Momentum-resolved superconducting gap in the bulk of Ba1−xKxFe2As2from combined ARPES and μSR measurements

Here we present a calculation of the temperature-dependent London penetration depth, λ( T ), in Ba 1- x K x Fe 2 As 2 (BKFA) on the basis of the electronic band structure (Zabolotnyy et al 2009 Nature 457 569, Zabolotnyy et al 2009 Physica C 469 448) and momentum-dependent superconducting gap (Evtushinsky et al 2009 Phys. Rev. B 79 054517) extracted from angle-resolved photoemission spectroscopy (ARPES) data. The results are compared to the direct measurements of λ( T ) by muon spin rotation (μSR) (Khasanov et al 2009 Phys. Rev. Lett. 102 187005). The value of λ( T =0), calculated with no adjustable parameters, equals 270 nm, while the directly measured one is 320 nm; the temperature dependence λ( T ) is also easily reproduced. Such agreement between the two completely different approaches allows us to conclude that ARPES studies of BKFA are bulk-representative. Our review of the available experimental studies of the superconducting gap in the new iron-based superconductors in general allows us to state that most of them bear two nearly isotropic gaps with coupling constants 2Δ/ k B T c =2.5±1.5 and 7±2.