Two Characteristic Contributions to the Superconducting State of 2H-NbSe2

Multiband superconductivity arises when multiple electronic bands contribute to the formation of the superconducting state, allowing distinct pairing interactions and gap structures. Here, we present field- and temperature-dependent data on the vortex lattice structure in 2H-NbSe₂ as a contribution to the ongoing debate as to whether the defining feature of the superconductivity is the anisotropy or the multiband nature. The field-dependent data clearly show that there are two distinct superconducting bands, and the contribution of one of them to the vortex lattice signal is completely suppressed for magnetic fields above ∼0.8 T, well below B_c2. By combining the temperature and field scans, we can deduce that there is a moderate degree of interband coupling. From the observed temperature dependences, we find that at low field and zero temperature, the two gaps in temperature units are 13.1 ± 0.2 and 6.5 ± 0.3 K (Δ₀ = 1.88 and 0.94 k_BT_c); the band with the larger gap gives just under two-thirds of the superfluid density. The penetration depth extrapolated to zero field and zero temperature is 160 ± 2 nm.