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

Evolution of Crustal Magnetic Fields in Isolated Neutron Stars : Combined Effects of Cooling and Curvature of Space-time

The ohmic decay of magnetic fields confined within the crust of neutron stars is considered by incorporating both the effect of neutron star cooling and the effect of space-time curvature produced by the intense gravitational field of the star. For this purpose a stationary and static gravitational field has been considered with the standard as well as the accelerated cooling models of neutron stars. It is shown that general relativistic effect reduces the magnetic field decay rate substantially. At the late stage of evolution when the field decay is mainly determined by the impurity-electron scattering, the effect of space-time curvature suppresses the role of the impurity content significantly and reduces the decay rate by more than an order of magnitude. Even with a high impurity content the decay rate is too low to be of observational interest if the accelerated cooling model along with the effect of space-time curvature is taken into account. It is, therefore, pointed out that if a decrease in the magnetic field strength by more than two orders of magnitude from its initial value is detected by observation then the existence of quark in the core of the neutron star would possibly be ruled out.Comment: 15 pages, AAS LATEX macros v4.0, 5 postscript figures, Accepted for publication in the Astrophysical Journal (Part I

General Relativistic Spectra from Accretion Disks around Rapidly Rotating Neutron Stars

We compute spectra from accretion disks around rapidly rotating neutron stars. The full effect of general relativity is considered for the structure calculation of the stars. We take into account the Doppler shift, gravitational redshift and light-bending effects in order to compute the observed spectra. To facilitate direct comparison with observations, a simple empirical function is presented which describes the numerically computed spectra well. This function can in principle be used to distinguish between the Newtonian spectra and the relativistic spectra. We also discuss the possibility of constraining neutron star's equation of state using our spectral models.Comment: 2 pages, to appear in the proceedings of 'The Physics of Cataclysmic Variables and Related Objects', Goettingen, August 5-10, 200

Spatially inhomogeneous electron state deep in the extreme quantum limit of strontium titanate

When an electronic system is subjected to a sufficiently strong magnetic field that the cyclotron energy is much larger than the Fermi energy, the system enters the "extreme quantum limit" (EQL) and becomes susceptible to a number of instabilities. Bringing a three-dimensional electronic system deeply into the EQL can be difficult, however, since it requires a small Fermi energy, large magnetic field, and low disorder. Here we present an experimental study of the EQL in lightly-doped single crystals of strontium titanate, which remain good bulk conductors down to very low temperatures and high magnetic fields. Our experiments probe deeply into the regime where theory has long predicted electron-electron interactions to drive the system into a charge density wave or Wigner crystal state. A number of interesting features arise in the transport in this regime, including a striking re-entrant nonlinearity in the current-voltage characteristics and a saturation of the quantum-limiting field at low carrier density. We discuss these features in the context of possible correlated electron states, and present an alternative picture based on magnetic-field induced puddling of electrons.Comment: 8 pages, 5 figures, 7 pages of supplementary information; to appear in Nature Communication

Pulling an adsorbed polymer chain off a solid surface

The thermally assisted detachment of a self-avoiding polymer chain from an adhesive surface by an external force applied to one of the chain ends is investigated. We perform our study in the "fixed height" statistical ensemble where one measures the fluctuating force, exerted by the chain on the last monomer when a chain end is kept fixed at height $h$ over the solid plane at different adsorption strength $\epsilon$. The phase diagram in the $h - \epsilon$ plane is calculated both analytically and by Monte Carlo simulations. We demonstrate that in the vicinity of the polymer desorption transition a number of properties like fluctuations and probability distribution of various quantities behave differently, if $h$ rather than $f$ is used as an independent control parameter.Comment: 17 pages, 9 picture

PRODUCTIVITY SPILLOVERS IN INDIAN MANUFACTURING FIRMS

Indian economic reform since early 1990s aims at improving productivity and competitiveness of major industries. The paper examines spillovers from foreign direct investment (FDI), research and development (R&D) and exporting activities on productivity both for foreign and domestic manufacturing firms. The data is obtained from the PROWESS database provided by the Centre for Monitoring Indian Economy (CMIE). Balanced panel of over 1,000 manufacturing firms in India between 1994 and 2006 are considered for our empirical analysis. Findings indicate that foreign presence has a significant spillover effect on the productivity of the Indian manufacturing firms compared to the alternative spillovers such as from R&D and export initiatives.Productivity, Spillovers, Indian manufacturing, FDI.