Linhua Yu

New development of nonlinear optical crystals for the ultraviolet region with molecular engineering approach

Potassium fluoroboratoberyllate KBe2BO3F2 (KBBF) has been revealed theoretically and experimentally as a novel ultraviolet nonlinear optical crystal, but it is found to be very difficult to grow in a large size, because of the weak binding interaction between the (Be2BO3)∞ units, which leads to an apparent layer habit in the growth. By using a molecular engineering approach, oxygen bridges when brought in to strengthen the binding between the infinite units are found to be useful to overcome the above shortcoming of KBBF, and in the light of it another new ultraviolet nonlinear optical crystal—strontium boratoberyllate Sr2Be2B2O7 (SBBO) has been discovered. The linear optical properties of SBBO are similar to KBBF’s, but its nonlinear optical properties are better than that of the latter. d22(SBBO)≂d22(β‐BaB2O4), which is two times higher than d11 of KBBF. SBBO has very good mechanical properties, and it is also not deliquescent. So SBBO is expected to have great potential for the application in ultraviol...

New development of nonlinear optical crystals for the ultraviolet region with molecular engineering

their frequency response were measured (Fig. 3). Frequency response improves with decreasing modulation-region length (e) , and large bandwidth (fMB: electrical) of 33 GHz is obtained for e = 50 p,m. In conclusion, we have proposed and demonstrated an MQW EA modulator integrated with waveguides. This modulator achieves a higher-speed modulation with a shorter modulation-region, while it is still long enough for easy fabrication and packaging. A fabricated 1-mm-long modulator with a 50-pm-long modulation-region showed a low insertion loss of 7 dB and a large bandwidth of 33 GHz.

Spin dynamics, electronic, and thermal transport properties of two-dimensional CrPS4 single crystal

2-Dimensional (2D) CrPS4 single crystals have been grown by the chemical vapor transport method. The crystallographic, magnetic, electronic and thermal transport properties of the single crystals were investigated by the room-temperature X-ray diffraction, electrical resistivity \r{ho}(T), specific heat CP(T) and the electronic spin response (ESR) measurements. CrPS4 crystals crystallize into a monoclinic structure. The electrical resistivity \r{ho}(T) shows a semiconducting behavior with an energy gap Ea=0.166 eV. The antiferromagntic (AFM) transition temperature is about TN=36 K. The spin flipping induced by the applied magnetic field is observed along the c axis. The magnetic phase diagram of CrPS4 single crystal has been discussed. The extracted magnetic entropy at TN is about 10.8 J/mol K, which is consistent with the theoretical value R ln(2S + 1) for S = 3/2 of the Cr3+ ion. Based on the mean-field theory, the magnetic exchange constants J1 and Jc corresponding to the interactions of the intralayer and between layers are about 0.143 meV and -0.955 meV are obtained based on the fitting of the susceptibility above TN, which agree with the results obtained from the ESR measurements. With the help of the strain for tuning the magnetic properties, monolayer CrPS4 may be a promising candidate to explore 2D magnetic semiconductors.

Optical absorption coefficients in two-dimensional semiconductors under strong magnetic field

We calculate the photon absorption coefficient of hot two-dimensional electrons in the presence of a strong magnetic field. The electrons interact strongly with the optical phonons and the acoustic phonons in quantum wells. The dependence of the optical absorption on the magnetic field is obtained by using the quantum mechanical kinetic theory. It is found that the photon absorption spectrum displays a local magnetophonon resonance. The magnetophonon absorption resulting from inelastic scattering between Landau levels is more pronounced at higher temperature. The effect of subband nonparabolicity on the absorption coefficient is also discussed.