The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model. On the basis of instanton technique in the spin-coherent-state path-integral representation, both the rigorous Wentzel-Kramers-Brillouin exponent and preexponential factor for the groundstate tunnel splitting are obtained. We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys. Rev. Lett. 80, 169 (1998)) , but also have great influnence on the intensity of the ground-state tunnel splitting. Those features clearly have no analogue in the ferromagnetic molecular magnets. We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets. The analytical results are complemented by exact diagonalization calculation.

The effect of an electric field on the subbands and excitons in a GaAs/Ga1-xAlxAs quantum well is studied by using a finite-potential-barrier model. The subbands of electrons and holes and the binding energies of excitons have been calculated for GaAs/Al0.34 Ga0.66 As quantum well (L = 105?) in electric field ranging from O to 1.2×105 V/cm. Based on these, the electron-hole overlap functions and the energy shifts of excitons corresponding to different subbands are obtained, they agree well with experimental results.

Since the discovery by Karl Alex Muller and Johannes Georg Bednorz (IBM Zurich) in January 1986 that an oxide of barium, lanthanum and copper might be superconducting at temperatures up to 35 K, the superconducting transition temperature has jumped to 125 K in only two years. A great tide of high Tc superconductor exploration has swept across the world. Like their counterparts in other countries, Chinese scientists also stood in the frontline of this revolution.When Prof. Zhao Zhongxian obtained Bednorz and Müller's paper in September 1986, he thought their ideas were reasonable. A team at the Institute of Physics, Academia Sinica was then organized to search for high Tc materials. In December 1986, Zhao and his colleagues successfully obtained superconducting samples of Sr0.25La4.75Cu5Ox with onset temperature Tcon 48.6 K and Ba0.5La4.5Cu5Ox with Tcon = 46.3 K (Figure 1). This occurred only a few days after the announcement of the confirmation of superconductivity by diamag-netic observation from Japan. These were the highest records for superconducting transition temperature Tcon in the world at that time. Moreover, a sign of superconductivity with Tc0 (zero resistivity) around 70 K was also observed in some La-Ba-Cu-O samples. Because these samples were unstable, however, the Tc decreased after several days storage in air. Since then Zhao and his colleagues have searched for materials with higher Tc by using various compositions and substitutions, different sintering processes, and heat treatments.

The concentration profiles of high-dose implanted N+ (5×1017 atom/cm2, 100 keV) in iron foils (about 4000? thick) and iron bulk sample (industrial purity) were measured by E. B. S. via α-particle of energy in order of MeV. A dip was found in backscat-tering spectrum of the substrate, as a result of the high-dose impurity, implantation a method was developed to calculate the concentration profile of impurity based on the dip.