Time management is very much important in IIT JAM. The eduncle test series for IIT JAM Mathematical Statistics helped me a lot in this portion. I am very thankful to the test series I bought from eduncle.
Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Somnath
For basic crystal structures you may follow "Introduction to solid state physics by Charles Kittel. For graphene you may read the following book... Graphene:Carbon in two dimension by Mikhail Katsnelson.