Surface states and the pseudogap in the topological nodal-line semimetal Sn_xNbSe_2-δ probed by soft-point-contact spectroscopy

Topological nodal-line semimetals have attracted great interest because of one-dimensional bulk nodal lines and two-dimensional dispersionless drumhead surface bands. Such bands have been experimentally verified in the noncentrosymmetric superconductor PbTaSe₂ [1]. Recently, unusual superconductivity has been reported in Sn_xNbSe_2-δ, which shares the same noncentrosymmetric crystal structure with PbTaSe₂ [2,3]. The superconducting transition temperature of Sn_xNbSe_2-δ can exceed 10 K, and the upper critical field can surpass the BCS Pauli paramagnetic limit by tuning the values of x and δ. To investigate its normal and superconducting properties, we conducted soft-point-contact spectroscopy of Sn_xNbSe_2-δ. We observe a zero-bias conductance peak in the differential conductance dI/dV in the superconducting state. Notably, the dI/dV curves show asymmetry, suggestive of quantum interference between bulk and dispersionless surface-state channels. When superconductivity is suppressed by applied magnetic fields, we detect a pseudogap-like behavior in dI/dV. We will discuss the relationship between the pseudogap-like behavior feature and the hybridization of bulk and surface states in Sn_xNbSe_2-δ.



[1] G. Bian et al., Nat. Commun. 7 10556 (2016).

[2] R. Munir et al., J. Phys.: Condens. Matter 33 23LT01 (2021).

[3] R. Munir et al., J. Phys.: Conf. Ser. 2164 012008 (2022).