Evidence of nodes in the order parameter of the superconducting doped topological insulator NbxBi2Se3 via penetration depth measurements.

The low-temperature variation of the London penetration depth λ(T) in the candidate topological superconductor NbxBi2Se3 (x=0.25) is reported for several crystals. The measurements were carried out by means of a tunnel-diode oscillator technique in both field orientations (Hrf∥c and Hrf∥ab planes). All samples exhibited power-law behavior at low temperatures (Δλ~T²) clearly indicating the presence of point nodes in the superconducting order parameter. The results presented here are consistent with a nematic odd-parity spin-triplet Eu pairing state in NbxBi2Se3. [ABSTRACT FROM AUTHOR]