Shifting donor-acceptor photoluminescence in N-doped ZnO

We have grown nitrogen-doped ZnO films grown by two kinds of epitaxial methods on lattice-matched ScAlMgO$_4$ substrates. We measured the photoluminescence (PL) of the two kinds of ZnO:N layers in the donor-acceptor-pair transition region. The analysis of excitation-intensity dependence of the PL peak shift with a fluctuation model has proven that our observed growth-technique dependence was explained in terms of the inhomogeneity of charged impurity distribution. It was found that the inhomogeneity in the sample prepared with the process showing better electrical property was significantly smaller in spite of the similar nitrogen concentration. The activation energy of acceptor has been evaluated to be $\approx 170$ meV, which is independent of the nitrogen concentration.Comment: 4 pages, 3 figures, 1 table, RevTeX4, to appear in the July issue of J. Phys. Soc. Jp

Hamiltonian Formalism of the de-Sitter Invariant Special Relativity

Lagrangian of the Einstein's special relativity with universal parameter $c$ ($\mathcal{SR}_c$) is invariant under Poincar\'e transformation which preserves Lorentz metric $\eta_{\mu\nu}$. The $\mathcal{SR}_c$ has been extended to be one which is invariant under de Sitter transformation that preserves so called Beltrami metric $B_{\mu\nu}$. There are two universal parameters $c$ and $R$ in this Special Relativity (denote it as $\mathcal{SR}_{cR}$). The Lagrangian-Hamiltonian formulism of $\mathcal{SR}_{cR}$ is formulated in this paper. The canonic energy, canonic momenta, and 10 Noether charges corresponding to the space-time's de Sitter symmetry are derived. The canonical quantization of the mechanics for $\mathcal{SR}_{cR}$-free particle is performed. The physics related to it is discussed.Comment: 24 pages, no figur

From the Complete Yang Model to Snyder's Model, de Sitter Special Relativity and Their Duality

By means of Dirac procedure, we re-examine Yang's quantized space-time model, its relation to Snyder's model, the de Sitter special relativity and their UV-IR duality. Starting from a dimensionless dS_5-space in a 5+1-d Mink-space a complete Yang model at both classical and quantum level can be presented and there really exist Snyder's model, the dS special relativity and the duality.Comment: 7 papge

Mode locking of vortex matter driven through mesoscopic channels

We investigated the driven dynamics of vortices confined to mesoscopic flow channels by means of a dc-rf interference technique. The observed mode-locking steps in the $IV$-curves provide detailed information on how the number of rows and lattice structure in the channel change with magnetic field. Minima in flow stress occur when an integer number of rows is moving coherently, while maxima appear when incoherent motion of mixed $n$ and $n\pm 1$ row configurations is predominant. Simulations show that the enhanced pinning at mismatch originates from quasi-static fault zones with misoriented edge dislocations induced by disorder in the channel edges.Comment: some minor changes were made, 4 pages, 4 figures, accepted for publication in Phys. Rev. Let

Electrical Characterization of 1.8 MeV Proton-Bombarded ZnO

We report on the electrical characterization of single-crystal ZnO and Au Schottky contacts formed thereon before and after bombarding them with 1.8 MeV protons. From capacitance–voltage measurements, we found that ZnO is remarkably resistant to high-energy proton bombardment and that each incident proton removes about two orders of magnitude less carriers than in GaN. Deep level transient spectroscopy indicates a similar effect: the two electron traps detected are introduced in extremely low rates. One possible interpretation of these results is that the primary radiation-induced defects in ZnO may be unstable at room temperature and anneal out without leaving harmful defects that are responsible for carrier compensation

Shapiro steps in a superconducting film with an antidot lattice

Shapiro voltage steps at voltages V_n=nV_0 (n integer) have been observed in the voltage-current characteristics of a superconducting film with a square lattice of perforating microholes (antidots)in the presence of radiofrequent radiation. These equidistant steps appear at the second matching field H_2 when the flow of the interstitial vortex lattice in the periodic potential created by the antidots and the vortices trapped by them, is in phase with the applied rf frequency. Therefore, the observation of Shapiro steps clearly reveals the presence of mobile intersitial vortices in superconducting films with regular pinning arrays. The interstitial vortices, moved by the driving current, coexist with immobile vortices strongly pinned at the antidots.Comment: 6 pages text, 3 EPS figures, RevTeX, accepted for publication in PRB Rapid Communication