• Title/Summary/Keyword: Gap symmetry

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Pairing symmetry analyzed by a peak shape of density of states in an Bi2Sr2CaCu2O8+x superconductor

  • Kim, Hyun-Tak;Kang, Kwang-Yong
    • Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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    • 2003.10a
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    • pp.30-34
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    • 2003
  • For an inhomogeneous superconductor, we reveal a relation of an observed superconducting gap, $\Delta$$_{obs}$ and the intrinsic true gap, $\Delta$$_{i}$, $\Delta$$_{obs}$(equation omitted) where band filling, 0<$\rho$<$\leq$1. $\Delta$$_{obs}$ is the effect of measurement when 0<$\rho$<1. The true gap is observed only when $\rho$=1. Parring symmetry analyzed by a coherence-peak shape of density of states, observed in B $i_2$S $r_2$CaC $u_2$ $O_{8}$$\chi$ superconductors, is s- wave.X> $O_{8}$$\chi$ superconductors, is s- wave. wave.

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WAKE CHARACTERISTICS BEHIND TWO SPHERES IN A SIDE-BY-SIDE ARRANGEMENT (병렬로 배열된 두 개의 구에서 발생하는 후류의 특성 연구)

  • Kim, Dong-Joo
    • Journal of computational fluids engineering
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    • v.12 no.4
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    • pp.61-67
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    • 2007
  • Numerical simulation of laminar flow over two spheres in a side-by-side arrangement is carried out to investigate the effect of the inter-sphere spacing on the flow characteristics. The Reynolds numbers considered are 100, 250, and 300, covering the steady axisymmetric, steady planar-symmetric, and unsteady planar-symmetric flows in the case of a single sphere. Results show that the drag and lift coefficients and wake structures are significantly modified depending on both the Reynolds number and the spacing between the spheres. At Re=100, the flow is steady planar-symmetric irrespective of the spacing, but it shows some variation according to the spacing at Re=250 and 300. That is, the flow maintains planar symmetry of the single-sphere wake at large spacings, while it loses the symmetry at small spacings due to the generation of new asymmetric vortical structures. It is also shown that the drag and lift coefficients generally increase with decreasing inter-sphere spacing because the high pressure region is formed near the gap between the spheres.

Energy Gap of $MgB_2$ from Point Contact Spectroscopy

  • Lee, Suyoun;Yonuk Chong;S. H. Moon;Lee, H. N.;Kim, H. G.
    • Progress in Superconductivity
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    • v.3 no.2
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    • pp.146-150
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    • 2002
  • We performed the point contact spectroscopy on newly discovered superconductor $MgB_2$ thin films with Au tip. In the point contact spectroscopy of the metallic Sharvin limit, the differential conductance below the gap is twice as that above the gap by virtue of Andreev Reflection. After some surface cleaning processes of sample preparation such as ion-milling and wet etching, the obtained dI/dV versus voltage curves are relatively well fitted to the Blonder-Tinkham-Klapwijk (BTK) formalism. Gaps determined by this technique were distributed in the range of 3meV~ 8meV with the BCS value of 5.9meV in the weak coupling limit. We attribute these discrepancies to the symmetry of the gap parameter and the degradation of the surface of the sample. We also present the temperature dependence of the conductance vs voltage curve and thereby the temperature dependence of the gap.

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Characteristics of Interface States in One-dimensional Composite Photonic Structures

  • Zhang, Qingyue;Mao, Weitao;Zhao, Qiuling;Wang, Maorong;Wang, Xia;Tam, Wing Yim
    • Current Optics and Photonics
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    • v.6 no.3
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    • pp.270-281
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    • 2022
  • Based on the transfer-matrix method (TMM), we report the characteristics of the interface states in one-dimensional (1D) composite structures consisting of two photonic crystals (PCs) composed of binary dielectrics A and B, with unit-cell configurations ABA (PC I) and BAB (PC II). The dependence of the interface states on the number of unit cells N and the boundary factor x are displayed. It is verified that the interface states are independent of N when the PC has inversion symmetry (x = 0.5). Besides, the composite structures support the formation of interface states independent of the PC symmetry, except that the positions of the interface states will be varied within the photonic band gaps. Moreover, the robustness of the interface states against nonuniformities is investigated by adding Gaussian noise to the layer thickness. In the case of inversion symmetry (x = 0.5) the most robust interface states are achieved, while for the other cases (x ≠ 0.5) interface states decay linearly with position inside the band gap. This work could shed light on the development of robust photonic devices.

Software development for the visualization of brain fiber tract by using 24-bit color coding in diffusion tensor image

  • Oh, Jung-Su;Song, In-Chan;Ik hwan Cho;Kim, Jong-Hyo;Chang, Kee-Hyun;Park, Kwang-Suk
    • Proceedings of the KSMRM Conference
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    • 2002.11a
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    • pp.133-133
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    • 2002
  • Purpose: The purpose of paper is to implement software to visualize brain fiber tract using a 24-bit color coding scheme and to test its feasibility. Materials and Methods: MR imaging was performed on GE 1.5 T Signa scanner. For diffusion tensor image, we used a single shot spin-echo EPI sequence with 7 non-colinear pulsed-field gradient directions: (x, y, z):(1,1,0),(-1,1,0),(1,0,1),(-1,0,1),(0,1,1),(0,1,-1) and without diffusion gradient. B-factor was 500 sec/$\textrm{mm}^2$. Acquisition parameters are as follows: TUTE=10000ms/99ms, FOV=240mm, matrix=128${\times}$128, slice thickness/gap=6mm/0mm, total slice number=30. Subjects consisted of 10 normal young volunteers (age:21∼26 yrs, 5 men, 5 women). All DTI images were smoothed with Gaussian kernel with the FWHM of 2 pixels. Color coding schemes for visualization of directional information was as follows. HSV(Hue, Saturation, Value) color system is appropriate for assigning RGB(Red, Green, and Blue) value for every different directions because of its volumetric directional expression. Each of HSV are assigned due to (r,$\theta$,${\Phi}$) in spherical coordinate. HSV calculated by this way can be transformed into RGB color system by general HSV to RGB conversion formula. Symmetry schemes: It is natural to code the antipodal direction to be same color(antipodal symmetry). So even with no symmetry scheme, the antipodal symmetry must be included. With no symmetry scheme, we can assign every different colors for every different orientation.(H =${\Phi}$, S=2$\theta$/$\pi$, V=λw, where λw is anisotropy). But that may assign very discontinuous color even between adjacent yokels. On the other hand, Full symmetry or absolute value scheme includes symmetry for 180$^{\circ}$ rotation about xy-plane of color coordinate (rotational symmetry) and for both hemisphere (mirror symmetry). In absolute value scheme, each of RGB value can be expressed as follows. R=λw|Vx|, G=λw|Vy|, B=λw|Vz|, where (Vx, Vy, Vz) is eigenvector corresponding to the largest eigenvalue of diffusion tensor. With applying full symmetry or absolute value scheme, we can get more continuous color coding at the expense of coding same color for symmetric direction. For better visualization of fiber tract directions, Gamma and brightness correction had done. All of these implementations were done on the IDL 5.4 platform.

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Growth and optical properties of undoped and Co-doped CdS single crystals (CdS 및 CdS:Co2+ 단결정의 성장과 광학적 특성)

  • Oh, Gum-kon;Kim, Nam-oh;Kim, Hyung-gon;Hyun, Seung-cheol;Park, hjung;Oh, Seok-kyun
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.51 no.3
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    • pp.137-141
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    • 2002
  • CdS and $CdS:Co^{2+}$ single crystals were grown by CTR method using iodine as transport material. The grown single crystals have defect chalcopyrite structure with direct band gap. The optical energy band gap was decreased according to add of Co-impurity. We can observed the Co-impurity optical absorption peaks assigned to the $Co^{2+}$ ion sited at the $T_d$ symmetry lattice and we consider that they were attributed to the electron transitions between energy levels of ions.

Optical Properties of $I^B-AI-VI^B_2$$I^B-AI-VI^B_2 :Co^{2+}$ Crystals ($I^B-AI-VI^B_2$$I^B-AI-VI^B_2 :Co^{2+}$결정의 광학적 특성연구)

  • 김화택;김창대;윤창선;진문석;최성휴
    • Journal of the Korean Vacuum Society
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    • v.4 no.3
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    • pp.334-341
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    • 1995
  • IB-AI-VIB2 및 IB-AI-VIB2 :Co2+ 결정을 고순도 원소를 출발 물질로 하고 iodine을 수송 매체로 사용하여 chemical transport reaction method로 성장시켰다. 성장된 결정의 결정구조는 chalcopyrite 구조였으며, energy gap은 direct band gap으로 3.514~1.814 eV 정도로 주어졌으며, cobalt를 불순물로 첨가할 때 energy gap은 감소하였다. IB-AI-VIB2 :Co2+ 결정에서 첨가된 cobalt가 모체결정의 Td symmetry site에 Co2+ ion으로 위치하여, Co2+ ion의 energy 준위 사이의 전자전이에 기인하는 불순물 광흡수 peaks가 나타났다. 이 불순물 광흡수 peaks에 결정장 이론을 적용하여 구산 1st-order spin-orbit coupling parameter(λ)는 -183~ -189cm-1정도였고, 2nd-order spin-orbit coupling parameter(P)는 225~239 cm-1정도였으며, crystal field parameter(Dq)는 328~395cm-1, Racah parameter(B)는 531~552cm-1정도였다.

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Optical properties and thermodynamic function properties of undoped and Co-doped $Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}$ Single Crystals ($Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}$$Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}:Co^{2+}$ 단결정의 광학적 특성과 열역학 함수 추정)

  • Hyun, Seung-Cheol;Kim, Hyung-Gon;Kim, Duck-Tae;Park, Kwang-Ho;Park, Hyun;Oh, Seok-Kyun
    • Proceedings of the KIEE Conference
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    • 2002.06a
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    • pp.88-93
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    • 2002
  • $Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}$ and $Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}:Co^{2+}$ + single crystals were grown by CTR method. The grown single crystals have defect chalcopyrite structure with lattice constant a= 5.5966A. c= 10.8042${{\AA}}$ for the pure. a= 5.6543${{\AA}}$. c= 10.8205${{\AA}}$ for the Co-doped single crystal. respectively. The optical energy band gap was given as indirect band gap. The optical energy band gap was decreased according to add of Co-impurity. Temperature dependence of optical energy band gap was fitted well to the Varshni equation. From this relation. we can deduced the entropy. enthalpy and heat capacity. Also. we can observed the Co-impurity optical absorption peaks assigned to the $Co^{2+}$ ion sited at the $T_d$ symmetry lattice and we consider that they were attributed to the electron transitions between energy levels of ions.

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Optical Properties of Photoferroelectric Semiconductors II (Optical Properties of BiSI, BiSI : Co, BiSeI and BiSeI : Co Single Crystals) (Photoferroelectric 반도체의 광학적 특성연구 II : (BiSI, BiSeI, BiSI : Co 및 BiSeI : Co 단결정의 광학적 특성에 관한 연구))

  • 고재모;윤상현;김화택;최성휴;김형곤;김창대;권숙일
    • Journal of the Korean Vacuum Society
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    • v.1 no.2
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    • pp.244-253
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    • 1992
  • BiSI, BiSI : Co, BiSeI 및 BiSeI : Co 단결정을 고순도의 성분원소와 8.6mole% 과잉의 Iodine를 투명석영관내에 넣고 진공봉입하여 합성한 ingot를 사용하여 수직 Bridgman 방법으로 성장시켰다. 성장된 단결정은 orthorhombic 구조였고, energy band 구 조는 간접전이형으로 293K에서 광학적 energy gap은 각각 1.590eV, 1.412eV, 1.282eV 및 1.249eV로 주어지며, energy gap의 온도의존성은 Varshni 방정식으로 잘 표현된다. Cobalt 를 첨가할 때 나타나는 불순물 광흡수 peak는 Td symmetry점에 위치한 Co2+, Co3+ ion의 energy 준위들 사이의 전자전이에 의해서 나타난다.

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