Abstract
We report a highly unusual angular variation of the upper critical field () in epitaxial superlattices , formed by alternating layers of and a 5 unit-cell thick heavy-fermion superconductor with a strong Pauli effect and normal metal , respectively. For the superlattice, changes smoothly as a function of the field angle . However, close to the superconducting transition temperature, exhibits a cusp near the parallel field (). This cusp behavior disappears for and 5 superlattices. This sudden disappearance suggests the relative dominance of the orbital depairing effect in the superlattice, which may be due to the suppression of the Pauli effect in a system with local inversion symmetry breaking. Taking into account the temperature dependence of as well, our results suggest that some exotic superconducting states, including a helical superconducting state, might be realized at high magnetic fields.
- Received 20 July 2012
DOI:https://doi.org/10.1103/PhysRevLett.109.157006
© 2012 American Physical Society