Browsing by Author "Sheng, Ping"

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A critical path approach for elucidating the temperature dependence of granular hopping conduction
(2018-10-01)
Wu, Tsz Chun
;
Lin, Juhn-Jong
;
Sheng, Ping
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電子物理學系
;
物理研究所
We revisit the classical problem of granular hopping conduction's sigma ae exp[-(T (o) /T)(1/2)] temperature dependence, where sigma denotes conductivity, T is temperature, and T (o) is a sample-dependent constant. By using the hopping conduction formulation in conjunction with the incorporation of the random potential that has been shown to exist in insulator-conductor composites, it is demonstrated that the widely observed temperature dependence of granular hopping conduction emerges very naturally through the immediate-neighbor critical-path argument. Here, immediate-neighbor pairs are defined to be those where a line connecting two grains does not cross or by-pass other grains, and the critical-path argument denotes the derivation of sample conductance based on the geometric percolation condition that is marked by the critical conduction path in a random granular composite. Simulations based on the exact electrical network evaluation of finite-sample conductance show that the configurationaveraged results agree well with those obtained using the immediate-neighbor critical-path method. Furthermore, the results obtained using both these methods show good agreement with experimental data on hopping conduction in a sputtered metal-insulator composite Ag (x) (SnO2)(1-x) , where x denotes the metal volume fraction. The present approach offers a relatively straightforward and simple explanation for the temperature behavior that has been widely observed over diverse material systems, but which has remained a puzzle in spite of the various efforts made to explain this phenomenon.
Large-scale Mesoscopic Transport in Nanostructured Graphene
(2013-02-06)
Zhang, Haijing
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Lu, Jianming
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Shi, Wu
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Wang, Zhe
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Zhang, Ting
Through exponential sample-size scaling of conductance, we demonstrate strong electron localization in three sets of nanostructured antidot graphene samples with localization lengths of 1.1, 2, and 3.4 mu m. The large-scale mesoscopic transport is manifest as a parallel conduction channel to 2D variable range hopping, with a Coulomb quasigap around the Fermi level. The opening of the correlation quasigap, observable below 25 K through the temperature dependence of conductance, makes possible the exponential suppression of inelastic electron-electron scatterings and thereby leads to an observed dephasing length of 10 mu m. DOI: 10.1103/PhysRevLett.110.066805
Negative correlation between charge carrier density and mobility fluctuations in graphene
(2014-08-26)
Lu, Jianming
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Pan, Jie
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Yeh, Sheng-Shiuan
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Zhang, Haijing
;
Zheng, Yuan
By carrying out simultaneous longitudinal and Hall measurements in graphene, we find that the 1/f noise for the charge carrier density is negatively correlated to that of mobility, with a governing behavior that differs significantly from the relation between their mean values. The correlation in the noise data can be quantitatively explained by a single-parameter theory whose underlying physics is the trapping and detrapping of the fluctuating charge carriers by the oppositely charged Coulomb scattering centers. This can alter the effective density of long-range scattering centers in a transient manner, with the consequent fluctuating effect on the mobility.