Physics

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Deformations of the canonical commutation relations lead to non-Hermitian momentum and position operators and therefore almost inevitably to non-Hermitian Hamiltonians. We demonstrate that such type of deformed quantum mechanical systems may be treated in a similar framework as quasi/pseudo and/or PT-symmetric systems, which have recently attracted much attention. For a newly proposed deformation of exponential type we compute the minimal uncertainty and minimal length, which are essential in almost all approaches to quantum gravity. © 2009 Elsevier B.V. All rights reserved.

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Physics Letters, Section A: General, Atomic and Solid State Physics

Minimal length in quantum mechanics and non-Hermitian Hamiltonian systems

At sufficiently high temperatures PLD deposited TaC films can be grown epitaxially on 4H-SiC (0001) substrates; at lower temperatures the films recrystallize and ball up forming a large number of pinholes. The growth temperature for epitaxy was found to be 1000°C, and it was facilitated by the epitaxial growth of a thin (2 nm) transition layer of hexagonal Ta 2C. High temperature annealing produced changes in the surface morphology, caused grain growth, and created pin holes through a recrystallization process in the films deposited at the lower temperatures, while the films deposited at the higher temperatures remained virtually unchanged. Using TEM it is shown that the (0001) basal planes of the hexagonal 4H-SiC and Ta2C phases are aligned, and they were also parallel to the (111) plane in the cubic TaC with the [101̄] cubic direction being parallel to the hexagonal [2110̄] hexagonal direction. The Ta2C interlayer most likely is formed because its lattice parameter in the basel plane (3.103 Å) is intermediate between that of the 4H-SiC (3.08 Å) and the TaC (3.150 Å). Given that Al.5Ga.5N is lattice matched to TaC, it could be an excellent substrate for the growth of GaN/AlGaN heterostructures. © (2009) Trans Tech Publications, Switzerland.

Materials Science Forum

Epitaxial TaC films for the selective area growth of SiC

dc magnetization and P 31 spin-lattice relaxation rate in the polycrystalline sample of LaCoPO suggest a spin-fluctuation dominated ferromagnetically ordered state. Moreover, NMR data clearly indicate a crossover from two-dimensional to three-dimensional spin fluctuations across TC. In contrast to isotropic hyperfine field, Hhf at the P 31 site in LaFePO, Hhf is anisotropic in LaCoPO. The data of spin-lattice relaxation rate also exhibit anisotropic spin fluctuation. The anisotropy vanishes near TC. {\textcopyright} 2009 The American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Crossover of the dimensionality of 3d spin fluctuations in LaCoPO

Physical Review B

75As NMR study of oriented CeFeAsO and CeFeAsO0.84F0.16

Electron paramagnetic resonance (EPR) spectroscopy of hydrogen-doped indium oxide (IO) tubular nanostructures shows presence of paramagnetic oxygen vacancies (VO) at room temperature. For temperatures below 80 K, the EPR spectra exhibit two distinct split resonances correspond to S= 1 2 hydrogen electron spin. Interestingly, presence of hydrogen EPR resonances is accompanied by absence of EPR signal of VO, which is restored above 80 K with the concomitant disappearance of signature resonances from hydrogen. The temperature dependent donor and passivation behavior of hydrogen has been directly observed in metal oxide. This could provide valuable explanations of various VO induced controversial properties of IO nanostructures. © 2009 American Institute of Physics.

Applied Physics Letters

Investigating the role of hydrogen in indium oxide tubular nanostructures as a donor or oxygen vacancy passivation center

We report on structural and optical properties of Mn-doped CdS thin films prepared by 190 keV Mn-ion implantation at different temperatures. Mn-ion implantation in the fluence range of 1× 1013-1× 10 16 ions cm-2 does not lead to the formation of any secondary phase. However, it induces structural disorder, causing a decrease in the optical band gap. This is addressed on the basis of band tailing due to creation of localized energy states and Urbach energy calculations. Mn-doped samples exhibit a new band in their photoluminescence spectra at 2.22 eV, which originates from the d-d (4T1 → 6A 1) transition of tetrahedrally coordinated Mn2+ ions. © 2009 American Institute of Physics.

Journal of Applied Physics

Structural and optical properties of Mn-doped CdS thin films prepared by ion implantation

Orthogonal-unitary and symplectic-unitary crossover ensembles of random matrices are relevant in many contexts, especially in the study of time reversal symmetry breaking in quantum chaotic systems. Using skew-orthogonal polynomials we show that the same generic form of n -level correlation functions are obtained for the Jacobi family of crossover ensembles, including the Laguerre and Gaussian cases. For large matrices we find universal forms of unfolded correlation functions when expressed in terms of a rescaled transition parameter with arbitrary initial level density. © 2009 The American Physical Society.

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics

Universal spectral correlations in orthogonal-unitary and symplectic-unitary crossover ensembles of random matrices

We have studied the phase behavior of concentrated aqueous solutions of cetylpyridinium bromide (CPB) and sodium 3-hydroxy-2-naphthoate (SHN) using X-ray diffraction and polarizing optical microscopy. The phase behavior of this system is found to be very similar to that of the cetyltrimethylammonium bromide (CTAB) - SHN - water system, reported by us recently (Ghosh, S. K., et al. Langmuir, 2007, 23, 3606), but with the important difference that the mesh-like aggregates in the present system have square symmetry, instead of the hexagonal symmetry seen in the earlier case. A random mesh phase without long-range correlations of the in-plane structure, as well as an ordered mesh phase, where the mesh-like aggregates lock into a three-dimensional lattice, are observed, as in the CTAB - SHN - water system. The mesh-like aggregates do not form when the hydroxynaphthoate counterion is replaced by either salicylate or tosylate, which are also known to bind strongly to the surfactant micelle. Instead, the phase behavior of these ternary mixtures is akin to that of the CPB - water binary system; the only liquid crystalline phase observed being the hexagonal phase made up of cylindrical micelles. These results show the extreme sensitivity of the structure and stability of mesh phases to subtle changes in the interheadgroup interactions. © Copyright 2009 American Chemical Society.

Langmuir

Structure of mesh phases in cationic surfactant systems with strongly bound counterions: Influence of the surfactant headgroup and the counterion

In this paper, we report on modifications in structural and optical properties of CdS thin films due to 190 keV Mn-ion implantation at 573 K. Mn-ion implantation induces disorder in the lattice, but does not lead to the formation of any secondary phase, either in the form of metallic clusters or impurity complexes. The optical band gap was found to decrease with increasing ion fluence. This is explained on the basis of band tailing due to the creation of localized energy states generated by structural disorder. Enhancement in the Raman scattering intensity has been attributed to the enhancement in the surface roughness due to increasing ion fluence. Mn-doped samples exhibit a new band in their photoluminescence spectra at 2.22 eV, which originates from the d-d ( 4 T 1 → 6 A 1 ) transition of tetrahedrally coordinated Mn 2+ ions. © 2009 Elsevier B.V.

Applied Surface Science

Modifications in structural and optical properties of Mn-ion implanted CdS thin films

Wide band gap InGaZn6O9 films of thickness ~ 350 nm were deposited on sapphire (0001) at room temperature by using the pulsed laser deposition technique. The transparent films showed the optical transmission of &gt; 80% with the room temperature Hall mobility of ~ 10 cm2/V s and conductivity of 4 × 102 S/cm at a carrier density &gt; 1020 cm- 3. The electrical properties as a function of deposition temperatures revealed that the conductivity and mobility almost retained up to the deposition temperature of 200 °C. The films annealed in different atmospheres suggested oxygen vacancy plays an important role in determining the electrical conductivity of the compound. Room temperature grown heterostructure of n-InGaZn6O9/p-SiC showed a good rectifying behavior with a leakage current density of less than 10- 9 A/cm2, current rectifying ratio of 105 with a forward turn on voltage ~ 3 V, and a breakdown voltage greater than 32 V. © 2008 Elsevier B.V. All rights reserved.