Does any paper use energy harvest to in the baseband?
No.

Your question neglects the fact that a mixer can't transfer the whole received power to baseband (mixers are typically active, and most of the baseband energy comes from the LO that the device has to generate itself).

You can use any nonlinear device, even one without an external power source, but the mixed output's energy will always be way lower than the energy of the inputs, simply by the pure math behind what mixing does.

In general, when asking such question, you'd start with "where does what energy come from?", and with a clean, and simplified, block diagram of the receive RF chain including the mixer, and that would have answered that. If you're researching power harvesting, this is the MAIN thing you'll need to understand!