Particle-Hole Asymmetry in Doped Mott Insulators: Implications for   Tunneling and Photoemission Spectroscopies
  In a system with strong local repulsive interactions it should be more difficult to add an electron than to extract one. We make this idea precise by deriving various exact sum rules for the one-particle spectral function independent of the details of the Hamiltonian describing the system and of the nature of the ground state. We extend these results using a variational ansatz for the superconducting ground state and low lying excitations. Our results shed light on the striking asymmetry in the tunneling spectra of high Tc superconductors and should also be useful in estimating the local doping variations in inhomogeneous materials. 
Mohit Randeria, Rajdeep Sensarma, Nandini Trivedi, and Fu-Chun Zhang