Results for "A. K. Sood"

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Insights into vibrational and electronic properties of MoS$_2$ using Raman, photoluminescence and transport studiesNov 01 2014We review vibrational and electronic properties of single and a few layer MoS$_2$ relevant to understand their resonant and non-resonant Raman scattering results. In particular, the optical modes and low frequency shear and layer breathing modes show ... More
Chaotic Dynamics in Shear-thickening Surfactant SolutionsDec 28 2000Aug 21 2001We report the observation of dynamical behaviour in dilute, aqueous solutions of a surfactant CTAT (cetyl trimethylammonium p-toluenesulphonate), below the overlap concentration c$^{\star}$. At these concentrations, CTAT forms cylindrical micelles and ... More
Effect of Screening of Intermicellar Interactions on the Linear and Nonlinear Rheology of a Viscoelastic GelDec 27 2000We report our studies of the linear and nonlinear rheology of aqueous solutions of the surfactant cetyl trimethylammonium tosylate (CTAT) with varying amounts of sodium chloride (NaCl). The CTAT concentration is fixed at 42mM and the salt concentration ... More
Universality and Scaling Behaviour of Injected Power in Elastic Turbulence in Worm-like Micellar GelJul 28 2011We study the statistical properties of spatially averaged global injected power fluctuations for Taylor-Couette flow of a worm-like micellar gel formed by surfactant CTAT. At sufficiently high Weissenberg numbers (Wi) the shear rate and hence the injected ... More
Out-of-equilibrium microrheology using optical tweezers to probe directional viscoelastic properties under shearOct 28 2010Many wormlike micellar systems exhibit appreciable shear thinning due to shear induced alignment. As the micelles get aligned introducing directionality in the system, the viscoelastic properties are no longer expected to be isotropic. An optical tweezers ... More
Irreversibility to Reversibility Crossover in Transient Response of an Optically Trapped ParticleMay 07 2011We study the transient response of a colloidal bead which is released from different heights and allowed to relax in the potential well of an optical trap. Depending on the initial potential energy, the system's time evolution shows dramatically different ... More
Ultrafast Response of Plasmonic NanostructuresFeb 02 2018Plasmonic metal nanostructures are an integral part of nanophotonic device applications owing to their ability to generate strong localized electromagnetic fields when illuminated from the far-field. These nanostructures can be prepared in the laboratory ... More
Rheology of Semi-dilute Solutions of Calf-thymus DNADec 25 2000We study the rheology of semi-dilute solutions of the sodium salt of calf-thymus DNA in the linear and nonlinear regimes. The frequency response data can be fitted very well to the hybrid model with two dominant relaxation times $\tau_{\circ}$ and $\tau_{1}$. ... More
Dynamical Behaviour in the Nonlinear Rheology of Surfactant SolutionsAug 01 2000Several surfactant molecules self-assemble in solution to form long, flexible wormlike micelles which get entangled with each other, leading to viscoelastic gel phases. We discuss our recent work on the rheology of such a gel formed in the dilute aqueous ... More
Effect of silica colloids on the rheology of viscoelastic gels formed by the surfactant cetyl trimethylammonium tosylateSep 16 2004The effects of the addition of sub-micrometer sized colloidal silica spheres on the linear and nonlinear rheology of semi-dilute solutions of a viscoelastic gel are studied. For a 1.4 wt.% solution of the surfactant CTAT, a peak in the zero shear rate ... More
Nonequilibrium Fluctuation Relation for Sheared Micellar Gel in a Jammed StateOct 02 2008We show that the shear rate at a fixed shear stress in a micellar gel in a jammed state exhibits large fluctuations, showing positive and negative values, with the mean shear rate being positive. The resulting probability distribution functions (PDF's) ... More
Tunable Brownian Vortex at the InterfaceMar 13 2011A general kind of Brownian vortexes are demonstrated by applying an external nonconservative force field to a colloidal particle bound by a conservative optical trapping force at a liquid-air interface. As the liquid medium is translated at a constant ... More
Deconstructing the glass transition through critical experiments on colloidsAug 31 2016The glass transition is the most enduring grand-challenge problem in contemporary condensed matter physics. Here, we review the contribution of colloid experiments to our understanding of this problem. First, we briefly outline the success of colloidal ... More
Symmetry properties of the large-deviation function of the velocity of a self-propelled polar particleSep 29 2010Dec 23 2010A geometrically polar granular rod confined in 2-D geometry, subjected to a sinusoidal vertical oscillation, undergoes noisy self-propulsion in a direction determined by its polarity. When surrounded by a medium of crystalline spherical beads, it displays ... More
Temperature-dependent chirped coherent phonon dynamics in Bi$_{2}$Te$_{3}$ using high intensity femtosecond laser pulsesNov 07 2010Degenerate pump-probe reflectivity experiments have been performed on a single crystal of bismuth telluride (Bi$_2$Te$_3$) as a function of sample temperature (3K to 296K) and pump intensity using $\sim$ 50 femtosecond laser pulses with central photon ... More
Formation of p-n junction in polymer electrolyte-top gated bilayer graphene transistorSep 05 2009We show simultaneous p and n type carrier injection in bilayer graphene channel by varying the longitudinal bias across the channel and the top gate voltage. The top gate is applied electrochemically using solid polymer electrolyte and the gate capacitance ... More
Observation of Chaotic Dynamics in Dilute Sheared Aqueous Solutions of CTATDec 29 1999The nonlinear flow behaviour of a viscoelastic gel formed due to entangled, cylindrical micelles in aqueous solutions of the surfactant CTAT has been studied. On subjecting the system to a step shear rate lying above a certain value, the shear and normal ... More
Raman spectroscopy of graphene on different substrates and influence of defectsOct 22 2007We show the evolution of Raman spectra with number of graphene layers on different substrates, SiO$_{2}$/Si and conducting indium tin oxide (ITO) plate. The G mode peak position and the intensity ratio of G and 2D bands depend on the preparation of sample ... More
Linear and nonlinear rheology of wormlike micellesJan 02 2000Several surfactant molecules self-assemble in solution to form long, cylindrical, flexible wormlike micelles. These micelles can be entangled with each other leading to viscoelastic phases. The rheological properties of such phases are very interesting ... More
Banded spatiotemporal chaos in sheared nematogenic fluidsFeb 01 2010We present the results of a numerical study of a model of the hydrodynamics of a sheared nematogenic fluid, taking into account the effects of order parameter stresses on the velocity profile, but allowing spatial variations only in the gradient direction. ... More
Granger Causality and Cross Recurrence Plots in RheochaosNov 19 2007Our stress relaxation measurements on wormlike micelles using a Rheo-SALS (rheology + small angle light scattering) apparatus allow simultaneous measurements of the stress and the scattered depolarised intensity. The latter is sensitive to orientational ... More
The backscattering of polarised light from turbid media - An analysis of the azimuthal intensity variations and its implications for the position of the source of diffusing radiationJun 15 1999We study the azimuthal variation in the backscattered intensity that is seen when polarised light is scattered by a turbid medium. We present experimental observations of these intensity variations in colloidal suspensions over a wide range of optical ... More
Optical tweezer for probing erythrocyte membrane deformabilityNov 15 2010We report that the average rotation speed of optically trapped crenated erythrocytes is direct signature of their membrane deformability. When placed in hypertonic buffer, discocytic erythrocytes are subjected to crenation. The deformation of cells brings ... More
Oscillatory settling in wormlike-micelle solutions: bursts and a long time scaleMar 09 2012We study the dynamics of a spherical steel ball falling freely through a solution of entangled wormlike-micelles. If the sphere diameter is larger than a threshold value, the settling velocity shows repeated short oscillatory bursts separated by long ... More
Influence of an amorphous wall on the distribution of localized excitations in a colloidal glass-forming liquidAug 10 2016Elucidating the nature of the glass transition has been the holy grail of condensed matter physics and statistical mechanics for several decades. A phenomenological aspect that makes glass formation a conceptually formidable problem is that structural ... More
Probing top-gated field effect transistor of reduced graphene oxide monolayer made by dielectrophoresisMay 13 2010We demonstrate top-gated field effect transistor made of reduced graphene oxide (RGO) monolayer (graphene) by dielectrophoresis. Raman spectrum of RGO flakes of typical size of 5{\mu}m x 5{\mu}m show a single 2D band at 2687 cm-1, characteristic of a ... More
Site-Specific Colloidal Crystal Nucleation by Template-enhanced Particle TransportMay 11 2016The monomer surface mobility is the single most important parameter that decides the nucleation density and morphology of islands during thin film growth. During template-assisted surface growth in particular, low surface mobilities can prevent monomers ... More
Direct measurements of growing amorphous order and non-monotonic dynamic correlations in a colloidal glass-formerAug 23 2014While the transformation of flowing liquids into rigid glasses is omnipresent, a complete understanding of vitrification remains elusive. Of the numerous approaches aimed at solving the glass transition problem, the Random First-Order Theory (RFOT) is ... More
Structure of Carbon Nanotube-dendrimer compositeDec 13 2012Using all atomistic molecular dynamics (MD) simulations we report the microscopic picture of the nanotube-dendrimer complex for PAMAM dendrimer of generation 2 to 4 and carbon nanotube of chirality (6,5). We find compact wrapping conformations of dendrimer ... More
Direct Evidence for an Absorbing Phase Transition Governing Yielding of a Soft GlassFeb 12 2014We present the first direct experimental evidence showing that yielding of a prototypical soft solid - a colloidal glass - is a non-equilibrium 'absorbing' phase transition. By simultaneously quantifying single-particle dynamics and bulk mechanical response, ... More
Strong Correlations and Fickian Water Diffusion in Narrow Carbon NanotubesDec 19 2007We have used atomistic molecular dynamics (MD) simulations to study the structure and dynamics of water molecules inside an open ended carbon nanotube placed in a bath of water molecules. The size of the nanotube allows only a single file of water molecules ... More
Femtosecond Photoexcited Carrier Dynamics in Reduced Graphene Oxide Suspensions and FilmsMay 08 2010Jun 29 2011We report ultrafast response of femtosecond photoexcited carriers in single layer reduced graphene oxide flakes suspended in water as well as few layer thick film deposited on indium tin oxide coated glass plate using pump-probe differential transmission ... More
Universalities in vortex transport at the melting transitionDec 01 1997We consider the jump in resistance at the melting transition, which is experimentally observed to be constant, independent of magnetic field (vortex density). We present an explanation of this effect based on vortex cuttings, and universalities of the ... More
Growing Dynamical Facilitation on Approaching the Random Pinning Colloidal Glass TransitionJun 25 2014Despite decades of research, it remains to be established whether the transformation of a liquid into a glass is fundamentally thermodynamic or dynamic in origin. While observations of growing length scales are consistent with thermodynamic perspectives ... More
Origin of the unusual dependence of Raman D band on excitation wavelength in graphite-like materialsOct 19 2001We have revisited the still unresolved puzzle of the dispersion of the Raman disordered-induced D band as a function of laser excitation photon energy E$_L$ in graphite-like materials. We propose that the D-mode is a combination of an optic phonon at ... More
Laser induced freezing of charge stabilized colloidal systemFeb 01 1999We present results from an extensive simulational study of the modulated liquid $\longleftrightarrow$ crystal transition in a 2-d charge-stabilized colloid subject to a 1-d laser field modulation commensurate with the crystalline phase. {\em {Contrary ... More
Electronic and vibrational Raman spectroscopy of Nd$_{0.5}$Sr$_{0.5}$MnO$_3$ through the phase transitionsApr 20 2005Raman scattering experiments have been carried out on single crystals of Nd$_{0.5}$Sr$_{0.5}$MnO$_3$ as a function of temperature in the range of 320-50 K, covering the paramagnetic insulator-ferromagnetc metal transition at 250 K and the charge-ordering ... More
Flow-induced voltage and current generation in carbon nanotubesJul 30 2004Sep 15 2004New experimental results, and a plausible theoretical understanding thereof, are presented for the flow-induced currents and voltages observed in single-walled carbon nanotube samples. In our experiments, the electrical response was found to be strongly ... More
Flocking at a distance in active granular matterFeb 18 2014Sep 22 2014The self-organised motion of vast numbers of creatures in a single direction is a spectacular example of emergent order. We recreate this phenomenon using actuated non-living components. We report here that millimetre-sized tapered rods, rendered motile ... More
Yielding and large deviations in micellar gels: a modelOct 06 2012Jan 04 2013We present a simple model to account for the rheological behavior observed in recent experiments on micellar gels. The model combines attachment-detachment kinetics with stretching due to shear, and shows well-defined jammed and flowing states. The large ... More
Recurrent ~24 h Periods in RXTE ASM DataFeb 01 2005Jul 12 2005Analysis of data from the Rossi X-ray Timing Explorer satellite's All Sky Monitor instrument for several X-ray binary sources has identified a recurrent \~24 h period. This period is sometimes highly significant, giving rise to the possibility of it being ... More
Bond-orientational ordering and shear rigidity in modulated colloidal liquidsMar 12 1999From Landau-Alexander-McTague theory and Monte-Carlo simulation results we show that the modulated liquid obtained by subjecting a colloidal system to a periodic laser modulation has long range bond-orientational order and non-zero shear rigidity. From ... More
Tuning Photoinduced Terahertz Conductivity in Monolayer Graphene: Optical Pump Terahertz Probe SpectroscopyJul 10 2014Optical pump-terahertz probe differential transmission measurements of as-prepared single layer graphene (AG)(unintentionally hole doped with Fermi energy $E_F$ at $\sim$180 meV), nitrogen doping compensated graphene (NDG) with $E_F$ $\sim$10 meV and ... More
Ultrafast photoinduced enhancement of nonlinear optical response in 15-atom gold clusters on indium tin oxide conducting filmFeb 27 2013We show that the third order optical nonlinearity of 15-atom gold clusters is significantly enhanced when in contact with indium tin oxide (ITO) conducting film. Open and close aperture z-scan experiments together with non-degenerate pump-probe differential ... More
Superorbital Period in the High Mass X-ray Binary 2S 0114+650Feb 01 2005Dec 20 2005We report the detection of a superorbital period in the high-mass X-ray binary 2S 0114+650. Analyses of data from the Rossi X-ray Timing Explorer (RXTE) All-Sky Monitor (ASM) from 1996 January 5 to 2004 August 25 reveal a superorbital period of 30.7 +/- ... More
Large-amplitude chirped coherent phonons in tellurium mediated by ultrafast photoexcited carrier diffusionOct 30 2010We report femtosecond time-resolved reflectivity measurements of coherent phonons in tellurium performed over a wide range of temperatures (3K to 296K) and pump laser intensities. A totally symmetric A$_{1}$ coherent phonon at 3.6 THz responsible for ... More
Imaging in turbid media using quasi-ballistic photonsJun 13 1999We study by means of experiments and Monte Carlo simulations, the scattering of light in random media, to determine the distance upto which photons travel along almost undeviated paths within a scattering medium, and are therefore capable of casting a ... More
Photon transport in thin disordered slabsMar 01 1999May 31 2001We examine using Monte Carlo simulations, photon transport in optically `thin' slabs whose thickness L is only a few times the transport mean free path $l^{*}$, with particles of different scattering anisotropies. The confined geometry causes an auto-selection ... More
Flow-induced currents in nanotubes: a Brownian dynamics approachMay 01 2005Motivated by recent experiments [Science {\bf 299}, 1042 (2003)] reporting that carbon nanotubes immersed in a flowing fluid displayed an electric current and voltage, we numerically study the behaviour of a collection of Brownian particles in a channel, ... More
Dilute stuffing in the pyrochlore iridate $Eu_2Ir_2O_7$May 04 2018The pyrochlore Eu$_2$Ir$_2$O$_7$ has recently attracted significant attention as a candidate Weyl semimetal. The previous reports on this compound unanimously show a thermally induced metal to insulator (MI) transition, concomitant with antiferromagnetic ... More
Disappearance of Transverse Flow in Central Heavy Ion CollisionsJun 25 2003Apr 28 2010We study the balance energy as a function of the composite mass of the system. The results are in very good agreement with data over a wide range of masses from very light (Ne+Al) to very heavy (Au+Au) for hard equation of state and nucleon-nucleon cross-section ... More
Study of Equilibrium Using Collision DynamicsJun 21 2003Jun 25 2003We discuss the possibility of equilibrium (and thermalization) in heavy-ion collisions at intermediate energies within a transport model. This was achieved by dividing the nuclear matter into different collision zones. We find that those nucleons which ... More
Dynamical facilitation governs glassy dynamics in suspensions of colloidal ellipsoidsAug 02 2014One of the greatest challenges in contemporary condensed matter physics is to ascertain whether the formation of glasses from liquids is fundamentally thermodynamic or dynamic in origin. While the thermodynamic paradigm has dominated theoretical research ... More
On the computational complexity of Data Flow AnalysisMar 18 2013We consider the problem of Data Flow Analysis over monotone data flow frameworks with a finite lattice. The problem of computing the Maximum Fixed Point (MFP) solution is shown to be P-complete even when the lattice has just four elements. This shows ... More
Collapse of Double-Walled Carbon Nanotube Bundles under Hydrostatic PressureJan 10 2006We use classical molecular dynamics simulations to study the collapse of single (SWNT) and double-walled (DWNT) carbon nanotube bundles under hydrostatic pressure. The collapse pressure (pc) varies as 1/R^3, where R is the SWNT radius or the DWNT effective ... More
Giant low frequency velocity fluctuations in a driven vortex latticeOct 01 2009The driven state of a well-ordered flux line lattice in a single crystal of 2H-NbSe2 in the time domain has revealed the presence of substantial fluctuations in velocity, with large and distinct time periods (~ seconds). A superposition of a periodic ... More
Detection of Sugar-Lectin Interactions by Multivalent Dendritic Sugar Functionalized Single-Walled Carbon NanotubesJul 30 2012We show that single walled carbon nanotubes (SWNT) decorated with sugar functionalized poly (propyl ether imine) (PETIM) dendrimer is a very sensitive platform to quantitatively detect carbohydrate recognizing proteins, namely, lectins. The changes in ... More
Raman evidence for coupling of superconducting quasi-particles with a phonon and crystal field excitation in superconductor Ce0.6Y0.4FeAsO0.8F0.2Oct 18 2013We report inelastic light scattering experiments on superconductor Ce0.6Y0.4FeAsO0.8F0.2 from 4K to 300K covering the superconducting transition temperature Tc ~ 48.6K. A strong evidence of the superconductivity induced phonon renormalization for the ... More
Manifestation of geometric frustration on magnetic and thermodynamic properties of pyrochlores $Sm_2X_2O_7$ (X=Ti, Zr)Dec 18 2007We present here magnetization, specific heat and Raman studies on single-crystalline specimens of the first pyrochlore member $Sm_2Ti_2O_7$ of the rare-earth titanate series. Its analogous compound $Sm_2Zr_2O_7$ in the rare-earth zirconate series is also ... More
Phonon renormalisation in doped bilayer grapheneJul 10 2008We report phonon renormalisation in bilayer graphene as a function of doping. The Raman G peak stiffens and sharpens for both electron and hole doping, as a result of the non-adiabatic Kohn anomaly at the $\Gamma$ point. The bilayer has two conduction ... More
Raman signatures of pressure induced electronic topological and structural transitions in Bi2Te3Nov 27 2011We report Raman signatures of electronic topological transition (ETT) at 3.6 GPa and rhombohedral ({\alpha}-Bi2Te3) to monoclinic ({\beta}-Bi2Te3) structural transition at ~ 8 GPa. At the onset of ETT, a new Raman mode appears near 107 cm-1 which is dispersionless ... More
Unraveling siRNA Unzipping Kinetics with GrapheneJul 19 2012Using all atom molecular dynamics simulations, we report spontaneous unzipping and strong binding of small interfering RNA (siRNA) on graphene. Our dispersion corrected density functional theory based calculations suggest that nucleosides of RNA have ... More
Structure of poly(propyl ether imine) (PETIM) dendrimer from fully atomistic molecular Dynamics Simulation and by Small Angle X-ray scatteringNov 18 2006We study the structure of carboxylic acid terminated neutral poly (propyl ether imine) (PETIM) dendrimer from generation 1 through 6 (G1-G6) in a good solvent (water) by fully atomistic molecular dynamics (MD) simulations. We determine as a function of ... More
Probing ultrafast carrier dynamics and nonlinear absorption and refraction in core-shell silicon nanowiresAug 21 2012We investigate the relaxation dynamics of photogenerated carriers in silicon nanowires consisting of a crystalline core and a surrounding amorphous shell, using femtosecond time-resolved differential reflectivity and transmission spectroscopy at photon ... More
Ultrafast Dynamics of Gold Nanorods: Tuning between Photo-Bleaching and Photo-Induced AbsorptionJun 29 2011We report ultrafast electron dynamics in gold nanorods investigated using 80 fs laser pulses centered at 1.57 eV. Five types of nanorod colloidal suspensions in water having their longitudinal surface plasmon peak (ELSP) on either side of the laser photon ... More
Binding of Nucleobases with Single-Walled Carbon NanotubesSep 19 2007We have calculated the binding energy of various nucleobases (guanine (G), adenine (A), thymine (T) and cytosine (C)) with (5,5) single-walled carbon nanotubes (SWNTs) using ab-initio Hartre-Fock method (HF) together with force field calculations. The ... More
Unzipping and binding of small interfering RNA with single walled Carbon Nanotube: a platform for small interfering RNA deliveryMar 12 2012In an effort to design efficient platform for siRNA delivery, we combine all atom classical and quantum simulations to study the binding of small interfering RNA (siRNA) by pristine single wall carbon nanotube (SWCNT). Our results show that siRNA strongly ... More
Ultrafast switching time and third order nonlinear coefficients of microwave treated single walled carbon nanotube suspensionsJul 09 2008Microwave treated water soluble and amide functionalized single walled carbon nanotubes have been investigated using femtosecond degenerate pump-probe and nonlinear transmission experiments. The time resolved differential transmission using 75 femtosecond ... More
Graphene analogue BCN: femtosecond nonlinear optical susceptibility and hot carrier dynamicsOct 12 2010Third-order nonlinear absorption and refraction coefficients of a few-layer boron carbon nitride (BCN) and reduced graphene oxide (RGO) suspensions have been measured at 3.2 eV in the femtosecond regime. Optical limiting behavior is exhibited by BCN as ... More
Superconducting Fluctuations and Anomalous Phonon Renormalization much above superconducting transition temperature in Ca4Al2O5.7Fe2As2May 31 2012Raman studies on Ca4Al2O5.7Fe2As2 superconductor in the temperature range of 5 K to 300 K, covering the superconducting transition temperature Tc ~ 28.3 K, reveal that the Raman mode at ~ 230 cm-1 shows a sharp jump in frequency by ~ 2 % and linewidth ... More
A Multicoloured View of 2S 0114+650Oct 16 2006We report the results of radio and X-ray observations of the high mass X-ray binary 2S 0114+650, made with the Giant Meterwave Radio Telescope and the Rossi X-ray Timing Explorer respectively. No emission was detected at radio wavelengths. The neutral ... More
An Electron Paramagnetic Resonance Study of Electron-Hole Asymmetry in Charge Ordered Pr_1-x Ca_xMnO_3 (x=0.64, 0.36)Oct 21 2002We present and compare the results of temperature-dependent electron paramagnetic resonance (EPR) studies on Pr_1-x Ca_xMnO_3 for x = 0.64 which is electron-doped with those on the hole doped x = 0.36 composition. The temperature dependence of the various ... More
Thermodynamics of Water Entry in Hydrophobic Channels of Carbon NanotubesAug 19 2011Experiments and computer simulations demonstrate that water spontaneously fills the hydrophobic cavity of a carbon nanotube. To gain a quantitative thermody- namic understanding of this phenomenon, we use the recently developed Two Phase Thermodynamics ... More
Temperature dependent magnetic, dielectric and Raman studies of partially disordered La2NiMnO6Dec 26 2013We report a detailed magnetic, dielectric and Raman studies on partially disordered and biphasic double perovskite La2NiMnO6. DC and AC magnetic susceptibility measurements show two magnetic anomalies at TC1 ~ 270 K and TC2 ~ 240 K, which may indicate ... More
Electron Paramagnetic Resonance Study of Phase Segregation in Nd$_{0.5}$Sr$_{0.5}$MnO$_3$Jan 18 2002Nov 11 2003We present results of an electron paramagnetic resonance (EPR) study of Nd$_{1-x}$Sr$_x$MnO$_3$ with x = 0.5 across the paramagnetic to ferromagnetic, insulator to metal transition at 260 K (T$_c$) and the antiferromagnetic, charge ordering transition ... More
Brillouin scattering studies in Fe$_3$O$_4$ across the Verwey transitionDec 13 2003Apr 20 2005Brillouin scattering studies have been carried out on high quality single crystals of Fe$_3$O$_4$ with [100] and [110] faces in the temperature range of 300 to 30 K. The room temperature spectrum shows a surface Rayleigh wave (SRW) mode at 8 GHz and a ... More
Ordered spin-ice state in the geometrically frustrated metallic-ferromagnet Sm2Mo2O7Jun 28 2007The recent discovery of Spin-ice is a spectacular example of non-coplanar spin arrangements that can arise in the pyrochlore A2B2O7 structure. We present magnetic and thermodynamic studies on the metallic-ferromagnet pyrochlore Sm2Mo2O7. Our studies, ... More
Critical behavior at de-pinning of a driven disordered vortex matter in 2H-NbS2Apr 05 2012We report unusual jamming in driven ordered vortex flow in 2H-NbS2. Reinitiating movement in these jammed vortices with a higher driving force, and halting it thereafter once again with a reduction in drive, unfolds a critical behavior centered around ... More
Pressure-induced phase transition in Bi$_2$Se$_3$ at 3 GPa: electronic topological transition or not?Feb 18 2016In recent years, a low pressure transition around P $\sim$ 3 GPa exhibited by the A$_2$B$_3$-type 3D topological insulators is attributed to an electronic topological transition (ETT) for which there is no direct evidence either from theory or experiments. ... More
Brillouin Scattering Studies of La_{0.77}Ca_{0.23}MnO_3 Across Metal-Insulator TransitionMar 03 2003Temperature-dependent Brillouin scattering studies have been carried out on La_{0.77}Ca_{0.23}MnO_3 across the paramagnetic insulator - ferromagnetic metal (I-M) transition. The spectra show a surface Rayleigh wave (SRW) and a high velocity pseudo surface ... More
Ultrafast quasiparticle dynamics in superconducting iron pnictide CaFe1.89Co0.11As2Sep 17 2012Feb 22 2013Nonequilibrium quasiparticle relaxation dynamics is reported in superconducting CaFe1.89Co0.11As2 single crystal using femtosecond time-resolved pump-probe spectroscopy. The carrier dynamics reflects a three-channel decay of laser deposited energy with ... More
Ultrafast electron dynamics and cubic optical nonlinearity of free standing thin film of double walled carbon nanotubesJun 17 2008Ultrafast degenerate pump-probe experiments performed on a free standing film of double walled carbon nanotubes near the first metallic transition energy of outer tube show ultrafast ($97 fs$) photobleaching followed by a photo-induced absorption with ... More
Non-resonant microwave absorption studies of superconducting MgB_2Mar 18 2001Mar 20 2001Non-resonant microwave absorption(NRMA) studies of superconducting MgB_2 at a frequency of 9.43 GHz in the field range -50 Gauss to 5000 Gauss are reported. The NRMA results indicate near absence of intergranular weak links. A linear temperature dependence ... More
Spatiotemporal rheochaos in nematic hydrodynamicsNov 05 2003Dec 22 2003Motivated by the observation of rheochaos in sheared wormlike micelles [Bandyopadhyay et al., Phys. Rev. Lett, 84 2022, (2000); Europhys. Lett. 56, 447 (2001); Pramana 53, 223 (1999)] we study the coupled nonlinear partial differential equations for the ... More
Acoustic and optical phonon dynamics from femtosecond time-resolved optical spectroscopy of superconducting iron pnictide Ca(Fe_0.944Co_0.056)_2As_2Sep 14 2012Sep 19 2012We report temperature evolution of coherently excited acoustic and optical phonon dynamics in superconducting iron pnictide single crystal Ca(Fe_0.944Co_0.056)_2As_2 across the spin density wave transition at T_SDW ~ 85 K and superconducting transition ... More
Complex outburst behaviour from the black-hole candidate 4U 1630-47Jun 13 1997We present data from different epochs in 1978, 1987-1991 and 1996 from the black-hole candidate 4U1630-47. For the first time we present almost complete coverage of the outbursts which started in 1987, 1988 and 1996. We find that the outburst behaviour ... More
Frequency shift of optical phonons in doped graphene layersFeb 27 2007Mar 15 2007We use first-principles density-functional calculations to determine the frequency shift of the A$'_1$-${\bf K}$ phonon (Raman D band) in monolayer graphene, as a function of the charge doping. A detailed DFT study on the electron-phonon coupling and ... More
An electron paramagnetic resonance study of Pr_{0.6}Ca_{0.4}MnO_{3} across the charge ordering transitionJun 05 2000We report the first electron paramagnetic resonance studies of single crystals and powders of Pr_{0.6}Ca_{0.4}MnO_{3} in the 300-4.2 K range, covering the charge ordering transition at ~ 240 K and antiferromagnetic transition (T_N) at ~ 170 K. The asymmetry ... More
Direct observation of low frequency confined acoustic phonons in silver nanoparticles: Terahertz time domain spectroscopyOct 12 2010Terahertz time domain spectroscopy has been used to study low frequency confined acoustic phonons of silver nanoparticles embedded in poly(vinyl alcohol) matrix in the spectral range of 0.1 to 2.5 THz. The real and imaginary parts of the dielectric function ... More
Laser induced reentrant freezing in two-dimensional attractive colloidal systemsSep 11 2005The effects of an externally applied one-dimensional periodic potential on the freezing/melting behaviour of two-dimensional systems of colloidal particles with a short-range attractive interaction are studied using Monte Carlo simulations. In such systems, ... More
Equilibrium glassy phase in a polydisperse hard sphere systemMar 29 2005Mar 30 2005The phase diagram of a polydisperse hard sphere system is examined by numerical minimization of a discretized form of the Ramakrishnan-Yussouff free energy functional. Crystalline and glassy local minima of the free energy are located and the phase diagram ... More
Coupling of the X-ray and radio emission in the black hole candidate a nd compact jet source GX 339-4Mar 30 2000We report the results of a long-term campaign of radio, soft- and hard- X-ray observations of the galactic black hole candidate GX 339-4. In the Low-Hard X-ray state the system displays a strong 3-way linear correlation between soft- and hard-X-rays and ... More
Electronic Raman scattering and photoluminescence from La$_{0.7}$Sr$_{0.3}$MnO$_3$ exhibiting giant magnetoresistanceMay 13 1996Raman and Photoluminescence (PL) experiments on correlated metallic La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ have been carried out using different excitation wavelengths as a function of temperature from 15 K to 300 K. Our data suggest a Raman mode centered at 1800 ... More
Routes to spatiotemporal chaos in the rheology of nematogenic fluidsAug 12 2004Jan 08 2005With a view to understanding the ``rheochaos'' observed in recent experiments in a variety of orientable fluids, we study numerically the equations of motion of the spatiotemporal evolution of the traceless symmetric order parameter of a sheared nematogenic ... More
Metallic monoclinic phase in VO$_2$ induced by electrochemical gating: in-situ Raman studyJun 28 2016We report in-situ Raman scattering studies of electrochemically top gated VO$_2$ thin film to address metal-insulator transition (MIT) under gating. The room temperature monoclinic insulating phase goes to metallic state at a gate voltage of 2.6 V. However, ... More
Large nonlinear absorption and refraction coefficients of carbon nanotubes estimated from femtosecond Z-scan measurementsOct 15 2007Dec 09 2007Nonlinear transmission of 80 and 140 femtosecond pulsed light with $0.79 \mu m$ wavelength through single walled carbon nanotubes suspended in water containing sodium dodecyl sulphate is studied. Pulse-width independent saturation absorption and negative ... More
Gap-dependent quasiparticle dynamics and coherent acoustic phonons in parent iron pnictide CaFe2As2 across the spin density wave phase transitionAug 18 2012Feb 22 2013We report ultrafast quasiparticle (QP) dynamics and coherent acoustic phonons in undoped CaFe_2As_2 iron pnictide single crystals exhibiting spin-density wave (SDW) and concurrent structural phase transition at temperature TSDW ~ 165 K using femtosecond ... More
Anomalous lattice contraction and emergent electronic phases in Bi-doped Eu$_2$Ir$_2$O$_7$Feb 08 2019We study the pyrochlore series (Eu$_{1-x}$Bi$_x$)$_2$Ir$_2$O$_7$ for $ 0 \leq x \leq 1$. We show that for small $x$, the lattice undergoes an anomalous contraction but the all-in/all-out and metal-to-insulator transitions remain robust, and the resistivity ... More
A Detailed Study of 2S 0114+650 with the RXTEOct 05 2007Jul 11 2008We present the results of a detailed study of the high mass X-ray binary 2S 0114+650 made with the pointed instruments onboard the Rossi X-ray Timing Explorer. The spectral and temporal behaviour of this source was examined over the pulse, orbital, and ... More
A Micrometer-sized Heat Engine Operating Between Bacterial ReservoirsJan 13 2016Artificial micro heat engines are prototypical models to explore and elucidate the mechanisms of energy transduction in a regime that is dominated by fluctuations [1-2]. Micro heat engines realized hitherto mimicked their macroscopic counterparts and ... More