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Transition from 2-D to 1-D Transport in Superconducting YBa2Cu3O7
V. D. Lam,L. V. Hong,P. H. Khoi,J.F. Hamet,F. Boyer,이영백,J.P. Maneval 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5
The resistive response of c-axis textured YBa₂Cu₃O7 bridges (100 nm thick and 10 m wide) has been studied dynamically on the nanosecond scale over a wide span of temperatures and currents. From Tc down to 75 K, dissipation is dominated by the viscosity of vortices spontaneously generated in the earth's magnetic eld. For 70 K < T < 75 K, vortex ow coexists with phase-slip centers (PSCs) characteristic of one-dimensional (1-D) transport. Eventually, below about 70 K, vortex ow is inhibited while, independently, PSCs transform into normal hot spots. All these resistive modes are identified by using a different time-varying voltage consecutive to the application of a step function of the current to the bridge.
Experimental observation of the electric coupling effect in split ring resonators and the prevention
Lam, V. D.,Kim, J. B.,Lee, S. J.,Wang, D. F.,Lee, Y. P. WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.12
<P>We studied experimentally the transmission properties of arrays of split-ring resonators (SRRs) for different electromagnetic polarizations in the microwave-frequency regime. It is known that, besides the electric response through the cut-wire like, another electric coupling to the magnetic resonance of the SRR appears when the incident electric field is parallel to the gap-bearing sides of the SRR. The resonance frequency of this effect is very close to the magnetic resonance. This might degrade or even destroy the left-handed properties of the material when the SRRs are combined with the wires. To avoid this effect we have changed the structure of SRRs from an asymmetric one with a single gap to a symmetric one with two gaps. The results are also compared with the previous studies. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>
Lam, T.D.,Hoang, T.V.,Quang, D.T.,Kim, J.S. Elsevier Sequoia 2009 Materials science & engineering. properties, micro Vol.501 No.1
The nanosized and surface-modified precipitated calcium carbonate (PCC) particles have been synthesized by carbonation reaction and used as reinforcing filler for preparing polypropylene (PP) composites. Both a crystallization inhibitor (sodium tripolyphosphate, TPP) and an organic surface modifier (stearic acid) were used to get narrow size distribution, uniform shape and nanometer size. The comprehensive results of morphological and mechanical analyses on PP composites, prepared with trivial, untreated PCC (t-PCC); nanosized and surface-unmodified PCC (n-PCC); nanosized and surface-modified PCC (ns-PCC) separately, were reported and discussed thoroughly.
Lam, V D,Tung, N T,Cho, M H,Park, J W,Jang, W H,Lee, Y P Institute of Physics [etc.] 2009 Journal of physics. D, applied physics Vol.42 No.11
<P>This report investigates the effect of the dielectric layer thickness on both magnetic and electric resonances of cut-wire-pair (CWP) structures in the microwave frequency regime. It was found that the resonances are sensitive to the thickness of the dielectric layer. As the thickness increases, the bandwidth of the magnetic resonance is slightly extended to a higher frequency, while the low-frequency edge of the electric-resonance band is remarkably shifted to a lower frequency. It was also found that the dependence of the magnetic resonance frequency on the dielectric layer thickness follows the trend of the closed formula based on the cavity model for the coupled metallic elements (Cai <I>et al</I> 2007 <I>Opt. Express</I> <B>15</B> 3333). In addition, we also studied the effect of the dielectric layer thickness on the left-handed behaviour of a combined structure consisting of CWP and continuous wire. The actual measurements are compared with the numerical simulation values to show a good coincidence.</P>
Electron-spin-resonance Spectra and Ferroelectricity of BaTi1−xFexO3
D. Ginting,S. C. Yu,판더롱,N. V. Dang,T. D. Thanh,V. D. Lam 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
We have studied electron-spin-resonance (ESR) spectra and the ferroelectricity of polycrystallineBaTi1−xFexO3 ceramics. The features of the ESR spectra recorded at room temperature revealthat the samples with x = 0.02 - 0.06 are paramagnetic while the others are ferromagnetic. Theseresults are in good agreement with those reported previously for magnetization measurements. In our case, the ESR spectra are mainly related to dipole-dipole interactions taking place betweenFe3+ and Fe4+ ions, which are co-present in the samples. Electrical investigations of the polarizationreveal room-temperature P −E hysteresis loops for all the samples. Both the remnant polarization(Pr) and the ferroelectric P − E loop decrease with increasing Fe content (x) in BaTi1−xFexO3,indicating a decrease in the ferroelectricity. This is ascribed to an incorporation of Fe dopants intothe tetragonal BaTiO3 lattice and to a structural phase separation.
Electromagnetic Behavior of Representative Metamaterial Structures
이영백,V. D. Lam,J. B. Kim,이성재 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
We investigated systematicaly the electromagnetic behavior of different magnetic metamaterials, from the split-ring resonator to the cut-wire pair, for providing a negative magnetic permeability. The combination of a cut-wire pair and a continuous wire was also studied experimentaly. We found that the combined structure exhibited both left- and right-handed transmision bands. Until the width of the cut-wire pair was increased to merge with the adjacent continuous wire to form the so-caled fishnet structure, the left-handed (LH) behavior continued to be observed. Finaly, the effect of the structural parameters on the LH behavior of the fishnet structure was also investigated. These structures were designed, built and measured in the microwave frequency range.
Highly dispersive transparency in coupled metamaterials
Thuy, V T T,Tung, N T,Park, J W,Lam, V D,Lee, Y P,Rhee, J Y IOP Publishing 2010 Journal of optics Vol.12 No.11
<P>We investigate the coupling between bright and quasi-dark eigenmodes in a planar metamaterial supporting highly dispersive transparency. The specific design of such a metamaterial consists of a cut wire (CW) and a single-gap split-ring resonator (SRR). Through the numerical simulation and the equivalent-circuit analysis, we demonstrate that the response of the SRR, which is weakly excited by external electric field, plays the role of a quasi-dark eigenmode in the presence of a strongly radiative CW. Furthermore, by extending and relating our study to the trapped mode resonances and the coupling between dark and bright modes, a more comprehensive perspective for the metamaterial realization of highly dispersive transmission and slow-light applications is provided.</P>