Anomalous Upper Critical Field in CeCoIn_5/YbCoIn_5 Superlattices with a   Rashba-type Heavy Fermion Interface
  We report a highly unusual angular variation of the upper critical field (H_c2) in epitaxial superlattices CeCoIn_5(n)/YbCoIn_5(5), formed by alternating layers of n and a 5 unit-cell thick heavy-fermion superconductor CeCoIn_5 with a strong Pauli effect and normal metal YbCoIn_5, respectively. For the n=3 superlattice, H_{c2}(\theta) changes smoothly as a function of the field angle \theta. However, close to the superconducting transition temperature, H_{c2}(\theta) exhibits a cusp near the parallel field (\theta=0 deg). This cusp behavior disappears for n=4 and 5 superlattices. This sudden disappearance suggests the relative dominance of the orbital depairing effect in the n=3 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 H_{c2}(\theta) as well, our results suggest that some exotic superconducting states, including a helical superconducting state, might be realized at high magnetic fields. 
S. K. Goh, Y. Mizukami, H. Shishido, D. Watanabe, S. Yasumoto, M.   Shimozawa, M. Yamashita, T. Terashima, Y. Yanase, T. Shi...
cond-mat.supr-con cond-mat.mtrl-sci cond-mat.str-el