Acoustic terahertz graphene plasmons revealed by photocurrent nanoscopy

Abstract

Terahertz (THz) fields are widely used for sensing, communication and quality control1. In future applications, they could be efficiently confined, enhanced and manipulated well below the classical diffraction limit through the excitation of graphene plasmons (GPs)2,3. These possibilities emerge from the strongly reduced GP wavelength, λp, compared with the photon wavelength, λ0, which can be controlled by modulating the carrier density of graphene via electrical gating4,5,6,7,8. Recently, GPs in a graphene/insulator/metal configuration have been predicted to exhibit a linear dispersion (thus called acoustic plasmons) and a further reduced wavelength, implying an improved field confinement9,10,11, analogous to plasmons in two-dimensional electron gases (2DEGs) near conductive substrates12. Although infrared GPs have been visualized by scattering-type scanning near-field optical microscopy (s-SNOM)6,7, the real-space imaging of strongly confined THz plasmons in graphene and 2DEGs has been elusive so far—only GPs with nearly free-space wavelengths have been observed13. Here we demonstrate real-space imaging of acoustic THz plasmons in a graphene photodetector with split-gate architecture. To that end, we introduce nanoscale-resolved THz photocurrent near-field microscopy, where near-field excited GPs are detected thermoelectrically14 rather than optically6,7. This on-chip detection simplifies GP imaging as sophisticated s-SNOM detection schemes can be avoided. The photocurrent images reveal strongly reduced GP wavelengths (λp ≈ λ0/66), a linear dispersion resulting from the coupling of GPs with the metal gate below the graphene, and that plasmon damping at positive carrier densities is dominated by Coulomb impurity scattering.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: THz photocurrent nanoscopy of graphene plasmons in a split-gate photodetector.
Figure 2: THz graphene plasmon wavelengths and dispersion.
Figure 3: Near-field distribution of THz graphene plasmons.
Figure 4: Wavelength and amplitude decay time of acoustic THz graphene plasmons as a function of carrier density.

References

  1. 1

    Tonouchi, M. Cutting-edge terahertz technology. Nat. Photon. 1, 97–105 (2007).

    CAS  Google Scholar 

  2. 2

    Wunsch, B., Stauber, T., Sols, F. & Guinea, F. Dynamical polarization of graphene at finite doping. New J. Phys. 8, 318 (2006).

    Article  Google Scholar 

  3. 3

    Jablan, M., Buljan, H. & Soljačić, M. Plasmonics in graphene at infrared frequencies. Phys. Rev. B 80, 245435 (2009).

    Article  Google Scholar 

  4. 4

    Ju, L. et al. Graphene plasmonics for tunable terahertz metamaterials. Nat. Nanotech. 6, 630–634 (2011).

    CAS  Article  Google Scholar 

  5. 5

    Yan, H. et al. Tunable infrared plasmonic devices using graphene/insulator stacks. Nat. Nanotech. 7, 330–334 (2012).

    CAS  Article  Google Scholar 

  6. 6

    Chen, J. et al. Optical nano-imaging of gate-tunable graphene plasmons. Nature 487, 77–81 (2012).

    CAS  Article  Google Scholar 

  7. 7

    Fei, Z. et al. Gate-tuning of graphene plasmons revealed by infrared nano-imaging. Nature 487, 82–85 (2012).

    CAS  Article  Google Scholar 

  8. 8

    Alonso-González, P. et al. Controlling graphene plasmons with resonant metal antennas and spatial conductivity patterns. Science 344, 1369–1373 (2014).

    Article  Google Scholar 

  9. 9

    Stauber, T. & Gomez-Santos, G. Plasmons in layered structures including graphene. New J. Phys. 14, 105018 (2012).

    Article  Google Scholar 

  10. 10

    Gu, X., Lin, I.-T. & Liu, J.-M. Extremely confined terahertz surface plasmon-polaritons in graphene-metal structures. Appl. Phys. Lett. 103, 071103 (2013).

    Article  Google Scholar 

  11. 11

    Principi, A., Asgari, R. & Polini, M. Acoustic plasmons and composite hole-acoustic plasmon satellite bands in graphene on a metal gate. Solid State Commun. 151, 1627–1630 (2011).

    CAS  Article  Google Scholar 

  12. 12

    Allen, S. J., Tsui, D. C. & Logan, R. A. Observation of the two-dimensional plasmon in silicon inversion layers. Phys. Rev. Lett. 38, 980–983 (1977).

    CAS  Article  Google Scholar 

  13. 13

    Mitrofanov, O. et al. Terahertz near-field imaging of surface plasmon waves in graphene structures. Solid State Commun. 224, 47–52 (2015).

    CAS  Article  Google Scholar 

  14. 14

    Lundeberg, M. B. et al. Thermoelectric detection and imaging of propagating graphene plasmons. http://dx.doi.org/10.1038/nmat4755 (2016).

  15. 15

    Wang, L. et al. One-dimensional electrical contact to a two-dimensional material. Science 342, 614–617 (2013).

    CAS  Article  Google Scholar 

  16. 16

    Huber, A. J., Keilmann, F., Wittborn, J., Aizpurua, J. & Hillenbrand, R. Terahertz near-field nanoscopy of mobile carriers in single semiconductor nanodevices. Nano Lett. 8, 3766–3770 (2008).

    CAS  Article  Google Scholar 

  17. 17

    Woessner, A. et al. Near-field photocurrent nanoscopy on bare and encapsulated graphene. Nat. Commun. 7, 10783 (2016).

    CAS  Article  Google Scholar 

  18. 18

    Keilmann, F. & Hillenbrand, R. Near-field microscopy by elastic light scattering from a tip. Phil. Trans. R. Soc. Lond. A 362, 787–805 (2004).

    CAS  Article  Google Scholar 

  19. 19

    Gabor, N. M. et al. Hot carrier–assisted intrinsic photoresponse in graphene. Science 334, 648–652 (2011).

    CAS  Article  Google Scholar 

  20. 20

    Cai, X. et al. Sensitive room-temperature terahertz detection via the photothermoelectric effect in graphene. Nat. Nanotech. 9, 814–819 (2014).

    CAS  Article  Google Scholar 

  21. 21

    Diaconescu, B. et al. Low-energy acoustic plasmons at metal surfaces. Nature 448, 57–59 (2007).

    CAS  Article  Google Scholar 

  22. 22

    Koppens, F. H. L., Chang, D. E. & García de Abajo, F. J. Graphene plasmonics: a platform for strong light–matter interactions. Nano Lett. 11, 3370–3377 (2011).

    CAS  Article  Google Scholar 

  23. 23

    Nikitin, A. Y., Guinea, F., Garcia-Vidal, F. J. & Martin-Moreno, L. Fields radiated by a nanoemitter in a graphene sheet. Phys. Rev. B 84, 195446 (2011).

    Article  Google Scholar 

  24. 24

    Christensen, J., Manjavacas, A., Thongrattanasiri, S., Koppens, F. H. L. & García de Abajo, F. J. Graphene plasmon waveguiding and hybridization in individual and paired nanoribbons. ACS Nano 6, 431–440 (2012).

    CAS  Article  Google Scholar 

  25. 25

    Profumo, R. E. V., Asgari, R., Polini, M. & MacDonald, A. H. Double-layer graphene and topological insulator thin-film plasmons. Phys. Rev. B 85, 085443 (2012).

    Article  Google Scholar 

  26. 26

    Shung, K. W. K. Dielectric function and plasmon structure of stage-1 intercalated graphite. Phys. Rev. B 34, 979–993 (1986).

    CAS  Article  Google Scholar 

  27. 27

    Vafek, O. Thermoplasma polariton within scaling theory of single-layer graphene. Phys. Rev. Lett. 97, 266406 (2006).

    Article  Google Scholar 

  28. 28

    Falkovsky, L. A. & Varlamov, A. A. Space-time dispersion of graphene conductivity. Eur. Phys. J. B 56, 281–284 (2007).

    CAS  Article  Google Scholar 

  29. 29

    Woessner, A. et al. Highly confined low-loss plasmons in graphene–boron nitride heterostructures. Nat. Mater. 14, 421–425 (2015).

    CAS  Article  Google Scholar 

  30. 30

    Principi, A. et al. Plasmon losses due to electron-phonon scattering: the case of graphene encapsulated in hexagonal boron nitride. Phys. Rev. B 90, 165408 (2014).

    Article  Google Scholar 

  31. 31

    Principi, A., Vignale, G., Carrega, M. & Polini, M. Impact of disorder on Dirac plasmon losses. Phys. Rev. B 88, 121405 (2013).

    Article  Google Scholar 

  32. 32

    Cai, Y., Zhang, L., Zeng, Q., Cheng, L. & Xu, Y. Infrared reflectance spectrum of BN calculated from first principles. Solid State Commun. 141, 262–266 (2007).

    CAS  Article  Google Scholar 

  33. 33

    Caldwell, J. D. et al. Sub-diffractional volume-confined polaritons in the natural hyperbolic material hexagonal boron nitride. Nat. Commun. 5, 5221 (2014).

    CAS  Article  Google Scholar 

Download references

Acknowledgements

We thank C. Crespo for technical assistance with the THz laser. R.H., P.A-G. and A.N. acknowledge support from the Spanish Ministry of Economy and Competitiveness (national projects MAT2015-65525-R, FIS2014-60195-JIN and MAT2014-53432-C5-4-R, respectively). F.H.L.K. acknowledges support from the Fundacio Cellex Barcelona, the ERC Career integration grant (294056, GRANOP), the ERC starting grant (307806, CarbonLight), the Government of Catalonia through the SGR grant (2014-SGR-1535), the Mineco grants Ramón y Cajal (RYC-2012-12281) and Plan Nacional (FIS2013-47161-P) and project GRASP (FP7-ICT-2013-613024-GRASP). R.H., F.H.L.K., A.P. and M.P. acknowledge support by the EC under the Graphene Flagship (contract no. CNECT-ICT-604391). Y.G. and J.H. acknowledge support from the US Office of Naval Research (N00014-13-1- 0662).

Author information

Affiliations

Authors

Contributions

P.A-G., A.J.H. and R.H. implemented the THz photocurrent near-field microscope. P.A-G. and A.W. performed the photocurrent nanoscopy experiments. A.Y.N. and A.W. performed the simulations of the GP near-field distributions and GP dispersion. Y.G. fabricated the h-BN/graphene/h-BN photodetector devices. A.P., N.F. and M.P. developed the analytic model for the acoustic GP dispersion and the theory of plasmon damping. W.Y. and S.V. fabricated photocurrent devices based on exfoliated and CVD-grown graphene. K.W. and T.T. synthesized the h-BN. F.C., L.E.H. and J.H. coordinated the fabrication of the different photocurrent samples. P.A-G., A.Y.N., A.W., M.B.L., M.P., F.H.L.M. and R.H. analysed the data. P.A-G., A.Y.N. and R.H. wrote the manuscript with input from all authors. All authors contributed to the scientific discussion and manuscript revisions.

Corresponding authors

Correspondence to Pablo Alonso-González or Rainer Hillenbrand.

Ethics declarations

Competing interests

R.H. is a co-founder of Neaspec GmbH, a company producing scattering-type scanning near-field optical microscope systems such as the one used in this study. All other authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 1355 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Alonso-González, P., Nikitin, A., Gao, Y. et al. Acoustic terahertz graphene plasmons revealed by photocurrent nanoscopy. Nature Nanotech 12, 31–35 (2017). https://doi.org/10.1038/nnano.2016.185

Download citation

Further reading

Search

Quick links

Find nanotechnology articles, nanomaterial data and patents all in one place. Visit Nano by Nature Research