Abstract
High-precision measurements of magnetic penetration depth in clean single crystals of LiFeAs and LiFeP superconductors reveal contrasting behaviors. In LiFeAs the low-temperature shows a flat dependence indicative of a fully gapped state, which is consistent with previous studies. In contrast, LiFeP exhibits a -linear dependence of superfluid density , indicating a nodal superconducting order parameter. A systematic comparison of quasiparticle excitations in the 1111, 122, and 111 families of iron-pnictide superconductors implies that the nodal state is induced when the pnictogen height from the iron plane decreases below a threshold value of .
- Received 25 July 2011
DOI:https://doi.org/10.1103/PhysRevLett.108.047003
© 2012 American Physical Society