Kramers nodal lines and superconductivity in intercalated transition metal dichalcogenides

It has been shown that, in all achiral crystals (non-centrosymmetric with additional mirror or roto-inversion symmetry), the energy bands connecting the time reversal invariant momenta (TRIM) are forced to be degenerate, forming Kramers nodal lines (KNLs) [1]. In our previous work, we experimentally observed KNLs in the paramagnetic state of SmAlSi [2]. However, the KNLs in SmAlSi are far from the Fermi energy, making them not relevant to the transport properties or exotic phases in SmAlSi.



Here we synthesized and characterized an achiral In-intercalated transition metal dichalcogenide, which was not available in single crystal form before our study. DFT calculations show that there are KNLs crossing the Fermi energy. The good crystal quality is demonstrated by a large residual resistivity ratio RRR = ρ(300K)/ρ(2K) = 55, and strong quantum oscillations up to 20 K. Further analysis of quantum oscillations yields a small electron effective mass m_eff ~ 0.2. Together with the large, non-saturating magnetoresistance, these results indicate possible linear band crossings. Moreover, the KNLs that cross the Fermi energy are directly observed in ARPES. Similar to the isostructural PbTaSe₂, bulk superconductivity is observed in our compound below 0.9 K. The existence of KNLs at the Fermi energy and the superconductivity points to a possible topological superconducting state in this compound.

[1] Xie, Y., et al. Nat. Commun. 12, 3064 (2021).

[2] Zhang, Y., et al. Commun. Phys. 6, 134 (2023).