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Electronic structure of the thermoelectric charge density wave material CeTe2-xSbx investigated via angle-resolved photoemission spectroscopy

2026-06-30T15:00:00Z

Title: Electronic structure of the thermoelectric charge density wave material CeTe2-xSbx investigated via angle-resolved photoemission spectroscopy Author(s): Seong, Seungho; Han, Sang Wook; Min, B. I.; Kwon, Yong Seung; Kang, J. -S Abstract: Employing angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structures of Sb-substituted CeTe2, CeTe2-xSbx(0 <= x <= 0.5), which exhibit charge density wave (CDW) transitions and enhanced thermoelectric (TE) properties and are also predicted to be topological material candidates. Two flat Ce 4 f states are observed, one at approximately-3.5 eV and the other at approximately-0.8 eV, which represent the 4 f (1)-> 4 f(0 )transition and the Kondo-like 4 f(1) L-0 -> 4 f(1) L(1 )transition (where L & strns; is a ligand hole) of trivalent Ce3+ ions, respectively. Two diamond-shaped inner and outer Fermi surfaces (FSs) are observed, which arise from the holelike band centered at P and from the folding of the two-dimensional Brillouin zone (BZ) into the three-dimensional (3D) BZ, respectively. The measured outer FSs demonstrate the non-negligible effect of the 3D electronic structures of CeTe2-xSbx. The CDW-induced zigzag features are observed in the FS of x = 0, but are not observed in the FSs of x > 0, indicating the rapid suppression of the CDW state by the Sb substitution. This finding suggests that the increased resistivity at x > 0, despite the weakened CDW formation, is possibly due to the disorder-induced localization by the Sb substitution, leading to the optimal TE properties at a specific x. The measured band structures of CeTe(2-x)Sb(x)via ARPES exhibit very similar features for different x values, except for the shift of the whole bands toward the Fermi level (EF) with increasing x. This reflects the hole doping introduced by the Sb substitution, which is in good agreement with the calculated band structures. In the ARPES data of x > 0, crossing bands are observed near the X point at approximately-1 eV, which closely resemble Dirac points, suggesting the existence of topological electronic structures of CeTe2-xSbx. Linear dichroism ARPES measurements on CeTe1.75Sb0.25 show that the EF-crossing Te/Sb p states along X-P-X and M-P-M have both in-plane and out-of-plane character, while those along M-X-M have mainly in-plane character.

A comparative synthesis study of α-MnTe across solid-state, Arc-melting, and Te-flux routes

2026-07-31T15:00:00Z

Title: A comparative synthesis study of α-MnTe across solid-state, Arc-melting, and Te-flux routes Author(s): Kim, Bomin; Jeong, Yunseong; Baek, Wonjung; Kim, Hobyeong; Rhee, Taeseong; Cho, Beopgil; Choi, Woo-Jae; Ha, Jae-Hyun; Park, Jaemun; Hong, Jung-Il; Kwon, Yong Seung; Seo, Jungpil; Park, Keeseong Abstract: Although alpha-MnTe has attracted renewed interest in both thermoelectric and altermagnetic contexts, direct comparisons of practically accessible synthesis routes within a common experimental framework remain limited. Here, we compare conventional solid-state reaction, arc melting and Te self-flux growth methods under a common framework of composition control and thermal history. Within the explored conditions, the phase outcome depends not only on the nominal starting composition but also on route-dependent synthesis environments, including volatilization in sealed ampoules, repeated remelting and rapid quenching in arc melting, and crystal-flux interfacial segregation in Te self-flux growth. In the solid-state route, slow heating with a slightly Mn-rich starting composition was associated with reduced MnTe2 and alpha-MnTe-dominant products. Arc melting yielded alpha-MnTe-dominant products without post-annealing, accompanied by dendritic-like microstructures. Te self-flux growth yielded single crystals, although a minor MnTe2-rich interfacial or surface layer often remained. While the present dataset does not define a rigorous phase boundary or a definitive mechanistic model, it provides a systematic comparative framework for route-dependent phase outcomes and impurity persistence in alpha-MnTe synthesis.

Manipulating nonlinear dephasing dynamics of Dirac fermions in nearly degenerate four-wave mixing

2026-05-31T15:00:00Z

Title: Manipulating nonlinear dephasing dynamics of Dirac fermions in nearly degenerate four-wave mixing Author(s): Ha, Seongju; Choi, Youngchan; Park, Nam Hun; Choi, Jungseok; Park, Jaedeok; Ahn, Kwang Jun; Park, Hee-Su; Lee, JaeDong; Lee, Sang Min; Yeom, Dong-Il Abstract: Graphene has led the exploration of nonlinear optical responses in two-dimensional materials with exceptionally strong third-order nonlinearity and its electrical controllability. Nonlinear wave mixing with difference-frequency is particularly interesting in graphene because of the divergent nature of third-order susceptibility as the frequency difference approaches zero, but the study on nearly degenerated four-wave mixing (NDFWM) process in graphene is largely unexplored. In this work, we report the giant third-order susceptibility of monolayer graphene, reaching the order of 10-13 m2 V-2 at the optical telecom C-band via the NDFWM process, and its electrical tunability with a high on-off contrast of 23 dB. Moreover, we observed that the NDFWM response under electrical doping exhibits a resonance feature at low pump intensity in ambient conditions, which is substantially altered by varying the pump power. Through non-perturbative quantum master equation calculations, we revealed that our observation is closely related to the dephasing nature of the Dirac fermion of graphene. The decoherence time of photoexcited carriers is estimated up to 70 fs at low pump intensity, which regime is not accessible by other nonlinear means such as high harmonic generation requiring high intensity light. Our findings not only pave an unprecedented route for probing nonlinear dynamics of photoexcited carriers across a wide range but also have a significant impact on ultrafast nonlinear information processing in graphene.

Crystallographic Stability and No Evidence of Higher-Order Saddle Points in the HfFe6Ge6-type Kagome Metal ScCo6Ge6

2026-03-31T15:00:00Z

Title: Crystallographic Stability and No Evidence of Higher-Order Saddle Points in the HfFe6Ge6-type Kagome Metal ScCo6Ge6 Author(s): Park, Jaemun; Rhee, Taeseong; Cho, Beopgil; Jeong, Yunseong; Hong, Seung-Tae; Kim, Heung-Sik; Park, Keeseong Abstract: While kagome RT6X6 (R = Li, Mg, Zr, and rare-earth metals; T = 3d transition metals; X = Ge/Sn) compounds are widely studied, Co-based RCo6X6 phases remain largely limited to structural reports, with few systematic studies of their physical properties. Here we report Sn-flux-grown single-crystalline ScCo6Ge6 and its structural and physical characterization. Single-crystal X-ray diffraction confirms that ScCo6Ge6 adopts the HfFe6Ge6-type structure rather than the vacancy-driven Y0.5Co3Ge3-type variant. Across the RCo6Ge6 series, structural preference correlates with the Shannon ionic radius of R (8-fold coordination), placing ScCo6Ge6 within the stability range of the HfFe6Ge6-type framework. Magnetization exhibits weak temperature dependence consistent with Pauli-like paramagnetism. The resistivity is well described by a Bloch-Gruneisen form with a Debye temperature exceeding 230 K, consistent with phonon-dominated scattering. Electrical transport also shows a conventional linear Hall response and negligible magnetoresistance, indicative of simple metallic behavior. Electronic structure calculations identify a Ge-derived quadratic saddle point similar to 0.35 eV below E F, with no evidence of higher-order saddle points near the Fermi level. These results highlight that crystallographic stability and physical properties in RCo6Ge6 are governed not only by the Co kagome lattice but also sensitively by the Ge sublattice.