Direct observation of particle-hole mixing in the superconducting state by angle-resolved photoemission

Abstract

Particle-hole ($p-h$) mixing is a fundamental consequence of the existence of a pair condensate. We present direct experimental evidence for $p-h$ mixing in the angle-resolved photoemission (ARPES) spectra in the superconducting state of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2\mathrm{Ca}{\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$. In addition to its pedagogical importance, this establishes unambiguously that the gap observed in ARPES is associated with superconductivity.