"Unlike refugees, IDPs have not crossed an international border to find sanctuary but have remained inside their home countries. Even if they have fled for similar reasons as refugees (armed conflict, generalized violence, human rights violations), IDPs legally remain under the protection of their own government – even though that government might be the cause of their flight. As citizens, they retain all of their rights and protection under both human rights and international humanitarian law." UNHCR
SOLO will find you books if you use the narrow subject search Internally displaced persons. But this may be too fine a filter: IDPs may well be considered in books just classified under refugees, humanitarian law, even human rights.