Wang Lab of Quantum Matter

Cuprate pseudogap

An unidentified quantum fluid designated the pseudogap (PG) phase is produced by electron-density depletion in the CuO₂ antiferromagnetic insulator. Current theories suggest that the PG phase may be a pair density wave (PDW) state characterized by a spatially modulating density of electron pairs. Such a state should exhibit a periodically modulating energy gap Δ_P(r) in real-space, and a characteristic quasiparticle scattering interference (QPI) signature Λ_P(q) in wavevector space. By studying strongly underdoped Bi₂Sr₂CaDyCu₂O₈ at hole-density ~0.08 in the superconductive phase, we detect the 8a₀-periodic Δ_P(r) modulations signifying a PDW coexisting with superconductivity. Then, by visualizing the temperature dependence of this electronic structure from the superconducting into the pseudogap phase, we find the evolution of the scattering interference signature Λ(q) that is predicted specifically for the temperature dependence of an 8a₀-periodic PDW. These observations are consistent with theory for the transition from a PDW state coexisting with d-wave superconductivity to a pure PDW state in the Bi₂Sr₂CaDyCu₂O₈ pseudogap phase.

Read more about our research → Nature Communications 12, 6087 (2021)