When certain elemental metals like Cu, Sr and Nb are intercalated between the layers of Bi2Se3, a topological insulator, the intercalated systems superconduct with critical temperatures around 3 K. Naturally, in all these cases, the possibility of topological superconductivity was suggested and explored. However, in cases of Cu and Sr intercalated systems, the low-temperature scanning tunneling microscopy (STM) experiments revealed fully formed gaps where no signature of low-energy states, a requisite for topological superconductivity, was found. Here, through STM spectroscopy down to 400 mK we show that in Nbx-Bi2Se3 (x = 0.25), the spectra deviate from a BCS-like behavior and the spectral weight at low-bias is large. Our observations are consistent with the idea that the order parameter of Nbx-Bi2Se3 is nodal. Therefore, our results conclude that compared to other members of the family, Nbx-Bi2Se3 has a stronger possibility of being a topological superconductor.
@article{arxiv.1806.11143,
title = {Low-energy excitations and non-BCS superconductivity in Nb$_x$-Bi$_2$Se$_3$},
author = {Anshu Sirohi and Shekhar Das and Prakriti Neha and Karn S. Jat and Satyabrata Patnaik and Goutam Sheet},
journal= {arXiv preprint arXiv:1806.11143},
year = {2018}
}