Quick suppression of superconductivity of NbSe2 by Rb intercalation

2H-NbSe2, a typical layered transition metal dichalcogenide (TMD), has attracted tremendous research interest for its higher superconducting transition temperature (T-c = 7.2 K) than T-c of other TMDs (2-4 K) and hosting of charge density wave (CDW). The van der Waals (vdW) bonding between NbSe2 layers makes it a good platform for tuning the crystal structure, CDW, and superconducting gap by intercalation. Here we report the crystal structure and superconductivity of Rb-intercalated NbSe2 prepared by solid-state reaction. For Rb intercalation with 0 <= x <= 0.025, there is only one phase with space group P6(3)/mmc. With Rb intercalation, T-c of RbxNbSe2 decreases from 7.2 K for x = 0 to 4.2 K for x = 0.025 in an L-shaped way. The suppression rate of T-c is similar to the one with magnetic Fe doping, but much quicker than those with Li, Ga, and Cu doping. The superconducting phase diagram of RbxNbSe2 is established accordingly and is compared with those of LixNbSe2, CuxNbSe2, FexNbSe2, and GaxNbSe2. The suppression of superconductivity is discussed based on the ionic radius, valence, and magnetism of doping elements and the expansion between the NbSe2 layers.