Yes
There seem to be a lot of scientific literature around this question. If you agree that higher productivity at work should be a consequence of higher concentration, we have a lot of evidences.
A. Smith: Effects of caffeine on human behavior
The paper provides us with an extensive literature review of the past researches done on the effects of caffeine. It shows that many studies has demonstrated that regular coffee consumers show better performance at work. Caffeine seems to stop the decrease of performance as time past at work. However, that is only true for moderate consumption of caffeine. When people drink a large amount, the exact opposite happens, lost of concentration and lower productivity.
As a side note, I also came across this paper about the effect of Red Bull (which compare to coffee):
C. Alford, H. Cox and R. Wescott: The effects of Red Bull Energy Drink on human performance and mood
