2 research outputs found
Absence of Luttinger's Theorem due to Zeros in the Single-Particle Green Function
We show exactly with an SU(N) interacting model that even if the ambiguity
associated with the placement of the chemical potential, , for a T=0
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 non-existence 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.Comment: Published version with supplemental material rebutting the recent
criticism that our theorem fails if the ground-state degeneracy is lifte
Universal features of Thermopower in High Tc systems and Quantum Criticality
In high Tc superconductors a wide ranging connection between the doping
dependence of the transition temperature Tc and the room temperature
thermopower Q has been observed. A "universal correlation" between these two
quantities exists with the thermopower vanishing at optimum doping as noted by
OCTHH (Obertelli, Cooper, Tallon, Honma and Hor). In this work we provide an
interpretation of this OCTHH universality in terms of a possible underlying
quantum critical point (QCP) at Tc. Central to our viewpoint is the recently
noted Kelvin formula relating the thermopower to the density derivative of the
entropy. Perspective on this formula is gained through a model calculation of
the various Kubo formulas in an exactly solved 1-dimensional model with various
limiting procedures of wave vector and frequency.Comment: 12 pages, 8 figure