Conservation of the particle–hole symmetry in the pseudogap state in optimally-doped Bi2Sr2CuO6+δ superconductor

The pseudogap state is one of the most enigmatic characteristics in the anomalous normal state properties of the high temperature cuprate superconductors.A central issue is to reveal whether there is a symmetry breaking and which symmetries are broken across the pseudogap transition.By performing high resolution laser-based angle-resolved pho-toemission measurements on the optimally-doped Bi2Sr1.6La0.4CuO6+δ superconductor,we report the observations of the particle-hole symmetry conservation in both the superconducting state and the pseudogap state along the entire Fermi sur-face.These results provide key insights in understanding the nature of the pseudogap and its relation with high temperature superconductivity.