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Multiple mobile excitons manifested as sidebands in quasi-one-dimensional metallic TaSe3


Charge neutrality and their expected itinerant nature makes excitons potential transmitters of information. However, exciton mobility remains inaccessible to traditional optical experiments that only create and detect excitons with negligible momentum. Here, using angle-resolved photoemission spectroscopy, we detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide, TaSe3. The low density of conduction electrons and the low dimensionality in TaSe3 combined with a polaronic renormalization of the conduction band and the poorly screened interaction between these polarons and photo-induced valence holes leads to various excitonic bound states that we interpret as intrachain and interchain excitons, and possibly trions. The thresholds for the formation of a photo-hole together with an exciton appear as side valence bands with dispersions nearly parallel to the main valence band, but shifted to lower excitation energies. The energy separation between side and main valence bands can be controlled by surface doping, enabling the tuning of certain exciton properties.

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Fig. 1: The crystalline and electronic structures of TaSe3 at 15 K.
Fig. 2: SVBs and polarons in pristine sample.
Fig. 3: Dependence on potassium doping of the electronic structure of TaSe3.
Fig. 4: Schematic of how mobile excitons show up in the form of SVBs in photoemission.

Data availability

The data that support the findings of this study are available in the MARVEL public repository (MARVEL Materials Cloud Archive: with the same title as this paper.


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We acknowledge E. Rienks, H. Li, Y. Hu and V. Strokov for help during the ARPES experiments. We thank D. van der Marel for discussions. M.S., J.Z.M. and J.J. were supported by the Sino-Swiss Science and Technology Cooperation (grant no. IZLCZ2-170075). M.S. was supported by the Swiss National Science Foundation under grant no. 200021_188413. M.S., O.V.Y. and D.G.-M. were supported by the NCCR MARVEL funded by the Swiss National Science Foundation. M.R. and J.Z.M. were supported by the Swiss National Science Foundation under grant no. 200021_182695. M.M. was supported by the Swiss National Science Foundation under grant no. 200021_166271. M.N. and N.K. have received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 701647; and M.N. has received funding from the Swiss National Science Foundation under grant no. 200021_159678. J.Z.M. was supported by City University of Hong Kong through the start-up project (project no. 9610489), the National Natural Science Foundation of China (12104379) and Shenzhen Research Institute, City University of Hong Kong. M.A.S. is supported by Deutsche Forschungsgemeinschaft through the Emmy-Noether programme (SE 2558/2). J.L.Z. was supported by Excellence Program of Hefei Science Center CAS 2021HSC-UE011. W.W.X. was supported by Beckman Young Investigator Programme funded by Arnold and Mabel Beckman Foundation and US NSF DMR-1944965. X.G. was supported by the US Department of Energy Division of Basic Energy Sciences (DG-FG02-98ER45706).

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Authors and Affiliations



J.Z.M. performed ARPES experiments with the help of M.N., J.J., N.C.P., M.R. and W.H.F. S.M.N. and Z.W. performed first-principles calculations of the band structure. J.Z.M. plotted all the figures. X.G. and W.W.X. synthesized the single crystals. C.Y.X. performed primary high magnetic field quantum oscillation measurements with the help of J.Z.M., J.L.Z., T.S. and Y.M.X. H.H. and U.D.G. analysed the possibility of boson driven band structures with the help of D.G.-M and O.V.Y. I.K. performed Raman measurements for checking the phonon energy. N.K. and Y.S. performed primary transport measurements with PPMS. M.A.S. helped by ruling out the bosonic strong coupling scenario. C.M. and M.M. analysed different physical scenarios on the basis of bound states and worked out the theory of excitonic sidebands. All authors contributed to the discussion of this project. J.Z.M., C.M., M.M. and M.S. wrote the paper.

Corresponding authors

Correspondence to Junzhang Ma, Markus Müller or Ming Shi.

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Supplementary information

Supplementary Information

I. Features of metallic TaSe3 that favour the observation of mobile bound states. II. Ruling out standard scenarios for replica bands. III. EDCs identifying SVBs and the polaronic QPs. IV. Doping dependence of ARPES spectra. V. Soft-X-ray ARPES spectra and bulk doping by W. VI. Mobile excitons in a 1D metal. VII. The effect of screening on a Q1D exciton problem. VIII. Doping dependence of 1D exciton characteristics. IX. Summary.

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Ma, J., Nie, S., Gui, X. et al. Multiple mobile excitons manifested as sidebands in quasi-one-dimensional metallic TaSe3. Nat. Mater. 21, 423–429 (2022).

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