  2H-NbSe2 is one of the most widely researched transition metal dichalcogenide
(TMD) superconductors, which undergoes charge-density wave (CDW) transition at
TCDW about 33 K and superconducting transition at Tc of 7.3 K. To explore the
relation between its superconductivity and Fermi surface nesting, we combined S
substitution with Cu intercalation in 2H-NbSe2 to make CuxNbSe2-ySy. Upon
systematic substitution of S and intercalation of Cu ions into 2H-NbSe2, we
found that when the Cu and S contents increases, the Tc decreases in
CuxNbSe2-ySy. While at higher x and y values, Tc keeps a constant value near 2
K, which is not commonly observed for a layered TMD. For comparison, we found
the simultaneous substitution of Nb by Cu and Se by S in CuxNb1-xSe2-ySy
lowered the Tc substantially faster. We construct a superconducting phase
diagrams for our double-doping compounds in contrast with the related
single-ions doping systems.
