Distribution of lattice constants in CePt₃Si observed by Larmor diffraction and SANS

The non-centrosymmetric heavy fermion compound CePt₃Si orders antiferromag-netically at T_N = 2.2K, followed by a superconducting transition, where T_s = 0.45 K for high quality samples and T _s = 0.75K for lower quality samples. We have used neutron Larmor diffraction to measure the temperature dependence and distribution of the lattice constants in a single crystal of CePt₃Si with T_s = 0.75K. In our study we observe an unusually wide range of lattice parameters for the a-axis and c-axis with Δa/a ≈ Δc/c ≈ 10^-3. Small angle neutron scattering suggests an abundance of defects along the lattice planes. When taking into account the pressure dependence of T _s our study attributes the increased value of T_s in low quality samples to an effective negative pressure.