Abstract
The upper critical field of purple bronze is found to exhibit a large anisotropy, in quantitative agreement with that expected from the observed electrical resistivity anisotropy. With the field aligned along the most conducting axis, increases monotonically with decreasing temperature to a value 5 times larger than the estimated paramagnetic pair-breaking field. Theories for the enhancement of invoking spin-orbit scattering or strong-coupling superconductivity are shown to be inadequate in explaining the observed behavior, suggesting that the pairing state in is unconventional and possibly spin triplet.
- Received 20 January 2011
DOI:https://doi.org/10.1103/PhysRevLett.108.187003
© 2012 American Physical Society