Line nodes in the superconducting gap function of noncentrosymmetric CePt3Si

The superconducting gap structure of recently discovered heavy fermion CePt3Si without spatial inversion symmetry was investigated by thermal transport measurements down to 40 mK. In zero field a residual T-linear term was clearly resolved as T→0, with a magnitude in good agreement with the value expected for a residual normal fluid with a nodal gap structure, together with a T2 dependence at high temperatures. With an applied magnetic field, the thermal conductivity grows rapidly, in dramatic contrast to fully gapped superconductors, and exhibits one-parameter scaling with T/H. These results place an important constraint on the order parameter symmetry; that is, CePt3Si is most likely to have line nodes.