Virtually all of Larry Niven's novels that don't have FTL touch on this. Also shows up in most of Alastair Reynolds' novels, and in the Three Body Problem series.
Most of Alastair Reynold's novels have FTL - I only know of one that counts, which is Pushing Ice.
The 3-body problem has FTL also.
The chronologically earlier novels in his Known Space universe (the Ringworld one) are mostly around near-c Bussard ramjets.
> Most of Alastair Reynold's novels have FTL
Hmm, wait, which ones? Only one I can think of is House of Suns, in a very restricted manner.
> The 3-body problem has FTL also.
It has FTL communications, but not travel.
For [science] read [magic], more or less, but yeah. In the very first stories they were Bussard ramjets, but this got retconned out (and a Bussard ramjet actually shows up in a later book as a failed experiment). In most of the books they're more or less applied magic, though.
This, incidentally, seems to be a common theme, as later discoveries tended to fall down on the side of Bussard ramjets not working (due to insufficient density etc). The last of Niven's Known Space books have some special pleading for how the pilot has to carefully direct the ramjet to get sufficient combustion volume, a detail that was never present in the old ones.