Signatures of two-dimensional superconductivity emerging within a three-dimensional host superconductor

Abstract

Spatial disorder has been shown to drive two-dimensional (2D) superconductors to an insulating phase through a superconductor–insulator transition (SIT). Numerical calculations predict that with increasing disorder, emergent electronic granularity is expected in these materials—a phenomenon where superconducting (SC) domains on the scale of the material’s coherence length are embedded in an insulating matrix and coherently coupled by Josephson tunneling. Here, we present spatially resolved scanning tunneling spectroscopy (STS) measurements of the three-dimensional (3D) superconductor BaPb1−xBixO3 (BPBO), which surprisingly demonstrate three key signatures of emergent electronic granularity, having only been previously conjectured and observed in 2D thin-film systems. These signatures include the observation of emergent SC domains on the scale of the coherence length, finite energy gap over all space, and strong enhancement of spatial anticorrelation between pairing amplitude and gap magnitude as the SIT is approached. These observations are suggestive of 2D SC behavior embedded within a conventional 3D s-wave host, an intriguing but still unexplained interdimensional phenomenon, which has been hinted at by previous experiments in which critical scaling exponents in the vicinity of a putative 3D quantum phase transition are consistent only with dimensionality d = 2.

Evidence of lattice strain as a precursor to superconductivity in BaPb0.75Bi0.25O3

“…above ∼7 K) in superconducting BaPb 0.78 Bi 0.22 O 3 . Further, recent study by Parra et al [6], shows that an electronic reorganization into a 2D granular superconductor takes place when BPBO approaches the superconductor-insulator transition before ultimately transforming to an insulator. Superconductivity is generally seen adjacent to exotic symmetry-breaking ground states, like antiferromagnetism (AFM) and CDW orders [5].…”

Superconductor–insulator transitions in three-dimensional indium-oxide at high pressures

“…Our 3D sample in proximity to the quantum critical point exhibits features which resemble those of the 2D SIT, one of them being a characteristic peak shaped MR in the insulating side of the HSIT. In contrast to the 2D studies, the peaks are less pronounced and a single crossing point of the isotherms in the MR is absent (see [15,16] for an example of a special case). In addition, the saturation of resistivity at low temperatures, which was reported in 2D systems of InOx at the 'failed superconductor' state, is observed in our 3D sample.…”

How planar superconductors cure their infrared divergences

“…This Higgsless, topological superconductivty [7,8] is the only possibility in the 2D, but may be realized also in the 3D bulk materials [36,37]. Indeed, 3D bulk materials with the emergent granularity typical of planar superconductors have been recently found [38].…”