Evidence for Line Nodes in the Superconducting Energy Gap of Noncentrosymmetric ${\mathrm{CePt}}_3\mathrm{Si}$ from Magnetic Penetration Depth Measurements

We report measurements of the magnetic penetration depth $\lambda (T)$ in high-quality ${\mathrm{CePt}}_3\mathrm{Si}$ samples down to 0.049 K. We observe a linear temperature dependence below $T\simeq 0.16T_c$, which is interpreted as evidence for line nodes in the energy gap of the low-temperature phase of this material. A kink in $\lambda (T)$ at about 0.53 K may be associated with the second superconducting transition recently reported. The results are discussed in terms of the symmetry of the superconducting order parameter.

Figure 1

The normalized $\Delta \lambda (T)$ vs $T/T_c$ for both samples of ${\mathrm{CePt}}_3\mathrm{Si}$ and for conventional superconducting cadmium.

Figure 2

(a) $\Delta \lambda (T)$ against $T/T_c$ for a polycrystalline sample of ${\mathrm{CePt}}_3\mathrm{Si}$ in the low-temperature region. For comparison, data of Cd (an isotropic gapped spin-singlet superconductor) are also presented. Note the difference in the vertical scales. The inset shows the linear temperature behavior of $\lambda (T)$ in the ${\mathrm{CePt}}_3\mathrm{Si}$ sample below $T\simeq 0.16T_c$. (b) $\Delta \lambda (T)$ against $T/T_c$ for the sedimented powder sample. Solid lines are visual guides.

Figure 3

(a) Results of the numerical evaluations of the models discussed in the text and $[\lambda (0)/\lambda (T){]}^2$ for the polycrystalline ${\mathrm{CePt}}_3\mathrm{Si}$ sample. The arrow indicates the point where the $T$ behavior of the superfluid density should have a crossover from the HTP to LTP.