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Among materials with strong electron correlations, those exhibiting superconductivity have attracted the most intense interest because a rich variety of unconventional SC states can be
investigated in detail. Furthermore, Cooper pairs in such systems are not formed by the interaction of electrons with phonons, resulting in general in the highly symmetric s-wave state, rather magnetic fluctuations are considered as the relevant pairing mechanism. If inversion symmetry in the crystal structure is missing, peculiar band splitting develops, which is detrimental to certain kinds of Cooper pairing channels. In particular, spin triplet pairing was claimed to become unlikely under these circumstances.
Ternary CePt3Si [1] is the first representative of heavy fermion superconductors without inversion symmetry. Macroscopic and microscopic studies carried out on CePt3Si evidenced a coexistence of superconductivity Tc = 0.75 K and magnetic order TN = 2.2 K on a microscopic scale. The absence of inversion symmetry favours a SC order parameter which may be composed of spin-singlet and spin-triplet components as indicated from a very unique NMR relaxation rate 1/T1 and a linear temperature dependence of the penetration depth ë. Furthermore, a helical modification of the order parameter would explain the absence of substantial anisotropy of the upper critical field. In the present work, recent experimental and theoretical findings on CePt3Si are presented and studies on substitutions of Ce by La, Si by Ge as well as Pt by Ni and Pd are introduced and results derived from a broad phase space of temperature, magnetic fields and hydrostatic pressure are discussed. Those results are compared with properties of more simple superconductors which do not possess a center of inversion. [1] E. Bauer et al., Phys. Rev. Lett. 92 (2004) 027003. |
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