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1. Operation of PAL-XFEL LLRF

Author

Hu, Jinyul, Hong, Juho, Kim, KwangHoon, Jung, Seonghoon, Na, Donghyun, Park, Yong Jung, Kim, Sang-Hee, Park, Soung-soo, Min, Chang-Ki, Kang, Heung-Sik, and Lee, Heung-Soo

Subjects
Physics - Accelerator Physics
Abstract

PAL-XFEL (Pohang Accelerator Laboratory X-ray Free Electron Laser) started RF conditioning in October 2015 and has been operating reliably for ~ 4 years. The machine's LLRF and SSA systems contributed to the stable operation of PAL-XFEL with over 99% availability. The LLRF and SSA systems showed some problems in rare cases. The delay caused by the problem is very small, but PAL-XFEL can stop working. Some issues have been identified and resolved. We want to share the experience., Comment: Poster presented at LLRF Workshop 2019 (LLRF2019, arXiv:1909.06754)

Published
2019

2. Infrared optical absorption spectra of CuO single crystals: Fermion-spinon band and dimensional crossover of the antiferromagnetic order

Author

Jung, SeongHoon, Kim, Jooyeon, Choi, E. J., Sekio, Y., Kimura, T., and Lorenzana, J.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity
Abstract

We have obtained mid-infrared optical absorption spectra of the S=1/2 quasi one-dimensional CuO using polarized transmission measurement and interpreted the spectra in terms of phonon assisted magnetic excitations. When the electric field is parallel to the main antiferromagnetic direction a Delta shaped peak is observed with the maximum at 0.23eV which is attributed to spinons along Cu-O chains. At low temperatures in the antiferromagnetic phase another peak appears at 0.16eV which is attributed to two-magnon absorption but the spinon peak remains. This behavior is interpreted as due to a dimensional crossover where the low temperature three-dimensional magnetic phase keeps short range characteristics of a one-dimensional magnet., Comment: 5 pages, 5 figures

Published
2009
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3. Hard X-ray free-electron laser with femtosecond-scale timing jitter

Author

Kang, Heung-Sik, Min, Chang-Ki, Heo, Hoon, Kim, Changbum, Yang, Haeryong, Kim, Gyujin, Nam, Inhyuk, Baek, Soung Youl, Choi, Hyo-Jin, Mun, Geonyeong, Park, Byoung Ryul, Suh, Young Jin, Shin, Dong Cheol, Hu, Jinyul, Hong, Juho, Jung, Seonghoon, Kim, Sang-Hee, Kim, KwangHoon, Na, Donghyun, Park, Soung Soo, Park, Yong Jung, Han, Jang-Hui, Jung, Young Gyu, Jeong, Seong Hun, Lee, Hong Gi, Lee, Sangbong, Lee, Sojeong, Lee, Woul-Woo, Oh, Bonggi, Suh, Hyung Suck, Parc, Yong Woon, Park, Sung-Ju, Kim, Min Ho, Jung, Nam-Suk, Kim, Young-Chan, Lee, Mong-Soo, Lee, Bong-Ho, Sung, Chi-Won, Mok, Ik-Su, Yang, Jung-Moo, Lee, Chae-Soon, Shin, Hocheol, Kim, Ji Hwa, Kim, Yongsam, Lee, Jae Hyuk, Park, Sang-Youn, Kim, Jangwoo, Park, Jaeku, Eom, Intae, Rah, Seungyu, Kim, Sunam, Nam, Ki Hyun, Park, Jaehyun, Park, Jaehun, Kim, Sangsoo, Kwon, Soonam, Park, Sang Han, Kim, Kyung Sook, Hyun, Hyojung, Kim, Seung Nam, Kim, Seonghan, Hwang, Sun-min, Kim, Myong Jin, Lim, Chae-yong, Yu, Chung-Jong, Kim, Bong-Soo, Kang, Tai-Hee, Kim, Kwang-Woo, Kim, Seung-Hwan, Lee, Hee-Seock, Lee, Heung-Soo, Park, Ki-Hyeon, Koo, Tae-Yeong, Kim, Dong-Eon, and Ko, In Soo

Published
2017
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7. FEL performance achieved at PAL-XFEL using a three-chicane bunch compression scheme

Author

Kang, Heung-Sik, primary, Yang, Haeryong, additional, Kim, Gyujin, additional, Heo, Hoon, additional, Nam, Inhyuk, additional, Min, Chang-Ki, additional, Kim, Changbum, additional, Baek, Soung Youl, additional, Choi, Hyo-Jin, additional, Mun, Geonyeong, additional, Park, Byoung Ryul, additional, Suh, Young Jin, additional, Shin, Dong Cheol, additional, Hu, Jinyul, additional, Hong, Juho, additional, Jung, Seonghoon, additional, Kim, Sang-Hee, additional, Kim, KwangHoon, additional, Na, Donghyun, additional, Park, Soung Soo, additional, Park, Yong Jung, additional, Han, Jang-Hui, additional, Jung, Young Gyu, additional, Jeong, Seong Hun, additional, Kim, Min Jae, additional, Lee, Hong Gi, additional, Lee, Sangbong, additional, Lee, Woul-Woo, additional, Oh, Bonggi, additional, Suh, Hyung Suck, additional, Park, Ki-Hyeon, additional, Lee, Heung-Soo, additional, Khan, D. Z., additional, Raubenheimer, T. O., additional, and Wu, Juhao, additional

Published
2019
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9. Electromagnon with Sensitive Terahertz Magnetochromism in a Room-Temperature Magnetoelectric Hexaferrite

Author

Chun, Sae Hwan, primary, Shin, Kwang Woo, additional, Kim, Hyung Joon, additional, Jung, Seonghoon, additional, Park, Jaehun, additional, Bahk, Young-Mi, additional, Park, Hyeong-Ryeol, additional, Kyoung, Jisoo, additional, Choi, Da-Hye, additional, Kim, Dai-Sik, additional, Park, Gun-Sik, additional, Mitchell, J. F., additional, and Kim, Kee Hoon, additional

Published
2018
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12. Construction and Commissioning of PAL-XFEL Facility

Author

Ko, In, primary, Kang, Heung-Sik, additional, Heo, Hoon, additional, Kim, Changbum, additional, Kim, Gyujin, additional, Min, Chang-Ki, additional, Yang, Haeryong, additional, Baek, Soung, additional, Choi, Hyo-Jin, additional, Mun, Geonyeong, additional, Park, Byoung, additional, Suh, Young, additional, Shin, Dong, additional, Hu, Jinyul, additional, Hong, Juho, additional, Jung, Seonghoon, additional, Kim, Sang-Hee, additional, Kim, KwangHoon, additional, Na, Donghyun, additional, Park, Soung, additional, Park, Yong, additional, Jung, Young, additional, Jeong, Seong, additional, Lee, Hong, additional, Lee, Sangbong, additional, Lee, Sojeong, additional, Oh, Bonggi, additional, Suh, Hyung, additional, Han, Jang-Hui, additional, Kim, Min, additional, Jung, Nam-Suk, additional, Kim, Young-Chan, additional, Lee, Mong-Soo, additional, Lee, Bong-Ho, additional, Sung, Chi-Won, additional, Mok, Ik-Su, additional, Yang, Jung-Moo, additional, Parc, Yong, additional, Lee, Woul-Woo, additional, Lee, Chae-Soon, additional, Shin, Hocheol, additional, Kim, Ji, additional, Kim, Yongsam, additional, Lee, Jae, additional, Park, Sang-Youn, additional, Kim, Jangwoo, additional, Park, Jaeku, additional, Eom, Intae, additional, Rah, Seungyu, additional, Kim, Sunam, additional, Nam, Ki Hyun, additional, Park, Jaehyun, additional, Park, Jaehun, additional, Kim, Sangsoo, additional, Kwon, Soonnam, additional, An, Ran, additional, Park, Sang, additional, Kim, Kyung, additional, Hyun, Hyojung, additional, Kim, Seung, additional, Kim, Seonghan, additional, Yu, Chung-Jong, additional, Kim, Bong-Soo, additional, Kang, Tai-Hee, additional, Kim, Kwang-Woo, additional, Kim, Seung-Hwan, additional, Lee, Hee-Seock, additional, Lee, Heung-Soo, additional, Park, Ki-Hyeon, additional, Koo, Tae-Yeong, additional, Kim, Dong-Eon, additional, and Lee, Ki, additional

Published
2017
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13. Ultrafast photocarrier dynamics related to defect states of Si1−xGex nanowires measured by optical pump–THz probe spectroscopy

Author

Bae, Jung Min, primary, Lee, Woo-Jung, additional, Jung, Seonghoon, additional, Ma, Jin Won, additional, Jeong, Kwang-Sik, additional, Oh, Seung Hoon, additional, Kim, Seongsin M., additional, Suh, Dongchan, additional, Song, Woobin, additional, Kim, Sunjung, additional, Park, Jaehun, additional, and Cho, Mann-Ho, additional

Published
2017
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41. Terahertz Study of Electromagnon in TbMnO[sub 3] (abstract)

Author

Jung, Seonghoon, primary, Noh, Jaehoon, additional, joo-youn, Kim, additional, Maeng, Inhee, additional, Oh, Seung Jae, additional, Son, Joo-Hiuk, additional, Cheong, S. W., additional, Choi, E. J., additional, Hartline, Beverly Karplus, additional, Horton, Renee K., additional, and Kaicher, Catherine M., additional

Published
2009
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43. Ultrafast photocarrier dynamics related to defect states of Si 1-x Ge x nanowires measured by optical pump-THz probe spectroscopy.

Author

Bae JM, Lee WJ, Jung S, Ma JW, Jeong KS, Oh SH, Kim SM, Suh D, Song W, Kim S, Park J, and Cho MH

Abstract

Slightly tapered Si 1-x Ge x nanowires (NWs) (x = 0.29-0.84) were synthesized via a vapor-liquid-solid procedure using Au as a catalyst. We measured the optically excited carrier dynamics of Si 1-x Ge x NWs as a function of Ge content using optical pump-THz probe spectroscopy. The measured -ΔT/T 0 signals of Si 1-x Ge x NWs were converted into conductivity in the THz region. We developed a fitting formula to apply to indirect semiconductors such as Si 1-x Ge x , which explains the temporal population of photo-excited carriers in the band structure and the relationship between the trapping time and the defect states on an ultrafast time scale. From the fitting results, we extracted intra- and inter-valley transition times and trapping times of electrons and holes of Si 1-x Ge x NWs as a function of Ge content. On the basis of theoretical reports, we suggest a physical model to interpret the trapping times related to the species of interface defect states located at the oxide/NW: substoichiometric oxide states of Si(Ge) 0+,1+,2+ , but not Si(Ge) 3+ , could function as defect states capturing photo-excited electrons or holes and could determine the different trapping times of electrons and holes depending on negatively or neutrally charged states.

Published
2017
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44. Enhancement of carrier lifetime by spin-orbit coupling in a topological insulator of an Sb 2 Te 3 thin film.

Author

Choi H, Jung S, Kim TH, Chae J, Park H, Jeong K, Park J, and Cho MH

Abstract

Electrons and phonons in chalcogenide-based materials are important factors in the performance of optical data-storage media and thermoelectric devices. However, the fundamental kinetics of carriers in chalcogenide materials remains controversial, and active debate continues over the mechanism responsible for carrier relaxation. In this study, we used optical-pump terahertz-probe spectroscopy, which permits the relationship between structural phase transition and optical property transitions to be examined, to investigate the ultrafast carrier dynamics in a multilayered [Sb(3 Å)/Te(9 Å)] n thin film during the transition from the disordered to crystalline phase. Using terahertz time-domain spectroscopy and a contact-free optical technique, we demonstrated that the optical conductance and carrier concentration vary as functions of annealing temperature. Moreover, we observed that the topological surface state (TSS) affects the enhancement of the carrier lifetime, which is closely related to the degree of spin-orbit coupling (SOC). The combination of the optical technique and proposed carrier relaxation mechanism provides a powerful tool for monitoring TSS and SOC. Consequently, it was determined that the response of the disordered phase is dominated by an electron-phonon coupling effect, while that of the crystalline structure is controlled by a Dirac surface state and SOC effects. These results are important for understanding the fundamental physics of phase change materials and for optimizing and designing materials with better performance in optoelectronic devices.

Published
2016
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45. Tuning the Fermi level with topological phase transition by internal strain in a topological insulator Bi2Se3 thin film.

Author

Kim TH, Jeong K, Park BC, Choi H, Park SH, Jung S, Park J, Jeong KH, Kim JW, Kim JH, and Cho MH

Abstract

In a three-dimensional topological insulator Bi2Se3, a stress control for band gap manipulation was predicted but no systematic investigation has been performed yet due to the requirement of large external stress. We report herein on the strain-dependent results for Bi2Se3 films of various thicknesses that are grown via a self-organized ordering process. Using small angle X-ray scattering and Raman spectroscopy, the changes of d-spacings in the crystal structure and phonon vibration shifts resulted from stress are clearly observed when the film thickness is below ten quintuple layers. From the UV photoemission/inverse photoemission spectroscopy (UPS/IPES) results and ab initio calculations, significant changes of the Fermi level and band gap were observed. The deformed band structure also exhibits a Van Hove singularity at specific energies in the UV absorption experiment and ab initio calculations. Our results, including the synthesis of a strained ultrathin topological insulator, suggest a new direction for electronic and spintronic applications for the future.

Published
2016
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