You're looking for magic, and there isn't any--there's no magic diet to increase the definition of a specific part of your body. Work will build the muscles, and a combination of aerobic exercise and diet to reduce body fat will let the definition show. If you have two inches of subcutaneous fat (I'm not assuming you do, I'm just saying if), no amount of muscle will show through. Also, muscle size and bulk is partly determined by genetics. I lifted weights pretty heavily for years, but never could develop impressive pecs--I was strong, but not showy.
Just keep riding, and reduce your body fat to a reasonable level if it isn't already. Some heavier resistance work (heavier than cycling, like squats or extensions on a weight machine) may help by increasing the size of the muscles, too.