Browsing by Author "Wu, J. C."

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A wide-angle dual-band infrared perfect absorber based on metal-dielectric-metal split square-ring and square array
(2012-05-23)
Lee, H. M.
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Wu, J. C.
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物理研究所
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Institute of Physics
The optical properties of a dual-band plasmonic absorber are delineated numerically by employing a finite element method. Based on a metal-dielectric-metal scheme, the key structure consists of a lossless dielectric layer that is sandwiched by a silver split square-ring enclosing a silver square array and ground silver plane. The simulation results clearly show that near-perfect absorption efficiency can be realized for two absorption bands in the near-infrared wavelength range. The near-perfect absorption bands exhibit polarization insensitivity and wide-angle incidence. Notably, the absorption band is independently governed by the size of each part of the patterned films where the silver split square-ring determines the shorter wavelength band and the silver square determines the longer wavelength band, respectively. The repositioning of two near-perfect absorption peaks possesses a linear relationship that is related to the dimensions of the patterned silver layer. This allows for a flexible reconfigurability over the entire near-infrared regime.
Anisotropic pinning in Nb thin films with triangular pinning arrays
(2007-07-01)
Cao, R.
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Wu, T. C.
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Kang, P. C.
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Wu, J. C.
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Yang, T. J.
A superconducting thin film with regular triangular arrays has been fabricated to explore the anisotropic vortex pinning behavior. We found that the critical currents for these films depend strongly on the current directions. Some interesting temperature-dependent phenomena are observed and discussed. We also made molecular dynamic simulations to study the dynamics of the vortex motion. The simulation results confirm the anisotropic features we found in the experiments. (c) 2007 Elsevier Ltd. All rights reserved.
Magnetic tunnel junction based out-of-plane field sensor with perpendicular magnetic anisotropy in reference layer
(2015-05-07)
Lee, Y. C.
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Chao, C. T.
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Li, L. C.
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Suen, Y. W.
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Horng, Lance
A magnetic tunnel junction (MTJ) with orthogonal magnetic anisotropy and consisting of Ta X/Co40Fe40B20 1.2 (reference)/MgO 2.0/Co20Fe60B20 2.3 (sensing)/Ta 5/Ru 5 (thickness in nanometers), where X ranges from 15 to 30, is proposed and investigated in response to the demand for out-of-plane field sensors. The reference layer with perpendicular magnetic anisotropy (PMA) demonstrates tuneable coercivity ranging from 72 Oe to 175 Oe. The sensing layer exhibits in-plane anisotropy with the avoidance of exchange coupling from the PMA reference layer because of a thick MgO barrier layer. The magnetization reversal behavior of micron scale devices not only corresponds well to the sheet film, but is also independent in terms of shape and size. The magnetoresistance curve exhibits a ratio of similar to 27% in the presence of a perpendicular field and is insensitive to the in-plane field. For perpendicular field sensing, the dynamic range with a sensitivity of similar to 0.3%/Oe can achieve +/- 25 Oe with a coercive field of less than 3 Oe. Additionally, even when bias is applied up to 9.1 mV, magnetic fluctuation still stays below 0.15 mOe. (C) 2015 AIP Publishing LLC.
Matching effect and flux pinning force in a Nb superconducting thin film with a triangular lattice of artificial pinning centers
(2004-05-01)
Horng, Lance
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Wu, J. C.
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Kang, P. C.
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Wu, T. C.
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Yang, T. J.
A strong pinning force in a Nb superconducting thin film is formed by a triangular lattice of defects due to the structural corrugation that acts as pinning centers. The magnetoresistance measurement close to the transition temperature shows a set of minima of magnetoresistance at equal external field intervals. A crossover in current-voltage relations with matching field and half-integer matching field occurs for currents exceeding a certain threshold value. The phenomenon is related to the presence of pinning structures at matching fields. (C) 2003 Elsevier B.V. All rights reserved.
Properties of vortex propagation in a niobium film with spacing-graded density of pinning sites
(2007-05-01)
Horng, Lance
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Wu, T. C.
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Wu, J. C.
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Cao, R.
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Yang, T. J.
The vortex propagation has been investigated in Nb superconductors with one dimension spacing-graded density of submicrometer-scaled holes in this research. A rectification effect can be discerned because the applied ac is transformed into a net dc voltage. These results demonstrate that the rectification is mainly characterized by the asymmetric pinning landscape and the rectified voltage depends considerably on temperature and the amplitude of applied ac. The dc voltage increases steeply up to the maximum value and then decreases to zero dc voltage with the increase of ac. The shape of peaks in the dc voltage signal become steeper and move to higher applied ac regime with the decrease of temperature.
Vortex ratchet effect in a niobium film with spacing-graded density of pinning sites
(2007-08-01)
Wu, T. C.
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Horng, Lance
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Wu, J. C.
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Cao, R.
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Kolacek, Jan
The vortex propagation exhibits rectification effect in Nb superconductors with spacing-graded density of holes. A rectified dc voltage is obtained when the vortex lattice is driven by ac current. The asymmetric geometry of the pinning array produces a significant influence on the vortex motion. The rectified voltage depends considerably on the amplitude of the applied ac current and the magnetic field. The experimental results reveal a drastic change of the vortex rectification for magnetic field above/below the first matching field. The reason may be that the interstitial vortices are formed in the film above the first matching field. A reversible vortex motion is induced by the interstitial vortices for the field above the first matching field. (c) 2007 American Institute of Physics.