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

The Generalised Raychaudhuri Equations : Examples

Specific examples of the generalized Raychaudhuri Equations for the evolution of deformations along families of $D$ dimensional surfaces embedded in a background $N$ dimensional spacetime are discussed. These include string worldsheets embedded in four dimensional spacetimes and two dimensional timelike hypersurfaces in a three dimensional curved background. The issue of focussing of families of surfaces is introduced and analysed in some detail.Comment: 8 pages (Revtex, Twocolumn format). Corrected(see section on string worldsheets), reorganised and shortened slightl

One Relator Quotients of Graph Products

In this paper, we generalise Magnus' Freiheitssatz and solution to the word problem for one-relator groups by considering one relator quotients of certain classes of right-angled Artin groups and graph products of locally indicable polycyclic groups

Exciton-photon coupling in a ZnSe based microcavity fabricated using epitaxial liftoff

We report the observation of strong exciton-photon coupling in a ZnSe based microcavity fabricated using epitaxial liftoff. Molecular beam epitaxial grown ZnSe/Zn$_{0.9}$Cd$_{0.1}$Se quantum wells with a one wavelength optical length at the exciton emission were transferred to a SiO$_2$/Ta$_2$O$_5$ mirror with a reflectance of 96% to form finesse matched microcavities. Analysis of our angle resolved transmission spectra reveals key features of the strong coupling regime: anticrossing with a normal mode splitting of $23.6 meV$ at $20 K$; composite evolution of the lower and upper polaritons; and narrowing of the lower polariton linewidth near resonance. The heavy hole exciton oscillator strength per quantum well is also deduced to be $1.78 \times 10^{13} cm^{-2}$.Comment: 3 pages, 3 figure

Removal of laser-melted material with an assist gas

Molten material is removed in many laser applications such as laser grooving and laser cutting. An assist gas is usually used to remove the molten material from the laser material interaction zone. The effect of assist gas pressure on the material removal rate is investigated in this article for laser cutting and grooving applications. The model for melt depth is based on the overall energy balance, and the cut depth is obtained by considering the effect of the assist gas. The model for kerf width is based on the modified Rosenthal solution taking into account the melting effect. The cut depths reach a constant value beyond a critical pressure if the kerf width is of the order of nozzle width and through cuts are assumed. Most of the molten material is removed by the assist gas at pressures below this critical pressure. The model predicts on the basis of the Prandtl or Meyer relation that the cutting speed decreases when the assist gas pressure exceeds a critical value if the kerf dimensions are smaller than the nozzle dimensions

Frequency-dependent (ac) Conduction in Disordered Composites: a Percolative Study

In a recent paper [Phys. Rev. B{\bf57}, 3375 (1998)], we examined in detail the nonlinear (electrical) dc response of a random resistor cum tunneling bond network ($RRTN$, introduced by us elsewhere to explain nonlinear response of metal-insulator type mixtures). In this work which is a sequel to that paper, we consider the ac response of the $RRTN$-based correlated $RC$ ($CRC$) model. Numerical solutions of the Kirchoff's laws for the $CRC$ model give a power-law exponent (= 0.7 near $p = p_c$) of the modulus of the complex ac conductance at moderately low frequencies, in conformity with experiments on various types of disordered systems. But, at very low frequencies, it gives a simple quadratic or linear dependence on the frequency depending upon whether the system is percolating or not. We do also discuss the effective medium approximation ($EMA$) of our $CRC$ and the traditional random $RC$ network model, and discuss their comparative successes and shortcomings.Comment: Revised and reduced version with 17 LaTeX pages plus 8 JPEG figure

Local cloning of Bell states and distillable entanglement

The necessary and sufficient amount of entanglement required for cloning of orthogonal Bell states by local operation and classical communication is derived, and using this result, we provide here some additional examples of reversible, as well as irreversible states.Comment: 5 pages, two columns, Latex. Few typos have been corrected. An explanation of the teleportation map (eqn. (3) in the manuscript) has been provide

The aeolian sedimentation record of the Thar desert

A review of the aeolian sedimentary record of the Thar desert is presented. This includes a regional survey of the major dune forms, their genesis and their relationship to climate and other regional landforms. A key aspect of this work is the chronometry of the dunes using luminescence methods. Luminescence dating of sand has enabled quantification of the duration of the phases of sand aggradation and quiescence, time scales of dune migration and the dating of pedogenic carbonates. We demonstrate that the conventional wisdom of synchronicity of dune aggradation with glacial epoch is not true in the context of Thar sands and here only a short durationwindow of opportunity existed for dune aggradation. Luminescence ages further suggest that this window occurred during a transitional climatic regime from glacial to interglacial about 4-10 ka after the glacial epoch. Other inferences included are that: • the aeolian activity in the Thar began over > 150 ka, resolving that Thar is not of anthropogenic origin as suggested previously; • the present spatial extent of the aeolian activity in the Thar is in a contracted stage compared to that in the geological past, which refutes the arguments on its rapid north-eastward expansion; • the current dune migration rates in areas of significant human-induced disturbances are much higher than during the geological past; • the monsoon activity in the Thar varied significantly, from being minimal during the isotopic marine stages 4 and 2 to being close to the present during stage 3; • on shorter time scales the dune activities correlated with the lacustrine records of the region with a phase difference of a few centuries and a periodicity of ~1500 years; • the sand aggradation climate in the southern margin in Gujarat gradually shrank northwards such that in general dunes older than 10 ka are seen in the extreme southern margin and dunes younger than 2ka ages occur mostly in the western part of Rajasthan