Influence of the nature of confinement on the melting of Wigner molecules in quantum dots

We analyze the quantum melting of two-dimensional Wigner molecules (WM) in confined geometries with distinct symmetries and compare it with corresponding thermal melting. Our findings unfold complementary mechanisms that drive the quantum and thermal crossovers in a WM and show that the symmetry of the confinement plays no significant role in determining the quantum crossover scale $n_X$. This is because the zero-point motion screens the boundary effects within short distances. The phase diagram as a function of thermal and quantum fluctuations determined from independent criteria is unique, and shows "melting" from the WM to both the classical and quantum "liquids." An intriguing signature of weakening liquidity with increasing temperature, $T$, is found in the extreme quantum regime. The crossover is associated with production of defects. However, these defects appear to play distinct roles in driving the quantum and thermal "melting." Our study will help comprehending melting in a variety of experimental traps - from quantum dots to complex plasma.Comment: 14 pages, 9 figure

Antiferromagnetism and charged vortices in high-Tc superconductors

The effect of the long-range Coulomb interaction on charge accumulation in antiferromagnetic vortices in high-Tc superconductors is studied within a Bogoliubov-de Gennes mean-field model of competing antiferromagnetic and d-wave superconducting orders. Antiferromagnetism is found to be associated with an accumulation of charge in the vortex core, even in the presence of the long-range Coulomb interaction. The manifestation of Pi-triplet pairing in the presence of coexisting dSC and AFM order, and the intriguing appearance of one-dimensional stripe-like ordering are discussed. The local density of states (LDOS) in the vortex core is calculated and is found to be in excellent qualitative agreement with experimental data.Comment: 14 pages, 8 figures, 2 column RevTex4 PRB forma

Combustion synthesized TiO2 for enhanced photocatalytic activity under the direct sunlight-optimization of titanylnitrate synthesis

Optimized synthesis of Ti-precursor ‘titanylnitrate’ for one step combustion synthesis of N- and C-doped TiO2 catalysts were reported and characterized by using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), diffused reflectance UV–vis spectroscopy, N2 adsorption and X-ray photoelectron spectroscopy (XPS). XRD confirmed the formation of TiO2 anatase and nano-crystallite size which was further confirmed by TEM. UV-DRS confirmed the decrease in the band gap to less than 3.0 eV, which was assigned due to the presence of C and N in the framework of TiO2 as confirmed by X-ray photoelectron spectroscopy. Degradation of methylene blue in aqueous solution under the direct sunlight was carried out and typical results indicated the better performance of the synthesized catalysts than Degussa P-25

Width of the Zero-Field Superconducting Resistive Transition in the Vicinity of the Localization Threshold

Resistive superconducting zero-field transition in amorphous In-O films in states from the vicinity of the insulator-superconductor transition is analyzed in terms of two characteristic temperatures: the upper one, $T_{c0}$, where the finite amplitude of the order parameter is established and the lower one, $T_c$, where the phase ordering takes place. It follows from the magnetoresistance measurements that the resistance in between, $T_c<T<T_{c0}$, cannot be ascribed to dissipation by thermally dissociated vortex pairs. So, it is not Kosterlitz-Thouless-Berezinskii transition that happens at $T_c$.Comment: 4 pages, 3 figure

Effect of carbon nanofibre addition on the mechanical properties of different Vf carbon-epoxy composites

Carbon-epoxy (C-epoxy) laminated composites having different fibre volume fractions (40, 50, 60 and 70) were fabricated with and without the addition of aminofunctionalized carbon nanofibres (A-CNF). Flexural strength, interlaminar shear strength (ILSS) and tensile strength of the composite laminates were determined. It was observed that, the ability of A-CNF to enhance the mechanical properties of C-epoxy diminished significantly as the fibre volume fraction (Vf) of the C-epoxy increased from 40 to 60. At 70Vf, the mechanical properties of the ACNF reinforced C-epoxy were found to be lower compared to the C-epoxy composite made without the addition of A-CNF. In this paper suitable mechanisms for the observed trends are proposed on the basis of the fracture modes of the composite

Effect of Trivalent Additions and Processing on Structural and Magnetic Transitions in Ni-Mn-Ga Ferromagnetic Shape Memory Alloys

Ferromagnetic shape memory Ni50Mn30Ga15Al5-xBx (x = 0, 1, and 4) alloys were prepared by vacuum arc melting and subsequent heat-treatment as well as by melt spinning to investigate the effect of trivalent element additions in ternary Ni-Mn-Ga alloys. The heat-treated alloys containing Al were reported to possess a modulated martensite structure, however alloy containing both Al and B showed a loss of modulated structure in martensite formed. The rapidly solidified alloys on the other hand showed the formation of a similar modulated structure without composition change in alloys containing Al and the alloys containing Al and B. In addition, the former showed a presence of an amorphous phase with latter showing crystalline boron rich phases. The magnetisation of the B containing alloys in both the processing technique was however very low, showing lower magnetic exchange interaction in such alloys.Defence Science Journal, 2012, 62(4), pp.252-260, DOI:http://dx.doi.org/10.14429/dsj.62.127

Simple Model for the Variation of Superfluid Density with Zn Concentration in YBCO

We describe a simple model for calculating the zero-temperature superfluid density of Zn-doped YBa_2Cu_3O_{7-\delta} as a function of the fraction x of in-plane Cu atoms which are replaced by Zn. The basis of the calculation is a ``Swiss cheese'' picture of a single CuO_2 layer, in which a substitutional Zn impurity creates a normal region of area $\pi\xi_{ab}^2$ around it as originally suggested by Nachumi et al. Here $\xi_{ab}$ is the zero-temperature in-plane coherence length at x = 0. We use this picture to calculate the variation of the in-plane superfluid density with x at temperature T = 0, using both a numerical approach and an analytical approximation. For $\delta = 0.37$, if we use the value $\xi_{ab}$ = 18.3 angstrom, we find that the in-plane superfluid decreases with increasing x and vanishes near $x_c = 0.01$ in the analytical approximation, and near $x_c = 0.014$ in the numerical approach. $x_c$ is quite sensitive to $\xi_{ab}$, whose value is not widely agreed upon. The model also predicts a peak in the real part of the conductivity, Re$\sigma_e(\omega, x)$, at concentrations $x \sim x_c$, and low frequencies, and a variation of critical current density with x of the form $J_c(x) \propto n_{S,e}(x)^{7/4}$ near percolation, where $n_{S,e}(x)$ is the in-plane superfluid density.Comment: 19 pages including 6 figures, submitted to Physica