Clue: Metal detected during drowsy phase in field (5)
Answer: REALM
Explanation: Metal detected during drowsy phase in field (5)
Al (Aluminium) in R.E.M. 
I'm no expert, but I don't think that R.E.M. and "drowsy phase" are synonymous, as R.E.M. is associated with deep sleep, whereas "drowsy" is more like "half asleep".