Spectroscopic evidence for a pseudogap in the normal state of underdoped high-Tc superconductors

摘要: IT is well known that BCS mean-field theory remarkably successful in describing conventional superconductors. A central concept of the energy gap electronic excitation spectrum below superconducting transition temperature, Tc. The also serves as order parameter: quite generally, long-range phase coherence and a non-zero go hand-in-hand1. But underdoped high-Tc superconductors there considerable evidence pseudogap (a suppression spectral weight) already formed normal state above Tc—first, from studies spin spectrum2–5,24, which measure 'spin gap', later variety other probes6–10. Here we present study Bi2Sr2CaCu2O8+δ (Bi2212) using angle-resolved photoemission spectroscopy (ARPES), directly measures momentum-resolved electron CuO2 planes. We find with d-wave symmetry opens up temperature T* > Tc, develops into once established