Another interesting question! Peak State is used to describe a set of circumstances in which the mind is working optimally, without friction or distraction, on a certain task. It is a theory that was originally hypothesized by Abraham Maslow and it has gained traction in both the fields of spirituality and sports psychology. - It works so well in sports psychology/medicine because, in general, sports are overlearned tasks that have a certain level of automaticity (a skilled action performed without detailed, step-by-step, conscious control/thought). The theory of Peak State is applied in the field of spirituality to refer to a state of optimal mood or happiness or "peace."
That being said, the theory of peak states isn't applied as much when it comes to tasks that take a lot of conscious thought (like homework). Therefore, it is difficult for me to apply that specific theory.
However, it makes sense that you would get into the zone, so to speak, after a nap or while listening to music with no words. After a nap, your mind is relatively blank - you haven't been engaging in a lot of conscious thought, so doing homework then might work well. Similarly, when one listens to music without words, it helps to stimulate your brain. The brain recognizes and responds to patterns in music whether one is aware of it or not, so this might help you too. Interestingly, listening to music with words is distracting because the human brain is wired with something called the "language acquisition device" and we want to make meaning out of anything we hear that resembles speech (don't believe me? Try doing homework with music playing in the background that has words in a foreign language - it should be just as distracting!) ;)
So - all that aside, if you want to help yourself with motivation, cognitive psychology says that small, achievable goals followed by predictable and pleasurable rewards is the best way to motivate behavior. So, for example, don't try to finish everything all at once. Set smaller, easier steps for yourself. Then, when you finish a step, reward yourself with something you like (within reason).
I hope this helps.