Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

144 Biennial Report 2005-07the XIth five year plan is in progress . Theoretical work on various aspects of plasma dynamics:wake fields, Astrophysical Plasmas, dusty plasmas, Geodesic Acoustic modes,plasma relaxation, Nonlinear MHD (Magnetohydrodynamics) etc. have been exploredin detail and some more in progress.5.1 Surface Physics5.1.1 Low-dimensional Properties5.1.1.1 Observation of charge density wave characteristics in conducting polymernanowires: Possibility of Wigner crystallizationLow temperature transport study of polypyrrole nanowires shows characteristics of charge densitywaves. The current-voltage characteristics of all these nanowires show a power-law dependenceon voltage and temperature and a “gap” that decreases rapidly with increase in temperature,confirming the existence of long-range electron-electron interaction in the nanowires. A switchingtransition to highly conducting state has been observed above a threshold voltage, which can betuned by changing the diameters of the nanowires and the temperature. Negative differentialresistance and enhancement of noise have been observed above the threshold. These experimentalresults give evidence of Wigner crystallization in these nanowires.Atikur Rahman, Milan K SanyalSP5.1.1.2 Enhancement of electron-electron interactions in chemically synthesized polymernanowiresComparison of electronic transport properties of conducting polymer nanowires synthesized bychemical and electrochemical method inside nanopores has been made. Electronic transport propertiesof these nanowires show a power-law behavior (I V) at low temperature. Chemically synthesizednanowires exhibit higher values of and these values increase further as the diameter ofnanowires are increased. Zero bias differential conductance of chemically synthesized nanowire ismuch lower than the electrochemical one and both the sample shows increase in zero bias differentialconductance with increasing diameter and also with increasing temperature. These resultsindicate enhancement of electron-electron interactions in chemically synthesized nanowires.Atikur Rahman, Milan K SanyalSP5.1.1.3 Novel switching transition of resistance observed in conducting polymernanowiresA novel switching property of conducting polymer nanowires is observed at low temperature. Thechange in resistance was found to be more than three orders of magnitude and the threshold voltage(current) can be tuned by playing with the diameter and/or temperature.