Competition between electron pairing and phase coherence in superconducting interfaces

• Published in: Nature communications Vol. 9; no. 1; pp. 407 - 8
• Main Authors: Singh, G., Jouan, A., Benfatto, L., Couëdo, F., Kumar, P., Dogra, A., Budhani, R. C., Caprara, S., Grilli, M., Lesne, E., Barthélémy, A., Bibes, M., Feuillet-Palma, C., Lesueur, J., Bergeal, N.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 29-01-2018; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/1003; 639/766/119/544; Carrier density; Competition; Electron gas; Energy; Fluids; Heterostructures; Humanities and Social Sciences; Interfaces; Laboratories; Magnetism; multidisciplinary; Oxides; Phase coherence; Phase transitions; Physics; Quantum wells; Science; Science (multidisciplinary); Stiffness; Strontium titanates; Superconductivity; Superfluidity
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-02907-8

In LaAlO
3
/SrTiO
3
heterostructures, a gate tunable superconducting electron gas is confined in a quantum well at the interface between two insulating oxides. Remarkably, the gas coexists with both magnetism and strong Rashba spin–orbit coupling. However, both the origin of superconductivity and the nature of the transition to the normal state over the whole doping range remain elusive. Here we use resonant microwave transport to extract the superfluid stiffness and the superconducting gap energy of the LaAlO
3
/SrTiO
3
interface as a function of carrier density. We show that the superconducting phase diagram of this system is controlled by the competition between electron pairing and phase coherence. The analysis of the superfluid density reveals that only a very small fraction of the electrons condenses into the superconducting state. We propose that this corresponds to the weak filling of high-energy
d
xz
/
d
yz
bands in the quantum well, more apt to host superconductivity.
The nature of the doping dependent superconducting transition remains elusive for a two dimensional electron gas at the LaAlO
3
/SrTiO
3
interface. Here, Singh et al. report superfluid stiffness and the superconducting gap energy at such interface as a function of carrier density.