Here we report muon spin rotation ( μ SR ) experiments on the temperature and field dependence of the effective magnetic penetration depth λ ( T ) in the η -carbide-type suboxide Ti 4 Ir 2 O , a superconductor with a considerably high upper critical field. The temperature dependence of λ ( T ) , obtained from transverse-field (TF)- μ SR measurements, is in perfect agreement with an isotropic fully gaped superconducting state. Furthermore, our ZF μ SR results confirm that the time-reversal symmetry is preserved in the superconducting state. We find, however, a remarkably small ratio of T c / λ 0 − 2 ∼ 1.22 . This value is close to most unconventional superconductors, showing that a very small superfluid density is present in the superconducting state of Ti 4 Ir 2 O . 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.

Published by the American Physical Society 2024