Deep levels and radiation effects in p-InP

A survey was conducted on past studies of hole traps in InP. An experiment was designed to evaluate hole traps in Zn-doped InP after fabrication, after electron irradiation and after annealing using deep level transient spectroscopy. Data similar to that of Yamaguchi was seen with observation of both radiation-induced hole and electron traps at E sub A=0.45 eV and 0.03 eV, respectively. Both traps are altered by annealing. It is also shown that trap parameters for surface-barrier devices are influenced by many factors such as bias voltage, which probes traps at different depths below the surface. These devices require great care in data evaluation

Tibet's relocated schooling: Popularization reconsidered

China has popularized relocated boarding schools for Tibetans in China. This paper examines the origin and development of these neidi schools, and the perspectives of their graduates. Despite their popularity among Tibetan households, this paper argues that their sustainability over the longer term is less certain. © 2009 By the Regents of the University of California.published_or_final_versio

Assessment of two hybrid van der Waals density functionals for covalent and non-covalent binding of molecules

Two hybrid van der Waals density functionals (vdW-DFs) are constructed using 25%, Fock exchange with i) the consistent-exchange vdW-DF-cx functional and ii) with the vdW-DF2 functional. The ability to describe covalent and non-covalent binding properties of molecules are assessed. For properties related to covalent binding, atomization energies (G2-1 set), molecular reaction energies (G2RC set), as well as ionization energies (G21IP set) are benchmarked against experimental reference values. We find that hybrid-vdW-DF-cx yields results that are rather similar to those of the standard non-empirical hybrid PBE0 [JCP 110, 6158 (1996)]. Hybrid vdW-DF2 follows somewhat different trends, showing on average significantly larger deviations from the reference energies, with a MAD of 14.5 kcal/mol for the G2-1 set. Non-covalent binding properties of molecules are assessed using the S22 benchmark set of non-covalently bonded dimers and the X40 set of dimers of small halogenated molecules, using wavefunction-based quantum chemistry results for references. For the S22 set, hybrid-vdW-DF-cx performs better than standard vdW-DF-cx for the mostly hydrogen-bonded systems. Hybrid-vdW-DF2 offers a slight improvement over standard vdW-DF2. Similar trends are found for the X40 set, with hybrid-vdW-DF-cx performing particularly well for binding involving the strongly polar hydrogen halides, but poorly for systems with tiny binding energies. Our study of the X40 set reveals both the potential of mixing Fock exchange with vdW-DF, but also highlights shortcomings of the hybrids constructed here. The solid performance of hybrid-vdW-DF-cx for covalent-bonded systems, as well as the strengths and issues uncovered for non-covalently bonded systems, makes this study a good starting point for developing even more precise hybrid vdW-DFs

Anderson transition in a three dimensional kicked rotor

We investigate Anderson localization in a three dimensional (3d) kicked rotor. By a finite size scaling analysis we have identified a mobility edge for a certain value of the kicking strength $k = k_c$. For $k > k_c$ dynamical localization does not occur, all eigenstates are delocalized and the spectral correlations are well described by Wigner-Dyson statistics. This can be understood by mapping the kicked rotor problem onto a 3d Anderson model (AM) where a band of metallic states exists for sufficiently weak disorder. Around the critical region $k \approx k_c$ we have carried out a detailed study of the level statistics and quantum diffusion. In agreement with the predictions of the one parameter scaling theory (OPT) and with previous numerical simulations of a 3d AM at the transition, the number variance is linear, level repulsion is still observed and quantum diffusion is anomalous with $\propto t^{2/3}$. We note that in the 3d kicked rotor the dynamics is not random but deterministic. In order to estimate the differences between these two situations we have studied a 3d kicked rotor in which the kinetic term of the associated evolution matrix is random. A detailed numerical comparison shows that the differences between the two cases are relatively small. However in the deterministic case only a small set of irrational periods was used. A qualitative analysis of a much larger set suggests that the deviations between the random and the deterministic kicked rotor can be important for certain choices of periods. Contrary to intuition correlations in the deterministic case can either suppress or enhance Anderson localization effects.Comment: 10 pages, 5 figure

Is it possible to observe experimentally a metal-insulator transition in ultra cold atoms?

Kicked rotors with certain non-analytic potentials avoid dynamical localization and undergo a metal-insulator transition. We show that typical properties of this transition are still present as the non-analyticity is progressively smoothed out provided that the smoothing is less than a certain limiting value. We have identified a smoothing dependent time scale such that full dynamical localization is absent and the quantum momentum distribution develops power-law tails with anomalous decay exponents as in the case of a conductor at the metal-insulator transition. We discuss under what conditions these findings may be verified experimentally by using ultra cold atoms techniques. It is found that ultra-cold atoms can indeed be utilized for the experimental investigation of the metal-insulator transition.Comment: 7 pages, 3 figure