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- A peak in the critical current for quantum critical superconductors
- A peak in the critical current for quantum critical superconductors Center for Quantum Materials and Superconductivity(CQMS), Department of Physics, Sungkyunkwan University, Soon-Gil Jung, Soonbeom Seo, Sangyun Lee & Tuson Park National Research Foundation of Korea announced that Professor Tuson Park and researcher Professor Soon-Gil Jung of Sungkyunkwan University clarified the principle of formation of unsteady superconductors, one of the unsolved problems in solid physics. [Abstract] Generally, studies of the critical current Ic are necessary if superconductors are to be of practical use, because Ic sets the current limit below which there is a zero-resistance state. Here, we report a peak in the pressure dependence of the zero-field Ic, Ic(0), at a hidden quantum critical point (QCP), where a continuous antiferromagnetic transition temperature is suppressed by pressure toward 0 K in CeRhIn5 and 4.4% Sn-doped CeRhIn5. The Ic(0)s of these Ce-based compounds under pressure exhibit a universal temperature dependence, underlining that the peak in zero-field Ic(P) is determined predominantly by critical fluctuations associated with the hidden QCP. The dc conductivity σdc is a minimum at the QCP, showing anti-correlation with Ic(0). These discoveries demonstrate that a quantum critical point hidden inside the superconducting phase in strongly correlated materials can be exposed by the zero-field Ic, therefore providing a direct link between a QCP and unconventional superconductivity. Source: http://www.nature.com/articles/s41467-018-02899-5
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- 작성일 2018-04-09
- 조회수 2600
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- Highly Efficient Thin-Film Transistor via Cross-Linking 1T Edge Functional 2H Molybdenum Disulfides
- Research on flexible thin film transistors (TFTs) has been steadily under way, with the next generation devices being noted. Molybdenum disulfide (MoS2), one of the two-dimensional materials, has excellent optical, electrical and chemical properties and is used in field effect transistors (FETs). However, most of the synthesis studies are concentrated on chemical vapor deposition, and it is necessary to make a method to manufacture MoS2 while maintaining crystallinity through an inexpensive solution process. In this study, MoS2 FET was implemented through a solution process by selectively modifying the edge of MoS2 only with organic compounds, without using metal ions at all. The paper was published in ACS Nano (2017, 11, 12832-12839) by the researchers led by Hyoyoung LEE (CINAP-IBS, Professor of Chemistry) with Mun Seok JEONG (Professor of Energy Science). To exfoliate the 2D MoS2 bulk materials into single-layer edge-1T basal-2H MoS2 sheets, they used 4-carboxy-benzenediazonium (+N2-benzene-COOH) tetrafluoroborate. Edge-exposed nucleophilic sulfides of the bulk MoS2 can act as substitutes for the electrophiles of +benzene-COOH diazonium salts. The chemically attached polar COOH functional group facilitates the exfoliation by creating an increased electrostatic repulsion force between the MoS2 nanosheets. As a result, the configuration of the resulting exfoliated HOOC-benzene-MoS2 sheets (e-MoS2) is changed to the conducting 1T or 1T′ phase through functionalization at the edge part, while remaining in the semiconducting 2H phase at the basal plane. Compared with n-BuLi exfoliated MoS2 (n-MoS2) and basal plane functionalized MoS2 (b-MoS2), which mainly have metallic 1T or 1T′ phase during the chemical treatment showing the on/off ratio of <100, e-MoS2 has a relatively high mobility (μ= 1.2 cm2/(V s) and on/off ratio (= 106) due to the low number of defect sites in the e-MoS2 nanosheets. PDDA (polydiallyldimethylammonium chloride) is used as a cationic layer, while e-MoS2 is used as an anionic layer for the channel film formation. Cross-linking via hydrogen bonding of the negatively charged COOH of the e-MoS2 sheets with the help of a cationic polymer provided good film formation for solution processing TFT channels. The e-MoS2 TFT exhibited great electrical performance (average mobility of 170.8 cm2/(V s) at 1 V and on/off ratio of 106) on SiO2/Si substrates and also a high mobility of 36.34 cm2/(V s) (on/off ratio of 103) on PDMS/PET substrates for flexible TFTs. This edge functionalization can be applied to various 2D layered bulk inorganic materials for the chemical, electronic, optical, and electrical modulation of 2D materials. This study is meaningful in terms of the significant potential of functionalized 2D materials in various bulk devices and low-cost electronics.
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- 작성일 2018-03-19
- 조회수 2540
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- Renowned physicist Stephen Hawking dies at age 76
- (CNN) — Stephen Hawking, the brilliant British theoretical physicist who overcame a debilitating disease to publish wildly popular books probing the mysteries of the universe, has died, according to a family spokesman. He was 76. Considered by many to be the world's greatest living scientist, Hawking was also a cosmologist, astronomer, mathematician and author of numerous books including the landmark "A Brief History of Time," which has sold more than 10 million copies. With fellow physicist Roger Penrose, Hawking merged Einstein's theory of relativity with quantum theory to suggest that space and time would begin with the Big Bang and end in black holes. Hawking also discovered that black holes are not completely black but emit radiation and will likely eventually evaporate and disappear. (the rest omitted) (source: https://edition.cnn.com/2018/03/14/health/stephen-hawking-dead/index.html)
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- 작성일 2018-03-14
- 조회수 10363
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- Development of a New Method for Converting MoS2 into MoTe2 by Prof. Young Hee LEE
- Prof. Young Hee LEE, Center for Integrated Nanostructure Physics, Institute for Basic Science at Sungkyunkwan University has successfully developed a new method for converting monolayer molybdenum disulfide (MoS2) into molybdenum ditelluride (MoTe2) via substitution of tellurium to MoS2 by chemical vapor deposition (CVD). In order to trigger such a substitutional reaction, High reaction temperature is necessary for Te-substitution but the instability arises because of lower thermal stability of MoTe2 than that of MoS2. Although the MoTe2, which is product after Te-substitution, is vaporized above 700 °C due to the thermal instability, the substitutional reaction below 700 °C is no longer possible. To resolve this issue, we introduced sodium telluride (Na2Te) as a telluriding catalyst and further was able to achieve stable MoTe2 by provoking substitutional reaction at temperature below 700 °C. The research team confirmed that the Te-substitution reaction occurs preferentially from the edge and grain boundary of the MoS2 flake and further constructed lateral hetero semiconductor junction of MoS2-MoTe2. Furthermore, various phases such as alloy (MoS2-xTex), semiconductor (2H-MoTe2), and metal (1T’-MoTe2) were obtained by adjusting experimental parameters of temperature and sodium concentration. We also demonstrated that the band gap of MoS2-xTex alloy can be modulated by controlling the tellurium composition. Dr. Seok Jun YUN, the leading scientist of the research team, predicted that "It is possible to synthesize compound materials by a substitutional technique even for the unstable compounds." The conversion method using the telluriding catalyst (Na2Te) can be applied not only to MoS2 but also to tungsten disulfide (WS2), which is another type of transition metal dichalcogenide. This research, conducted by prof. Young Hee Lee and Seok Joon Yun who is the first author of this research, was published in Nature Communications (IF 12.124), a worldwide scientific journal in science and technology, on December 18. Source: https://www.nature.com/articles/s41467-017-02238-0
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- 작성일 2018-03-12
- 조회수 2542
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- Central spot formed in dried coffee-water-mixture droplets: Inverse coffee-ring effect
- Central spot formed in dried coffee-water-mixture droplets: Inverse coffee-ring effect A research paper 'Central Spot Formed in Dried coffee-Water-Mixture Droplets: Inverse Coffee-Ring Effect', in which the first author, Sungkyunkwan University physicis student, Baek Ji Min, and a correspondent author, Jooyull Rhee, participated, was finally approved in the 'Current Applied Physics' (Impact Factor: 1.971) on the 10th. Baek identified the cause of the reverse phenomenon in the coffee-ring effect that is commonly found in everyday life. A coffee-ring effect is a phenomenon in which when a coffee droplet falls on a smooth surface such as a table, the coffee powder drifts to the edge of the coffee droplet and dries up, leaving only a ring-shaped trail on the edge. This phenomenon occurs when most of the colloidal solution is dry. Especially, it is an important phenomenon to be solved in the field of display industry utilizing inkjet printing technology. In this study, Baek discovered that coffee powder was collected in the middle of the coffee drop as opposed to the coffee-ring effect, resulting in spots in the center of the coffee drop. In other words, the cause of the phenomenon opposite to the coffee-ring effect is identified. This article is a translation of dhnews. (Source 1: https://www.sciencedirect.com/science/article/pii/S1567173918300075 Source 2: http://www.dhnews.co.kr/news/articleView.html?idxno=78037)
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- 작성일 2018-03-05
- 조회수 2586
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- The retirement ceremony for Professor Killyong Kim of the department of Biological Sciences was held
- On December 15, 2017, a retirement ceremony for Professor Killyong Kim of the Department of Biological Sciences was held at the Natural Science 2, Songchun lecture room (No. 32255). Since his appointment in 2001, Professor Kim has served in the Department of Biological Sciences for 17 years and has achieved a number of research results including publishing numerous papers in internationally renowned journals as experts in biochemistry. He also served as Chairman of the Asia-Pacific International Peptide Symposium and President of the Korean Society of Peptide Protein. The retirement ceremony was attended by more than 50 professors, undergraduates, and graduate students from the department of biological sciences and Intae Yu, dean of College of Science. After Professor Kim's retirement commemorative lecture - 'Dementia', the retirement ceremony, which consisted of a photo slide with the theme of 'Times in Biological Sciences', a delivery ceremony of the appreciation plaque, and a congratulatory speech, was finished.
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- 작성일 2018-02-27
- 조회수 2512
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- AORC hosted an international conference on “Matrix theory with Applications”
- The “Applied Algebra and Optimization Research Center” (AORC, Director Gi-Sang Cheon), a Scientific Research Center (SRC) in mathematics field designated by the National Research Foundation of Korea, hosted an international conference on “Matrix theory with Applications” from December 14th to 17th at the Natural Sciences campus, with the International Research Center for Tensor and Matrix Theory (IRCTMT, director Qing-Wen Wang) in Shanghai University in China as a cohost. This conference was agreed in the MoU on joint academic research between two research centers and our university held this conference following the hosting of Shanghai university in last year. It is well understood that the matrix theory is very useful in data analysis, and therefore, hosting an international workshop on “Big data and Optimization” as a parallel meeting appealed to many participants (https://sites.google.com/view/icmta2017/home). The address of welcome given by the Vice President Ji-Beom Yoo and the Dean of the College of Science Intae Yu opened the conference and there were 103 participants from 16 countries in total and 60 research presentations were given which were all invited talks. Especially, professor R. Brualdi (U. Of Wisconsin-Madison), the editor of 「Linear Algebra and Its Applications」 which is a world-renowned journal in matrix theory and applications, gave the plenary talk and the President of the International Linear Algebra Society P. Semrl (U. of Ljubljana), last Vice Presidents served in the past C.-K. Li (College of William & Mary), B. Shader (U. of Wyoming) and many world-famous scholars in the field of matrix theory, big data and optimization including J. Lawson (Louisiana St. U), H. Park (Georgia Tech), J-S. Chen (National Taiwan Normal U) and Y. Shi(Shanghai Tech U) gave invited talks.
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- 작성일 2018-02-13
- 조회수 2672
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- Team of Prof. Pil Joon Seo (dept. Life Science), Identifying the induction mechanism of Cellular Dedifferentiation
- Team of Prof. Pil Joon Seo (dept. Life Science at SKKU), Identified the induction mechanism of Cellular Dedifferentiation and published the paper on Science signaling (IF: 6.494) on November 28th. * Cellular dedifferentiation: the already differentiated cells are converted into the undifferentiated state and the cell division ability is restored Prof. Pil Joon Seo and his colleagues have identified chromatin modifications that specifically regulate the derived process of stem cells, and have identified the action mechanism of these proteins for the first time in the world. Since the possibility of regeneration into plants with desired characteristics is opened through the enhancement of the dedifferentiation efficiency, the present study suggests that it will contribute greatly to the improvement of the traits of crops in the future. This study was conducted as the Bio Green 21 project (Plant Molecular Breeding Project) of the RDA and the basic laboratory project of the Korea Research Foundation. Fig. 1 Callus formation in leaf explants from atxr2 mutant and ATXR2-overexpressing plants. (A) Callus formation in leaves explanted from young wild-type (Col-0), atxr2-1, atxr2-3, and 35S:ATXR2-MYC plants. Scale bar, 5 mm. n > 30 plants of each genotype. (B) Fresh weight of calli from wild-type (Col-0), atxr2-1, atxr2-3, and 35S:ATXR2-MYC plants. Bars indicate the SE of the mean. *P < 0.05 (Student’s t test). n = 30 calli of each genotype. (Source: http://stke.sciencemag.org/content/10/507/eaan0316.full)
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- 작성일 2018-02-09
- 조회수 2600
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- The 10th anniversary celebration of the establishment of the Hyocheon Cho Kyuhak Scholarship
- Hyochen Cho Kyuhak Scholarship held a ceremony to celetrate the 10th anniversary of its establishment at Lotte Hotel in Sogong-dong on November 18th at 5pm. Kyuhak Cho, the president of the Cho Kyuhak Scholarship started with the greetings, and Kyusang Chung(president of SKKU) celebrated this ceremony. Bong-chul Choi(dean of law school) and Jin-yong Lee(head of chemistry department) gave thankful messages, Yong-geun Son explained the current management status of scholarship fund, and people watched the 10th anniversary video and received the 2017 scholarship certificates. In particular, all scholarship students have presented a plaque of appreciation with appreciation of his exemplary love for juniors and his university for the past 10 years. The Hyocheon Cho Kyuhak Scholarship was founded in April 2008 as a donation of KRW 2.6 billion for the purpose of "securing the international status of SKKU chemical department and cultivating human resources with international competitiveness". In order to improve the status and development of law schools as well as chemistry students, scholarships are offered to law school students starting in 2009. From 2008 to 2017, a total of 688 million KRW was awarded to 158 students for 10 years.
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- 작성일 2018-01-29
- 조회수 2625
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- Prof. Rathinasamy Sakthivel (Dep. of Mathematics) Named Most Highly Cited Researchers in the world
- Three researchers from the SKKU are included on the 2017 Highly Cited Researchers list among 3,300 individuals compiled by Clarivate Analytics, which was previously part of Thomson Reuters. One of the three researchers is College of Science faculty, Rathinasamy Sakthivel. The list includes the most frequently cited researchers in 21 fields of the sciences and social sciences based on “the extent to which their papers have supported, influenced, inspired and challenged other researchers around the globe.” It identifies authors who have consistently won peer approval from international researchers in the form of high citation counts in Clarivate’s Web of Science database between 2005-2015.
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- 작성일 2018-01-17
- 조회수 2989