Nonmagnetic heavy-fermion superconductor, CePt3Si

We have studied the effect of heat treatment and the Ge substitution in place of Si in the recently discovered heavy-fermion superconductor CePt₃Si. The annealed CePt₃Si exhibited nonmagnetic heavy-fermion behavior instead of the antiferromagnetism (AF) found in quenched samples. The AF state was destroyed by only about 1 at.% of Ge-substitution and may not be a stable phase. Specific-heat measurements on the annealed CePt₃Si and the Ge-substituted samples revealed a large hump around 2.2 K, originally claimed as Néel temperature. Its true nature is not clarified yet but conjectured at present as a sort of quadrupolar transition rather than AF long-range order. The superconducting transition around 0.75 K was equally sharp with ΔC_p/γT_c=0.7 for clean quenched and annealed samples. The interplay between the 2.2 K-anomaly and the superconductivity is discussed.