https://scholar.dgist.ac.kr/handle/20.500.11750/31 2026-04-04T22:47:13Z https://scholar.dgist.ac.kr/handle/20.500.11750/59272 Title: Polaronic Quasiparticles in the Valence-Transition Compound TmSe_{1-x}Te_{x} Author(s): Min, Chul-Hee; Müller, Simon; Choi, Woojae; Dudy, Lenart; Zabolotnyy, Volodymyr B.; Heber, Michael; Denlinger, Jonathan D.; Kang, Chang-jong; Kalläne, Matthias; Wind, Nils O.; Scholz, Markus R.; Lee, Tienlin; Schlueter, Christoph; Gloskovskii, Andrei V.; Rienks, Emile D.L.; Hinkov, Vladimir; Bentmann, Hendrik; Kwon, Yong Seung; Reinert, Friedrich T.; Kim, H. D.; Rossnagel, Kai Abstract: Exotic quasiparticle states have been proposed in mixed-valent compounds exhibiting valence transitions. However, clear spectroscopic evidence identifying these states has remained elusive. Using synchrotron-based hard x-ray and extreme ultraviolet photoemission spectroscopy, we have probed the Tm 3d and 4f emissions in TmSe_{1-x}Te_{x}, where a Te concentration-dependent semimetal-insulator transition occurs alongside the valence transition. Our photoemission results, which are characteristic of the bulk, track this combined transition across the critical concentration (x_{c}=0.29). Notably, our results reveal a noninteger valence for the insulating phase and a novel quasiparticle excitation in the semimetallic phase: a Holstein polaron that extends beyond the standard periodic Anderson model. 2025-09-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58383 Title: Glassy relaxation and weak vortex pinning in anisotropic (Ca0.85La0.15)10(Pt3As8)(Fe2As2)5 single crystals Author(s): Haberkorn, Néstor; Kwon, Yong Seung Abstract: We present a comprehensive study on the vortex dynamics of (Ca0.85La0.15)10(Pt3As8)(Fe2As2)5 ​ single crystals, characterized by magnetization measurements. With a superconducting critical temperature of 32 K, this material is notable for its substantial anisotropy (5–6), which significantly influences the intrinsic vortex fluctuations. Our results reveal low critical current densities, i. e. Jc∼0.6 MA/cm2 at 1.8 K and low magnetic fields. The magnetic field dependences of Jc exhibit a fishtail or second peak in the magnetization, a feature commonly associated with weak vortex pinning and vortex relaxation crossovers. Moreover, the flux creep rates are exceptionally large at low fields and temperatures. Through Maley's analysis, we extract low vortex pinning energies (∼50 K) and glassy exponents that are consistent with expectations for single-vortex pinning, progressively evolving towards vortex bundles. These findings enhance our understanding of vortex dynamics in iron-based superconductors, highlighting the key role of intrinsic vortex fluctuations in the vortex phase diagram. © 2025 Elsevier B.V. 2025-05-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58375 Title: Nominal Kagome Antiferromagnetic Mn3Sn: Effects of excess Mn and its novel synthesis method Author(s): Park, Jaemun; Kim, Woo-Yong; Cho, Beopgil; Choi, Woojae; Kwon, Yong Seung; Seo, Jungpil; Park, Keeseong Abstract: The antiferromagnetic (AFM) Weyl semimetal Mn3Sn has attracted significant interest due to its intriguing topological and transport properties. However, the reproducibility of experimental results has been limited, potentially stemming from the thermodynamically stable Mn3+xSn1-x phase, where excess Mn substitutes at Sn sites and alters its intrinsic helical ordering. In this study, we present a Bi flux-assisted recrystallization method for synthesizing high-quality nominal Mn3Sn single crystals. Our approach yields stoichiometric and homogeneous samples with the largest residual resistivity ratio (RRR > 23) and sharper magnetic phase transitions, confirming their high purity. While the triangular AFM phase at room temperature is independent of sample quality, the helical magnetic ordering exhibits strong quality dependence, with additional helical phases emerging between 250 K and 280 K. At low temperatures, the system retains a semimetallic nature, as evidenced by the lower Sommerfeld coefficient (gamma), differential conductance (dI/dV) spectra, and magnetoresistance measurements. These findings highlight the interplay between chemical composition and magnetic phase transitions in Mn3Sn and establish a direct link between its helical ordering and electronic structure tuning. Our results not only provide a pathway for producing high-quality Mn3Sn single crystals but also offer a valuable platform for exploring unresolved aspects of its helical phases and potential applications in AFM spintronics. 2025-05-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58359 Title: Thermally activated flux flow of vortex liquid and suppression of vortex glass in Ca10(Pt4As8)(Fe2As2)5 Author(s): Cho, Beopgil; Park, Jaemun; Choi, Woojae; Park, Keeseong; Kwon, Yong Seung Abstract: To investigate the presence and role of magnetic fluctuations below the superconducting transition temperature in Ca10(Pt4As8)(Fe2As2)5 superconductors, which exhibit static non-magnetic behavior and linear temperature-dependent electrical resistivity in the normal state, we conducted detailed measurements of electrical resistivity under magnetic fields applied along the c-axis (H//c) and the ab-plane (H//ab) to analyze the vortex creep behavior. For H//c, vortex liquid and low-temperature vortex glass phases were observed, similar to those in typical iron pnictide superconductors. In contrast, for H//ab, no vortex glass phase was observed at low temperatures, but instead, a vortex liquid phase extended over a wide temperature range was observed. This behavior has never been reported in iron pnictide systems. This suppression of the vortex glass phase is attributed to the presence of antiferromagnetic fluctuations within the superconducting dome. © 2025 Elsevier Ltd 2025-09-30T15:00:00Z