In LaAlO3/SrTiO3 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 LaAlO3/SrTiO3 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 highenergy dxz/dyz bands in the quantum well, more apt to host superconductivity.
Bibliographical noteFunding Information:
We acknowledge R. Lobo, C. Castellani, and J. Lorenzana for useful discussions. This work has been supported by the Région Ile-de-France in the framework of CNano IdF, OXYMORE, and Sesame programs, by CNRS through a PICS program (S2S) and ANR JCJC (Nano-SO2DEG). L.B. acknowledges financial support by the Italian MAECI under the Italian-India collaborative project SUPERTOP-PGR04879. Part of this work has been supported by the IFCPAR French-Indian program (contract 4704-A). Research in India was funded by the CSIR and DST, Government of India.
1Laboratoire de Physique et d’Etude des Matériaux, ESPCI Paris, PSL Research University, CNRS, 10 Rue Vauquelin, 75005 Paris, France. 2Université Pierre and Marie Curie, Sorbonne-Universités, 75005 Paris, France. 3Institute for Complex Systems (ISC-CNR), UOS Sapienza, Piazzale A. Moro 5, 00185 Roma, Italy. 4Dipartimento di Fisica Università di Roma “La Sapienza”, Piazzale A. Moro 5, 00185 Roma, Italy. 5National Physical Laboratory, Council of Scientific and Industrial Research (CSIR), Dr. K.S. Krishnan Marg, New Delhi, 110012, India. 6Condensed Matter Low Dimensional Systems Laboratory, Department of Physics, Indian Institute of Technology, Kanpur, 208016, India. 7Unité Mixte de Physique CNRS-Thales, 1 Av. A. Fresnel, 91767 Palaiseau, France. G. Singh and A. Jouan contributed equally to this work. Correspondence and requests for materials should be addressed to L.B. (email: firstname.lastname@example.org) or to N.B. (email: email@example.com)
© The Author(s) 2018.