If you're looking for manga similar to Steins;Gate, you might like these titles. All recommendations are made by Anime-Planet users like you!
Both of these series can be heavy on the science, both real and pseudo. They both have emotionally charged stories that are told through things such as timeskips, parallel worlds and alternate realities. Both can be confusing at times as the technical jargon piles up, Qualia in particular can get extremely difficult to process at times, but it's never confusing for confusing's sake, everything has a reason or purpose for being there.
If you enjoyed the scientific aspect of either series, then the other is sure to hold some enjoyment for you.