Search Results (5 total)

We experimentally studied the spin-dependent collision dynamics of ⁸⁷Rb spin-2 Bose-Einstein condensates confined in an optical trap. The condensed atoms were initially populated in the ∣F=2,m_F=0⟩ state, and their time evolutions in the trap were measured in the presence of external magnetic field strengths ranging from 0.1 to 3.0  G. The atom loss rate due to inelastic two-body collisions was found to be 1.4(2)×10⁻¹³  cm³  s⁻¹. Spin mixing in the F=2 manifold developed dramatically for the first few tens of milliseconds, and the oscillations in the population distribution between different magnetic components were observed over a limited range of magnetic field strengths. The antiferromagnetic property of this system was deduced from the magnetic field dependence on the evolution of relative populations for each m_F component.

ZnO/GaN heterointerfaces are engineered to control the polarity of ZnO films grown by plasma-assisted molecular beam epitaxy on Ga-polar GaN templates. The polarity of ZnO films is determined both by coaxial impact collision ion scattering spectroscopy (CAICISS) and by convergent beam electron diffraction (CBED). Polarity inversion can be achieved by inserting an interface layer with a center of symmetry, because the polarity comes from a lack of the center of symmetry. An O-polar (anion-polar) ZnO film can be grown on Ga-polar (cation-polar) GaN by inserting a Ga₂O₃ layer at the interface, while Zn-polar ZnO is grown on GaN without forming an interface layer. A single-crystalline monoclinic Ga₂O₃ layer, which has a center of symmetry, is formed by O-plasma preexposure on the Ga-polar GaN surface prior to ZnO growth, while the ZnO/GaN interface without any extra layer is formed by Zn preexposure. The orientation relationship between ZnO, Ga₂O₃, and GaN is determined as [2-1-10]_ZnO∥[010]_Ga2O3∥[2-1-10]_GaN and (0001)_ZnO∥(001)_Ga2O3∥(0001)_GaN. The CAICISS results reveal the growth of an O-polar ZnO film on O-plasma-preexposed GaN, while a Zn-polar ZnO film on Zn-preexposed GaN. The origin of the observed features in polar-angle-dependent CAICISS spectra can be analyzed by considering the shadow cones of Zn and O atoms formed by incident ions and shadowing and focusing effects of scattered ions. Azimuthal-angle-dependent CAICISS spectra reveal the surfaces of both Zn- and O-polar ZnO films as mixture of c and c/2 planes with a ratio of about 50:50. The ZnO film with a Ga₂O₃ interface layer shows a degradation in the crystal quality as evidenced by a broadening of the x-ray rocking curves. The CBED results for the O-plasma-preexposed samples reveal Ga-polar GaN and O-polar ZnO for the O-plasma-preexposed samples, which directly confirms polarity inversion from cation to anion polar. On the other hand, Zn-polar ZnO CBED patterns are obtained from ZnO films grown on Zn-preexposed Ga-polar GaN, which indicates the same cation polarity for a ZnO/GaN interface without the formation of an interface layer. It is noted that no planar or faceted inversion domain boundaries are formed to invert the polarity (from Ga polar to O polar). This indicates that we can control the polarity by engineering interfaces.

We report on the first measurement of a hypernuclear γ-transition probability. γ rays emitted in the E2(5/2⁺→1/2⁺) transition of _Λ⁷Li were detected by a large-acceptance germanium detector array (Hyperball), and the lifetime of the parent state ( 5/2⁺) was determined by the Doppler shift attenuation method. The obtained result, 5.8_-0.7^+0.9±0.7 ps, was then converted into the reduced transition probability [ B(E2)] to be B(E2;5/2⁺→1/2⁺)  =  3.6±0.5_-0.4^+0.5 e² fm⁴. Compared with the B(E2) of the corresponding E2(3⁺→1⁺) transition in the ⁶Li nucleus, our result gives evidence that the size of the ⁶Li core in _Λ⁷Li is smaller than the ⁶Li nucleus in the free space.

Using a large-acceptance germanium detector array (Hyperball), we have observed a spin-flip M1 γ transition between the ground-state spin doublet of _Λ⁷Li ( 3 / 2⁺→1 / 2⁺). The observed energy of 691.7±0.6(stat)±1.0(syst) keV provides crucial information on the strength of the spin-spin interaction between a Λ and a nucleon. This is the first observation of well-identified hypernuclear γ transitions using germanium detectors.

Using orthonormal divergence-free vector wavelets, we analyzed the nonlinear transfer in three-dimensional homogeneous, isotropic turbulence. Wavelet analysis supports the predominance of local interactions in the nonlinear energy transfer process, which is consistent with Kolmogorov's phenomenology. Analogous Fourier analysis is also carried out for comparison. It is verified that the predominance of nonlocal interactions [J. A. Domaradzki and R. S. Rogallo, Phys. Fluids A 2, 413 (1990); P. K. Yeung and J. G. Brasseur, Phys. Fluids A 3, 884 (1991); K. Ohkitani and S. Kida, Phys. Fluids A 4, 794 (1992)] results from linearly binned Fourier analysis, whose shortcomings are also discussed.