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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 [1]. 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 [2]. [1] Yufan Li, Xiaoying Xu, M. H. Lee, M. W. Chu, and C. L. Chien, Science, 366, 238 (2019). [2] Xiaoying Xu, Yufan Li, and C. L. Chien, Phys. Rev. Lett. 124, 167001 (2020).

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