Giant spin-splitting and gap renormalization driven by trions in single-layer WS2/h-BN heterostructures

Abstract

In two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), new electronic phenomena such as tunable bandgaps1,2,3 and strongly bound excitons and trions emerge from strong many-body effects4,5,6, beyond the spin and valley degrees of freedom induced by spin–orbit coupling and by lattice symmetry7. Combining single-layer TMDs with other 2D materials in van der Waals heterostructures offers an intriguing means of controlling the electronic properties through these many-body effects, by means of engineered interlayer interactions8,9,10. Here, we use micro-focused angle-resolved photoemission spectroscopy (microARPES) and in situ surface doping to manipulate the electronic structure of single-layer WS2 on hexagonal boron nitride (WS2/h-BN). Upon electron doping, we observe an unexpected giant renormalization of the spin–orbit splitting of the single-layer WS2 valence band, from 430 meV to 660 meV, together with a bandgap reduction of at least 325 meV, attributed to the formation of trionic quasiparticles. These findings suggest that the electronic, spintronic and excitonic properties are widely tunable in 2D TMD/h-BN heterostructures, as these are intimately linked to the quasiparticle dynamics of the materials11,12,13.

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Fig. 1: Spatially resolved electronic structure mapping of a WS2/h-BN heterostructure supported on TiO2.
Fig. 2: Electronic structure of strongly electron-doped WS2/h-BN.
Fig. 3: Evolution of single-layer WS2 VBM and CBM dispersion with charge-carrier density.
Fig. 4: Quasiparticle dynamics in doped single-layer WS2.

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Acknowledgements

We thank A. H. MacDonald for discussions. S.U. acknowledges financial support from the Danish Council for Independent Research, Natural Sciences, under the Sapere Aude programme (grant no. DFF-4090-00125) and from VILLUM FONDEN (grant no. 15375). R.J.K. is supported by a fellowship within the postdoctoral programme of the German Academic Exchange Service (DAAD). S.M. acknowledges support by the Swiss National Science Foundation (grant no. P2ELP2-155357). The work at Ohio State was primarily supported by NSF-MRSEC (grant DMR-1420451). Work at the US Naval Research Laboratory (NRL) was supported by core programmes and the NRL Nanoscience Institute, and by the Air Force Office of Scientific Research under contract number AOARD 14IOA018- 134141. This research used resources of the Advanced Light Source, which is a US Department of Energy Office of Science User Facility under contract no. DE-AC02-05CH11231.

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J.K. and S.U. conceived and planned the experiments. K.M.M. and B.T.J. synthesized the single-layer WS2 flakes on SiO2. J.K., S.S., J.X. and R.K.K. assembled the WS2/h-BN heterostructures on TiO2. S.U., R.J.K., S.M., J.K., A.B., E.R. and C.J. performed the microARPES experiments. The microARPES set-up was developed and maintained by C.J., A.B. and E.R. S.U. analysed the experimental data with inputs from C.J. and E.R. All authors contributed to the interpretation and writing of the manuscript.

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Correspondence to Chris Jozwiak.

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Katoch, J., Ulstrup, S., Koch, R.J. et al. Giant spin-splitting and gap renormalization driven by trions in single-layer WS2/h-BN heterostructures. Nature Phys 14, 355–359 (2018). https://doi.org/10.1038/s41567-017-0033-4

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