Competition between electron pairing and phase coherence in superconducting interfaces

Abstract

The large diversity of exotic electronic phases displayed by two-dimensional superconductors confronts physicists with new challenges. These include the recently discovered quantum Griffith singularity in atomic Ga films, topological phases in proximized topological insulators and unconventional Ising pairing in transition metal dichalcogenide layers. 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 and is a candidate system for the creation of Majorana fermions. However, both the origin of superconductivity and the nature of the transition to the normal state over the whole doping range remain elusive. Missing such crucial information impedes harnessing this outstanding system for future superconducting electronics and topological quantum computing. Here we show that the superconducting phase diagram of LaAlO3/SrTiO3 is controlled by the competition between electron pairing and phase coherence. Through resonant microwave experiments, we measure the superfluid stiffness and infer the gap energy as a function of carrier density. Whereas a good agreement with the Bardeen-Cooper-Schrieffer (BCS) theory is observed at high carrier doping, we find that the suppression of Tc at low doping is controlled by the loss of macroscopic phase coherence instead of electron pairing as in standard BCS theory. We find that only a very small fraction of the electrons condenses into the superconducting state and propose that this corresponds to the weak filling of a high-energy dxz/yz band, more apt to host superconductivity

References in corpus (10)

• Electric Field Control of the LaAlO${}_3$/SrTiO${}_3$ Interface Ground State
• Phase fluctuations in a strongly disordered s-wave superconductor close to the metal-insulator transition
• Rashba induced magnetoconductance oscillations in the LaAlO3-SrTiO3 heterostructure
• Superconductivity vs bound state formation in a two-band superconductor with small Fermi energy -- applications to Fe-pnictides/chalcogenides and doped SrTiO3
• Evidence of weak superconductivity at the room-temperature grown LaAlO${}_3$/SrTiO${}_3$ interface
• Broadband method for precise microwave spectroscopy of superconducting thin films near the critical temperature
• Modulation of the superconducting critical temperature due to quantum confinement at the LaAlO${}_3$/SrTiO${}_3$ interface
• Effect of disorder on superconductivity and Rashba spin-orbit coupling in LaAlO3/SrTiO3 interfaces
• High field magneto-transport in two-dimensional electron gas LaAlO3/SrTiO3
• Slowing down of vortex motion in thin NbN films near the superconductor-insulator transition

Cited by in corpus (19)

• Spin-charge interconversion in KTaO${}_3$ two-dimensional electron gases
• Superfluid stiffness of a KTaO3-based two-dimensional electron gas
• Non-linear $IV$ characteristics in two-dimensional superconductors: Berezinskii-Kosterlitz-Thouless physics vs inhomogeneity
• Universal behavior of the bosonic metallic ground state in a two-dimensional superconductor
• Negative electronic compressibility and nanoscale inhomogeneity in ionic-liquid gated two-dimensional superconductors
• Gate-tunable hallmarks of unconventional superconductivity in non-centrosymmetric nanowires
• BKT universality class in the presence of correlated disorder
• Correlation between Superconductivity, Band Filling and Electron Confinement at the LaAlO${}_3$-SrTiO${}_3$ Interface
• Interplay between singlet and triplet pairings in multi-band two-dimensional oxide superconductors
• Bimodal Phase Diagram of the Superfluid Density in LaAlO3/SrTiO3 Revealed by an Interfacial Waveguide Resonator
• Quantized critical supercurrent in SrTiO${}_3$-based quantum point contacts
• Interplay between the extended s-wave symmetry of the gap and the spin-orbit coupling in the low-electron concentration regime of quasi-two-dimensional superconductors
• Spin-orbit-assisted electron pairing in 1D waveguides
• Mean-field theory of first-order quantum superconductor-insulator transition
• Understanding the onset of negative electronic compressibility in one- and two-band 2D electron gases: Application to LaAlO${}_3$/SrTiO${}_3$
• Fluctuations superconductivity and giant negative magnetoresistance in a gate voltage tuned 2D electron liquid with strong spin-orbit impurity scattering
• Externally controlled and switchable 2D electron gas at the Rashba interface between ferroelectrics and heavy $d$ metals
• Sample-based calibration for cryogenic broadband microwave reflectometry measurements
• Superfluid response of two-dimensional filamentary superconductors