Particle-hole symmetry in the pseudogap phase of cuprate superconductors evidenced from joint density of states analysis

The mechanism underlying high-temperature superconductivity remains elusive, primarily due to the limited characterization of the normal state from which superconductivity emerges. Unlike conventional superconductors, the energy gap persists well above the superconducting transition temperature (T_c) in high-temperature superconductors (HTSCs). This anomalous state above T_c is commonly referred to as the pseudogap (PG) phase. A widely held view in the field is that understanding the origin of the energy gap in the PG phase, and its relationship to the superconducting energy gap, is key to uncovering the pairing mechanism in HTSCs. In this study, we present temperature-dependent investigations of the joint density of states (JDOS) across T_c in moderately underdoped Bi₂Sr₂CaCu₂O_8+δ cuprate HTSC samples, using autocorrelated angle-resolved photoemission spectroscopy (ARPES) data. Our analysis reveals that both the dispersion of JDOS peaks and the characteristic JDOS patterns—along with their energy-dependent evolution—exhibit particle-hole symmetry and remain invariant across T_c. These persistent features support the preformed pairing theoretical scenario in which the pseudogap phase represents a phase-incoherent superconducting state.