technically its just an A chord played over a C# bass note. so the guitar would play an A and the bass would play a C#, and they sound good together.

butttt there is an acual chord for any of these "split chords"

an A/C# chord looks something like this tabbed out.

e 0
B 2
G 2 <- see, an A/C# chord is easy to understand. its an A chord
D 2
A 4 <- ...over a C# bass note.
E x