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Search Results: 1 - 10 of 3765 matches for " Tae Won Noh "
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Selective growth of perovskite oxides on SrTiO3 (001) by control of surface reconstructions
Soo-hyon Phark,Young Jun Chang,Tae Won Noh
Physics , 2010, DOI: 10.1063/1.3583443
Abstract: We report surface reconstruction (RC)-dependent growths of SrTiO3 and SrVO3 on a SrTiO3 (001) surface with two different coexisting surface RCs, namely (2x1) and c(6x2). Up to the coverage of several layers, epitaxial growth was forbidden on the c(6x2) RC under the growth conditions that permitted layer-by-layer epitaxial growth on the (2x1) RC. Scanning tunneling microscopy examination of the lattice structure of the c(6x2) RC revealed that this RC-selective growth mainly originated from the significant structural/stoichiometric dissimilarity between the c(6x2) RC and the cubic perovskite films. As a result, the formation of SrTiO3 islands was forbidden from the nucleation stage.
Dimensional crossover of polaron dynamics in Nb:SrTiO3/SrTiO3 superlattices: Possible mechanism of thermopower enhancement
Woo Seok Choi,Hiromichi Ohta,Soon Jae Moon,Yun Sang Lee,Tae Won Noh
Physics , 2009, DOI: 10.1103/PhysRevB.82.024301
Abstract: Using optical spectroscopy, we investigated the electrodynamic properties of Nb:SrTiO3/SrTiO3 superlattices. In these superlattices, a large enhancement of the Seebeck coefficient (S) has been reported with decreasing Nb:SrTiO3 layer thickness [refer to H. Ohta et al., Nature Mater. 6, 129 (2007)]. By analyzing the optical spectra, we found that the polaron plays an important role in determining the electrodynamic properties of the superlattices. With decreasing Nb:SrTiO3 layer thickness from eleven to one unit cell, we observed a threefold enhancement of the polaron effective mass and relaxation time. Such increases were attributed to a dimensional crossover of polaron from 3D to quasi-2D. Moreover, the modified nature of the polaron at low dimensions enhanced the thermoelectric properties of the oxide superlattice, by simultaneously increasing S and preventing the decrease of carrier mobility. Our results indicate that strong electron-phonon coupling can provide an alternative pathway in searching efficient thermoelectric materials.
Two opposite hysteresis curves in semiconductors with mobile dopants
Jae Sung Lee,Shin Buhm Lee,Byungnam Kahng,Tae Won Noh
Physics , 2012,
Abstract: Recent experimental researches on semiconductors with mobile dopants (SMD) have reported unconventional hysteretic current-voltage (I-V) curves, which form dynamically in either one of the two opposite directions, the counter-figure-eight and figure-eight ways. However the fundamental theory for the formation of the two directions is still absent, and this poses a major barrier for researches oriented to applications. Here, we introduce a theoretical model to explain the origin of the two directions, and find that the two ways originate from the spatial inhomogeneity of the dopant distribution in SMD. The counter-figure-eight (figure-eight) way of the hysteretic curve is obtained when dopants are driven from far from (near) the Schottky interface to the opposite side in the SMD. This finding indicates that the directions of hysteretic curve in SMD can be controlled.
Ferromagnetic properties of SrRuO3 thin films deposited on the spin-triplet superconductor Sr2RuO4
Yusuke Sugimoto,Muhammad Shahbaz Anwar,Seung Ran Lee,Yeong Jae Shin,Shingo Yonezawa,Tae Won Noh,Yoshiteru Maeno
Physics , 2015,
Abstract: We report magnetic properties of epitaxial thin films of the itinerant ferromagnet SrRuO3 deposited on the cleaved ab surface of the spin-triplet superconductor Sr2RuO4. The films exhibit ferromagnetic transition near 160 K as in the bulk SrRuO3, although the films are under 1.7% compressive strain. The observed magnetization is even higher than that of the bulk SrRuO3. In addition, we newly found that the magnetization relaxation after field removal is strongly anisotropic: two relaxation processes are involved when magnetic domains are aligned along the ab-plane.
Prevalence of and Factors Associated with Lens Opacities in a Korean Adult Population with and without Diabetes: The 2008–2009 Korea National Health and Nutrition Examination Survey
Tae Nyun Kim, Joo Eun Lee, Eun Ju Lee, Jong Chul Won, Jung Hyun Noh, Kyung Soo Ko, Byoung Doo Rhee, Dong-Jun Kim
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0094189
Abstract: Objective We examined the prevalence of and factors associated with lens opacities in a Korean adult population with and without diabetes. Research Design and Methods Among the 11,163 adults (≥19 years old) from the fourth Korea National Health and Nutrition Examination Survey in 2008–2009, the data from laboratory tests, nutritional surveys, and slit-lamp examinations of 10,248 persons (4,397 men, 5,851 women) were examined. Cataract was defined as the presence of any nuclear, cortical, subcapsular, or mixed cataract in at least one eye, using the Lens Opacities Classification System III. Results The weighted prevalence of cataracts were 23.5% [95% confidence interval (CI), 21.7–25.4] in a Korean adult population (19–39 years old, 1.8% [1.3–2.5], 40–64 years old, 25.2% [22.5–28.1],≥65 years old, 87.8% [85.4–89.9])and 54.7% [50.1–59.2] in a diabetic population(19–39 years old, 11.6% [4.5–26.5], 40–64 years old, 41.1% [35.4–47.0], ≥65 years old, 88.3% [83.5–91.8]). In a logistic regression analysis, age, myopia, and the presence of diabetes were independent risk factors. For young (age 19–39 years) and middle aged (age 40–65 years) adults with diabetes, the OR of having a lens opacity is 5.04 [1.41–17.98] and 1.47 [1.11–1.94], respectively, as those without diabetes, whereas for adults aged 65 and older, there was no difference in the prevalence of cataract. Conclusions According to these national survey data, ~ 24% of Korean adults and ~ 55% of people with diabetes have cataracts. The presence of diabetes was independently associated with cataracts in young and middle aged adults.
Optical spectroscopic investigation on the coupling of electronic and magnetic structure in multiferroic hexagonal RMnO3 (R = Gd, Tb, Dy, and Ho) thin films
Woo Seok Choi,Soon Jae Moon,Sung Seok A. Seo,Daesu Lee,Jung Hyuk Lee,Pattukkannu Murugavel,Tae Won Noh,Yun Sang Lee
Physics , 2008, DOI: 10.1103/PhysRevB.78.054440
Abstract: We investigated the effects of temperature and magnetic field on the electronic structure of hexagonal RMnO3 (R = Gd, Tb, Dy, and Ho) thin films using optical spectroscopy. As the magnetic ordering of the system was disturbed, a systematic change in the electronic structure was commonly identified in this series. The optical absorption peak near 1.7 eV showed an unexpectedly large shift of more than 150 meV from 300 K to 15 K, accompanied by an anomaly of the shift at the Neel temperature. The magnetic field dependent measurement clearly revealed a sizable shift of the corresponding peak when a high magnetic field was applied. Our findings indicated strong coupling between the magnetic ordering and the electronic structure in the multiferroic hexagonal RMnO3 compounds.
Double polarization hysteresis loop induced by the domain pinning by defect dipoles in HoMnO3 epitaxial thin films
Daesu Lee,Heung-Sik Kim,Seung Yup Jang,Kwon Woo Joh,Tae Won Noh,Jaejun Yu,Cheol Eui Lee,Jong-Gul Yoon
Physics , 2009, DOI: 10.1103/PhysRevB.81.012101
Abstract: We report on antiferroelectriclike double polarization hysteresis loops in multiferroic HoMnO3 thin films below the ferroelectric Curie temperature. This intriguing phenomenon is attributed to the domain pinning by defect dipoles which were introduced unintentionally during film growth process. Electron paramagnetic resonance suggests the existence of Fe1+ defects in thin films and first principles calculations reveal that the defect dipoles would be composed of oxygen vacancy and Fe1+ defect. We discuss migration of charged point defects during film growth process and formation of defect dipoles along ferroelectric polarization direction, based on the site preference of point defects. Due to a high-temperature low-symmetry structure of HoMnO3, aging is not required to form the defect dipoles in contrast to other ferroelectrics (e.g., BaTiO3).
Dimensionality Control of d-orbital Occupation in Oxide Superlattices
Da Woon Jeong,Woo Seok Choi,Satoshi Okamoto,Jae-Young Kim,Kyung Wan Kim,Soon Jae Moon,Deok-Yong Cho,Ho Nyung Lee,Tae Won Noh
Physics , 2014, DOI: 10.1038/srep06124
Abstract: Manipulating the orbital state in a strongly correlated electron system is of fundamental and technological importance for exploring and developing novel electronic phases. Here, we report an unambiguous demonstration of orbital occupancy control between t2g and eg multiplets in quasi-twodimensional transition metal oxide superlattices (SLs) composed of a Mott insulator LaCoO3 and a band insulator LaAlO3. As the LaCoO3 sublayer thickness approaches its fundamental limit (i.e. one unit-cell-thick), the electronic state of the SLs changed from a Mott insulator, in which both t2g and eg orbitals are partially filled, to a band insulator by completely filling (emptying) the t2g (eg) orbitals. We found the reduction of dimensionality has a profound effect on the electronic structure evolution, which is, whereas, insensitive to the epitaxial strain. The remarkable orbital controllability shown here offers a promising pathway for novel applications such as catalysis and photovoltaics, where the energy of d level is an essential parameter.
Ferromagnetic SrRuO3 thin-film deposition on a spin-triplet superconductor Sr2RuO4 with highly conducting interface
M. S. Anwar,Yeong Jae Shin,Seung Ran Lee,Sung Jin Kang,Yuske Sugimoto,Shingo Yonezawa,Tae Won Noh,Yoshiteru Maeno
Physics , 2014, DOI: 10.7567/APEX.8.015502
Abstract: Ferromagnetic SrRuO3 thin films are deposited on the ab-surface of single crystals of the spin-triplet superconductor Sr2RuO4 as substrates using pulsed laser deposition. The films are under a severe in-plane compressive strain. Nevertheless, the films exhibit ferromagnetic order with the easy axis along the c-direction below the Curie temperature of 158 K. The electrical transport reveals that the SrRuO3/Sr2RuO4 interface is highly conducting, in contrast with the interface between other normal-metals and the ab-surface of Sr2RuO4. Our results will stimulate the investigations on proximity effects between a ferromagnet and a spin-triplet superconductor.
Counterfactual Quantum Cryptography
Tae-Gon Noh
Physics , 2008, DOI: 10.1103/PhysRevLett.103.230501
Abstract: Quantum cryptography allows one to distribute a secret key between two remote parties using the fundamental principles of quantum mechanics. The well-known established paradigm for the quantum key distribution relies on the actual transmission of signal particle through a quantum channel. This paper shows that the task of a secret key distribution can be accomplished even though a particle carrying secret information is not in fact transmitted through the quantum channel. The proposed protocols can be implemented with current technologies and provide practical security advantages by eliminating the possibility that an eavesdropper can directly access the entire quantum system of each signal particle.
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