Browsing by Author "Wu, Ya-Nan"

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Electron-electron interaction effect on longitudinal and Hall transport in thin and thick Ag-x(SnO2)(1-x) granular metals
(2015-03-03)
Wu, Ya-Nan
;
Wei, Yan-Fang
;
Li, Zhi-Qing
;
Lin, Juhn-Jong
;
電子物理學系
We study the temperature behaviors of the Hall coefficient, R-H, and longitudinal conductivity, sigma, of two series of Ag-x(SnO2)(1-x) (x being the Ag volume fraction) granular films lying in the metallic regime. The first (second) series of films are similar to 500 (similar to 9) nm thick and constitute a three-(two-) dimensional granular array. In the high-x regime with g(T) >> g(T)(c) (g(T) being the dimensionless intergrain tunneling conductance, and g(T)(c) being the critical tunneling conductance at the percolation threshold), we observe a R-H alpha ln T law from similar to 6 to 300K. This ln T behavior is independent of array dimensionality. We also observe a sigma alpha ln T law in the temperature range similar to 20-100 K. Below similar to 10 K, the temperature behavior of sigma changes to a root T dependence in thick films, while it changes to a different ln T dependence in thin films. The overall R-H and sigma characteristics can be explained by the electron-electron interaction (EEI) effects in the presence of granularity. As x is reduced and approaches the percolation threshold, we found that the ln T dependences of R-H and sigma still hold for a wide temperature range. We propose an explanation for the long-standing puzzle of the sigma alpha ln T dependence, which has previously been frequently observed in composite systems near the quantum percolation threshold, as arising from the same EEI effect considered in the recent theory of granular metals.
Giant Hall effect in nonmagnetic Mo/SnO(2) granular films
(2010-09-17)
Wu, Ya-Nan
;
Li, Zhi-Qing
;
Lin, Juhn-Jong
;
電子物理學系
;
物理研究所
We have measured the resistivities and Hall coefficients, R(H), of a series of nonmagnetic Mo(x)(SnO(2))(1-x) nanogranular films with the Mo volume fraction x ranging from similar to 0.29 to 1. We found that the magnitude of R(H)(2 K) largely increased by a factor of similar to 800 as x was reduced from similar to 0.8 to similar or equal to 0.36. Then, it slightly decreased with a further decrease in x down to similar or equal to 0.32, which was determined to be the classical percolation threshold, x(c), from the resistivity dependence on x. This nearly 3 orders of magnitude enhancement in R(H) at a metal volume fraction x > x(c) is explained in terms of the recent theoretical concept of the local quantum-interference effect induced giant Hall effect in granular systems.
Giant Hall effect in nonmagnetic Mo/SnO2 granular films
(2010-09-17)
Wu, Ya-Nan
;
Li, Zhi-Qing
;
Lin, Juhn-Jong
;
電子物理學系
;
物理研究所
We have measured the resistivities and Hall coefficients, R-H, of a series of nonmagnetic Mo-x(SnO2)(1-x) nanogranular films with the Mo volume fraction x ranging from similar to 0.29 to 1. We found that the magnitude of R-H(2 K) largely increased by a factor of similar to 800 as x was reduced from similar to 0.8 to similar or equal to 0.36. Then, it slightly decreased with a further decrease in x down to similar or equal to 0.32, which was determined to be the classical percolation threshold, x(c), from the resistivity dependence on x. This nearly 3 orders of magnitude enhancement in R-H at a metal volume fraction x > x(c) is explained in terms of the recent theoretical concept of the local quantum-interference effect induced giant Hall effect in granular systems.