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TT: Fachverband Tiefe Temperaturen

TT 25: f-Electron Systems

TT 25.11: Vortrag

Dienstag, 10. März 2026, 12:15–12:30, HSZ/0101

Polaronic quasiparticles in the valence-transition compound TmSe_1−xTe_x — •chul-hee min^1,2, simon müller³, lenart dudy⁴, michael heber⁵, woojae choi⁶, jonathan denligner⁷, chang jong kang⁸, matthias kalläne², nils wind⁵, markus scholz⁵, christoph schlueter⁵, andrei gloskovskii⁵, emile rienks⁸, vladimir hinkov³, hendrik bentmann¹, yong seung kwon⁶, friedrich reinert³, hyeong do kim⁹, and kai rossnagel^2,5 — ¹FYI, NTNU, Norway — ²IEAP, CAU Kiel, Germany — ³Uni. Würzburg, Germany — ⁴SOLEIL, France — ⁵DESY, Germany — ⁶DGIST, South Korea — ⁷ALS, USA — ⁸BESSY II, Germany — ⁹PAL, South Korea

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 photoemission spectroscopy, we have probed the Tm 3d and 4f emissions in TmSe_1−xTe_x, where a semimetal–insulator transition occurs. Our photoemission results reveal a novel quasiparticle excitation in the semimetallic phase: a Holstein polaron. This local lattice distortion, induced by 4f photohole, is surprising in a metallic system where efficient screening is expected. We interpret this observation as evidence that, in heavy fermion systems, the conduction electrons’ screening response is slower than the characteristic atomic distortion. Our finding underscores the critical role of electron-phonon coupling, which necessitates an extension of the standard Periodic Anderson Model.
[1] Phys. Rev. Lett. 135, 186501 (2025)

Keywords: photoelectron spectroscopy; mixed valence