Gap suppression at a Lifshitz transition in a multi-condensate superconductor

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Abstract

In multi-orbital materials, superconductivity can exhibit several coupled condensates. In this context, quantum confinement in two-dimensional superconducting oxide interfaces offers new degrees of freedom to engineer the band structure and selectively control the occupancy of 3d orbitals by electrostatic doping. Here, we use resonant microwave transport to extract the superfluid stiffness of the (110)-oriented LaAlO3/SrTiO3 interface in the entire phase diagram. We provide evidence of a transition from single-condensate to two-condensate superconductivity driven by continuous and reversible electrostatic doping, which we relate to the Lifshitz transition between 3d bands based on numerical simulations of the quantum well. We find that the superconducting gap is suppressed while the second band is populated, challenging Bardeen–Cooper–Schrieffer theory. We ascribe this behaviour to the existence of superconducting order parameters with opposite signs in the two condensates due to repulsive coupling. Our findings offer an innovative perspective on the possibility to tune and control multiple-orbital physics in superconducting interfaces.

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Fig. 1: Superconductivity and multi-band transport in (110)-oriented LaAlO3/SrTiO3 interfaces.
Fig. 2: Resonant microwave transport in the superconducting state.
Fig. 3: Superfluid stiffness in the UD and OD regimes.
Fig. 4: Single-condensate to two-condensate superconductivity transition in the superfluid stiffness.
Fig. 5: Superconducting phase diagram.

Data availability

All data that support the findings of this study are available from the corresponding authors on reasonable request.

References

  1. 1.

    Imada, M., Fujimori, A. & Tokura, Y. Metal-insulator transitions. Rev. Mod. Phys. 70, 1039–1263 (1998).

  2. 2.

    Ohtomo, A. & Hwang, H. Y. A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface. Nature 427, 423–426 (2004).

  3. 3.

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

  4. 4.

    Biscaras, J. et al. Two-dimensional superconductivity at a Mott insulator/band insulator interface LaTiO3/SrTiO3. Nat. Commun. 1, 89 (2010).

  5. 5.

    Popovic, Z. S., Satpathy, S. & Martin, R. M. Origin of the two-dimensional electron gas carrier density at the LaAlO3 on SrTiO3 interface. Phys. Rev. Lett. 101, 256801 (2008).

  6. 6.

    Delugas, P. et al. Spontaneous 2-dimensional carrier confinement at the n-type SrTiO3/LaAlO3 interface. Phys. Rev. Lett. 106, 166807 (2011).

  7. 7.

    Pentcheva, R. & Pickett, W. Charge localization or itineracy at LaAlO3/SrTiO3 interfaces: hole polarons, oxygen vacancies and mobile electrons. Phys. Rev. B 74, 035112 (2006).

  8. 8.

    Pavlenko, N., Kopp, T., Tsymbal, E., Sawatzky, G. & Mannhart, J. Magnetic and superconducting phases at the LaAlO3/SrTiO3 interface: the role of interfacial Ti 3d electrons. Phys. Rev. B 85, 020407(R) (2012).

  9. 9.

    Scopigno, N. et al. Phase separation from electron confinement at oxide interfaces. Phys. Rev. Lett. 116, 026804 (2016).

  10. 10.

    Salluzzo, M. et al. Orbital reconstruction and the two-dimensional electron gas at the LaAlO3/SrTiO3 interface. Phys. Rev. Lett. 102, 166804 (2009).

  11. 11.

    Seo, S. S. A. et al. Multiple conducting carriers generated in LaAlO3/SrTiO3 heterostructures. Appl. Phys. Lett. 95, 082107 (2009).

  12. 12.

    Biscaras, J. et al. Two-dimensional superconductivity induced by high-mobility carrier doping in LaTiO3/SrTiO3 heterostructures. Phys. Rev. Lett. 108, 247004 (2012).

  13. 13.

    Kim, J. S. et al. Nonlinear Hall effect and multichannel conduction in LaTiO3/SrTiO3 superlattices. Phys. Rev. B 82, 201407 (2010).

  14. 14.

    Ohtsuka, R., Matvejeff, M., Nishio, N., Takahashi, R. & Lippmaa, M. Transport properties of LaTiO3/SrTiO3 heterostructures. Appl. Phys. Lett. 96, 192111 (2010).

  15. 15.

    Caviglia, A. et al. Two-dimensional quantum oscillations of the conductance at LaAlO3/SrTiO3 interfaces. Phys. Rev. Lett. 105, 236802 (2010).

  16. 16.

    Shalom, M. B., Ron, A., Palevski, A. & Dagan, Y. Shubnikov–de Haas oscillations in SrTiO3/LaAlO3 interface. Phys. Rev. Lett. 105, 206401 (2010).

  17. 17.

    Yang, M. et al. High-field magneto-transport in two-dimensional electron gas LaAlO3/SrTiO3. Appl. Phys. Lett. 109, 122106 (2016).

  18. 18.

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

  19. 19.

    Neville, R. C., Hoeneisen, B. & Mead, C. A. Permittivity of strontium titanate. J. Appl. Phys. 43, 2124 (1972).

  20. 20.

    Joshua, A., Pecker, S., Ruhman, J., Altman, E. & Ilani, S. A universal critical density underlying the physics of electrons at the LaAlO3/SrTiO3 interface. Nat. Commun. 3, 1129 (2012).

  21. 21.

    Gariglio, S., Gabay, M. & Triscone, J.-M. Research update: conductivity and beyond at the LaAlO3/SrTiO3 interface. APL Mater. 4, 060701 (2016).

  22. 22.

    Singh, G. et al. Competition between electron pairing and phase coherence in superconducting interfaces. Nat. Commun. 9, 407 (2018).

  23. 23.

    Herranz, G. et al. Engineering two-dimensional superconductivity and Rashba spin–orbit coupling in LaAlO3/SrTiO3 quantum wells by selective orbital occupancy. Nat. Commun. 6, 6028 (2015).

  24. 24.

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

  25. 25.

    Bert, J. A. et al. Gate-tuned superfluid density at the superconducting LaAlO3/SrTiO3 interface. Phys. Rev. B 86, 060503(R) (2012).

  26. 26.

    Monteiro, A. M. R. V. L. et al. Two-dimensional superconductivity at the (111) LaAlO3/SrTiO3 interface. Phys. Rev. B 96, 020504(R) (2017).

  27. 27.

    Rout, P. K., Maniv, E. & Dagan, Y. Link between the superconducting dome and spin–orbit interaction in the (111) LaAlO3/SrTiO3 interface. Phys. Rev. Lett. 119, 237002 (2017).

  28. 28.

    Davis, S. et al. Superconductivity and frozen electronic states at the (111) LaAlO3/SrTiO3 interface. Phys. Rev. Lett. 119, 237002 (2017).

  29. 29.

    Biscaras, J. et al. Limit of the electrostatic doping in two-dimensional electron gases of LaXO3(X = Al,Ti)/SrTiO3. Sci. Rep. 4, 6788 (2014).

  30. 30.

    Hurand, S. et al. Field-effect control of superconductivity and Rashba spin–orbit coupling in top-gated LaAlO3/SrTiO3 devices. Sci. Rep. 5, 12751 (2015).

  31. 31.

    Singh, G. et al. Effect of disorder on superconductivity and Rashba spin–orbit coupling in LaAlO3/SrTiO3 interfaces. Phys. Rev. B 96, 024509 (2017).

  32. 32.

    Mattis, C. & Bardeen, J. Theory of the anomalous skin effect in normal and superconducting metals. Phys. Rev. 111, 412 (1958).

  33. 33.

    Dressel, M. Electrodynamics of metallic superconductors. Adv. Condens. Matter Phys. 2013, 104379 (2013).

  34. 34.

    Kogan, V. G., Martin, C. & Prozorov, R. Superfluid density and specific heat within a self-consistent scheme for a two-band superconductor. Phys. Rev. B 80, 014507 (2009).

  35. 35.

    Kim, H., Tanatar, M. A., Song, YooJang, Yong Seung Kwon, Y. S. & Prozorov, R. Nodeless two-gap superconducting state in single crystals of the stoichiometric iron pnictide LiFeAs. Phys. Rev. B 83, 100502(R) (2011).

  36. 36.

    Binning, G., Baratoff, A., Hoenig, H. E. & Bednorz, J. C. Two-band superconductivity in Nb-doped SrTiO3. Phys. Rev. Lett. 45, 1352–1355 (1980).

  37. 37.

    Fernandes, R. M., Haraldsen, J. T., Wölfle, P. & Balatsky, A. V. Two-band superconductivity in doped SrTiO3 films and interfaces. Phys. Rev. B 87, 014510 (2013).

  38. 38.

    Trevisan, T. V., Schütt, M. & Fernandes, R. M. Unconventional multi-band superconductivity in bulk SrTiO3 and LaAlO3/SrTiO3 interfaces. Phys. Rev. Lett. 121, 127002 (2018).

  39. 39.

    Lin, X. et al. Critical doping for the onset of a two-band superconducting ground state in SrTiO3−δ. Phys. Rev. Lett. 112, 207002 (2014).

  40. 40.

    Swartz, A. G. et al. Polaronic behavior in a weak-coupling superconductor. Proc. Natl Acad. Sci. USA 115, 1475–1480 (2018).

  41. 41.

    Thiemann, M. et al. Single-gap superconductivity and dome of superfluid density in Nb-doped SrTiO3. Phys. Rev. Lett. 120, 237002 (2018).

  42. 42.

    Pesquera, D. et al. Two-dimensional electron gases at LaAlO3/SrTiO3 interfaces: orbital symmetry and hierarchy engineered by crystal orientation. Phys. Rev. Lett. 113, 156802 (2014).

  43. 43.

    Mazin, I. I., Singh, D. J., Johannes, M. D. & Du, M. H. Unconventional superconductivity with a sign reversal in the order parameter of LaFeAsO1−xFx. Phys. Rev. Lett. 101, 057003 (2008).

  44. 44.

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

  45. 45.

    Wang, F. & Lee, D.-H. The electron-pairing mechanism of iron-based superconductors. Science 332, 200–204 (2011).

  46. 46.

    Prozorov, R. & Kogan, V. G. London penetration depth in iron-based superconductors. Rep. Prog. Phys. 74, 124505 (2011).

  47. 47.

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

  48. 48.

    Sprau, P. O. et al. Discovery of orbital-selective cooper pairing in FeSe. Science 357, 75–80 (2017).

  49. 49.

    Kogan, V. G. & Prozorov, R. Interband coupling and nonmagnetic interband scattering in ±s superconductors. Phys. Rev. B 93, 224515 (2016).

  50. 50.

    Chen, C.-T., Tsuei, C. C., Ketchen, M. B., Ren, Z.-A. & Zhao, Z. X. Integer and half-integer flux-quantum transitions in a niobium-iron pnictide loop. Nat. Phys 6, 260–264 (2010).

  51. 51.

    Bell, C. et al. Dominant mobility modulation by the electric field effect at the LaAlO3/SrTiO3 interface. Phys. Rev. Lett. 103, 226802 (2009).

  52. 52.

    Hemberger, J., Lunkenheimer, P., Viana, R., Bohmer, R. & Loidl, A. Electric-field-dependent dielectric constant and nonlinear susceptibility in SrTiO3. Phys. Rev. B 52, 13159 (1995).

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Acknowledgements

The authors thank K. Behnia and J. Lorenzana for useful discussions. This work was supported by the Région Ile-de-France in the framework of CNano IdF, OXYMORE and Sesame programmes, by CNRS through a PICS programme (S2S) and ANR JCJC (Nano-SO2DEG). This work was supported by the Spanish MAT2017-85232-R, MAT2014-56063-C2-1-R and Severo Ochoa SEV-2015-0496 grants and the Generalitat de Catalunya (2017 SGR 1377). This work was supported by the Italian MAECI under the Italia–India collaborative project SUPERTOP-PGR04879. The authors acknowledge funding from the project Quantox of QuantERA ERA-NET Cofund in Quantum Technologies (grant agreement no. 731473) implemented within the European Union’s Horizon 2020 Programme. The authors also acknowledge the COST project Nanoscale Coherent Hybrid Devices for Superconducting Quantum Technologies–Action CA16218.

Author information

N.B. conceived and directed the project. G.Si. and A.J. performed the measurements under the supervision of N.B. Samples were fabricated by G.H., M.S. and F.S. G.Si., A.J. and N.B. carried out analysis of the results and wrote the manuscript with the help of L.B. and J.L. G.Si.,G.Sa, G.H., S.C., M.G. and C.F.-P. contributed to discussions of the results and commented on the final manuscript.

Correspondence to N. Bergeal.

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Supplementary Notes 1–2, Supplementary Figs. 1–7, Supplementary refs. 1–7

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