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Broad spectral tuning of ultra-low-loss polaritons in a van der Waals crystal by intercalation


Phonon polaritons—light coupled to lattice vibrations—in polar van der Waals crystals are promising candidates for controlling the flow of energy on the nanoscale due to their strong field confinement, anisotropic propagation and ultra-long lifetime in the picosecond range1,2,3,4,5. However, the lack of tunability of their narrow and material-specific spectral range—the Reststrahlen band—severely limits their technological implementation. Here, we demonstrate that intercalation of Na atoms in the van der Waals semiconductor α-V2O5 enables a broad spectral shift of Reststrahlen bands, and that the phonon polaritons excited show ultra-low losses (lifetime of 4 ± 1 ps), similar to phonon polaritons in a non-intercalated crystal (lifetime of 6 ± 1 ps). We expect our intercalation method to be applicable to other van der Waals crystals, opening the door for the use of phonon polaritons in broad spectral bands in the mid-infrared domain.

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Fig. 1: Physical properties of α-V2O5.
Fig. 2: Real-space imaging of a α-V2O5 flake.
Fig. 3: Real-space nano-spectroscopy of α-V2O5 and intercalated α’-(Na)V2O5 flakes.
Fig. 4: PhPs dispersion and ab initio permittivity in α-V2O5 and intercalated α’-(Na)V2O5 crystals.
Fig. 5: Anisotropy and lifetimes of PhPs in α-V2O5 and intercalated α’-(Na)V2O5 flakes.

Data availability

The data represented in Figs. 15 are provided with the paper as source data. All other data that support results in this Letter are available from the corresponding author on reasonable request.

Code availability

The custom code employed in this work to perform all calculations is available from the corresponding authors on reasonable request.


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J.T.-G. and G.Á.-P. acknowledge support through the Severo Ochoa Program from the Government of the Principality of Asturias (nos. PA-18-PF-BP17-126 and PA-20-PF-BP19-053, respectively). J.M.-S. acknowledges finantial support from the Clarín Programme from the Government of the Principality of Asturias and a Marie Curie-COFUND grant (PA-18-ACB17-29) and the Ramón y Cajal Program from the Government of Spain (RYC2018-026196-I). K.C., X.P.A.G., H.V. and M.H.B. acknowledge the Air Force Office of Scientific Research (AFOSR) grant no. FA 9550-18-1-0030 for funding support. I.E. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (grant no. FIS2016-76617-P). A.Y.N. acknowledges the Spanish Ministry of Science, Innovation and Universities (national project no. MAT2017-88358-C3-3-R) and the Basque Government (grant no. IT1164-19). Q.B. acknowledges the support from Australian Research Council (grant nos. FT150100450, IH150100006 and CE170100039). R.H. acknowledges support from the Spanish Ministry of Economy, Industry, and Competitiveness (national project RTI2018-094830-B-100 and the Project MDM-2016-0618 of the María de Maeztu Units of Excellence Program) and the Basque Goverment (grant no. IT1164-19). P.A.-G. acknowledges support from the European Research Council under starting grant no. 715496, 2DNANOPTICA.

Author information




P.A.-G. and J.T.-G. conceived the study. P.A.-G. and J.M.-S. supervised the project. J.T.-G. and J.D. carried out the near-field imaging experiments with the help of M.A., S.L. and W.M. G.A.-P., A.B., R.H., Q.B. and A.Y.N. participated in data analysis. P.A.-G. wrote the manuscript with input from J.T.-G., G.A.-P., J.M.-S., A.N., J.D., Q.B., I.E., X.P.A.G., K.C. and R.H. I.E. carried out ab initio calculations. G.A.-P. and A.Y.N. conducted the analytical calculations. K.K., T.K., K.C. and X.P.A.G. contributed to material synthesis and sample preparation. H.V. and M.H.B. performed the transmission electron microscopy characterization. K.C. performed X-ray diffraction indexing and characterization. I.P. contributed to sample fabrication.

Corresponding authors

Correspondence to Javier Martín-Sánchez or Pablo Alonso-González.

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Competing interests

R.H. is cofounder of Neaspec GmbH, a company producing s-SNOM systems, such as the one used in this study. The remaining authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Sections 1–11, Figs. 1–21 and Tables 1–4.

Source data

Source Data Fig. 1

Fig1c.xlsx is an excel file containing the permittivity values of α-V2O5 along the three crystallographic directions.

Source Data Fig. 2

This contains four sheets: Fig2a, Fig2b and Fig2c with the ascii data matrix files of the third harmonic s-SNOM images, and Fig. 2g with the dispersion values.

Source Data Fig. 3

This contains four sheets: Fig3b_100 and Fig3b_001 are the ascii data matrix values of the α-V2O5 nanoFTIR measurements shown in Fig. 3b, and Fig3d_100, and Fig3d_001 are the ascii data matrix values of the α′- NaV2O5 nanoFTIR measurements shown in Fig. 3d.

Source Data Fig. 4

This contains two sheets: Fig4a with six columns corresponding to the measured dispersions for α-V2O5 and α′-NaV2O5 shown in Fig. 4a,b and Fig. 4b with the ab initio calculated permittivity values for α-V2O5 and α′-NaV2O5 shown in Fig. 4b.

Source Data Fig. 5

This contains two sheets: Figure5a corresponding to the s-SNOM measurement of a gold disk on top of a α-V2O5 flake shown in Fig. 5a and Fig. 5b corresponding to the SNOM measurement of a gold disk on top of a α′- NaV2O5 flake shown in Fig. 5b.

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Taboada-Gutiérrez, J., Álvarez-Pérez, G., Duan, J. et al. Broad spectral tuning of ultra-low-loss polaritons in a van der Waals crystal by intercalation. Nat. Mater. 19, 964–968 (2020).

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