Where can I learn cycles material in-depth, is there any book or Website available?
I would take a look through Youtube …there are MANY MANY videos / Tutorials…
Andrew Price is a very good start…https://www.youtube.com/user/AndrewPPrice/videos
as well as Zach Reinhardt https://www.youtube.com/c/CGBoost/videos...and once you take a look a a few of those…you will get similar videos showing up in the recommended bar…and find many more.
For “IN-DEPTH”, only Blender tutorials do not enough. look UE3, UE4, Unity, HLSL, GLSL tutorials, physics tutorials, math tutorials, color tutorials etc.