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2. Direct observation of orbital driven strong interlayer coupling in puckered two-dimensional PdSe2

Author

Ryu, Jung Hyun, Kim, Jeong-Gyu, Kim, Bongjae, Kim, Kyoo, Kim, Sooran, Park, Byeong-Gyu, Kim, Younghak, Ko, Kyung-Tae, and Lee, Kimoon

Subjects
Condensed Matter - Materials Science
Abstract

Interlayer coupling between individual unit layers has played a critical role for layer-dependent properties in two-dimensional (2D) materials. While recent studies have revealed the significant degrees of interlayer interactions, the overall electronic structure of the 2D material has been mostly addressed by the intralayer interactions. Here, we report the direct observation of a highly dispersive single electronic band along the interlayer direction in puckered 2D PdSe2 as an experimental hallmark of strong interlayer couplings. Remarkably large band dispersion along kz-direction near Fermi level, which is even wider than the in-plane one, is observed by the angle-resolved photoemission spectroscopy measurement. Employing the X-ray absorption spectroscopy and density functional theory calculations, we reveal that the strong interlayer coupling in 2D PdSe2 originates from the unique directional bonding of Pd d orbitals associated with unexpected Pd 4d9 configuration, which consequently gives rise to the strong layer-dependency of the band gap.

Published
2021
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4. Restoration of Topological Surface State by Vacuum Annealing in Magnetically Doped Topological Insulator

Author

Kim, Jinsu, Shin, Eun-Ha, Sharma, Manoj K., Ihm, Kyuwook, Dugerjav, Otgonbayar, Hwang, Chanyong, Lee, Hwangho, Ko, Kyung-Tae, Park, Jae-Hoon, Kim, Miyoung, Kim, Hanchul, and Jung, Myung-Hwa

Subjects
Condensed Matter - Materials Science
Abstract

The introduction of magnetic order on the surface of topological insulators in general breaks the two-dimensional character of topological surface state (TSS). Once the TSS disappears, it is improbable to restore the topological surface properties. In this report, we demonstrate that it is possible to restore the inherent TSS by ultra-high vacuum annealing. Starting from an antiferromagnetic Gd-doped Bi2Te3, that has surface state gap without TSS properties, after annealing we observed the gap closing as well as typical TSS features in physical properties. The microscopic mechanism of atomic migration and TSS restoration by annealing process is unraveled by the combination of scanning tunneling microscopy measurements and density functional theory calculations. This approach to control the surface of topological insulators and stabilize the TSS simply by vacuum annealing provides a new platform towards the exploitation of their topological properties., Comment: 21 pages, 4 figures, Supplementary information

Published
2017

5. Strain-gradient-induced magnetic anisotropy in straight-stripe mixed-phase bismuth ferrites: An insight into flexomagnetic phenomenon

Author

Lee, Jin Hong, Kim, Kwang-Eun, Jang, Byung-Kweon, Ünal, Ahmet A., Valencia, Sergio, Kronast, Florian, Ko, Kyung-Tae, Kowarik, Stefan, Seidel, Jan, and Yang, Chan-Ho

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Abstract

Implementation of antiferromagnetic compounds as active elements in spintronics has been hindered by their insensitive nature against external perturbations which causes difficulties in switching among different antiferromagnetic spin configurations. Electrically-controllable strain gradient can become a key parameter to tune the antiferromagnetic states of multiferroic materials. We have discovered a correlation between an electrically-written straight-stripe mixed-phase boundary and an in-plane antiferromagnetic spin axis in highly-elongated La-5%-doped BiFeO$_{3}$ thin films by performing polarization-dependent photoemission electron microscopy in conjunction with cluster model calculations. Model Hamiltonian calculation for the single-ion anisotropy including the spin-orbit interaction has been performed to figure out the physical origin of the link between the strain gradient present in the mixed phase area and its antiferromagnetic spin axis. Our findings enable estimation of the strain-gradient-induced magnetic anisotropy energy per Fe ion at around 5$\times$10$^{-12}$ eV m, and provide a new pathway towards an electric-field-induced 90$^{\circ}$ rotation of antiferromagnetic spin axis at room temperature by flexomagnetism., Comment: 32 pages, 5 figures

Published
2017
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9. Realization of giant magnetoelectricity in helimagnets

Author

Chun, Sae Hwan, Chai, Yi Sheng, Oh, Yoon Seok, Jaiswal-Nagar, Deepshikha, Haam, So Young, Kim, Ingyu, Lee, Bumsung, Nam, Dong Hak, Ko, Kyung-Tae, Park, Jae-Hoon, Chung, Jae-Ho, and Kim, Kee Hoon

Subjects
Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons
Abstract

We show that low field magnetoelectric (ME) properties of helimagnets Ba0.5Sr1.5Zn2(Fe1-xAlx)12O22 can be efficiently tailored by Al-substitution level. As x increases, the critical magnetic field for switching electric polarization is systematically reduced from ~1 T down to ~1 mT, and the ME susceptibility is greatly enhanced to reach a giant value of 2.0 x 10^4 ps/m at an optimum x = 0.08. We find that control of nontrivial orbital moment in the octahedral Fe sites through the Al-substitution is crucial for fine tuning of magnetic anisotropy and obtaining the conspicuously improved ME characteristics.

Published
2010
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12. Tunable Magnetism and Morphology of Ferromagnetic Nanocups in Perovskite Ferroelectric Films via Co Exsolution of Transition Metals

Author

An, Hyunji, primary, Kim, Jeong-Kyu, additional, Jung, Soon-Gil, additional, Kim, Sangmo, additional, Na, Kyeongho, additional, Yang, Jiwoong, additional, Song, Jaesun, additional, Park, Tuson, additional, Bark, Chung Wung, additional, Kim, Sooran, additional, Ko, Kyung-Tae, additional, Kim, Bongjae, additional, and Lee, Sanghan, additional

Published
2022
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16. Orbital Order Melting at Reduced Dimensions

Author

Kim, Yong-Jin, primary, Lee, Changhoon, additional, Park, Heung-Sik, additional, Yeo, Youngki, additional, Safarina, Giovanni Annur, additional, Le, Duc Duy, additional, Kim, Jeong-Gyu, additional, Bang, Daehyeon, additional, Cho, Byeong-Gwan, additional, Park, Jae-Hoon, additional, Ko, Kyung-Tae, additional, Koo, Tae Yeong, additional, Shim, Ji Hoon, additional, and Yang, Chan-Ho, additional

Published
2022
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19. Role Of Orbital Bond and Local Magnetism In Fe3GeTe2 and Fe4GeTe2: Implication For Ultrathin Nano Devices.

Author

Kim, Seong-Rae, Park, In Kee, Yoo, Jong-Gyu, Seo, Junho, Kim, Jeong-Gyu, Park, Jae-Hoon, Kim, Jun Sung, Kim, Kyoo, Lee, Geunsik, and Ko, Kyung-Tae

Abstract

We investigated the role of the bonding environment and Coulomb screening in the van der Waals (vdW) metallic ferromagnets Fe3GeTe2 (FGT3) and Fe4GeTe2 (FGT4). The electronic origins of the contrasting magnetic anisotropy of FGT3 and FGT4 were examined using X-ray absorption spectroscopy (XAS) and ab initio calculations. We found that the orbital magnetic moment of FGT4 (0.050 μB/Fe) is smaller than that of FGT3 (0.11 μB/Fe). Here, the difference in Fe dumbbell structure gives rise to the more (less) localized d3z2–r2 states in FGT3-(FGT4), and an effective orbital level splitting of t2g manifolds results in the large magnetocrystalline anisotropy in FGT3. The XAS measurements and the calculations additionally show that the Coulomb interaction is more effectively screened in FGT4 than in FGT3. The following theoretical analyses show that the screened Coulomb interaction becomes a key parameter to determine the magnetic anisotropy energy, especially in the thickness dependence. Finally, we discuss that the recent experimental demonstrations can be understood upon the effect of the bonding environment. Our investigation reveals essential electronic degrees of freedom to control the magnetism of the vdW ferromagnet for ultrathin nano devices. [ABSTRACT FROM AUTHOR]

Published
2022
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23. High‐Voltage‐Driven Surface Structuring and Electrochemical Stabilization of Ni‐Rich Layered Cathode Materials for Li Rechargeable Batteries

Author

Song, Seok Hyun, primary, Cho, Moses, additional, Park, Inchul, additional, Yoo, Jong‐Gyu, additional, Ko, Kyung‐Tae, additional, Hong, Jihyun, additional, Kim, Jongsoon, additional, Jung, Sung‐Kyun, additional, Avdeev, Maxim, additional, Ji, Sungdae, additional, Lee, Seongsu, additional, Bang, Joona, additional, and Kim, Hyungsub, additional

Published
2020
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24. Development and validation of a symptom assessment tool for postmicturition dribble: A prospective, multicenter, observational study in Korea

Author

Jeong, Hyun Cheol, primary, Ko, Kyung Tae, additional, Yang, Dae Yul, additional, Lee, Won Ki, additional, Lee, Sang Kon, additional, Cho, Sung Tae, additional, Oh, Cheol Young, additional, Cho, Jin Seon, additional, Kim, Jong Keun, additional, Han, Jun Hyun, additional, Choo, Min Soo, additional, and Lee, Seong Ho, additional

Published
2019
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25. Experimental realization of strain-induced room-temperature ferroelectricity in SrMnO3 films via selective oxygen annealing.

Author

An, Hyunji, Choi, Young-Gyun, Jo, Yong-Ryun, Hong, Hyo Jin, Kim, Jeong-Kyu, Kwon, Owoong, Kim, Sangmo, Son, Myungwoo, Yang, Jiwoong, Park, Jun-Cheol, Choi, Hojoong, Lee, Jongmin, Song, Jaesun, Ham, Moon-Ho, Ryu, Sangwoo, Kim, Yunseok, Bark, Chung Wung, Ko, Kyung-Tae, Kim, Bong-Joong, and Lee, Sanghan

Subjects
RUTHENIUM oxides, STRONTIUM compounds, THIN films, STRONTIUM oxide, FERROELECTRICITY, PERMITTIVITY
Abstract

Antiferromagnetic-paraelectric SrMnO3 (SMO) has aroused interest because of the theoretical strong coupling between the ferroelectric and ferromagnetic states with increasing epitaxial strain. In strained SMO films, the <110> polarized state and polar distortions have been observed, although high leakage currents and air degradation have limited their experimental verification. We herein provide a conclusive demonstration of room-temperature ferroelectricity and a high dielectric constant (εr = 138.1) in tensile-strained SMO by securing samples with insulating properties and clean surfaces using selective oxygen annealing. Furthermore, a paraelectricity and low dielectric constant (εr = 6.7) in the strain-relaxed SMO film have been identified as properties of the bulk SMO, which directly proves that the ferroelectricity of the tensile-strained SMO film is due to strain-induced polarization. We believe that these findings not only provide a cornerstone for exploring the physical properties of multiferroic SMO but also inspire new directions for single-phase multiferroics. Strain engineering: oxygen locks in room-temperature ferroelectricity Thin cracks and other defects which appear in multifunctional next-generation memory materials can be suppressed through a new synthetic technique. Compounds such as strontium manganese oxide (SrMnO3) transform from insulators into electrically and magnetically active materials when fabricated into thin films that strain the crystal's natural atom-atom separations. Sanghan Lee from the Gwangju Institute of Science and Technology, South Korea, and colleagues now report the first example of room-temperature electrical activity in strained SrMnO3 thin films. The team achieved this result by capping SrMnO3 with a layer of strontium ruthenium oxide (SrRuO3), and then annealing their new material in an oxygen-rich atmosphere. The team showed that the upper capping layer maintained the strained structure while also permitting oxygen to incorporate into the lower SrMnO3 film to eliminate vacancy defects. We provide a conclusive demonstration of strain-induced room-temperature ferroelectricity in SrMnO3 thin films by securing samples with insulating properties and clean surfaces using selective oxygen annealing. These findings will not only provide a cornerstone for exploring the physical properties of multiferroic SrMnO3 but will also inspire new directions for single-phase multiferroics. [ABSTRACT FROM AUTHOR]

Published
2021
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28. First Observation of Ferroelectricity in ∼1 nm Ultrathin Semiconducting BaTiO3 Films

Author

Lee, Seung Ran, primary, Baasandorj, Lkhagvasuren, additional, Chang, Jung Won, additional, Hwang, In Woong, additional, Kim, Jeong Rae, additional, Kim, Jeong-Gyu, additional, Ko, Kyung-Tae, additional, Shim, Seung Bo, additional, Choi, Min Woo, additional, You, Mujin, additional, Yang, Chan-Ho, additional, Kim, Jinhee, additional, and Song, Jonghyun, additional

Published
2019
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36. Electric-field-induced spin disorder-to-order transition near a multiferroic triple phase point

Author

Jang, Byung-Kweon, primary, Lee, Jin Hong, additional, Chu, Kanghyun, additional, Sharma, Pankaj, additional, Kim, Gi-Yeop, additional, Ko, Kyung-Tae, additional, Kim, Kwang-Eun, additional, Kim, Yong-Jin, additional, Kang, Kyungrok, additional, Jang, Han-Byul, additional, Jang, Hoyoung, additional, Jung, Min Hwa, additional, Song, Kyung, additional, Koo, Tae Yeong, additional, Choi, Si-Young, additional, Seidel, Jan, additional, Jeong, Yoon Hee, additional, Ohldag, Hendrik, additional, Lee, Jun-Sik, additional, and Yang, Chan-Ho, additional

Published
2016
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37. AB143. Relationship between post-voided dribbling & erectile dysfunction in men with lower urinary tract symptoms

Author

Yang, Dae Yul, Lee, Won Ki, Lee, Sang Kon, Lee, Seong Ho, Ko, Kyung Tae, Kim, Sung Yong, Kim, Ha Young, and Yang, Sang Kuk

Subjects
Erectile dysfunction, lower urinary tract symptoms, urologic and male genital diseases, Moderated Poster Presentation, post-voided dribbling (PVD)
Abstract

Objective Post-voided dribbling (PVD) in men is the symptom of experiencing involuntary loss of urine immediately after a person has finished passing urine, usually after leaving the toilet which distinguished from terminal dribbling. Researches on the PVD are very limited because no proper tool to evaluate PVD even though many patients with benign prostate hyperplasia (BPH) complained the PVD clinically. This study is to assess the correlation between PVD & ED in men with LUTS. Methods From October 2014 to February 2015, one hundred twelve patients were enrolled. All patients were more than 40 years. Patients filled in international prostate symptom score (IPSS) and Hayllm PMD questionnaire (HPMDQ) that was made by authors. Prostate size via TRUS, PSA, uroflowmetry including Qmax & PVR, IPSS, IIEF-5 were checked. Results Patients were classified as ED and non ED groups. Mean age were 65.2 (ED 62.8, non ED 63.8), mean prostate size 40.1 mL (ED 38.5 mL, non ED 38.8 mL), mean IPSS 13.9 (ED 11.6, non ED 14.4). Average HPVDQ score for non ED and group were 0.6, 1.3 respectively (P

Published
2015

38. Enhanced Oxygen Evolution Electrocatalysis in Strained A-Site Cation Deficient LaNiO3Perovskite Thin Films

Author

Choi, Min-Ju, Kim, Taemin Ludvic, Kim, Jeong Kyu, Lee, Tae Hyung, Lee, Sol A., Kim, Changyeon, Hong, Kootak, Bark, Chung Wung, Ko, Kyung-Tae, and Jang, Ho Won

Abstract

As the BO6octahedral structure in perovskite oxide is strongly linked with electronic behavior, it is actively studied for various fields such as metal–insulator transition, superconductivity, and so on. However, the research about the relationship between water-splitting activity and BO6structure is largely lacking. Here, we report the oxygen evolution reaction (OER) of LaNiO3(LNO) by changing the NiO6structure using compositional change and strain. The 5 atom % La deficiency in LNO resulted in an increase of the Ni—O—Ni bond angle and an expansion of bandwidth, enhancing the charge transfer ability. In-plane compressive strain derives the higher dz2orbital occupancy, leading to suitable metal–oxygen bond strength for OER. Because of the synergistic effect of A-site deficiency and compressive strain, the overpotential (η) of compressively strained L0.95NO film is reduced to 130 mV at j= 30 μA/cm2compared with nonstrained LNO (η = 280 mV), indicating a significant enhancement in OER.

Published
2020
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43. Electric-field-induced spin disorder-to-order transition near a multiferroic triple phase point

Author

Jang, Byung-Kweon, Lee, Jin Hong, Chu, Kanghyun, Sharma, Pankaj, Kim, Gi-Yeop, Ko, Kyung-Tae, Kim, Kwang-Eun, Kim, Yong-Jin, Kang, Kyungrok, Jang, Han-Byul, Jang, Hoyoung, Jung, Min Hwa, Song, Kyung, Koo, Tae Yeong, Choi, Si-Young, Seidel, Jan, Jeong, Yoon Hee, Ohldag, Hendrik, Lee, Jun-Sik, and Yang, Chan-Ho

Abstract

The emergence of a triple phase point in a two-dimensional parameter space (such as pressure and temperature) can offer unforeseen opportunities for the coupling of two seemingly independent order parameters. On the basis of this, we demonstrate the electric control of magnetic order by manipulating chemical pressure: lanthanum substitution in the antiferromagnetic ferroelectric BiFeO3. Our demonstration relies on the finding that a multiferroic triple phase point of a single spin-disordered phase and two spin-ordered phases emerges near room temperature in Bi0.9La0.1FeO3ferroelectric thin films. By using spatially resolved X-ray absorption spectroscopy, we provide direct evidence that the electric poling of a particular region of the compound near the triple phase point results in an antiferromagnetic phase while adjacent unpoled regions remain magnetically disordered, opening a promising avenue for magnetoelectric applications at room temperature.

Published
2017
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44. Concurrent transition of ferroelectric and magnetic ordering near room temperature

Author

Ko, Kyung-Tae, primary, Jung, Min Hwa, additional, He, Qing, additional, Lee, Jin Hong, additional, Woo, Chang Su, additional, Chu, Kanghyun, additional, Seidel, Jan, additional, Jeon, Byung-Gu, additional, Oh, Yoon Seok, additional, Kim, Kee Hoon, additional, Liang, Wen-I, additional, Chen, Hsiang-Jung, additional, Chu, Ying-Hao, additional, Jeong, Yoon Hee, additional, Ramesh, Ramamoorthy, additional, Park, Jae-Hoon, additional, and Yang, Chan-Ho, additional

Published
2011
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45. Publisher’s Note: Realization of Giant Magnetoelectricity in Helimagnets [Phys. Rev. Lett.104, 037204 (2010)]

Author

Chun, Sae Hwan, primary, Chai, Yi Sheng, additional, Oh, Yoon Seok, additional, Jaiswal-Nagar, Deepshikha, additional, Haam, So Young, additional, Kim, Ingyu, additional, Lee, Bumsung, additional, Nam, Dong Hak, additional, Ko, Kyung-Tae, additional, Park, Jae-Hoon, additional, Chung, Jae-Ho, additional, and Kim, Kee Hoon, additional

Published
2010
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46. Realization of Giant Magnetoelectricity in Helimagnets

Author

Chun, Sae Hwan, primary, Chai, Yi Sheng, additional, Oh, Yoon Seok, additional, Jaiswal-Nagar, Deepshikha, additional, Haam, So Young, additional, Kim, Ingyu, additional, Lee, Bumsung, additional, Nam, Dong Hak, additional, Ko, Kyung-Tae, additional, Park, Jae-Hoon, additional, Chung, Jae-Ho, additional, and Kim, Kee Hoon, additional

Published
2010
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47. Giant Zeeman splitting in nucleation-controlled doped CdSe:Mn2+ quantum nanoribbons

Author

Yu, Jung Ho, primary, Liu, Xinyu, additional, Kweon, Kyoung Eun, additional, Joo, Jin, additional, Park, Jiwon, additional, Ko, Kyung-Tae, additional, Lee, Dong Won, additional, Shen, Shaoping, additional, Tivakornsasithorn, Kritsanu, additional, Son, Jae Sung, additional, Park, Jae-Hoon, additional, Kim, Young-Woon, additional, Hwang, Gyeong S., additional, Dobrowolska, Margaret, additional, Furdyna, Jacek K., additional, and Hyeon, Taeghwan, additional

Published
2009
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