Abstract
We used atomic-layer molecular beam epitaxy to synthesize bilayers of a cuprate metal (LaSrCuO) and a cuprate insulator (LaCuO) film, in which each layer is just one unit cell thick. We have studied the magnetic field and temperature dependences of the complex sheet conductance, σ(ω), of these films. Experiments have been carried out at frequencies between 2 and 20 MHz using the single-spiral coil technique. We found that (i) the inductive response, (), starts at 1.7 K lower temperatures than Reσ(), which in turn is characterized by a peak close to the transition, (ii) this shift is almost constant with magnetic field up to 8 T; (iii) the vortex diffusion constant () is not linear with at low temperature, as in the case of free vortices, but rather is exponential due to pinning of vortex cores, and (iv) the Berezinski-Kosterlitz-Thouless (BKT) transition temperature occurs at the point where = (/) = 1. Our experimental results can be described well by the extended dynamic theory of the BKT transition and the dynamics of bound vortex-antivortex pairs with short separation lengths.
- Received 7 August 2012
DOI:https://doi.org/10.1103/PhysRevB.86.094523
©2012 American Physical Society