Zero-field μSR search for a time-reversal-symmetry-breaking mixed pairing state in superconducting Ba1-xKxFe2As2

We report the results of a zero-field muon-spin relaxation (ZF-mu SR) study of superconducting Ba1-xKxFe2As2 (0.5 <= x <= 0.9) in search of weak spontaneous internal magnetic fields associated with proposed time-reversal-symmetry-breaking mixed pairing states. The measurements were performed on polycrystalline samples, which do not exhibit the mesoscopic phase separation previously observed in single crystals of Ba1-xKxFe2As2. No evidence of spontaneous internal magnetic fields is found in any of the samples at temperatures down to T similar to 0.02 K.