107 results on '"Myung Joon Han"'
Search Results
2. Magnetic Force Response Theory
- Author
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Do-Hoon Kiem, Hyeong-Jun Lee, and Myung-Joon Han
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- 2022
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Catalog
3. Strain engineering and the hidden role of magnetism in monolayer VTe2
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Myung Joon Han, Do Hoon Kiem, Min Yong Jeong, and Hongkee Yoon
- Subjects
General Materials Science - Abstract
‘Hidden’ antiferromagnetism is shown to be the key to stabilize the observed ground state and to clarify the controversial issues in this material. This finding also provides a way to manipulate the material properties through strain. more...
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- 2022
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4. Wearable anti-temperature interference strain sensor with metal nanoparticle thin film and hybrid ligand exchange
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Young Kyun Choi, Taesung Park, Dong Hyun David Lee, Junhyuk Ahn, Yong Hwan Kim, Sanghyun Jeon, Myung Joon Han, and Soong Ju Oh
- Subjects
General Materials Science - Abstract
Anti-interference characteristics, whereby undesirable signal interference is minimized, are required for multifunctional sensor platforms. In this study, an anti-temperature-interference resistive-type strain sensor, which does not respond to temperature but only to strain, is designed. Anti-interference properties were achieved by modulating the temperature coefficient of resistance (TCR) of metal nanoparticles (NPs) through hybrid chemical treatment with organic and halide ligands that induce negative and positive TCRs, respectively. Consequently, a very low TCR of 1.9 × 10 more...
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- 2022
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5. Epitaxially strained ultrathin LaNiO$_3$/LaAlO$_3$ and LaNiO$_3$/SrTiO$_3$ superlattices: a density functional theory + $U$ study
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Heung-Sik Kim, Sang Hyeon Park, and Myung Joon Han
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,General Physics and Astronomy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Materials Science - Abstract
By employing first-principles electronic structure calculations we investigate nickelate superlattices [LaNiO$_3$]$_1$/[LaAlO$_3$]$_1$ and [LaNiO$_3$]$_1$/[SrTiO$_3$]$_1$ with (001) orientation under epitaxial tensile strain. Within density functional theory augmented by mean-field treatement of on-site electronic correlations, the ground states show remarkable dependence on the correlation strength and the strain. In the weakly and intermediately correlated regimes with small epitaxial strain, the charge-disproportionated insulating states with antiferromagneitc order is favored over the other orbital and spin ordered phases. On the other hand, in the strongly correlated regime or under the large tensile strain, ferromagnetic spin states with Jahn-Teller orbital order become most stable. The effect from polar interfaces in LaNiO$_3$]$_1$/[SrTiO$_3$]$_1$ is found to be noticeable in our single-layered geometry. Detailed discussion is presented in comparison with previous experimental and theoretical studies., Comment: 9 pages, 8 figures more...
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- 2023
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6. Fe3GeTe2: a site-differentiated Hund metal
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Taek Jung Kim, Siheon Ryee, and Myung Joon Han
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Mechanics of Materials ,Modeling and Simulation ,General Materials Science ,Computer Science Applications - Abstract
Magnetism in two-dimensional (2D) van der Waals (vdW) materials has lately attracted considerable attention from the point of view of both fundamental science and device applications. Obviously, establishing a detailed and solid understanding of their magnetism is the key first step toward various applications. Although Fe3GeTe2 is a representative ferromagnetic (FM) metal in this family, many aspects of its magnetic and electronic behaviors still remain elusive. Here, we report our new finding that Fe3GeTe2 is a special type of correlated metal known as “Hund metal”. Furthermore, we demonstrate that Hund metallicity in this material is quite unique by exhibiting remarkable site dependence of Hund correlation strength, hereby dubbed “site-differentiated Hund metal”. Within this new picture, many of the previous experiments can be clearly understood, including the ones that were seemingly contradictory to one another. more...
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- 2022
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7. Metallization of Quantum Material GaTa4Se8 at High Pressure
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Qingyang Hu, Bijuan Chen, Shuai Zhang, Takeshi Nakagawa, Xinguo Hong, Hongshan Deng, Hai-Qing Lin, Hongming Weng, Ji-Chang Ren, Xia Yin, Dong Wang, Jianbo Zhang, Yang Ding, Jun Chang, Ho-kwang Mao, Min Yong Jeong, Raimundas Sereika, Hong Xiao, and Myung Joon Han more...
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Superconductivity ,Materials science ,Condensed matter physics ,Band gap ,Magnetism ,Mott insulator ,02 engineering and technology ,Quantum phases ,021001 nanoscience & nanotechnology ,01 natural sciences ,Phase (matter) ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology ,Quantum ,Phase diagram - Abstract
Pressure is a unique thermodynamic variable to explore the phase competitions and novel phases inaccessible at ambient conditions. The resistive switching material GaTa4Se8 displays several quantum phases under pressure, such as a Jeff = 3/2 Mott insulator, a correlated quantum magnetic metal, and d-wave topological superconductivity, which has recently drawn considerable interest. Using high-pressure Raman spectroscopy, X-ray diffraction, extended X-ray absorption, transport measurements, and theoretical calculations, we reveal a complex phase diagram for GaTa4Se8 at pressures exceeding 50 GPa. In this previously unattained pressure regime, GaTa4Se8 ranges from a Mott insulator to a metallic phase and exhibits superconducting phases. In contrast to previous studies, we unveil a hidden correlation between the structural distortion and band gap prior to the insulator-to-metal transition, and the metallic phase shows superconductivity with structural and magnetic properties that are distinctive from the lower-pressure phase. These discoveries highlight that GaTa4Se8 is a unique material to probe novel quantum phases from a structural, metallicity, magnetism, and superconductivity perspective. more...
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- 2021
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8. Low thermal conductivity of SrTiO 3 −LaTiO 3 and SrTiO 3 −SrNbO 3 thermoelectric oxide solid solutions
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Myung-Chul Jung, Kenyu Sugo, Hai Jun Cho, Woosuck Shin, Yao Hua Zhuang, Myung Joon Han, Bin Feng, Yuqiao Zhang, Yu-Miin Sheu, Sungmin Woo, Masashi Mikami, Woo Seok Choi, Yuichi Ikuhara, and Hiromichi Ohta more...
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chemistry.chemical_compound ,Materials science ,Thermal conductivity ,Condensed matter physics ,chemistry ,Thermoelectric oxide ,Materials Chemistry ,Ceramics and Composites ,Lattice distortion ,Strontium titanate ,Thermoelectric materials ,Polaron ,Solid solution - Published
- 2021
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9. Strain engineering and the hidden role of magnetism in monolayer VTe
- Author
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Do Hoon, Kiem, Min Yong, Jeong, Hongkee, Yoon, and Myung Joon, Han
- Abstract
Two-dimensional transition-metal dichalcogenides have attracted great attention recently. Motivated by a recent study of crystalline bulk VTe
- Published
- 2022
10. Crucial role of out-of-plane Sb p orbitals in Van Hove singularity formation and electronic correlations in the superconducting kagome metal CsV3Sb5
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Min Yong Jeong, Hyeok-Jun Yang, Hee Seung Kim, Yong Baek Kim, SungBin Lee, and Myung Joon Han
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- 2022
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11. Switching interlayer magnetic order in bilayer CrI3 by stacking reversal
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Hongkee Yoon, Myung Joon Han, Xiangru Kong, and Liangbo Liang
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Materials science ,Ferromagnetism ,Condensed matter physics ,Magnetism ,Bilayer ,Magnet ,Stacking ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Ground state ,Magnetic field - Abstract
CrI3, a hot two-dimensional (2D) magnet, exhibits complex magnetism depending on the number of layers and interlayer stacking patterns. For bilayer CrI3, the interlayer magnetism can be tuned between ferromagnetic (FM) and antiferromagnetic (AFM) order by manipulating the stacking order. However, the stacking is mostly modified through translation between the layers, while the effect of rotation between the layers on the interlayer magnetic order has not yet been fully investigated. Here, we considered three energetically stable stacking patterns R, C2/m and AA in bilayer CrI3, and their reversed counterparts R-r, C2/m-r and AA-r through rotating one layer by 180° with respect to the other layer. Our first-principles calculations suggest that the interlayer magnetic ground state can be switched from AFM to FM (or FM to AFM) by reversing the stacking pattern. A detailed microscopic analysis was carried out by magnetic force theory calculations on C2/m stacking which favors AFM and C2/m-r stacking which favors FM. The interlayer magnetic interactions and the origin of the magnetic order change were revealed through specific orbital analysis. Our work demonstrates that stacking rotation can also tune the interlayer magnetism of CrI3 and provides insight into its interlayer magnetic properties at the microscopic level. more...
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- 2021
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12. Pressure-induced topological superconductivity in the spin–orbit Mott insulator GaTa4Se8
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SungBin Lee, Archana Mishra, Moon Jip Park, Min Yong Jeong, GiBaik Sim, and Myung Joon Han
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Josephson effect ,02 engineering and technology ,Topology ,lcsh:Atomic physics. Constitution and properties of matter ,01 natural sciences ,law.invention ,law ,Condensed Matter::Superconductivity ,0103 physical sciences ,lcsh:TA401-492 ,010306 general physics ,Quantum tunnelling ,Superconductivity ,Physics ,Mott insulator ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,lcsh:QC170-197 ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,lcsh:Materials of engineering and construction. Mechanics of materials ,Scanning tunneling microscope ,Cooper pair ,0210 nano-technology ,Random phase approximation - Abstract
Lacunar spinel GaTa4Se8 is a unique example of spin–orbit coupled Mott insulator described by molecular jeff = 3/2 states. It becomes superconducting at Tc = 5.8 K under pressure without doping. In this work, we show, this pressure-induced superconductivity is a realization of a new type topological phase characterized by spin-2 Cooper pairs. Starting from first-principles density functional calculations and random phase approximation, we construct the microscopic model and perform the detailed analysis. Applying pressure is found to trigger the virtual interband tunneling processes assisted by strong Hund coupling, thereby stabilizing a particular d-wave quintet channel. Furthermore, we show that its Bogoliubov quasiparticles and their surface states exhibit novel topological nature. To verify our theory, we propose unique experimental signatures that can be measured by Josephson junction transport and scanning tunneling microscope. Our findings open up new directions searching for exotic superconductivity in spin–orbit coupled materials. more...
- Published
- 2020
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13. Strain-controlled evolution of electronic structure indicating topological phase transition in the quasi-one-dimensional superconductor TaSe3
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Jounghoon Hyun, Min Yong Jeong, Myung-Chul Jung, Yeonghoon Lee, Younsik Kim, Saegyeol Jung, Byeongjun Seok, Junseong Song, Chan-young Lim, Jaehun Cha, Gyubin Lee, Yeojin An, Makoto Hashimoto, Donghui Lu, Jonathan D. Denlinger, Sung Wng Kim, Changyoung Kim, Myung Joon Han, Sunghun Kim, and Yeongkwan Kim more...
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- 2022
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14. First principles investigation of screened Coulomb interaction and electronic structure of low-temperature phase TaS2
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Taek Jung Kim, Min Yong Jeong, and Myung Joon Han
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Multidisciplinary - Published
- 2023
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15. Erratum: Induced magnetic two-dimensionality by hole doping in the superconducting infinite-layer nickelate Nd1−xSrxNiO2 [Phys. Rev. B 101 , 064513 (2020)]
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Siheon Ryee, Hongkee Yoon, Taek Jung Kim, Min Yong Jeong, and Myung Joon Han
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- 2022
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16. Field-tunable toroidal moment and anomalous Hall effect in noncollinear antiferromagnetic Weyl semimetal Co1/3TaS2
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Pyeongjae Park, Yoon-Gu Kang, Junghyun Kim, Ki Hoon Lee, Han-Jin Noh, Myung Joon Han, and Je-Geun Park
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Condensed Matter::Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Abstract
Combining magnetism with band topology provides various novel phases that are otherwise impossible. Among several cases, noncollinear metallic antiferromagnets can reveal particularly rich topological physics due to their diverse magnetic ground states. However, there are only a few experimental studies due to the lack of suitable materials, especially with triangular lattice antiferromagnets. Here, we report that metallic triangular antiferromagnet Co1/3TaS2 exhibits a substantial anomalous Hall effect (AHE) related to its noncollinear magnetic order. Our first-principles calculations found that hourglass Weyl fermions from the non-symmorphic symmetry trigger AHE. We further show that AHE in Co1/3TaS2 can be characterized by the toroidal moment, a vortex-like multipole component that arises from a combination of chiral lattice and geometrical frustration. Finally, the unusual field-tunability of the toroidal moment puts Co1/3TaS2 as a rare example of a noncollinear metallic antiferromagnet filled with interesting magnetic and topological properties., Comment: 20 pages, 4 figures, Accepted for publication in npj Quantum Materials more...
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- 2022
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17. Intertwining orbital current order and superconductivity in Kagome metal
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Hyeok-Jun Yang, Hee Seung Kim, Min Yong Jeong, Yong Baek Kim, Myung Joon Han, and SungBin Lee
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Superconductivity (cond-mat.supr-con) ,Nuclear and High Energy Physics ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Superconductivity ,Condensed Matter::Superconductivity ,FOS: Physical sciences ,Statistical and Nonlinear Physics ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics - Abstract
The nature of superconductivity in newly discovered Kagome materials, $\text{AV}_3\text{Sb}_5$ (A=K, Rb, Cs), has been a subject of intense debate. Recent experiments suggest the presence of orbital current order on top of the charge density wave (CDW) and superconductivity. Since the orbital current order breaks time-reversal symmetry, it may fundamentally affect possible superconducting states. In this work, we investigate the mutual influence between the orbital current order and superconductivity in Kagome metal with characteristic van Hove singularity (vHS). By explicitly deriving the Landau-Ginzburg theory, we classify possible orbital current order and superconductivity. It turns out that distinct unconventional superconductivities are expected, depending on the orbital current ordering types. Thus, this information can be used to infer the superconducting order parameter when the orbital current order is identified and vice versa. We also discuss possible experiments that may distinguish such superconducting states coexisting with the orbital current order., Comment: 22 pages, 8 figures more...
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- 2022
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18. Ab initio prediction of nontrivial topological band and superconductivity in stable metallic Si allotropes at ambient pressure
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In-Ho Lee, Myung Joon Han, Kee-Joo Chang, and Yoon-Gu Kang
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Superconductivity ,Materials science ,Physics and Astronomy (miscellaneous) ,Silicon ,business.industry ,chemistry.chemical_element ,Electronic structure ,Crystal structure ,Topology ,Metal ,Semiconductor ,chemistry ,Condensed Matter::Superconductivity ,visual_art ,visual_art.visual_art_medium ,General Materials Science ,business ,Topology (chemistry) ,Ambient pressure - Abstract
Silicon is a semiconductor and widely used as the key element for modern electronic devices. Various metallic superconducting phases have been reported, but most retain their crystal structure at high pressures. Thus, it remains a challenge to search for potential superconducting Si allotropes. In this article, the authors propose novel metallic Si allotropes that meet the conditions for dynamic, mechanical, and thermal stability at ambient pressure through machine learning and first-principles electronic structure calculations. The new allotropes are superconductors and even exhibit a nontrivial band topology, providing a promising platform for realizing a topological superconducting state in all-Si systems. more...
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- 2021
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19. Switching interlayer magnetic order in bilayer CrI
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Xiangru, Kong, Hongkee, Yoon, Myung Joon, Han, and Liangbo, Liang
- Abstract
CrI
- Published
- 2021
20. Origin of ferromagnetism and the effect of doping on Fe3GeTe2
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Heung-Sik Kim, Siheon Ryee, Min Yong Jeong, Myung Joon Han, Hongkee Yoon, and Seung Woo Jang
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Materials science ,Condensed matter physics ,Doping ,Ab initio ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic field ,Condensed Matter::Materials Science ,Ferromagnetism ,Phase (matter) ,0103 physical sciences ,Moment (physics) ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Density functional theory ,010306 general physics ,0210 nano-technology - Abstract
Recent experimental findings of two dimensional ferromagnetism in Fe3GeTe2, whose critical temperature can reach room temperature by gating, has attracted great research interest. Here we performed elaborate ab initio studies using density functional theory, dynamical mean-field theory and magnetic force response theory. In contrast to the conventional wisdom, it is unambiguously shown that Fe3GeTe2 is not ferromagnetic but is antiferromagnetic, carrying zero net moment in its stoichiometric phase. Fe defect and hole doping are the keys to make this material ferromagnetic as supported by previously disregarded experiments. Furthermore, we found that electron doping also induces the antiferro- to ferro-magnetic transition. It is crucial to understand the notable recent experiments on gate-controlled ferromagnetism. Our results not only reveal the origin of ferromagnetism of this material but also show how it can be manipulated with defects and doping. more...
- Published
- 2020
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21. Post-synthetic oriented attachment of CsPbBr3 perovskite nanocrystal building blocks: from first principle calculation to experimental demonstration of size and dimensionality (0D/1D/2D)
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Jongchul Jeon, Junsung Bang, Myung Joon Han, Donggyu Kim, Soong Ju Oh, Taejong Paik, Ho Young Woo, Myung-Chul Jung, Ho Kun Woo, Junhyuk Ahn, Sanghyun Jeon, and Sang Yeop Lee
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Materials science ,Nanowire ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Solvent ,Nanocrystal ,Chemical physics ,Quantum dot ,Phase (matter) ,General Materials Science ,Density functional theory ,Thin film ,0210 nano-technology ,Perovskite (structure) - Abstract
Post-synthesis engineering methods that employ oriented attachment to precisely control the size and dimensionality (0D/1D/2D) of as-synthesized CsPbBr3 nanocrystals (NCs) are demonstrated. We investigated the chemical effects of the properties of polar solvents, including their immiscibility, polarity, and boiling point, on the surfaces of NCs, as well as their effect on the structural and optical properties of NCs. Appropriate exploitation of the solvent properties made it possible to use a polar solvent to mildly affect the NCs indirectly such that they discarded their ligands and became attached to proximal NCs without being destroyed. Based on our observations, we developed a method whereby a solution of the NCs in a non-polar solvent is mixed with a polar solvent to form an immiscible phase to induce epitaxial growth of CsPbBr3 NCs. The method enables the size of NCs to be easily regulated from 5 to 50 nm by controlling the engineering time. Taking advantage of the minimal effect of a mild solvent, we also developed a self-assembly method that operates at the liquid–air interface to systematically control the dimensionality. At this interface, the NCs self-assemble in the horizontal direction and grow into micron-sized, single-crystalline, defect-free nanowires (1D) and nanoplates (2D) via oriented attachment. Finally, we discuss the origin of the non-destructive oriented attachment phenomenon and the surface chemistry of a perovskite NC using density functional theory (DFT) simulations and a proposed model system. more...
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- 2020
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22. Designing High-Performance CdSe Nanocrystal Thin-Film Transistors Based on Solution Process of Simultaneous Ligand Exchange, Trap Passivation, and Doping
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Myung Joon Han, Donggyu Kim, Soong Ju Oh, Junhyuk Ahn, Woo Seok Lee, Ji Hyuk Choi, Sanghyun Jeon, Yoon-Gu Kang, Haneun Kim, and Ho Kun Woo
- Subjects
Materials science ,Passivation ,business.industry ,Ligand ,General Chemical Engineering ,Doping ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Nanocrystal ,Thin-film transistor ,Materials Chemistry ,Surface modification ,Optoelectronics ,Field-effect transistor ,0210 nano-technology ,business ,Solution process - Abstract
We report a simple, solution-based, and postsynthetic process for simultaneous ligand exchange, surface passivation, and doping of CdSe nanocrystals (NCs) for the design of high-performance field-e... more...
- Published
- 2019
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23. Metallization of Quantum Material GaTa
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Hongshan, Deng, Jianbo, Zhang, Min Yong, Jeong, Dong, Wang, Qingyang, Hu, Shuai, Zhang, Raimundas, Sereika, Takeshi, Nakagawa, Bijuan, Chen, Xia, Yin, Hong, Xiao, Xinguo, Hong, Jichang, Ren, Myung Joon, Han, Jun, Chang, Hongming, Weng, Yang, Ding, Hai-Qing, Lin, and Ho-Kwang, Mao more...
- Abstract
Pressure is a unique thermodynamic variable to explore the phase competitions and novel phases inaccessible at ambient conditions. The resistive switching material GaTa
- Published
- 2021
24. Hund Physics Landscape of Two-Orbital Systems
- Author
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Sangkook Choi, Myung Joon Han, and Siheon Ryee
- Subjects
Superconductivity ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Hubbard model ,Condensed matter physics ,Metallicity ,Mott insulator ,FOS: Physical sciences ,General Physics and Astronomy ,Coupling (probability) ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,Coulomb ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics - Abstract
Motivated by the recent discovery of superconductivity in infinite-layer nickelates ${\mathrm{RE}}_{1\ensuremath{-}\ensuremath{\delta}}{\mathrm{Sr}}_{\ensuremath{\delta}}{\mathrm{NiO}}_{2}$ ($\mathrm{RE}=\mathrm{Nd}$, Pr), we study the role of Hund coupling $J$ in a quarter-filled two-orbital Hubbard model, which has been on the periphery of the attention. A region of negative effective Coulomb interaction of this model is revealed to be differentiated from three- and five-orbital models in their typical Hund metal active fillings. We identify distinctive regimes including four different correlated metals, one of which stems from the proximity to a Mott insulator, while the other three, which we call ``intermediate'' metal, weak Hund metal, and valence-skipping metal, from the effect of $J$ being away from Mottness. Defining criteria characterizing these metals is suggested, establishing the existence of Hund metallicity in two-orbital systems. more...
- Published
- 2021
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25. Complete mapping of magnetic anisotropy for prototype Ising van der Waals FePS$_3$
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Younjung Jo, Je-Geun Park, Muhammad Nauman, Do Hoon Kiem, Myung Joon Han, Woun Kang, Sungmin Lee, and Suhan Son
- Subjects
Condensed Matter - Materials Science ,Materials science ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Mechanical Engineering ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Chemistry ,Condensed Matter Physics ,Magnetic anisotropy ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,Mechanics of Materials ,symbols ,General Materials Science ,Ising model ,van der Waals force - Abstract
Several Ising-type magnetic van der Waals (vdW) materials exhibit stable magnetic ground states. Despite these clear experimental demonstrations, a complete theoretical and microscopic understanding of their magnetic anisotropy is still lacking. In particular, the validity limit of identifying their one-dimensional (1-D) Ising nature has remained uninvestigated in a quantitative way. Here we performed the complete mapping of magnetic anisotropy for a prototypical Ising vdW magnet FePS$_3$ for the first time. Combining torque magnetometry measurements with their magnetostatic model analysis and the relativistic density functional total energy calculations, we successfully constructed the three-dimensional (3-D) mappings of the magnetic anisotropy in terms of magnetic torque and energy. The results not only quantitatively confirm that the easy axis is perpendicular to the $ab$ plane, but also reveal the anisotropies within the $ab$, $ac$, and $bc$ planes. Our approach can be applied to the detailed quantitative study of magnetism in vdW materials., Accepted in IOP 2D Materials more...
- Published
- 2021
26. Hund's physics and the magnetic ground state ofCrOX(X=Cl,Br)
- Author
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Juhyeok Lee, Yoon-Gu Kang, Do Hoon Kiem, Seung Woo Jang, Myung Joon Han, and Hongkee Yoon
- Subjects
Physics ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Order (ring theory) ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic field ,symbols.namesake ,0103 physical sciences ,Monolayer ,symbols ,Antiferromagnetism ,General Materials Science ,Density functional theory ,van der Waals force ,010306 general physics ,0210 nano-technology ,Ground state - Abstract
To understand the magnetic property of layered van der Waals materials $\mathrm{CrO}X$ $(X=\text{Cl,Br})$, we performed detailed first-principles calculations for both the bulk and monolayer. We found that the charge-only density functional theory combined with the explicit on-site interaction terms (so-called $\mathrm{cDFT}+U$) well reproduces the experimental magnetic ground state of bulk $\mathrm{CrO}X$, which is not the case for the use of spin-dependent density functional theory (so-called $\mathrm{sDFT}+U$). Unlike some of the previous studies, our results show that $\mathrm{CrO}X$ monolayers are antiferromagnetic as in the bulk. It is also consistent with our magnetic force linear response calculation of exchange couplings, ${J}_{\mathrm{ex}}$. The result of orbital-decomposed ${J}_{\mathrm{ex}}$ calculations shows that the Cr ${t}_{2g}\text{\ensuremath{-}}{t}_{2g}$ component contributes mainly to the antiferromagnetic order in both the bulk and monolayer. Our result and analysis show that taking the correct Hund's physics into account is of key importance in constructing the magnetic phase diagram and describing the electronic structure. more...
- Published
- 2021
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27. Highly Luminescent and Multifunctional Zero‐Dimensional Cesium Lanthanide Chloride (Cs 3 LnCl 6 ) Colloidal Nanocrystals
- Author
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Minji Lee, Dong Hyun David Lee, Seong Vin Hong, Ho Young Woo, Ji‐Yeon Chae, Da Won Lee, Myung Joon Han, and Taejong Paik
- Subjects
Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials - Published
- 2022
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28. Discovery of New Metallic and Superconducting Phase in GaTa4Se8 Under High Pressure
- Author
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Bijuan Chen, Yang Ding, Ho-kwang Mao, Xia Yin, Takeshi Nakagawa, Hongming Weng, Jianbo Zhang, Myung Joon Han, Dong Wang, Hongshan Deng, Raimundas Sereika, Jun Chang, Ji-Chang Ren, and Min Yong Jeong
- Subjects
Superconductivity ,Metal ,Materials science ,Condensed matter physics ,High pressure ,visual_art ,Phase (matter) ,visual_art.visual_art_medium ,Condensed Matter::Strongly Correlated Electrons - Abstract
Pressure is a unique thermodynamic variable to explore the phase competitions and novel phases inaccessible at ambient conditions. The resistive switching material GaTa4Se8 displays several quantum phases under pressure, such as Jeff = 3/2 Mott insulator, correlated quantum magnetic metal, and d-wave topological superconductivity, which has recently drawn mounting interest. Using high-pressure Raman, X-ray diffraction, extended X-ray absorption, and transport measurements, together with theoretical calculations, we reveal a remarkably rich phase diagram of this molecular magnetic Mott insulator at pressures up to ~ 68 GPa. In this previously unreached pressure regime, we find, GaTa4Se8 exhibits a new metallic phase whose structural and magnetic properties are clearly distinctive from the lower pressure one. Further, we identify a new superconducting phase in this high-pressure regime below Tc ~ 5.5K. Our discoveries highlight GaTa4Se8 as a unique playground in which novel quantum phases and orders coexist and compete with each other; ranges from Mott insulator to Fermi liquid and exhibits multiple metallic and superconducting states. more...
- Published
- 2020
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29. Origin of ferromagnetism and the effect of doping on Fe
- Author
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Seung Woo, Jang, Hongkee, Yoon, Min Yong, Jeong, Siheon, Ryee, Heung-Sik, Kim, and Myung Joon, Han
- Abstract
Recent experimental findings of two dimensional ferromagnetism in Fe3GeTe2, whose critical temperature can reach room temperature by gating, has attracted great research interest. Here we performed elaborate ab initio studies using density functional theory, dynamical mean-field theory and magnetic force response theory. In contrast to the conventional wisdom, it is unambiguously shown that Fe3GeTe2 is not ferromagnetic but is antiferromagnetic, carrying zero net moment in its stoichiometric phase. Fe defect and hole doping are the keys to make this material ferromagnetic as supported by previously disregarded experiments. Furthermore, we found that electron doping also induces the antiferro- to ferro-magnetic transition. It is crucial to understand the notable recent experiments on gate-controlled ferromagnetism. Our results not only reveal the origin of ferromagnetism of this material but also show how it can be manipulated with defects and doping. more...
- Published
- 2020
30. Post-synthetic oriented attachment of CsPbBr
- Author
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Sanghyun, Jeon, Myung-Chul, Jung, Junhyuk, Ahn, Ho Kun, Woo, Junsung, Bang, Donggyu, Kim, Sang Yeop, Lee, Ho Young, Woo, Jongchul, Jeon, Myung Joon, Han, Taejong, Paik, and Soong Ju, Oh
- Abstract
Post-synthesis engineering methods that employ oriented attachment to precisely control the size and dimensionality (0D/1D/2D) of as-synthesized CsPbBr
- Published
- 2020
31. Nonlocal Coulomb interaction and spin-freezing crossover as a route to valence-skipping charge order
- Author
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Myung Joon Han, Sangkook Choi, Siheon Ryee, and Patrick Semon
- Subjects
Spin states ,Population ,Crossover ,FOS: Physical sciences ,02 engineering and technology ,Electron ,lcsh:Atomic physics. Constitution and properties of matter ,01 natural sciences ,Instability ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,lcsh:TA401-492 ,Coulomb ,010306 general physics ,education ,Multiplet ,Physics ,education.field_of_study ,Valence (chemistry) ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,lcsh:QC170-197 ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Strongly Correlated Electrons ,lcsh:Materials of engineering and construction. Mechanics of materials ,0210 nano-technology - Abstract
Multiorbital systems away from global half-filling host intriguing physical properties promoted by Hund’s coupling. Despite increasing awareness of this regime dubbed Hund’s metal, effect of nonlocal interaction is still elusive. Here we study a three-orbital model with 1/3 filling (two electrons per site) including the intersite Coulomb interaction (V). Using the GW plus extended dynamical mean-field theory, the valence-skipping charge order transition is shown to be driven by V. Most interestingly, the instability to this transition is significantly enhanced in the spin-freezing crossover regime, thereby lowering the critical V to the formation of charge order. This behavior is found to be closely related to the population profile of the atomic multiplet states in the spin-freezing regime. In this regime, maximum spin states are dominant in each total charge subspace with substantial amount of one- and three-electron occupations, which leads to almost equal population of one- and the maximum spin three-electron state. Our finding unveils another feature of the Hund’s metal and has potential implications for the broad range of multiorbital systems as well as the recently discovered charge order in iron pnictides. more...
- Published
- 2020
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32. Electronic Structures of Group III–V Element Haeckelite Compounds: A Novel Family of Semiconductors, Dirac Semimetals, and Topological Insulators
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Mohammad Khazaei, Ahmad Ranjbar, Yoon‐Gu Kang, Yunye Liang, Rasoul Khaledialidusti, Soungmin Bae, Hannes Raebiger, Vei Wang, Myung Joon Han, Hiroshi Mizoguchi, Mohammad S. Bahramy, Thomas D. Kühne, Rodion V. Belosludov, Kaoru Ohno, and Hideo Hosono more...
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Biomaterials ,Electrochemistry ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2022
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33. Ligand Exchange and Impurity Doping in 2D CdSe Nanoplatelet Thin Films and Their Applications
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Manoj K. Sharma, Weon-kyu Koh, Yong Min Lee, Ashma Sharma, Soong Ju Oh, Myung Joon Han, Hilmi Volkan Demir, Woo Seok Lee, Sanghyun Jeon, Yoon-Gu Kang, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, LUMINOUS! Centre of Excellence for Semiconductor Lighting & Displays, and Demir, Hilmi Volkan more...
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Ligand exchange ,Materials science ,business.industry ,Ligand ,Nanoplatelets ,Doping ,Electronic, Optical and Magnetic Materials ,Field-effect transistors ,Physics [Science] ,Electrical and electronic engineering [Engineering] ,Optoelectronics ,Charge Transport ,Field-effect transistor ,Thin film ,Impurity doping ,business - Abstract
The effects of halide-ligand exchange and Cu and Ag doping are studied on structural, optical, and electrical properties of four monolayer CdSe nanoplatelet (NPL) and NPL thin films. Combinational study shows that NH4Cl-treatment on CdSe NPL and NPL thin films show tetragonal lattice distortion of NPL, side-to-side attachment between NPLs, bathochromic shift in absorption spectra, and complete quenching of band-edge and dopant-induced emissions. First-principle calculations reveal that Cl creates states below valence band maximum while Ag and Cu dopants create acceptor-like states, explaining the change of their optical property. Field-effect transistors are fabricated to investigate the effect of doping and reduced interplatelet distance on electrical properties of CdSe NPL thin films, demonstrating Cu and Ag dopants mitigate n-type character of CdSe NPL thin films. Temperature-dependent electrical characterization is conducted to further understand charge transport behavior depending on the existence of dopants. This work provides scientific information on the influence of surface chemistry and impurity doping on quantum confined semiconductors and new directions for the design of high-performance nanomaterial-based electronic and optoelectronic devices. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version The authors would like to acknowledge the financial support from Singapore National Research Foundation under the Program of NRF-NRFI2016-08, the Competitive Research Program NRF-CRP14-2014-03, and Singapore Ministry of Education Tier 1 grant (MOE-RG62/20). The authors acknowledge the financial support from National Science Foundation the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2019R1C1C1003319), Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science, ICT and Future Planning (NRF-2018M3D1A1059001), and Korea University Future Research Grant. H.V.D. also acknowledges support from TUBA. Y.G.K. and M.J.H. were supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2021R1A2C1009303). more...
- Published
- 2021
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34. N , N ‐Dimethylformamide‐Assisted Shape Evolution of Highly Uniform and Shape‐Pure Colloidal Copper Nanocrystals
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Taejong Paik, Ji Yeon Chae, Myung-Chul Jung, Da Won Lee, Jong Bae Kim, Myung Joon Han, Donguk Lee, Dong Hyun David Lee, Minji Lee, and Ho Young Woo
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Materials science ,chemistry.chemical_element ,Dimethylformamide ,Disproportionation ,General Chemistry ,Copper ,Biomaterials ,chemistry.chemical_compound ,Colloid ,Chemical engineering ,Nanocrystal ,chemistry ,Octahedron ,Bromide ,Nanoparticles ,General Materials Science ,Density functional theory ,Acetonitrile ,Oxidation-Reduction ,Biotechnology - Abstract
In this paper, the N,N-dimethylformamide (DMF)-assisted shape evolution of highly uniform and shape-pure copper nanocrystals (Cu NCs) is presented for the first time. Colloidal Cu NCs are synthesized via the disproportionation reaction of copper (I) bromide in the presence of a non-polar solvent mixture. It is observed that the shape of Cu NCs is systematically controlled by the addition of different amounts of DMF to the reaction mixture in high-temperature reaction conditions while maintaining a high size uniformity and shape purity. With increasing amount of DMF in the reaction mixture, the morphology of the Cu NCs change from a cube enclosed by six {100} facets, to a sphere with mixed surface facets, and finally, to an octahedron enclosed by eight {111} facets. The origin of this shape evolution is understood via first-principles density functional theory calculations, which allows the study of the change in the relative surface stability according to surface-coordinating adsorbates. Further, the shape-dependent plasmonic properties are systematically investigated with highly uniform and ligand-exchanged colloidal Cu NCs dispersed in acetonitrile. Finally, the facet-dependent electrocatalytic activities of the shape-controlled Cu NCs are investigated to reveal the activities of the highly uniform and shape-pure Cu NCs in the methanol oxidation reaction. more...
- Published
- 2021
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35. Van der Waals electride: Toward intrinsic two-dimensional ferromagnetism of spin-polarized anionic electrons
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Kyu Hyoung Lee, Sung Wng Kim, Chandani N. Nandadasa, Kang Se-Hwang, Joonho Bang, Kimoon Lee, Wei Li, Duhee Yoon, Dinesh Thapa, Seong-Gon Kim, Byung Il Yoo, Jin-Ho Choi, Myung Joon Han, and Hyun Yong Song more...
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Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Magnetism ,Electron ,Bohr magneton ,Condensed Matter::Materials Science ,symbols.namesake ,Paramagnetism ,chemistry.chemical_compound ,Ferromagnetism ,chemistry ,Physics::Atomic and Molecular Clusters ,symbols ,Electride ,Curie temperature ,General Materials Science ,van der Waals force ,Energy (miscellaneous) - Abstract
Discoveries of two-dimensional (2D) magnetism originated from confined atomic layers in van der Waals (vdW) crystals provide an interesting arena for elucidating its fundamentals and enrich magneto-electric and quantum properties. However, a material that exhibits intrinsic 2D magnetism of interstitial electrons occupying layered space, as a root system of magnetic vdW crystals, remains obscure. In this work, 2D ferromagnetic vdW electride, [RECl]2+·2e− (RE = Y and La) is reported with perfectly isolated ferromagnetic 2D blocks encompassing quasi-atomic electron layers. The ferromagnetism of the vdW electride with Curie temperature of 100 K originates from the spin-polarized quasi-atomic electrons with a substantial moment up to ∼0.91 Bohr magneton, which behave as magnetic elements in paramagnetic lattice framework. Invariable ferromagnetism at the monolayer limit strongly supports the 2D ferromagnetism of quasi-atomic electrons. These findings expand the variety of 2D magnetic crystals, providing a promising platform to study the emergent magnetism of low-dimensional electron phases. more...
- Published
- 2021
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36. First-principles Electronic Structure Calculations of Strongly Correlated Electron Systems: DFT+U and DFT+DMFT
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Myung Joon Han and Ji Hoon Shim
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Physics ,Strongly correlated material ,Electronic structure ,Molecular physics - Published
- 2017
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37. Induced magnetic two-dimensionality by hole doping in the superconducting infinite-layer nickelate Nd1−xSrxNiO2
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Min Yong Jeong, Siheon Ryee, Myung Joon Han, Hongkee Yoon, and Taek Jung Kim
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Superconductivity ,Physics ,Condensed matter physics ,Inverse ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic field ,Atomic orbital ,0103 physical sciences ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,Cuprate ,Local-density approximation ,010306 general physics ,0210 nano-technology - Abstract
To understand the superconductivity recently discovered in ${\mathrm{Nd}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{NiO}}_{2}$, we carried out $\mathrm{LDA}+\mathrm{DMFT}$ (local density approximation plus dynamical mean-field theory) and magnetic force response calculations. The on-site correlation in Ni-$3d$ orbitals causes notable changes in the electronic structure. The calculated temperature-dependent susceptibility exhibits the Curie-Weiss behavior, indicating the localized character of its moment. From the low-frequency behavior of self-energy, we conclude that the undoped phase of this nickelate is Fermi-liquid-like contrary to cuprates. Interestingly, the estimated correlation strength by means of the inverse of quasiparticle weight is found to increase and then decrease as a function of hole concentration, forming a domelike shape. Another finding is that magnetic interactions in this material become two-dimensional by hole doping. While the undoped ${\mathrm{NdNiO}}_{2}$ has the sizable out-of-plane interaction, hole dopings strongly suppress it. This two-dimensionality is maximized at the hole concentration $\ensuremath{\delta}\ensuremath{\approx}0.25$. Further analysis as well as the implications of our findings are presented. more...
- Published
- 2020
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38. First-principles-based calculation of branching ratio for 5d, 4d, and 3dtransition metal systems
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Hongkee Yoon, Jae-Hoon Sim, Myung Joon Han, and Do Hoon Kiem
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Physics ,Coupling ,Branching fraction ,Computation ,02 engineering and technology ,Spin–orbit interaction ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Computational physics ,Transition metal ,Atomic orbital ,0103 physical sciences ,General Materials Science ,Density functional theory ,010306 general physics ,0210 nano-technology ,Valence electron - Abstract
A new first-principles computation scheme to calculate 'branching ratio' has been applied to various 5d, 4d, and 3d transition metal elements and compounds. This recently suggested method is based on a theory which assumes the atomic core hole interacts barely with valence electrons. While it provides an efficient way to calculate the experimentally measurable quantity without generating spectrum itself, its reliability and applicability should be carefully examined especially for the light transition metal systems. Here we select 36 different materials and compare the calculation results with experimental data. It is found that our scheme well describes 5d and 4d transition metal systems whereas, for 3d materials, the difference between the calculation and experiment is quite significant. It is attributed to the neglect of core-valence interaction whose energy scale is comparable with the spin-orbit coupling of core p orbitals. more...
- Published
- 2020
39. 50 Years History of JKPS
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Keun-Young Kim, Soonjae Moon, and Myung Joon Han
- Published
- 2018
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40. Polymorphic Spin, Charge, and Lattice Waves in Vanadium Ditelluride
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Jeongyong Kim, Min Yong Jeong, Changwon Seo, Dongyeun Won, Dohyun Kim, Heejun Yang, Do Hoon Kiem, Younghak Kim, Suyeon Cho, Je-Geun Park, Myung Joon Han, and Hwanbeom Cho
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Phase transition ,Materials science ,Condensed matter physics ,Magnetism ,Mechanical Engineering ,Charge density ,02 engineering and technology ,Quantum phases ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Mechanics of Materials ,Spin wave ,Quantum state ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,0210 nano-technology ,Phase diagram - Abstract
Lattice distortion, spin interaction, and dimensional crossover in transition metal dichalcogenides (TMDs) have led to intriguing quantum phases such as charge density waves (CDWs) and 2D magnetism. However, the combined effect of many factors in TMDs, such as spin-orbit, electron-phonon, and electron-electron interactions, stabilizes a single quantum phase at a given temperature and pressure, which restricts original device operations with various quantum phases. Here, nontrivial polymorphic quantum states, CDW phases, are reported in vanadium ditelluride (VTe2 ) at room temperature, which is unique among various CDW systems; the doping concentration determines the formation of either of the two CDW phases in VTe2 at ambient conditions. The two CDW polymorphs show different antiferromagnetic spin orderings in which the vanadium atoms create two different stripe-patterned spin waves. First-principles calculations demonstrate that the magnetic ordering is critically coupled with the corresponding CDW in VTe2 , which suggests a rich phase diagram with polymorphic spin, charge, and lattice waves all coexisting in a solid for new conceptual quantum state-switching device applications. more...
- Published
- 2019
41. Dynamical mean-field study of Vanadium diselenide monolayer ferromagnetism
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Sangkook Choi, Taek Jung Kim, Siheon Ryee, and Myung Joon Han
- Subjects
Condensed Matter - Materials Science ,Materials science ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Magnetism ,Mechanical Engineering ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Charge density ,Charge (physics) ,General Chemistry ,Condensed Matter Physics ,Magnetic susceptibility ,Condensed Matter::Materials Science ,Condensed Matter - Strongly Correlated Electrons ,Mean field theory ,Ferromagnetism ,Mechanics of Materials ,Monolayer ,General Materials Science ,Density functional theory - Abstract
To understand the magnetism of VSe$_2$, whose monolayer form has recently been reported to be a room temperature ferromagnet, Here, the combined method of conventional density functional theory with dynamical mean-field theory has been adopted. This higher-level computation method enables us to resolve many of existing controversies and contradictions in between theory and experiment. First of all, this new approach is shown to give the correct magnetic properties of both bulk and two-dimensional limit of VSe$_2$ which demonstrates its superiority to the conventional methods. The results demonstrate that monolayer VSe$_2$ without charge density waves is a ferromagnet with ordering temperature of 250K. From the direct simulation of temperature-dependent magnetic susceptibility and ordered moment, it is shown that its ferromagnetism is clearly two-dimensional in nature. Further, it is shown that this ferromagnetic order is vulnerable to extra charge dopings which provides the important insight to elucidate recent experimental controversies., 10 pages, 4 figures more...
- Published
- 2019
42. Tetrahedral coordination and low-spin configuration in a 5d oxide
- Author
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Fei Han, Q. Zhao, B. Tian, Q. Xu, J.-H. Sim, Zhongshan Zhang, Myung Joon Han, John F. Mitchell, H. Su, Chun-Gang Duan, and Q. Zhang
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Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Spin states ,Transition metal ,Crystal field theory ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Density functional theory ,Electron configuration ,Coupling (probability) ,Realization (systems) ,Spin-½ - Abstract
Spin state plays a key role in a plethora of physical, biological, and geological phenomena. In octahedral coordination, spin state of $3d$ transition metals can be high spin or low spin, and can be tuned with external stimuli. In a tetrahedral coordination environment, with the smaller crystal field splitting energy, only high spin is considered possible for oxides. Herein we report the realization of low spin state in tetrahedral coordination in a novel oxide, $\mathrm{S}{\mathrm{r}}_{9}\mathrm{I}{\mathrm{r}}_{3}{\mathrm{O}}_{17}$. The low spin configuration was confirmed with density functional theory (DFT) calculations, including the effect of spin-orbit coupling (SOC), electron-electron repulsion (U), magnetic data, and crystal chemical consideration. This exotic electronic configuration was realized with the confluence of extended $5d$ orbitals, short bond lengths, and an electron count maximizing the crystal field stabilization energy. The discovery of low spin state for a tetrahedral environment provides a novel platform for spin state manipulation in solid state materials. more...
- Published
- 2019
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43. Microscopic understanding of magnetic interactions in bilayer CrI3
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Myung Joon Han, Siheon Ryee, Min Yong Jeong, Hongkee Yoon, and Seung Woo Jang
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Materials science ,Physics and Astronomy (miscellaneous) ,Magnetism ,FOS: Physical sciences ,02 engineering and technology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,symbols.namesake ,0103 physical sciences ,Antiferromagnetism ,General Materials Science ,010306 general physics ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Materials Science (cond-mat.mtrl-sci) ,Order (ring theory) ,021001 nanoscience & nanotechnology ,Magnetic field ,Ferromagnetism ,symbols ,Condensed Matter::Strongly Correlated Electrons ,van der Waals force ,0210 nano-technology ,Ground state ,Monoclinic crystal system - Abstract
We performed the detailed microscopic analysis of the inter-layer magnetic couplings for bilayer CrI$_3$. As the first step toward understanding the recent experimental observations and utilizing them for device applications, we estimated magnetic force response as well as total energy. Various van der Waals functionals equivocally point to the ferromagnetic ground state for the low-temperature structured bilayer CrI$_3$ which is further confirmed independently by magnetic force response calculations. The calculated orbital-dependent magnetic forces clearly show that $e_g$-$t_{2g}$ interaction is the key to stabilize this ferromagnetic order. By suppressing this ferromagnetic interaction and enhancing antiferromagnetic orbital channels of $e_g$-$e_g$ and $t_{2g}$-$t_{2g}$, one can realize the desirable antiferromagnetic order. We showed that high-temperature monoclinic stacking can be the case. Our results provide unique information and insight to understand the magnetism of multi-layer CrI$_3$ paving the way to utilize it for applications., Comment: 15 pages, 3 figures, one-column more...
- Published
- 2019
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44. MXene Phase with C 3 Structure Unit: A Family of 2D Electrides
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Mohammad Khazaei, Yoon-Gu Kang, Hideo Hosono, Kaoru Ohno, Myung Joon Han, Soungmin Bae, Gustavo M. Dalpian, W.F. Espinosa-García, Kazuaki Kuwahata, Noriyuki Egawa, Juho Lee, Hannes Raebiger, and Yong-Hoon Kim more...
- Subjects
Biomaterials ,Crystallography ,chemistry.chemical_compound ,Materials science ,chemistry ,Phase (matter) ,Electrochemistry ,Structure (category theory) ,Electride ,Condensed Matter Physics ,Unit (ring theory) ,Electronic, Optical and Magnetic Materials - Published
- 2021
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45. Electronic and magnetic properties of carbide MXenes—the role of electron correlations
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Myung Joon Han, Soungmin Bae, Kee-Joo Chang, Mohammad Khazaei, Hannes Raebiger, Yoon-Gu Kang, Kaoru Ohno, and Yong-Hoon Kim
- Subjects
ab initio calculation ,Materials science ,Condensed matter physics ,Mechanical Engineering ,Electron ,Nitride ,Carbide ,Transition metal ,Ab initio quantum chemistry methods ,Density functional theory ,lcsh:TA401-492 ,lcsh:Materials of engineering and construction. Mechanics of materials ,General Materials Science ,MXene ,MXenes - Abstract
Transition metal compounds are known to be tricky for ab initio calculations mainly because of the strongly localized nature of transition metal d electrons. Nonetheless, the bulk of current theoretical studies of MXenes (transition metal carbide or nitride) relies on the density functional theory using a semilocal PBE functional, whose notorious self-interaction error grossly misrepresents electronic and magnetic properties of many well-known transition metal compounds. Although several studies have adopted Hubbard-U corrections to MXenes, the lack of systematic guidelines on how to determine the U parameters has led to a cornucopia of different results. To shed some light on the reliability of different methods (different functionals or different U parameters), we performed ab initio calculations for 22 carbide MXenes (M2CT2 with M= Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Mo, W, and T= O, F) using density functional theory and four different methods: PBE, SCAN, HSE06, and PBE+U. In addition to trivial improvement of electronic structures of MXenes by SCAN, HSE06, and PBE+U, we found new ground-state structures for two MXenes (Hf2CF2 and Ta2CF2) and magnetic states for three MXenes (V2CO2, V2CF2, and Mo2CF2), which have not previously been reported. In addition, we found that SCAN, HSE06, and PBE+U dramatically improve the dynamical stability of V2CO2 and Mo2CF2 compared with PBE. This paper offers an overview of a broad range of MXenes with a systematic verification of various methods. more...
- Published
- 2021
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46. Extraordinary Off-Stoichiometric Bismuth Telluride for Enhanced n-Type Thermoelectric Power Factor
- Author
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In Chung, Kyunghan Ahn, Taeghwan Hyeon, Joonil Cha, Kunsu Park, Siheon Ryee, Sanghwa Lee, Jae-Ki Lee, Sue In Chae, Sung-Pyo Cho, Su-Dong Park, Jino Im, and Myung Joon Han
- Subjects
business.industry ,Chemistry ,Nanochemistry ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Power factor ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Thermal conductivity ,Thermoelectric generator ,Seebeck coefficient ,Optoelectronics ,Bismuth telluride ,0210 nano-technology ,business ,Tellurium - Abstract
Thermoelectrics directly converts waste heat into electricity and is considered a promising means of sustainable energy generation. While most of the recent advances in the enhancement of the thermoelectric figure of merit (ZT) resulted from a decrease in lattice thermal conductivity by nanostructuring, there have been very few attempts to enhance electrical transport properties, i.e., the power factor. Here we use nanochemistry to stabilize bulk bismuth telluride (Bi2Te3) that violates phase equilibrium, namely, phase-pure n-type K0.06Bi2Te3.18. Incorporated potassium and tellurium in Bi2Te3 far exceed their solubility limit, inducing simultaneous increase in the electrical conductivity and the Seebeck coefficient along with decrease in the thermal conductivity. Consequently, a high power factor of ∼43 μW cm–1 K–2 and a high ZT > 1.1 at 323 K are achieved. Our current synthetic method can be used to produce a new family of materials with novel physical and chemical characteristics for various applications. more...
- Published
- 2016
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47. Polar Metal Phase Induced by Oxygen Octahedral Network Relaxation in Oxide Thin Films
- Author
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Yong-Ryun Jo, Si-Young Choi, Myung Joon Han, Jeong Rae Kim, Tae Won Noh, Jinkwon Kim, Bong-Joong Kim, Myung-Chul Jung, Jeong Gi Choi, Do Young Noh, Kyoung-June Go, Yeong Jae Shin, Jong Seok Lee, Chang Jae Roh, and Ho Jun Oh more...
- Subjects
Phase boundary ,Colossal magnetoresistance ,Materials science ,Ferromagnetic material properties ,Condensed matter physics ,Oxide ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,0104 chemical sciences ,Biomaterials ,Condensed Matter::Materials Science ,Tetragonal crystal system ,chemistry.chemical_compound ,Strain engineering ,chemistry ,Condensed Matter::Superconductivity ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Thin film ,0210 nano-technology ,Biotechnology - Abstract
ABO3 perovskite materials and their derivatives have inherent structural flexibility due to the corner sharing network of the BO6 octahedron, and the large variety of possible structural distortions and strong coupling between lattice and charge/spin degrees of freedom have led to the emergence of intriguing properties, such as high-temperature superconductivity, colossal magnetoresistance, and improper ferroelectricity. Here, an unprecedented polar ferromagnetic metal phase in SrRuO3 (SRO) thin films is presented, arising from the strain-controlled oxygen octahedral rotation (OOR) pattern. For compressively strained SRO films grown on SrTiO3 substrate, oxygen octahedral network relaxation is accompanied by structural phase separation into strained tetragonal and bulk-like orthorhombic phases, and the asymmetric OOR evolution across the phase boundary allows formation of the polar phase, while bulk metallic and ferromagnetic properties are maintained. From the results, it is expected that other oxide perovskite thin films will also yield similar structural environments with variation of OOR patterns, and thereby provide promising opportunities for atomic scale control of material properties through strain engineering. more...
- Published
- 2020
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48. Influence of stacking disorder on cross-plane thermal transport properties in TMPS3 (TM = Mn, Ni, Fe)
- Author
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Jong Seok Lee, Soonmin Kang, Bong-Joong Kim, Wan-Gil Jung, Myung Joon Han, Young-Gwan Choi, Suhan Son, Hwiin Ju, Je-Geun Park, Myung-Chul Jung, and Do-Gyeom Jeong
- Subjects
010302 applied physics ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Phonon scattering ,Scattering ,Stacking ,Heterojunction ,02 engineering and technology ,Conductivity ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,Thermal conductivity ,0103 physical sciences ,symbols ,Graphite ,van der Waals force ,0210 nano-technology - Abstract
We investigated the thermal transport properties of magnetic van der Waals materials, TMPS3 (TM = Mn, Ni, and Fe), using the time-domain thermoreflectance technique. We determined the cross-plane thermal conductivity, which turns out to be relatively low, i.e., about 1 W m−1 K−1 for all TMPS3 investigated. When compared with previous results of graphite and transition metal dichalcogenides (TMDs), thermal conductivity becomes smaller as it goes from graphite to TMDs to TMPS3, and the difference is larger at low temperature, e.g., around 50 K. From the Callaway model analysis, we could attribute the large thermal conductivity reduction for TMPS3, particularly at low temperature, to the phonon scattering from the boundary. We actually confirmed the existence of the large population of the stacking faults with the cross-sectional transmission electron microscopy image of MnPS3. This suggests that intrinsic or extrinsic stacking faults formed in van der Waals materials and their heterostructures can play an important role in reducing the cross-plane thermal conductivity as a source of the boundary scattering. more...
- Published
- 2020
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- View/download PDF
49. Magnetic force theory combined with quasi-particle self-consistent GW method
- Author
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Myung Joon Han, Jae-Hoon Sim, Takao Kotani, Seung Woo Jang, and Hongkee Yoon
- Subjects
Physics ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Magnetic field ,Condensed Matter - Strongly Correlated Electrons ,Ferromagnetism ,0103 physical sciences ,Quasiparticle ,Antiferromagnetism ,General Materials Science ,Density functional theory ,Cuprate ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Wave function ,Eigenvalues and eigenvectors - Abstract
We report a successful combination of magnetic force linear response theory with quasiparticle self-consistent GW method. The self-consistently determined wavefunctions and eigenvalues can just be used for the conventional magnetic force calculations. While its formulation is straightforward, this combination provides a way to investigate the effect of GW self-energy on the magnetic interactions which can hardly be quantified due to the limitation of current GW methodology in calculating the total energy difference in between different magnetic phases. In ferromagnetic $3d$ elements, GW self-energy slightly reduces the $d$ bandwidth and enhances the interactions while the same long-range feature is maintained. In antiferromagnetic transition-metal monoxides, QSGW significantly reduces the interaction strengths by enlarging the gap. Orbital-dependent magnetic force calculations show that the coupling between $e_g$ and the nominally-empty $4s$ orbital is noticeably large in MnO which is reminiscent of the discussion for cuprates regarding the role of Cu-$4s$ state. This combination of magnetic force theory with quasiparticle self-consistent GW can be a useful tool to study various magnetic materials., 11 pages, 3 figures more...
- Published
- 2019
50. Quantified Degeneracy, Entropy and Metal-Insulator Transition in Complex Transition-Metal Oxides
- Author
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Myung Joon Han, Hunpyo Lee, Siheon Ryee, and Jae-Hoon Sim
- Subjects
Physics ,Phase transition ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Superlattice ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Transition metal ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Metal–insulator transition ,010306 general physics ,0210 nano-technology ,Entropy (order and disorder) - Abstract
Understanding complex correlated oxides and their phase transitions has long been a challenge. The difficulty largely arises from the intriguing interplay between multiple degrees of freedoms. While degeneracy can play an important role in determining material characteristics, there is no well-defined way to quantify and to unveil its role in real materials having complicated band structures. Here we suggest a way to quantify the `effective degeneracy' relevant to metal-insulator transition by introducing entropy-like terms. This new quantity well describes the electronic behaviors of transition-metal oxides as a function of external and internal parameters. With $3d$ titanates, $4d$ ruthenates, and $5d$ iridates as our examples, we show that this new effective quantity provides useful insights to understand these systems and their phase transitions. For LaTiO$_3$/LaAlO$_3$ superlattice, we suggest a novel `degeneracy control' metal-insulator transition., First submitted (to other journal) on 13 Jul 2017. Eventually accepted in PRB more...
- Published
- 2018
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