The overwhelming majority of the known superconductors (SCs) possess superconducting pairs that are spin antisymmetric (spin singlets) and space symmetric — usually s-wave but the high Tc materials tend to be d-wave. Spin symmetric SCs (spin triplets), crucial for Majorana physics and fault tolerant quantum computing, are very rare and difficult to identify. A large upper critical field (Hc2) and an NMR Knight shift suggest but do not confirm triplet SC (e.g., in Sr2RuO4). With Φ0 = hc/2e the flux quantum, flux measurements on rings of singlet SCs universally find integer quantum fluxes nΦ0. However, using a phase-sensitive method we have observed half-quantum fluxes (HQF) of the form (n + ½)Φ0 in patterned sub-μm rings of β-Bi2Pd thin films . A flux of (n + ½)Φ0 is a signature of spin triplet pairing. Noncentrosymmetric SCs have an admixture of spin triplet pairing, and have been found to exhibit HQF .
 Yufan Li, Xiaoying Xu, M. H. Lee, M. W. Chu, and C. L. Chien, Science, 366, 238 (2019).
 Xiaoying Xu, Yufan Li, and C. L. Chien, Phys. Rev. Lett. 124, 167001 (2020).