Momentum dependence of the superconducting gap in Ba1xKxFe2As2

Received 24 September 2008; revised manuscript received 30 December 2008; published 17 February 2009 The precise momentum dependence of the superconducting gap in the iron-arsenide superconductor Ba1�xKxFe2As2 BKFA with Tc = 32 K was determined from angle-resolved photoemission spectroscopy ARPES via fitting the distribution of the quasiparticle density to a model. The model incorporates finite lifetime and experimental resolution effects, as well as accounts for peculiarities of BKFA electronic structure. We have found that the value of the superconducting gap is practically the same for the inner barrel, X pocket, and “blade” pocket, and equals 9 meV, while the gap on the outer barrel is estimated to be less than 4 meV, resulting in 2 /kBTc = 6.8 for the large gap and 2 /kBTc 3 for the small gap. A large 77 3 % nonsuperconducting component in the photoemission signal is observed below Tc. Details of gap extraction from ARPES data are discussed in Appendixes A and B.