VIDEO: Unconventional multi-band superconductivity at two-dimensional oxide interfaces

by Gyanendra Singh, Department of Microtechnology and Nanoscience MC2, Chalmers University of Technology, Gothenburg, Sweden.

Delivered on Wednesday, 2 December 2020 @ 12 pm

Abstract:

A presence of two-dimensional superconductivity at the interface between LaAlO3 and SrTiO3, together with strong Rashba spin-orbit coupling, is of particular interest as theory predicts unconventional superconducting pairing and topological superconductivity [1,2]. While these interfaces share the interesting properties of bulk SrTiO3, quantum confinement, crystal orientation, and electrostatic gating also offer extra degrees of freedom to engineer the electronic band structure [3]. The filling of the bands can be precisely controlled with a gate voltage [4]. Using, resonant microwave experiment to extract the phase rigidity and the gap energy of the superconductor, and upper critical magnetic field, we demonstrate that multi-condensate superconductivity can occur at the interface as theoretically predicted. In addition, we observe a transition from single-band to two-band superconductivity at the Lifshitz transition corresponding to the filling threshold of the highest energy band. Interestingly, the superconducting gap is suppressed when the second band is populated, which challenges the standard Bardeen-Cooper-Schrieffer theory. We ascribed this behavior to the presence of repulsive interaction between the two condensates leading to an unconventional s±-wave superconducting state [5].

Moreover, we have investigated the current-voltage characteristics as a function of gate voltages, temperature, and the dimension of the superconducting nanowires of these interfaces. The critical current shows very strong anomalous enhancement with magnetic fields applied perpendicular to the plane, which cannot be explained with the classical model of superconductivity. We argued that the presence of Rashba spin-orbit-coupling and multi-band occupation leads to the formation of superconducting channels with intrinsic 0 and p phase shifts.

References:

  1. D. Caviglia et al. Nature 456, 624–627 (2008).
  2. S. Scheurer Nature Commun. 6, 6005 (2015).
  3. Gervasi Herranz et al. Nature Communications 6, 6028 (2015).
  4. Gyanendra Singh et al. Nature communications 9, 407 (2018).
  5. Gyanendra Singh et al. Nature Materials 18, 948 (2019),

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