Tunnelling spectroscopy of gate-induced superconductivity in MoS2

Abstract

The ability to gate-induce superconductivity by electrostatic charge accumulation is a recent breakthrough in physics and nanoelectronics. With the exception of LaAlO3/SrTiO3 interfaces, experiments on gate-induced superconductors have been largely confined to resistance measurements, which provide very limited information about the superconducting state. Here, we explore gate-induced superconductivity in MoS2 by performing tunnelling spectroscopy to determine the energy-dependent density of states (DOS) for different levels of electron density n. In the superconducting state, the DOS is strongly suppressed at energy smaller than the gap Δ, which is maximum (Δ ~2 meV) for n of ~1 × 1014 cm−2 and decreases monotonously for larger n. A perpendicular magnetic field B generates states at E < Δ that fill the gap, but a 20% DOS suppression of superconducting origin unexpectedly persists much above the transport critical field. Conversely, an in-plane field up to 10 T leaves the DOS entirely unchanged. Our measurements exclude that the superconducting state in MoS2 is fully gapped and reveal the presence of a DOS that vanishes linearly with energy, the explanation of which requires going beyond a conventional, purely phonon-driven Bardeen–Cooper–Schrieffer mechanism.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Nanofabricated MoS2 devices for tunnelling spectroscopy measurements.
Fig. 2: Temperature evolution of the bias-dependent tunnelling conductance.
Fig. 3: Investigating the nature of the superconducting state in MoS2.
Fig. 4: Magnetic field dependence of the tunnelling DOS.

Change history

  • 17 May 2018

    In the version of this Article originally published, an error during typesetting led to the curve in Fig. 2a being shifted to the right, and the curves in the inset of Fig. 2a being displaced. The figure has now been corrected in all versions of the Article; the original and corrected Fig. 2a are shown below.

References

  1. 1.

    Bardeen, J., Cooper, L. N. & Schrieffer, J. R. Theory of superconductivity. Phys. Rev. 108, 1175–1204 (1957).

  2. 2.

    Giaever, I. Energy gap in superconductors measured by electron tunneling. Phys. Rev. Lett. 5, 147–148 (1960).

  3. 3.

    Giaever, I. Electron tunneling between two superconductors. Phys. Rev. Lett. 5, 464–466 (1960).

  4. 4.

    Giaever, I., Hart, H. R. & Megerle, K. Tunneling into superconductors at temperatures below 1 K. Phys. Rev. 126, 941–948 (1962).

  5. 5.

    McMillan, W. L. & Rowell, J. M. Lead phonon spectrum calculated from superconducting density of states. Phys. Rev. Lett. 14, 108–112 (1965).

  6. 6.

    Parks, R. D. Superconductivity: Part 1 (Marcel Dekker, New York, 1969).

  7. 7.

    Fischer, O., Kugler, M., Maggio-Aprile, I., Berthod, C. & Renner, C. Scanning tunneling spectroscopy of high-temperature superconductors. Rev. Mod. Phys. 79, 353–419 (2007).

  8. 8.

    Yin, Y., Zech, M., Williams, T. L. & Hoffman, J. E. Scanning tunneling microscopy and spectroscopy on iron-pnictides. Phys. C Supercond. 469, 535–544 (2009).

  9. 9.

    Hanaguri, T., Niitaka, S., Kuroki, K. & Takagi, H. Unconventional s-wave superconductivity in Fe(Se,Te). Science 328, 474–476 (2010).

  10. 10.

    Ye, J. T. et al. Superconducting dome in a gate-tuned band insulator. Science 338, 1193–1196 (2012).

  11. 11.

    Caviglia, A. D. et al. Electric field control of the LaAlO3/SrTiO3 interface ground state. Nature 456, 624–627 (2008).

  12. 12.

    Richter, C. et al. Interface superconductor with gap behaviour like a high-temperature superconductor. Nature 502, 528–531 (2013).

  13. 13.

    Ueno, K. et al. Electric-field-induced superconductivity in an insulator. Nat. Mater. 7, 855–858 (2008).

  14. 14.

    Ye, J. T. et al. Liquid-gated interface superconductivity on an atomically flat film. Nat. Mater. 9, 125–128 (2010).

  15. 15.

    Ueno, K. et al. Discovery of superconductivity in KTaO3 by electrostatic carrier doping. Nat. Nanotech. 6, 408–412 (2011).

  16. 16.

    Taniguchi, K., Matsumoto, A., Shimotani, H. & Takagi, H. Electric-field-induced superconductivity at 9.4 K in a layered transition metal disulphide MoS2. Appl. Phys. Lett. 101, 42603 (2012).

  17. 17.

    Shi, W. et al. Superconductivity series in transition metal dichalcogenides by ionic gating. Sci. Rep. 5, 12534 (2015).

  18. 18.

    Jo, S., Costanzo, D., Berger, H. & Morpurgo, A. F. Electrostatically induced superconductivity at the surface of WS2. Nano Lett. 15, 1197–1202 (2015).

  19. 19.

    Costanzo, D., Jo, S., Berger, H. & Morpurgo, A. F. Gate-induced superconductivity in atomically thin MoS2 crystals. Nat. Nanotech. 11, 339–344 (2016).

  20. 20.

    Li, L. J. et al. Controlling many-body states by the electric-field effect in a two-dimensional material. Nature 529, 185–189 (2016).

  21. 21.

    Lu, J. M. et al. Evidence for two-dimensional Ising superconductivity in gated MoS2. Science 350, 1353–1357 (2015).

  22. 22.

    Saito, Y. et al. Superconductivity protected by spin–valley locking in ion-gated MoS2. Nat. Phys. 12, 144–149 (2016).

  23. 23.

    Geim, A. K. & Grigorieva, I. V. Van der Waals heterostructures. Nature 499, 419–425 (2013).

  24. 24.

    Dvir, T. et al. Spectroscopy of bulk and few-layer superconducting NbSe2 with van der Waals tunnel junctions. Nat. Commun. 9, 598 (2018).

  25. 25.

    de Gennes, P. G. Superconductivity of Metals and Alloys (CRC Press, Boca Raton, 1999).

  26. 26.

    Tinkham, M. Introduction to Superconductivity 2nd edn (Dover, New York, 2004).

  27. 27.

    Tsen, A. W. et al. Nature of the quantum metal in a two-dimensional crystalline superconductor. Nat. Phys. 12, 208–212 (2016).

  28. 28.

    Cheiwchanchamnangij, T. & Lambrecht, W. R. L. Quasiparticle band structure calculation of monolayer, bilayer, and bulk MoS2. Phys. Rev. B 85, 205302 (2012).

  29. 29.

    Yuan, N. F. Q., Mak, K. F. & Law, K. T. Possible topological superconducting phases of MoS2. Phys. Rev. Lett. 113, 97001 (2014).

  30. 30.

    Xi, X. et al. Ising pairing in superconducting NbSe2 atomic layers. Nat. Phys. 12, 139–143 (2016).

  31. 31.

    Giubileo, F. et al. Two-gap state density in MgB2: a true bulk property or a proximity effect? Phys. Rev. Lett. 87, 177008 (2001).

  32. 32.

    Iavarone, M. et al. Two-band superconductivity in MgB2. Phys. Rev. Lett. 89, 187002 (2002).

  33. 33.

    Schmidt, H., Zasadzinski, J. F., Gray, K. E. & Hinks, D. G. Break-junction tunneling on MgB2. Phys. C Supercond. 385, 221–232 (2003).

  34. 34.

    Boaknin, E. et al. Heat conduction in the vortex state of NbSe2: evidence for multiband superconductivity. Phys. Rev. Lett. 90, 117003 (2003).

  35. 35.

    Noat, Y. et al. Quasiparticle spectra of 2H-NbSe2: two-band superconductivity and the role of tunneling selectivity. Phys. Rev. B 92, 134510 (2015).

  36. 36.

    Roldán, R., Cappelluti, E. & Guinea, F. Interactions and superconductivity in heavily doped MoS2. Phys. Rev. B 88, 54515 (2013).

  37. 37.

    Ge, Y. & Liu, A. Y. Phonon-mediated superconductivity in electron-doped single-layer MoS2: a first-principles prediction. Phys. Rev. B 87, 241408 (2013).

  38. 38.

    Khezerlou, M. & Goudarzi, H. Transport properties of spin–triplet superconducting monolayer MoS2. Phys. Rev. B 93, 115406 (2016).

  39. 39.

    Nakamura, Y. & Yanase, Y. Odd-parity superconductivity in bilayer transition metal dichalcogenides. Phys. Rev. B 96, 54501 (2017).

  40. 40.

    Hsu, Y.-T., Vaezi, A., Fischer, M. H. & Kim, E.-A. Topological superconductivity in monolayer transition metal dichalcogenides. Nat. Commun. 8, 14985 (2017).

  41. 41.

    Mazin, I. I. & Schmalian, J. Pairing symmetry and pairing state in ferropnictides: theoretical overview. Phys. C Supercond. 469, 614–627 (2009).

  42. 42.

    Mazin, I. I. Superconductivity gets an iron boost. Nature 464, 183–186 (2010).

  43. 43.

    Hirschfeld, P. J., Korshunov, M. M. & Mazin, I. I. Gap symmetry and structure of Fe-based superconductors. Rep. Prog. Phys. 74, 124508 (2011).

  44. 44.

    Bang, Y. & Stewart, G. R. Superconducting properties of the s+/− wave state: Fe-based superconductors. J. Phys. Condens. Matter 29, 123003 (2017).

Download references

Acknowledgements

The authors acknowledge A. Ferreira for continued technical support of the experiments. The authors also thank K.T. Law for extended and extremely useful discussions. Financial support from the Swiss National Science Foundation, the NCCR QSIT and the EU Graphene Flagship project is acknowledged.

Author information

D.C., H.Z. and B.A.R. fabricated the devices and performed electrical measurements. D.C. and H.Z. analysed the data. H.B. provided high-quality MoS2 crystals. A.F.M. conceived the experiment, directed the research and wrote the manuscript. All authors read the manuscript and provided comments.

Correspondence to Alberto F. Morpurgo.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary text and Supplementary Figures 1–7

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Costanzo, D., Zhang, H., Reddy, B.A. et al. Tunnelling spectroscopy of gate-induced superconductivity in MoS2. Nature Nanotech 13, 483–488 (2018). https://doi.org/10.1038/s41565-018-0122-2

Download citation

Further reading