Cooper pair as a preexisting quasiparticle, from the perspective of fluctuating pair density wave*

The apparently missing electron density and the 'incomplete Fermi surface' are big mysteries of the pseudogap phase. Their relation with charge density waves, which are ubiquitous at lower temperatures in the pseudogap region, especially with an applied magnetic field, is also unclear. We provide a new perspective using quantum fluctuating pair density waves to unify the phenomenology of charge density waves and the electron spectrum. The resulting theory contains both gapped Cooper pairs made of antinodal electrons, and a Fermi pocket of nodal electrons. The gapped Cooper pair offers a potential solution to numerous experimental puzzles, including the ARPES spectrum, the 'incoherent' optical conductivity, and the photo-induced superconductivity.