Partial suppression of superconductivity by fast cooling has been observed in
the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br by two means:
a marked sample size effect on the magnetic susceptibility and direct imaging
of insulating regions by scanning microregion infrared reflectance
spectroscopy. Macroscopic insulating regions are found in the vicinity of the
crystalline surface after fast cooling, with diameters of 50--100 μm and
depths of a few μm. The very large in-plane penetration depth reported to
date (∼ 24--100 μm) can be explained by the existence of the
insulating regions.Comment: Several rhetoric alternations to avoid misleadings. 6 pages, 3
figures. to be publihsed in Phys. Rev.