Ultrathin underdoped films of YBa 2 Cu 3 O 7-δ (YBCO) exhibit a prominent and abrupt downturn in ab-plane superfluid density n S (T) at a temperature consistent with a 2D vortex-pair unbinding transition. In this paper, we show that this characteristic feature of 2D superconductors diminishes with increasing film thickness consistent with theory, provided one uses the full film thickness rather than a copper-oxide bilayer thickness to calculate T C . In thick films, there is no evidence for 3D-XY fluctuations preceding the 2D downturn, as would be expected in a quasi-2D superconductor.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering