Volume 84, Number 5, December 2008
Article Number 57003
Number of page(s) 5
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
Published online 27 November 2008
EPL, 84 (2008) 57003
DOI: 10.1209/0295-5075/84/57003

Potassium fluoride doped LaOFeAs multi-band superconductor: Evidence of extremely high upper critical field

J. Prakash1, S. J. Singh2, S. L. Samal1, S. Patnaik2 and A. K. Ganguli1

1   Department of Chemistry, Indian Institute of Technology - New Delhi, 110016 India
2   School of Physical Sciences, Jawaharlal Nehru University - New Delhi, 110067 India

received 15 July 2008; accepted in final form 21 October 2008; published December 2008
published online 27 November 2008

The recently discovered superconductors based on oxypnictides have rekindled the search for new non-copper based high-$T_{{\rm c}}$ superconductors. After the initial report by Kamihara et al. of superconductivity in (La-O/F-Fe-As)-based compounds, there have been several reports on these new superconductors but the synthesis of pure phases of these oxypnictides has remained a challenge. Here we describe a new methodology of synthesizing these oxypnictide superconductors with the commonly available potassium fluoride (KF) as a source of fluorine instead of the expensive LaF3. This route also allows the substitution of potassium at lanthanum sites which leads to an increase in the upper critical field as would be expected for a multi-band superconductor. We also report the highest-$T_{{\rm c}}$ (onset) of 28.50 K and highest upper critical field at ambient pressure in the family of La-based oxypnictides.

74.70.-b - Superconducting materials.
74.10.+v - Occurrence, potential candidates.

© EPLA 2008