Abstract
We show exactly with an interacting model that even if the ambiguity associated with the placement of the chemical potential, , for a gapped system is removed by using the unique value , Luttinger’s sum rule is violated even if the ground-state degeneracy is lifted by an infinitesimal hopping. The failure stems from the nonexistence of the Luttinger-Ward functional for a system in which the self-energy diverges. Since it is the existence of the Luttinger-Ward functional that is the basis for Luttinger’s theorem which relates the charge density to sign changes of the single-particle Green function, no such theorem exists. Experimental data on the cuprates are presented which show a systematic deviation from the Luttinger count, implying a breakdown of the electron quasiparticle picture in strongly correlated electron matter.
- Received 26 July 2012
DOI:https://doi.org/10.1103/PhysRevLett.110.090403
© 2013 American Physical Society