In my German courses in Munich, I use a special blend to accelerate my students' German learning. I was skeptical at first, but when I tried it myself, I found, that it helped me focus and concentrate. Therefore, I now use it in my German classes in Munich.
It's called "Leichter lernen", which means "Focus & Learn" and it comes with a mini-stone diffuser in a nice tin. The scent is a blend of lemon, grapefruit and orange.
That's my two scents for today ;-)