Abstract
The superconducting penetration depth has been measured in (, Nd) single crystals (). In Nd-1111, we find an upturn in upon cooling and attribute it to the paramagnetism of the Nd ions, similar to the case of the electron-doped cuprate Nd-Ce-Cu-O. After the correction for paramagnetism, the London penetration depth variation is found to follow a power-law behavior, at low temperatures. The same variation of was found in nonmagnetic La-1111 crystals. Analysis of the superfluid density and of penetration depth anisotropy over the full temperature range is consistent with two-gap superconductivity. Based on this and on our previous work, we conclude that both the RFeAsO (1111) and (122) families of pnictide superconductors exhibit unconventional two-gap superconductivity.
- Received 12 March 2009
DOI:https://doi.org/10.1103/PhysRevLett.102.247002
©2009 American Physical Society