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Abstract

Here we report muon spin rotation (mu SR) experiments on the temperature and field dependence of the effective magnetic penetration depth lambda ( T ) in the eta-carbide-type suboxide Ti4Ir2O, a superconductor with a considerably high upper critical field. The temperature dependence of lambda ( T ), obtained from transverse-field (TF)-mu SR measurements, is in perfect agreement with an isotropic fully gaped superconducting state. Furthermore, our ZF mu SR results confirm that the time-reversal symmetry is preserved in the superconducting state. We find, however, a remarkably small ratio of T c /lambda - 2 0 similar to 1.22. This value is close to most unconventional superconductors, showing that a very small superfluid density is present in the superconducting state of Ti4Ir2O. The presented results will pave the way for further theoretical and experimental investigations to obtain a microscopic understanding of the origin of such a high upper critical field in an isotropic single-gap superconducting system.