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Unconventional superconductivity at mesoscopic point contacts on the 3D Dirac semimetal Cd3As2

Nature Materials volume 15, pages 32–37 (2016)Cite this article

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Abstract

Three-dimensional (3D) Dirac semimetals1,2,3 exist close to topological phase boundaries4 which, in principle, should make it possible to drive them into exotic new phases, such as topological superconductivity5, by breaking certain symmetries. A practical realization of this idea has, however, hitherto been lacking. Here we show that the mesoscopic point contacts between pure silver (Ag) and the 3D Dirac semimetal Cd3As2 (ref. 2) exhibit unconventional superconductivity6 with a critical temperature (onset) greater than 6 K whereas neither Cd3As2 nor Ag are superconductors. A gap amplitude of 6.5 meV is measured spectroscopically in this phase that varies weakly with temperature and survives up to a remarkably high temperature of 13 K, indicating the presence of a robust normal-state pseudogap7. The observations indicate the emergence of a new unconventional superconducting phase that exists in a quantum mechanically confined region under a point contact between a Dirac semimetal and a normal metal.

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Figure 1: Evidence of superconductivity in Cd3As2 point contacts.
Figure 2: Magnetic field dependence of transport in thermal and intermediate regimes of point contact.
Figure 3: Evidence of a normal state pseudogap from the ballistic regime spectra.
Figure 4: The zero-bias conductance peak.

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References

  1. Liu, Z. K. et al. Discovery of a three-dimensional topological Dirac semimetal, Na3Bi. Science 343, 864–867 (2014).

    Article  CAS  Google Scholar 

  2. Liu, Z. K. et al. A stable three-dimensional topological Dirac semimetal Cd3As2 . Nature Mater. 13, 677–681 (2014).

    Article  CAS  Google Scholar 

  3. Young, S. M. S. et al. Dirac semimetal in three dimensions. Phys. Rev. Lett. 108, 140405 (2012).

    Article  CAS  Google Scholar 

  4. Wang, Z. et al. Dirac semimetal and topological phase transitions in A3Bi (A = Na, K, Rb). Phys. Rev. B 85, 195320 (2012).

    Article  Google Scholar 

  5. Qi, X.-L. & Zhang, S.-C. Topological insulators and superconductors. Rev. Mod. Phys. 83, 1057–1110 (2011).

    Article  CAS  Google Scholar 

  6. Norman, M. R. The challenge of unconventional superconductivity. Science 332, 196–200 (2011).

    Article  CAS  Google Scholar 

  7. Buchanan, M. Mind the pseudogap. Nature 409, 8–11 (2001).

    Article  CAS  Google Scholar 

  8. Hasan, M. Z. & Kane, C. L. Colloquium: Topological insulators. Rev. Mod. Phys. 82, 3045–3067 (2010).

    CAS  Google Scholar 

  9. Burkov, A. A. & Balents, L. Weyl semimetal in a topological insulator multilayes. Phys. Rev. Lett. 107, 127205 (2011).

    Article  CAS  Google Scholar 

  10. Wan, X., Turner, A. M., Vishwanath, A. & Savrasov, S. Y. Topological semimetal and Fermi-arc surface states in the electronic structure of pyrochlore iridates. Phys. Rev. B 83, 205101 (2011).

    Article  Google Scholar 

  11. Fu, L. & Kane, C. Superconducting proximity effect and Majorana fermions at the surface of a topological insulator. Phys. Rev. Lett. 100, 096407 (2008).

    Article  Google Scholar 

  12. Wang, Z., Weng, H., Wu, Q., Dai, X. & Fang, Z. Three-dimensional Dirac semimetal and quantum transport in Cd3As2 . Phys. Rev. B 88, 125427 (2013).

    Article  Google Scholar 

  13. Qi, X.-L., Hughes, T. L. & Zhang, S.-C. Topological invariants for the Fermi surface of a time-reversal-invariant superconductor. Phys. Rev. B 81, 134508 (2010).

    Article  Google Scholar 

  14. Jeon, S. et al. Landau quantization and quasiparticle interference in the three-dimensional Dirac semimetal Cd3As2 . Nature Mater. 13, 851–856 (2014).

    Article  CAS  Google Scholar 

  15. Blonder, G. E., Tinkham, M. & Klapwijk, T. M. Transition from metallic to tunneling regimes in superconducting microconstrictions: Excess current, charge imbalance, and supercurrent conversion. Phys. Rev. B 25, 4515–4532 (1982).

    Article  CAS  Google Scholar 

  16. Tinkham, M. Introduction to Superconductivity 2nd edn (McGraw-Hill, 2004).

    Google Scholar 

  17. Sheet, G., Mukhopadhyay, S. & Raychaudhuri, P. Role of critical current on the point-contact Andreev reflection spectra between a normal metal and a superconductor. Phys. Rev. B 69, 134507 (2004).

    Article  Google Scholar 

  18. Naidyuk, Y. G. & Yanson, I. K. Point-contact Spectroscopy (Springer, 2004).

    Google Scholar 

  19. Renner, Ch., Revaz, B., Genoud, J. Y., Kadowaki, K. & Fischer, O. Pseudogap precursor of the superconducting gap in under- and overdoped Bi2Sr2CaCu2O8+δ . Phys. Rev. Lett. 80, 149–152 (1998).

    Article  CAS  Google Scholar 

  20. Sheet, G. et al. Phase-incoherent superconducting pairs in the normal state of Ba(Fe1−xCox)2As2 . Phys. Rev. Lett. 105, 167003 (2010).

    Article  Google Scholar 

  21. Arham, H. Z. et al. Gap-like feature in the normal state of X(Fe1−xCox)2As2, X = Ba, Sr and Fe1+yTe revealed by point contact spectroscopy. J. Phys. 400, 022001 (2012).

    Google Scholar 

  22. Choi, H. Y., Bang, Y. & Campbell, D. K. Andreev reflections in the pseudogap state of cuprate superconductors. Phys. Rev. B 61, 9748–9751 (2000).

    Article  CAS  Google Scholar 

  23. Tanaka, Y. & Kashiwaya, S. Theory of tunneling spectroscopy of d-wave superconductors. Phys. Rev. Lett. 74, 3451 (1995).

    Article  CAS  Google Scholar 

  24. Tanaka, Y., Tanuma, Y., Kuroki, K. & Kashiwaya, S. Theory of magnetotunneling spectroscopy in spin triplet p-wave superconductors. J. Phys. Soc. Jpn 71, 2102 (2002).

    Article  CAS  Google Scholar 

  25. Sato, M., Tanaka, Y., Yada, K. & Yokoyama, T. Topology of Andreev bound states with flat dispersion. Phys. Rev. B 83, 224511 (2011).

    Article  Google Scholar 

  26. Tanaka, Y., Sato, M. & Nagaosa, N. Symmetry and topology in superconductors- odd- frequency pairing and edge states. J. Phys. Soc. Jpn 81, 011013 (2012).

    Article  Google Scholar 

  27. Sasaki, S. et al. Topological superconductivity in CuxBi2Se3 . Phys. Rev. Lett. 107, 217001 (2011).

    Article  Google Scholar 

  28. Takami, S. et al. Quasi-classical theory of tunneling spectroscopy in superconducting topological insulator. J. Phys. Soc. Jpn 83, 064705 (2014).

    Article  Google Scholar 

  29. Yamakage, A., Yada, K., Sato, M. & Tanaka, Y. Theory of tunneling conductance and surface-state transition in superconducting topological insulators. Phys. Rev. B 85, 180509 (2012).

    Article  Google Scholar 

  30. Kobayashi, S. & Sato, M. Topological superconductivity in Dirac semimetals. Preprint at http://arxiv.org/abs/1504.07408 (2015).

  31. Wang, H. et al. Observation of superconductivity induced by a point contact on 3D Dirac semimetal Cd3As2 crystals. Nature Mater. http://dx.doi.org/10.1038/nmat4456 (2015)

  32. Wexler, A. The size effect and the non-local Boltzmann transport equation in orifice and disk geometry. Proc. Phys. Soc. 89, 927–941 (1966).

    Article  CAS  Google Scholar 

  33. Datta, S. Electronic Transport in Mesoscopic Systems (Cambridge Univ. Press, 1995).

    Book  Google Scholar 

  34. Plecenik, A., Grajcar, M., Beaka, S., Seidel, P. & Pfuch, A. Finite-quasiparticle-lifetime effects in the differential conductance of Bi2Sr2CaCu2Oy/Au junctions. Phys. Rev. B 49, 10016 (1994).

    Article  CAS  Google Scholar 

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Acknowledgements

We thank professors S. Ramakrishnan, P. Raychaudhuri and I. Mazin for fruitful discussion. We would like to thank D. Chakraborty, Y. Singh and S. Kumar for critically reading the manuscript. We thank Y. Singh for helping us with the bulk transport measurements. We acknowledge the support of A. Singh, S. Jyotsna, P. Saha and A. Aggarwal during various stages of this work. A.K.G. thanks Department of Science and Technology (DST) for financial support. G.S. would like to acknowledge partial financial support from a research grant of a Ramanujan Fellowship awarded by the Department of Science and Technology (DST), Govt. of India under grant number SR/S2/RJN-99/2011 and a research grant from DST-Nanomission under grant number SR/NM/NS-1249/2013.

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  1. Leena Aggarwal and Abhishek Gaurav: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Physical Sciences, Indian Institute of Science Education and Research (IISER), Mohali, Sector 81, S. A. S. Nagar Manauli, PO 140306, India,

    Leena Aggarwal, Abhishek Gaurav & Goutam Sheet

  2. Department of Chemistry, Indian Institute of Technology, New Delhi 110016, India

    Gohil S. Thakur, Zeba Haque & Ashok K. Ganguli

  3. Institute of Nano Science and Technology, Mohali 160064, India

    Ashok K. Ganguli

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  1. Leena Aggarwal
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  6. Goutam Sheet
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Contributions

L.A. and A.G. contributed equally to this work. G.S. conceived the idea, designed the experiments and developed the analysis tools. L.A., A.G. and G.S. performed all the low-temperature experiments and analysed the data. G.S.T., Z.H. and A.K.G. synthesized and characterized the materials. G.S. wrote the manuscript.

Corresponding authors

Correspondence to Ashok K. Ganguli or Goutam Sheet.

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Aggarwal, L., Gaurav, A., Thakur, G. et al. Unconventional superconductivity at mesoscopic point contacts on the 3D Dirac semimetal Cd3As2. Nature Mater 15, 32–37 (2016). https://doi.org/10.1038/nmat4455

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