The role of critical current on point contact Andreev Reflection spectrum between a normal metal and a superconductor

The point contact spectrum between a normal metal and a superconductor often shows unexpected sharp dips in the conductance at voltage values larger than the superconducting energy gap. These dips are not predicted in the Blonder-Tinkham-Klapwizk (BTK) theory, commonly used to analyse these contacts. We present here a systematic study of these dips in a variety of contacts between different combinations of a superconductor and a normal metal. From the correlation between the characteristics of these dips with the contact area, we can surmise that such dips are caused by the contact not being in the ballistic limit. An analysis of the possible errors introduced while analysing such a spectrum with the standard BTK model is also presented.Comment: 16 pages, PS, figure include

Anomalous Triple Gauge Vertices at the Large Hadron-Electron Collider

At a high energy $ep$ collider, such as the Large Hadron-Electron Collider (LHeC) which is being planned at CERN, one can access the $WW\gamma$ vertex exclusively in charged current events with a radiated photon, with no interference from the $WWZ$ vertex. We find that the azimuthal angle between the jet and the missing momentum in each charged current event is a sensitive probe of anomalous $WW\gamma$ couplings, and show that for quite reasonable values of integrated luminosity, the LHeC can extend the discovery reach for these couplings beyond all present experimental bounds.Comment: 11 pages, LaTeX2e, 5 EPS figure

On a Raychaudhuri equation for hot gravitating fluids

We generalize the Raychaudhuri equation for the evolution of a self gravitating fluid to include an Abelian and non-Abelian hybrid magneto fluid at a finite temperature. The aim is to utilize this equation for investigating the dynamics of astrophysical high temperature Abelian and non-Abelian plasmas.Comment: 13 pages, Invited contribution to Pramana special issue dedicated to A.K. Raychaudhuri, "The Raychaudhuri equation and its role in Modern Cosmology". Pramana style files include

Localized reversible nanoscale phase separation in Pr_0.63Ca_0.37MnO_3 single crystal using a scanning tunneling microscope tip

We report the destabilization of the charge ordered insulating (COI) state in a localized region of Pr_0.63Ca_0.37MnO_3 single crystal by current injection using a scanning tunneling microscope tip. This leads to controlled phase separation and formation of localized metallic nanoislands in the COI matrix which have been detected by local tunneling conductance mapping. The metallic regions thus created persist even after reducing the injected current to lower values. The original conductance state can be restored by injecting a current of similar magnitude but of opposite polarity. We thus achieve reversible nanoscale phase separation that gives rise to the possibility to "write, read, and erase" nanosized conducting regions in an insulating matrix with high spatial resolution.Comment: 8 pages, 4 figures, Appl. Phys. Lett (accepted for publication

Direct observation of large temperature fluctuations during DNA thermal denaturation

In this paper we report direct measurement of large low frequency temperature fluctuations in double stranded (ds) DNA when it undergoes thermal denaturation transition. The fluctuation, which occurs only in the temperature range where the denaturation occurs, is several orders more than the expected equilibrium fluctuation. It is absent in single stranded (ss) DNA of the same sequence. The fluctuation at a given temperature also depends on the wait time and vanishes in a scale of few hours. It is suggested that the large fluctuation occurs due to coexisting denaturated and closed base pairs that are in dynamic equilibrium due to transition through a potential barrier in the scale of 25-30k_{B}T_{0}(T_{0}=300K).Comment: 4 pages, 5 figures, Replaced with revised versio

Singularity: Raychaudhuri Equation once again

I first recount Raychaudhuri's deep involvement with the singularity problem in general relativity. I then argue that precisely the same situation has arisen today in loop quantum cosmology as obtained when Raychaudhuri discovered his celebrated equation. We thus need a new analogue of the Raychaudhuri equation in quantum gravity.Comment: 11 pages, Contribution to Special issue of Pramana on Raychaudhuri Equation at Cross-roads, edited by Naresh Dadhich, Pankaj Joshi and Probir Ro