Approaching two-dimensional superconductivity in ultrathin DyBa${}_2$Cu${}_3$O${}_{7-\delta }$

Abstract

The temperature dependence of the superfluid density ${\rho }_s(T)$ has been measured for a series of ultrathin MBE-grown DyBa${}_2$Cu${}_3$O${}_{7-\delta }$ superconducting (SC) films by sub-mm wave interferometry combined with time-domain THz spectroscopy and IR ellipsometry. We find that all films 10 u.c. and thicker show the same universal temperature dependence of ${\rho }_s(T)$, which follows the critical behavior characteristic of single crystal YBa${}_2$Cu${}_3$O${}_{7-\delta }$ as $T$ approaches $T_c$. In 7 u.c. thick films, ${\rho }_s(T)$ declines steeply upon approaching $T_c$, as expected for the Berezinskii-Kosterlitz-Thouless vortex unbinding transition. Our analysis provides evidence for a sharply defined 4 u.c. non-SC interfacial layer, leaving a quasi-2D SC layer on top. We propose that the SC state in this interfacial layer is suppressed by competing (possibly charge) order.

arXiv comment6 pages, 3 figures

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