripetal force.

Investigations on Yb 3+ :ScBO 3 - a novel laser crystal in rare-earth ions doped orthoborate systems

Optical-quality Yb3+:ScBO3 crystal has been grown by the Czochralski method. The thermal and spectral properties were studied. The continuous-wave Yb3+:ScBO3 crystal laser has been demonstrated which indicates its promising utilization in moderate-power lasers.