Abstract

Abstract

The study of the co-existence of singlet superconductivity and ferromagnetism is one of the most fascinating and challenging areas of resaerch since both the phenomenon are quantum mechanically antagonistic to each other. However, the coexistence can easily be achieved in artificially fabricated superconductor–ferromagnet heterostructures and these systems offer unique opportunities to study the interplay beteween two competing order parameters and to conceive novel quantum states. Our investigations on different superconducting(S)/ferromagnetic(F) heterostructures fabricated by pulsed laser deposition reveal an intense suppression of superconductivity due to the magnetic proximity effect and the injection of spin polarised quasiparticles from the F electrode. The current dependent transport studies exhibit a significant reduction of the superconducting Tc in the S/F bilayers as compared to single S layer and strictly adhers to I2/3 de-pairing effect. Astonishingly, the superconducting Tc in YBa2Cu3O7-/ La0.5Sr0.5CoO3 bilayers is observed to be much lower as compared to YBa2Cu3O7-/La0.7Sr0.3MnO3 ones. This points to the fact that in addition to the spin polarisation of the ferromagnetic electrode, other factors such as (a) interfce transparency (b) magnetic domain state and (c) the stray field associated with the F layer might play important role in tuning the S order parameter. Magnetotransport studies reveal a remarakable reduction of activation energy (U) and a logarithmic dependence of “U” on the applied magnetic field in S/F heterostructures. This signifies the signature of the existence of decoupled 2D pancake vortices that can arise from the weakening of the S coherence length () due to the presence of F layers and the dominance of intralayer vortex-vortex interaction over the interlayer one.References:1. A.I. Buzdin, Rev. Mod. Phys. 77, 935-976 (2005).2. D. Samal, C. Shivakumara and P.S. Anil Kumar, Phys. Rev.B 77, 094510 (2008)3. D. Samal, and P.S. Anil Kumar, J. Phys.: Condens. Matter. 21, 492203 (2009) (IOP Select)4. D. Samal, Chanchal Sow and P.S. Anil Kumar, J. Phys.:Condens. Matter. 22, 295701(2010)5. D. Samal and P. S. Anil Kumar (J. Supercond. Nov. Magn. in press)Delete & Prev | Delete & NextMove to:

Abstract

Detection of flammable and toxic gases is a subject of growing importancein both domestic and industrial environments. Different deviceconfigurations based on metal oxides have been used so far. MIM is onesuch important configuration to achieve high sensitivity and fastresponse.Polycrystalline titanium dioxide was grown by thermal oxidation at 800oCon 0.25 mm thick titanium substrates with gold coating on the backsurface. Resistivity, carrier density & mobility were measured at roomtemperature. The grown oxide showed n-type conducitivity. Pd metal dots(1.5 mm dia) were deposited on the oxide surface, using e-beam evaporationtechnique, to fabricate Pd/TiOx/Ti-Au (x<2) MIM sensor structure. The I-Vstudy was carried out with 500 ppm hydrogen in the temperature range 200 -350oC and the current increased upon exposure to hydrogen. The sensitivityand the change in barrier height were calculated and were found tomaximize at 300oC beyond which the values started decreasing. The responsetime as calculated from the transient response characteristics was 16 secat 300oC.In this talk, the thin film preparation technique and associatedcharacterizations along with the sensor response will be discussed indetail.

Abstract

The intense electronic excitations and ionizations released in the wake ofswift heavy ions can induce important structural modifications in solids.It is well known that the irradiation of many crystalline materials withswift heavy ions generally leads to structural disorder which spans frompoint defect creation up to total amorphization. However, there is nowgrowing evidence that the structural changes induced by the irradiationwith swift heavy ions are not limited to damage creation but can alsocomprise crystalline-to-crystalline phase transitions. More recently,these effects were also enriched by the finding that swift heavy ions caninduce epitaxial recrystallization of predamaged layers produced bynuclear collisions.From the fundamental point of view, two types of models, either based onthe ‘Coulomb explosion’ concept or the ‘thermal spike’ mechanism areusually proposed to account for swift heavy ion induced atomic movements.Since for both models the timescales of the involved processes are quiteinaccessible to usual characterization techniques, it is very difficult toidentify the actual mechanism. Nevertheless, the recent study ofirradiation effects in the twin oxides zirconia and hafnia, which sharemany physical and chemical properties, offered the unique opportunity toimpose drastic constraints on the models. This comparative study allowedto demonstrate that the thermal spike is the appropriate mechanism whichgoverns the transition from the monoclinic to the tetragonal phase inzirconia and hafnia rather than the Coulomb explosion process.In this contribution, these different types of swift heavy ion inducedphase transitions in solids (i.e., crystalline-to-amorphous,crystalline-to-crystalline and amorphous-to-crystalline transformations)will be illustrated with recent experiments performed at the GANILaccelerator and the mechanisms leading to these effects will be discussedand interpreted within a single view based on the thermal spike process.

Abstract

Coarse grained hydrodynamic theories have so far been successful indescribing patterns formed in in vitro mixtures of active polar filaments(eg Actin, Microtubules) and motors (Myosin, Dyenin, Kinesin). Thereexists little evidence of their validity in vivo.In this talk I will present a theoretical stdy of the dynamics of activepolar filaments on a two dimensional substrate. We determine that thesteady states of the equations of motion of these filaments aregenerically composed of inward pointing asters in different arrangements.The asters display an interesting dynamics in the presence of noise- theybreak up and reform with characteristic residence times, whosedistribution depends on the noise strength.I will further present evidence that the results are applicable to thepatterning of molecules on the cell surface. The evidence is based onanisotropy experiments of GPI-anchored proteins, a class of proteins thatassociate with Actin.