We consider an isotropic spin-degenerate interacting uniform
D-dimensional electron gas (DDEG) with
D>1 within the Luttinger-Ward (LW) formalism. We derive the asymptotically exact semiclassical/infrared limit of the LW functional at large distances, $r\ensuremath{\gg}{\ensuremath{\lambda}}_{F}$, and large times, $\ensuremath{\tau}\ensuremath{\gg}1/{E}_{F}$, where ${\ensuremath{\lambda}}_{F}$ and
EF are the Fermi wavelength and the Fermi energy, respectively. The LW functional is represented by skeleton diagrams, each skeleton diagram consists of appropriately connected dressed fermion loops. First, we prove that every
D-dimensional skeleton diagram consisting of a single fermion loop is reduced to a one-dimensional (1D) fermion loop with the same diagrammatic structure, which justifies the name dimensional reduction. This statement, combined with the fermion loop cancellation theorem (FLCT), agrees with results of multidimensional bosonization. Here we show that the backscattering and the spectral curvature, both explicitly violate the FLCT and both are irrelevant for a 1DEG, become relevant at
D>1 and
D>2, respectively. The reason for this is a strong infrared divergence of the skeleton diagrams containing multiple fermion loops at
D>1. These diagrams, which are omitted within the multidimensional bosonization approaches, account for the noncollinear scattering processes. Thus, the dimensional reduction provides the framework to go beyond predictions of the multidimensional bosonization. A simple diagrammatic structure of the reduced LW functional is another advantage of our approach. The dimensional reduction technique is also applicable to the thermodynamic potential and various approximations, from perturbation theory to self-consistent approaches.
Abstract Luttinger’s theorem is a major result in many-body physics that states the volume of the Fermi surface is directly proportional to the particle density. In its ‘hard’ form, Luttinger’s theorem implies that the Fermi volume is invariant with respect to interactions (as opposed to a ‘soft’ Luttinger’s theorem, where this invariance is lost). Despite it is simplicity, the conditions on the fermionic self energy under which Luttinger’s theorem is valid remains a matter of debate, with possible requirements for its validity ranging from particle-hole symmetry to analyticity about the Fermi surface. In this paper, we propose the minimal requirements for the application of a hard Luttinger’s theorem to a generic fermionic system of arbitrary interaction strength by invoking the Atiyah–Singer index theorem to quantify the topologically-robust behavior of a generalized Fermi surface. We show that the applicability of a hard Luttinger’s theorem in a D-dimensional system is directly dependent on the existence of a (D − 1)-dimensional manifold of gapless chiral excitations at the Fermi level, regardless of whether the system exhibits Luttinger or Fermi surfaces (i.e., manifolds of zeroes of the Green’s function and inverse Green’s function, respectively). The exact form of the self-energy which guarantees validity of a hard Luttinger’s theorem is derived, and agreement with current experiments, numerics, and theories are discussed.
Using the density matrix renormalization group method, we systematically investigate the evolution of the Luttinger integral in the one-dimensional generalized
t-
V model as a function of filling and interaction strength, and identify three representative phases. In the weak-coupling regime, the zero-frequency Green's function exhibits a branch-cut structure at the Fermi momentum, and the Luttinger integral accurately reflects the particle density, indicating that the Luttinger theorem holds. As the interaction increases, the spectral weight near the Fermi momentum is gradually suppressed. Interestingly, in the strong coupling regime near half-filling, this singularity is progressively destroyed, accompanied by the emergence of momentum-space zeros in the real part of the Green's function, leading to a novel non-Fermi liquid metallic phase beyond the classic Luttinger liquid paradigm, where the Luttinger surface is no longer defined by a single singularity. While finite spectral weight remains at the original Fermi momentum, the singularity gradually diminishes. Meanwhile, zeros with negligible spectral weight appear away from this momentum, significantly affecting the integral. At exact half-filling, a single-particle gap opens, and the Green's function becomes nearly vanishing across the entire momentum space, indicating the complete suppression of low-energy electronic states consistent with the nature of an insulating charge-density-wave phase. These results suggest that the breakdown of the Luttinger theorem is not triggered by a single mechanism, but rather results from the interplay between interaction-driven evolution of excitation modes and the breaking of particle-hole symmetry, ultimately leading to a continuous reconstruction of the generalized Fermi surface from topologically protected to correlation-driven.