• Title/Summary/Keyword: Superlattices

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Metal-to-Insulator Transitions in La2/3Sr1/3MnO3/LaMnO3 (LSMO/LMO) Superlattices

  • Ryu, Sang-Woo;Jang, Hyun-M.
    • Journal of the Korean Ceramic Society
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    • v.43 no.11 s.294
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    • pp.734-737
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    • 2006

  • A series of manganite-based superlattices composed of half-metallic $La_{2/3}Sr_{1/3}MnO_3/LaMnO_3$ and insulating LaMnO$_3$ stacking layers were fabricated by employing pulsed laser deposition method. The dc resistivity increased drastically by simply reducing the stacking periodicity. The resistivity enhancement was accompanied by a gradual decrease in the temperature (T$_c$) of the Metal-to-Insulator Transition (MIT). This observation was interpreted as a small decrease in the effective metallic fraction near the percolation threshold. For the stacking periodicity less than a certain critical value, there appeared another transition to an insulating state at temperatures far below T$_c$. This low-temperature transition seems to be closely related to the AF-type (C-type) orbital ordering in newly formed insulating domains.

  • https://doi.org/10.4191/KCERS.2006.43.11.734 인용 PDF KSCI

Observations on the Modulated Structure in Pyrochlore-type Compounds, $In_2(Ti_{1.7}Zn_{0.3})O_{0.67}$ and $In_2(Ti_{1.7}Mg_{0.3})O_{6.7}$ (Pyrochlore형 화합물 $In_2(Ti_{1.7}Zn_{0.3})O_{0.67}$과 $In_2(Ti_{1.7}Mg_{0.3})O_{6.7}$에서의 변조구조 관찰)

  • Lee, Hwack-Joo;Park, Hyun-Min;Cho, Yang-Koo;Ryu, Hyun;Nahm, Sahn;Bando, Y.
    • Applied Microscopy
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    • v.29 no.4
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    • pp.471-477
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    • 1999

  • Microstructural observations on the pyrochlore-type $Lu_2Ti_2O_7$ and the similar type of compounds, $In_2(Ti_{1.7}Zn_{0.3})O_{6.7}$ and $In_2(Ti_{1.7}Mg_{0.3})O_{6.7}$ which were made by the isothermal heat-treatment at 1623K for 18 days in Pt tube, were carried out using a top-entry HRTEM working at 200 kV. The modulated structures were found in both compounds, however, not in $Lu_2Ti_2O_7$. From the electron diffraction pattern analysis, the modulated superlattices are incommensurate and are 2.69 times of sublattices along (220) direction. The high resolution TEM images have shown that the superlattices consist of alternate superlattices which are composed of two or three sublattices, resulting in the average of 2.7 times of sublattices in accordance with the analysis of electron diffraction patterns. The crystal structures of both compounds are found to quite similar to those of pyrochlore, however the evidence that the cubic axes are slightly deviated from right angle. The modulated structure has gradually changed to the unmodulated structure induced by electron irradiation.

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Measurement of Quantum Efficiency of Er-doped Si/$SiO_2$ Superlattices and Application to the Photonic-Crystal Cavity-QED Experiments (어븀이 첨가된 실리콘/실리카 초격자의 양자효율 측정과 광결정공진기 양자전기동력학의 응용)

  • 최용석;성주연;신중훈;이용희
    • Proceedings of the Optical Society of Korea Conference
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    • 2003.02a
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    • pp.186-187
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    • 2003

  • 실리콘을 기반으로 한 광학적 능동매질에 대한 연구는 학문적으로나 산업적으로 큰 중요성을 갖고 있다. 최근 실리콘 양자점을 이용한 연구에서는 상온에서도 활용 가능한 광학적 이득을 얻게 되었는데, 이를 이용한 LED가 보고되었으며 실리콘을 기반으로 한 레이저의 실현 가능성도 제기되고 있다. 실리콘 양자점에서 나오는 빛을 이용하는 것은 양자점이 제공하는 크기 효과를 이용하여 원하는 영역에서 원하는 광학적 이득을 얻을 수 있다는 장점이 있으나, 기술적으로는 고난도의 크기 제어가 필요하다는 어려움이 있다. (중략)

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Optical phonon and scattering in uniaxial crystals

  • Lee, B.C
    • Proceedings of the Korean Vacuum Society Conference
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    • 2000.02a
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    • pp.118-118
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    • 2000

  • We investigate Frohlich-like electron--optical-phonon interactionsin uniaxial crytals based on the macroscopic dielectric continuum model. In general, the optical-phonon branches support mixed longitudinal and transverse modes due to the anisotropy. For heterostructures with double interfaces and superlattices, it is known that confined, interface, and half-space optical phonon modes exist in zincblende cystals. In uniaxial structures, additional propagating modes may exist in wurtzite heterosystems due to anisotropic phonon dispersion. This is especially the case when the dielectric properties of the adjacent heterostructure materials do not differ substantially. The dispersion relations and the interaction Hamiltonians for each of these modes are derived.

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