S. K. Goh, Y. Mizukami, H. Shishido, D. Watanabe, S. Yasumoto, M. Shimozawa, M. Yamashita, T. Terashima, Y. Yanase, T. Shibauchi, A. I. Buzdin, Y. Matsuda
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 5 unit-cells thick heavy-fermion superconductor CeCoIn_5 with strong Pauli effect and normal metal YbCoIn_5, respectively. For the n=3 superlattice, H_{c2}(\theta) changes smoothly as a function of field angle \theta. However, close to the superconducting transition temperature, H_{c2}(\theta) exhibits a cusp near parallel field (\theta=0 degree). 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 together the temperature dependence of H_{c2}(\theta), our results suggest that some exotic superconducting states, including a helical superconducting state, might be realized at high magnetic field.
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http://arxiv.org/abs/1207.4889
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